U.S. patent application number 10/822826 was filed with the patent office on 2004-11-25 for voltage generating circuit.
This patent application is currently assigned to MITSUBISHI DENKI KABUSHIKI KAISHA. Invention is credited to Tobita, Youichi.
Application Number | 20040232974 10/822826 |
Document ID | / |
Family ID | 33455503 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040232974 |
Kind Code |
A1 |
Tobita, Youichi |
November 25, 2004 |
Voltage generating circuit
Abstract
A first transistor is arranged between a reference voltage node
and a first node, and is connected at its gate to a second node. A
second transistor is arranged between the second node and the
reference voltage node, and is connected at its gate to the first
node. Charges are supplied to the first and second nodes via
capacitance elements receiving first and second control signals,
respectively. Further, a third transistor is arranged between the
second node and an output node, and is connected at its gate node
to a third control signal .phi.CT via a third capacitance element.
A fourth transistor is connected between the output node and a gate
node of the third transistor, and is connected at its gate to the
second node. An internal voltage at an intended level can be
generated with low power consumption while efficiently using
charges without causing an ineffective current flow.
Inventors: |
Tobita, Youichi; (Hyogo,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
MITSUBISHI DENKI KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
33455503 |
Appl. No.: |
10/822826 |
Filed: |
April 13, 2004 |
Current U.S.
Class: |
327/536 |
Current CPC
Class: |
H01L 27/0214 20130101;
G11C 5/14 20130101; G11C 11/4074 20130101 |
Class at
Publication: |
327/536 |
International
Class: |
H01L 027/108 |
Foreign Application Data
Date |
Code |
Application Number |
May 19, 2003 |
JP |
2003-140079 |
Dec 17, 2003 |
JP |
2003-419716 |
Claims
What is claimed is:
1. A voltage generating circuit comprising: a first transistor of a
first conductivity type connected between a reference voltage node
supplied with a predetermined voltage and a first internal node,
and having a control electrode connected to a second internal node;
a second transistor of the first conductivity type connected
between said reference voltage node and said second internal node,
and having a control electrode connected to said first internal
node; a first capacitance element connected between a first input
node receiving a first control signal controlling a precharging
operation and said first internal node; a second capacitance
element connected between a second input node receiving a second
control signal controlling charge accumulation and said second
internal node; a third transistor of a second conductivity type
connected between said second internal node and an output node, and
having a control electrode connected to a third internal node; a
third capacitance element connected between said third internal
node and a third input node receiving a third control signal
controlling charge transfer; and a fourth transistor of the second
conductivity type connected between said output node and said third
internal node, and having a control electrode connected to said
second internal node.
2. The voltage generating circuit according to claim 1, further
comprising: at least one voltage drive stage connected between said
output node and a final output node, for generating a final voltage
on said final output node, said voltage drive stage including; a
fifth transistor of the second conductivity type connected between
an input node of said voltage drive stage and an output node of
said voltage drive stage, and having a control electrode connected
to a fourth internal node, a fourth capacitance element coupled to
the input node of said voltage drive stage, the first and second
control signals being applied alternately to the fourth capacitance
elements in a connection sequence when said at least one voltage
drive stage includes a plurality of such voltage drive stages, a
sixth transistor of the second conductivity type connected between
said fourth internal node and the output node of said voltage drive
stage, and having a control electrode connected to the input node
of said voltage drive stage, and a fifth capacitance element
coupled to said fourth internal node, a fourth control signal and
said third control signal being applied alternately to the fifth
capacitance elements in the connection sequence when said at least
one voltage drive stage includes a plurality of such voltage drive
stages.
3. The voltage generating circuit according to claim 2, wherein
said second control signal attains a first logical level when a
predetermined time elapses since said first control signal changes
from the first logical level to a second logical level, and changes
from said first logical level to said second logical level before
said first control signal changes from said second logical level to
said first logical level, said third control signal changes from
said first logical level to said second logical level when a
predetermined time elapses since said second control signal changes
to said first logical level, and changes from said second logical
level to said first logical level before said second control signal
changes from said first logical level to said second logical level,
said third control signal changes from said first logical level to
said second logical level when a predetermined time elapses since
said second control signal changes to said first logical level, and
changes from said second logical level to said first logical level
before said second control signal changes from said first logical
level to said second logical level, and said fourth control signal
is set at the second logical level for a predetermined time period
when said first control signal is at the first logical level and
said second control signal is at the second logical level, before
said first control signal changes to the second logic level after
elapse of a predetermined time since transition of said second
control signal to the second logic level.
4. The voltage generating circuit according to claim 2, wherein
said at least one voltage drive stage includes a plurality of
cascaded voltage drive stages.
5. The voltage generating circuit according to claim 2, wherein the
final voltage is applied from said final output node to internal
circuitry, and said voltage generating circuit further includes a
capacitance element connected to said final output node.
6. The voltage generating circuit according to claim 1, wherein
said output node generates an internal voltage applied to internal
circuitry, and said voltage generating circuit further includes a
capacitance element connected to said output node.
7. A voltage generating circuit comprising: a first transistor
connected between a precharge voltage supply node supplying a
precharge voltage and a first internal node, and having a control
electrode connected to a second internal node; a first capacitance
element connected between a first input node receiving a first
control signal for precharging and said second internal node; a
second transistor connected between the first and second internal
nodes, and having a control electrode receiving a second control
signal controlling charge accumulation; a third transistor
connected between said first internal node and an output node, and
having a control electrode connected to a third internal node; a
fourth transistor connected between said output node and said third
internal node, and having a control electrode connected to said
first internal node; a second capacitance element connected between
a third input node receiving a third control signal controlling
second charge precharging and said first internal node; and a third
capacitance element connected between a fourth input node receiving
a fourth control signal controlling charge transfer and said third
internal node.
8. The voltage generating circuit according to claim 7, wherein
said precharge voltage supply node is supplied with a constant
voltage at a predetermined voltage level.
9. The voltage generating circuit according to claim 7, wherein
said precharge voltage supply node is supplied with said second
control signal.
10. The voltage generating circuit according to claim 7, wherein
said third control signal attains and maintains for a predetermined
time period a second logical level when said second control signal
is at a first logical level, and said fourth control signal attains
and maintains for a predetermined time period the first logical
level when said third control signal is at the second logical
level, and precharging of said first internal node is performed
when said first control signal attains the first logical level
while said second control signal is at the second logical
level.
11. The voltage generating circuit according to claim 7, further
comprising: at least one voltage drive stage connected between said
output node and said final output node, and generating a final
voltage on said final output node, said voltage drive stage
including; a fifth transistor connected between an input node of
said voltage drive stage and an output node of said voltage drive
stage, and having a control electrode connected to a fourth
internal node, a fourth capacitance element coupled to the input
node of said voltage drive stage, a fifth capacitance coupled to
said fourth internal node, and a sixth transistor connected between
said fourth internal node and the output node of said voltage drive
stage, and having a control electrode connected to the input node
of said voltage drive stage, and when said at least voltage drive
stage includes a plurality of such voltage drive stages, the second
and third control signals being alternately applied to the fourth
capacitance elements in a connection sequence of the voltage drive
stages, and said first and fourth control signals are alternately
applied to the fifth capacitance elements in the connection
sequence.
12. The voltage generating circuit according to claim 11, wherein
said first control signal attains a first logical level and is
maintained thereat for a predetermined time period when a
predetermined time elapses since said second control signal changes
from the first logical level to a second logical level, and said
second control signal changes from the second logical level to the
first logical level after said first control signal changes from
the first logical level to the second logical level, said third
control signal attains the second logical level and is maintained
thereat for a predetermined period since said second control signal
changes to the first logical level, and said second control signal
attains the second logical level after said third control signal
changes to the first logical level, and said fourth control signal
attains the first logical level and is maintained thereat for a
predetermined time after said third control signal changes to the
second logical level, and said third control signal changes to the
first logical level after said fourth control signal changes to the
second logical level.
13. The voltage generating circuit according to claim 11, wherein
said final output node applies a final voltage to internal
circuitry, and said voltage generating circuit further comprises a
capacitance element connected to said final output node.
14. The voltage generating circuit according to claim 7, wherein
said output node generates an internal voltage to be applied to
internal circuitry, and said voltage generating circuit further
comprises a capacitance element connected to said output node.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a voltage generating
circuit for generating an internal voltage at a desired voltage
level, and particularly to a structure of a voltage generating
circuit efficiently generating an internal voltage by utilizing a
charge pump operation of a capacitance element.
[0003] 2. Description of the Background Art
[0004] Semiconductor device are configured to use internal voltages
at various voltage levels in many cases. For example, in a DRAM
(Dynamic Random Access Memory), a negative voltage is used for
biasing a substrate region of a memory cell array at a constant
voltage, and a high positive voltage higher than a power supply
voltage is supplied to a selected word line. In a nonvolatile
memory, negative and positive voltages are used for rewriting
data.
[0005] When externally supplying such voltages at levels different
from a power supply voltage level, a system scale increases, and
power consumption of a whole system increases. In addition, a
semiconductor device is required of pin terminals dedicated to
reception of such voltages, and also increases the size.
[0006] In view of the above, semiconductor devices are generally
configured to generate internally the voltages at required levels.
An example of the circuit generating such an internal voltage is
disclosed in Reference 1 (Japanese Patent Laying-Open No.
4-372792).
[0007] An internal voltage generating circuit disclosed in
Reference 1 generates a negative voltage by utilizing a charge pump
operation of a capacitance element. According to the structure of
the internal voltage generating circuit of Reference 1, electric
charges are accumulated in a charge-accumulation node through
charge pump operation of a charging capacitance element. A
discharge control transistor is turned on through capacitance
coupling of a controlling capacitance element to discharge the
charge-accumulation node to a ground voltage level. Thereafter, the
charging capacitance element performs the charge pump operation to
pull out the charges from the charge-accumulation node, to drive
that node to a negative voltage level. The charge-accumulation node
is changed with an amplitude of the power supply voltage. Negative
charges of this charge-accumulation node are supplied to an output
node through an output transistor so that a negative voltage at a
level of -VCC is supplied, where VCC represents the power supply
voltage.
[0008] A gate potential of the output transistor changes between a
ground voltage GND and a negative voltage -VCC under control of an
output control transistor having a gate connected to the
charge-accumulation node.
[0009] Reference 1 intends to generate a negative voltage at an
adequate voltage level even under a low power supply voltage by
changing the charge-accumulation node with an amplitude of VCC.
[0010] In the structure generating an internal voltage by utilizing
the charge pump operation of the capacitance element, it is
required, in view of power consumption of the semiconductor device,
to transmit efficiently the charges produced through the charge
pump operation to the output node for generation of the internal
voltage.
[0011] In Reference 1, in order to change the voltage level of the
charge-accumulation node with an amplitude of -VCC, the
charge-accumulation node is precharged to the ground voltage level
by the discharge control transistor, and then is discharged to the
voltage level of -VCC through the charge pump operation of the
charging capacitance element. For turning off the discharge control
transistor in such operation, a second control transistor is
provided to be made conductive to connect the charge-accumulation
node to the gate of the discharge control transistor. The second
control transistor is made conductive to connect electrically the
gate of the discharging control transistor to the
charge-accumulation node when the voltage on the
charge-accumulation node lowers to or below -Vth, where Vth denotes
a threshold voltage of the second control transistor.
[0012] However, the capacitance element receiving a control signal
is connected to the discharge control transistor for turning on it.
Therefore, the gate potential of this discharge control transistor
changes at a time constant, which is determined by an on-resistance
of the second control transistor and a capacitance existing at the
gate of the discharge control transistor. Therefore, a certain time
is required until the discharge control transistor is turned off.
Accordingly, the discharge control transistor maintains the
on-state for a certain time period while the charge-accumulation
node is at the voltage level of -VCC, and a current flows to the
charge-accumulation node from the ground node. This impedes the
operation of extracting the charges through the charge pump of the
charging capacitance element, and an ineffective current is
consumed.
[0013] In an operation of precharging the charge-accumulation node
to the ground voltage level, if the output transistor is not made
non-conductive, precharged charges are supplied to the output node
at a negative level through the output transistor so that the
voltage level of the negative potential rises. For the on/off
control of this output transistor, an output control transistor
having substantially the same structure as that for on/off control
of the discharge control transistor is employed. Accordingly, in
precharging of the charge-accumulation node to the ground voltage
level, the output transistor likewise is made conductive for a
certain time period so that a current is wasted.
[0014] In the structure of Reference 1, as described above, the
charges produced through the charge pump operation of the
capacitance element are wasted, and it is difficult to generate
efficiently the voltage at a desired level with low power
consumption.
SUMMARY OF THE INVENTION
[0015] An object of the invention is to provide a voltage
generating circuit, which can efficiently utilizes the charges, to
generate a voltage at an intended level.
[0016] According to a first aspect of the invention, a voltage
generating circuit includes a first transistor of a first
conductivity type connected between a reference voltage node
supplied with a predetermined voltage and a first internal node,
and having a control electrode connected to a second internal node;
a second transistor of the first conductivity type connected
between the reference voltage node and the second internal node,
and having a control electrode connected to the first internal
node; a first capacitance element connected between a first input
node receiving a first control signal for precharging and the first
internal node; a second capacitance element connected between a
second input node receiving a second control signal for charge
accumulation and the second internal node; a third transistor of a
second conductivity type connected between the second internal node
and an output node, and having a control electrode connected to a
third internal node; a third capacitance element connected between
the third internal node and a third input node receiving a third
control signal for charge transfer; and a fourth transistor of the
second conductivity type connected between the output node and the
third internal node, and having a control electrode connected to
the second internal node.
[0017] According to another aspect of the invention, a voltage
generating circuit includes a first transistor connected between a
precharge voltage supply node supplying a precharge voltage and a
first internal node, and having a control electrode connected to a
second internal node; a first capacitance element connected between
a first input node receiving a first control signal for precharging
and a second internal node; a second transistor connected between
the first and second internal nodes, and having a control electrode
connected to a second input node receiving a second control signal
for charge accumulation; a third transistor connected between the
first internal node and an output node, and having a control
electrode connected to a third internal node; a fourth transistor
connected between the output node and the third internal node, and
having a control electrode connected to the first internal node; a
second capacitance element connected between a third input node
receiving a third control signal for second charge precharging and
the first internal node; and a third capacitance element connected
between a fourth input node receiving a fourth control signal for
charge transfer and the third internal node.
[0018] In the voltage generating circuit according to the first
aspect, through cross-coupling of the first and second transistors,
and the first and second transistors can be turned on/off at
optimal timing to change the voltages at the first and second
internal nodes at high speed, to held at the changed voltage
levels. Therefore, the second transistor is made off during the
change in voltage on the second internal node serving as the
charge-accumulation node, and then the charge pump operation is
effected on the second internal node, so that unnecessary current
can be prevented from flowing into the second internal node.
[0019] According to the voltage generating circuit of the another
aspect, the first internal node is precharged with the precharging
voltage, and is coupled with the third control signal via the
second capacitance element. Further, the first internal node is
connected to the control electrode of the fourth transistor.
Therefore, the on/off state of the respective transistors can be
individually controlled by the charge pump operation through the
capacitance elements, and flow of an ineffective current can be
suppressed so that the charges can be efficiently used to produce
the internal voltage at the intended level.
[0020] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows a construction of a voltage generating circuit
according to a first embodiment of the invention.
[0022] FIG. 2 is a signal waveform diagram illustrating an
operation of the voltage generating circuit shown in FIG. 1.
[0023] FIG. 3 shows a structure of a voltage generating circuit
according to a second embodiment of the invention.
[0024] FIG. 4 is a signal waveform diagram illustrating an
operation of the circuit shown in FIG. 3.
[0025] FIG. 5 schematically shows a construction of an internal
voltage generating circuit according to a third embodiment of the
invention.
[0026] FIG. 6 schematically shows a structure of a control signal
generating circuit shown in FIG. 5.
[0027] FIG. 7 is a timing chart illustrating an operation of the
circuit shown in FIG. 6.
[0028] FIG. 8 shows a construction of a voltage generating circuit
according to a fourth embodiment of the invention.
[0029] FIG. 9 is a signal waveform diagram illustrating an
operation of the circuit shown in FIG. 8.
[0030] FIG. 10A shows a construction of a voltage generating
circuit according to a fifth embodiment of the invention, and FIG.
10B shows a structure of a charge transfer stage shown in FIG.
10A.
[0031] FIG. 11 is a signal waveform diagram illustrating an
operation of the circuits shown in FIGS. 10A and 10B.
[0032] FIG. 12 schematically shows a structure of a circuit
generating a control signal shown in FIG. 10A.
[0033] FIG. 13 is a signal waveform diagram illustrating an
operation of a circuit shown in FIG. 12.
[0034] FIG. 14 shows a construction of a voltage generating circuit
according to a sixth embodiment of the invention.
[0035] FIG. 15 is a signal waveform diagram illustrating an
operation of a circuit shown in FIG. 14.
[0036] FIG. 16 shows a structure of a voltage generating circuit
according to a seventh embodiment of the invention.
[0037] FIG. 17 is a signal waveform diagram illustrating an
operation of the circuit shown in FIG. 16.
[0038] FIG. 18 shows a structure of a voltage generating circuit
according to an eighth embodiment of the invention.
[0039] FIG. 19 is a timing chart illustrating an operation of the
voltage generating circuit shown in FIG. 18.
[0040] FIG. 20 shows a structure of a voltage generating circuit
according to a ninth embodiment of the invention.
[0041] FIG. 21 is a timing chart representing an operation of the
voltage generating circuit shown in FIG. 20.
[0042] FIGS. 22, 23 and 24 show constructions of voltage generating
circuits according to tenth, eleventh and twelfth embodiments of
the invention, respectively.
[0043] FIG. 25 shows a construction of a voltage generating circuit
according to a modification of the twelfth embodiment of the
invention.
[0044] FIG. 26 shows a construction of a voltage generating circuit
according to a thirteenth embodiment of the invention.
[0045] FIG. 27 shows a structure of a voltage generating circuit
according to a modification of the thirteenth embodiment of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] [First Embodiment]
[0047] FIG. 1 shows a structure of a voltage generating circuit
according to a first embodiment of the invention. The voltage
generating circuit shown in FIG. 1 generates a negative voltage
lower than a reference potential. In this embodiment, a ground
potential GND is used as the reference potential, and a signal for
controlling a charge pump operation changes between a ground
voltage and a power supply voltage VCC so that a negative voltage
of -VCC is produced.
[0048] In FIG. 1, the voltage generating circuit includes a
P-channel MOS transistor (insulated gate field-effect transistor)
PQ1 connected between an internal node ND1 and a reference
potential node (referred to as a "ground node" hereinafter) GC and
having a gate connected to an internal node ND2, a P-channel MOS
transistor PQ2 connected between internal node ND2 and ground node
GG and having a gate connected to internal node ND1, a capacitance
element C1 connected between a control signal input node S1
receiving a precharging control signal .phi.P and internal node
ND1, and a capacitance element C2 connected between a control
signal input node S2 receiving a control signal .phi.CP for charge
accumulation and internal node ND2.
[0049] MOS transistors PQ1 and PQ2 correspond to the first and
second transistors, respectively, and capacitance elements C1 and
C2 correspond to the first and second capacitance elements,
respectively. Control signals .phi.P and .phi.CP correspond to the
first and second control signals, respectively. Internal nodes ND1
and ND2 correspond to the first and second internal nodes,
respectively.
[0050] The voltage generating circuit further includes an N-channel
MOS transistor NQ1 connected between internal node ND2 and an
output node OD1 and having a gate connected to an internal node
ND3, an N-channel MOS transistor NQ2 connected between internal
node ND3 and output node OD1 and having a gate connected to
internal node ND2, and a capacitance element C3 connected between a
control signal input node S3 receiving a control signal .phi.CT for
charge transference and internal node ND3.
[0051] MOS transistors NQ1 and NQ2 correspond to the third and
fourth transistors, respectively, capacitance element C3
corresponds to the third capacitance element, and control signal
.phi.CT corresponds to the third control signal.
[0052] A capacitance element C4 is connected between output node
OD1 and the ground node. This capacitance element C4 serves to
stabilize an output voltage of -VCC against variation of an output
load, and may be eliminated if the variation in output load is
small and therefore, the variation in output voltage of -VCC is
small. A voltage on output node OD1 is applied to internal
circuitry, not shown.
[0053] Each of control signals .phi.P, .phi.CP and .phi.CT changes
between ground voltage GND and power supply voltage VCC.
[0054] FIG. 2 is a timing chart illustrating an operation of the
voltage generating circuit shown in FIG. 1. For the sake of
simplicity, FIG. 2 shows operation waveforms for the case when the
voltage on output node OD1 is at the predetermined voltage level of
-VCC. Referring to FIG. 2, an operation of the voltage generating
circuit shown in FIG. 1 will now be described.
[0055] Control signals .phi.P, .phi.CP and .phi.CT change at a
cycle of T. FIG. 2 illustrates signal waveforms over a time period
of 2.multidot.T.
[0056] At a time t0, control signals .phi.P, .phi.CP and .phi.CT
are at the levels of ground voltage GND, power supply voltage VCC
and ground voltage GND, respectively. In this state, through a
charge pulling-out operation of capacitance element C1, node ND1 is
at the voltage level of -VCC, and through a charge supplying
operation of the capacitance element C2, node ND2 is at the voltage
level of ground voltage GND.
[0057] For P-channel MOS transistor PQ1, node ND1 serves as a drain
node, and ground node GG serves as a source node. P-channel MOS
transistor PQ1 is of an enhancement type, and has a threshold
voltage of a predetermined magnitude. Therefore, P-channel MOS
transistor PQ1 maintains the non-conductive state due to equal
potentials at its gate and source, and no current flows between
node ND1 and ground node GG.
[0058] MOS transistor PQ2 receives a negative potential -VCC at its
gate, and equal potentials at its drain (node ND2) and source
(ground node) so that no current flows between the drain and source
of MOS transistor PQ2.
[0059] As for N-channel MOS transistor NQ1, node ND2 is at the
level of ground voltage GND, output node OD1 is at the level of
negative voltage -VCC and node ND3 is at the level of negative
voltage -VCC. N-channel MOS transistor NQ1 is of an enhancement
type, has a threshold voltage of a constant magnitude, and
maintains the non-conductive state when the gate potential is equal
to the source potential.
[0060] N-channel MOS transistor NQ2 has a gate potential at the
level of the voltage on node ND2 or the level of ground voltage
GND, and has the drain and source at the equal potential because
node ND3 and output node OD1 are at equal potential levels. Thus,
no current flows between the drain and source of MOS transistor
NQ2. According to control signal .phi.P, MOS transistor PQ2 is made
conductive to precharge node ND2 to the ground voltage level. In an
initial stage of the charge pumping operation, the precharge
voltage level of node ND2 is lowered toward the ground voltage.
[0061] At a time t1, when control signal .phi.P changes from the
level of ground voltage GND to the level of power supply voltage
VCC, the charge pumping by capacitance element C1 raises the
voltage level of node ND1 from negative voltage -VCC to ground
voltage GND. In the stable state, the drain and source of MOS
transistor PQ1 are at the same voltage level, and no current flows
through MOS transistor PQ1.
[0062] In a transition time period of an initial stage of the
charge pumping operation, node ND1 is at the voltage level not
lower than ground voltage GND, and node ND1 and the ground node
serve as the source and drain of MOS transistor PQ1, respectively.
However, the voltage level of node ND2 is high in this state. MOS
transistor PQ1 is of the enhancement type, receives the gate to
source voltage not higher than an absolute value of the threshold
voltage, and maintains the non-conductive state. Thus, no current
flows between the drain and the source of MOS transistor PQ1.
[0063] Since node ND2 is at the level of ground voltage GND, MOS
transistor PQ2 has the drain and the source at equal potentials,
and no current flows between the drain and source of MOS transistor
PQ2 even when the voltage level of node ND1 rises from negative
voltage -VCC to the ground voltage GND. By raising control signal
.phi.P, MOS transistor PQ2 is made non-conductive for preparing for
the next charge pump operation on node ND2.
[0064] Node ND2 holds the level of ground voltage GND, and node ND3
is at the negative voltage level. In this state, MOS transistor NQ2
is conductive, and electrically connects output node OD1 to
internal node ND3, so that internal node ND3 becomes equal in
voltage level to output node OD1. Thereby, MOS transistor NQ1
reliably maintains the non-conductive state. When the voltage
levels of internal node ND3 and output node OD1 become equal to
each other, a current stops flowing through MOS transistor NQ2.
[0065] By equalizing the voltage levels on internal node ND3 and
output node OD1, the gate to source voltage of MOS transistor NQ1
is maintained at or below the threshold voltage to prevent MOS
transistor NQ1 of the enhancement type from turning on before
transferring charges, even when internal node ND2 is driven to the
negative voltage level and internal node ND2 serves as the source
of MOS transistor NQ1. In an initial stage of the charge pumping
operation, when internal node ND2 is driven to the negative voltage
level, internal node ND3 is at a high voltage level, and MOS
transistor NQ1 may be rendered conductive. In this case, however,
negative charges are merely transferred to output node OD1 before
generation of control signal .phi.CT, and the charges are utilized
for lowering the output voltage. Thus, the charges are effectively
utilized.
[0066] At a time t2, control signal .phi.CP lowers from the level
of power supply voltage VCC to the level of ground voltage GND, and
the charge pumping by capacitance element C2 lowers the voltage
level of node ND2. Even when the voltage level of node ND2 changes
from ground voltage GND to a negative voltage, both the drain and
source of MOS transistor PQ1 is at the level of ground voltage GND,
and no current flows between its drain and source.
[0067] Since MOS transistor PQ2 has node ND2 serving as the drain,
the gate and source (ground node) are both at the level of ground
voltage. MOS transistor PQ2 is of the enhancement type, and has the
gate-source voltage smaller than the absolute value of its
threshold voltage so that MOS transistor PQ2 maintains the
non-conductive state. Accordingly, node ND2 lowers to the level of
negative voltage -VCC through the charge pump operation of
capacitance element C2. In this state, node ND3 is at the level of
negative voltage -VCC, and MOS transistor NQ1 has output node OD1
serving as the source, has the gate and source at the equal
potentials, and maintains the non-conductive state.
[0068] When node ND2 is driven to the negative voltage level, the
voltage level of node ND2 becomes lower than the voltage level of
output node OD1. The voltage level at node ND3 is the voltage level
at the output node. When control signal .phi.CT is at the ground
voltage level, MOS transistor NQ1 is of the enhancement type, and
has the gate-source voltage smaller than the threshold voltage
during the transition and stable stages, and maintains the
non-conductive state so that node ND2 can be accurately driven to
the negative voltage level.
[0069] When node ND2 is driven to the negative voltage level in the
transition time period, MOS transistor PQ1 is made conductive to
lower the voltage level of node ND1 if the voltage level of node
ND1 is higher than the ground voltage.
[0070] In the charge pump operation on node ND2, therefore, there
is no path allowing flow of an ineffective current adversely
affecting the voltage level of node ND2, and the charges can be
efficiently utilized to set node ND2 to the level of negative
voltage -VCC.
[0071] In MOS transistor NQ2, the drain and source are at the same
level of negative voltage -VCC, so that no current flows between
the drain and source.
[0072] At a time t3, control signal .phi.CT rises from the level of
ground voltage GND to the level of power supply voltage VCC. At
this time, control signal .phi.P is at the level of power supply
voltage VCC, and control signal .phi.CP is at the level of ground
voltage GND. In this state, the charge pumping by capacitance
element C3 raises the voltage level of node ND3 from negative
voltage -VCC to the level of ground voltage GND. Since node ND2 is
at the level of negative voltage -VCC, MOS transistor NQ1 is
rendered conductive to couple node ND2 to output node OD1. If the
voltage level of output node OD1 is higher than negative voltage
-VCC, negative electric charges move from output node OD1 to node
ND2, so that output node OD1 and node ND2 attain the equal voltage
level. Specifically, in the stable state, output node OD1 is at the
voltage level of -VCC. In this case, MOS transistor NQ2 has the
gate and source at the equal potentials, and therefore maintains
the non-conductive state so that no current flows between the drain
and source of MOS transistor NQ2.
[0073] In a transition period such as a start of the charge
pumping, MOS transistor NQ2 has internal node ND3 serving as the
drain, has the gate in potential lower than the source upon start
of charge transfer start, and maintains the non-conductive state.
Even if the gate and source are made equal in potential to each
other through charge transfer, MOS transistor NQ2 maintains the
non-conductive state due to its threshold voltage, and does not
adversely affect the charge transfer operation.
[0074] Thus, node ND3 is driven to the power supply voltage level
in accordance with control signal .phi.CT, and negative charges can
be efficiently supplied to output node OD1 to produce negative
voltage -VCC of the intended voltage level.
[0075] At a time t4, control signal .phi.CT falls from the level of
power supply voltage VCC to the level of ground voltage GND, and
the voltage level of node ND3 lowers from ground voltage GND to
negative voltage -VCC. The lowest possible potential of the source
node (node ND2) of MOS transistor NQ1 is the negative voltage -VCC,
and MOS transistor NQ1 is reliably made non-conductive.
[0076] MOS transistor NQ2 has the drain and source at the levels of
negative voltage -VCC, and causes no current flow therethrough.
[0077] In the transition period at the start of the charge pumping,
when nodes ND2 and OD1 are at the voltage levels higher than
negative voltage -VCC, node ND3 merely returns to the voltage level
of output node OD1 in the preceding cycle, and MOS transistor NQ2
has output node OD1 serving as the source, and has the gate and
source equal in potential, and maintains the non-conductive state.
Even when MOS transistor NQ1 is turned on, output node OD1 and
internal node ND2, which serve as the source and drain of MOS
transistor NQ1, respectively, are at the same voltage level, and no
current flow through MOS transistor NQ1. In the transition period,
the voltage level, to which node ND3 returns, is the voltage level
at which MOS transistor NQ1 is set non-conductive, and no charge is
wasted.
[0078] At a time t5, control signal .phi.CP rises from the level of
ground voltage GND to the level of power supply voltage VCC. In
this period, control signal .phi.P is at the level of power supply
voltage VCC. Control signal .phi.CT is at the level of ground
voltage GND. In accordance with the rising of control signal
.phi.CP, through charge pumping operation by capacitance element
C2, the voltage level of node ND2 rises from negative voltage -VCC
to the ground voltage GND. In this operation, MOS transistor PQ1
has both the drain and source kept at the level of ground voltage
GND, and turns non-conductive in accordance with the rising of its
gate potential. Thus, no current flows through MOS transistor
PQ1.
[0079] In MOS transistor PQ2, the voltage level of node ND2 merely
rises from negative voltage -VCC to ground voltage GND, and does
not exceed the ground voltage GND, so that the ground node serves
as the source of MOS transistor PQ2, which in turn maintains the
non-conductive state.
[0080] When node ND2 is raised in potential, node ND2 may be held
at a voltage level higher than ground voltage GND (node ND2 serves
as a source) in the transition period such as a start period of the
charge pumping operation. In this case, control signal .phi.P is
lowered to render MOS transistor PQ2 conductive so that node ND2 is
reliably discharged toward the ground voltage level. Therefore, a
particular problem does not occur.
[0081] At time t5, even when the voltage level of node ND2 rises to
the ground voltage level, node ND3 is at the level of negative
voltage -VCC so that MOS transistor NQ1 maintains the
non-conductive state. Even when MOS transistor NQ2 turns
conductive, internal node ND3 is at the voltage level of output
node OD1, i.e., the level of negative voltage -VCC so that MOS
transistor NQ2 has the gate and the source at the equal voltages,
and thus maintains the non-conductive state. Therefore, no current
flows between the drain and source of MOS transistor NQ2.
[0082] At time t6, control signal .phi.P falls to the level of
ground voltage GND. Accordingly, capacitance element C1 lowers the
voltage level of node ND1 from ground voltage GND to negative
voltage -VCC. In accordance with this voltage lowering of node ND1,
MOS transistor PQ2 turns conductive, and node ND2 is reliably set
to the level of ground voltage GND.
[0083] Even in the case where node ND2 is driven to a high voltage
level higher than ground voltage GND in the transition period, the
voltage level of node ND2 can be reliably lowered. In the next
cycle, the voltage level of node ND2 can be further lowered in
accordance with control signal .phi.CP, and the output voltage
level can be lowered.
[0084] In the potential lowering of node ND2, MOS transistor PQ1
has the ground node serving as its source, and accordingly has the
gate and the source at the same voltage level, so that MOS
transistor PQ1 maintains the non-conductive state.
[0085] At time t8, a cycle T for one charge pump operation
completes, and the operation stating at time t0 will be
repeated.
[0086] In the voltage generating circuit shown in FIG. 1,
therefore, an ineffective current does not flow during the charge
pump operation, and the charges can be efficiently utilized to
generate the internal voltage at an intended level.
[0087] MOS transistors PQ1 and PQ2 are cross-coupled, and the gate
potentials thereof are individually set by the charge pump
operations of the capacitance elements. After these MOS transistors
PQ1 and PQ2 are made non-conductive, the voltage levels of nodes
ND1 and ND2 can be reliably and rapidly changed in accordance with
the control signals.
[0088] For the sake of simplicity, an effect of a parasitic
capacitance at internal node ND2 is neglected in the above
description. If internal node ND2 has a parasitic capacitance of an
innegligible magnitude, the voltage amplitude on node ND2 is
smaller than power supply voltage VCC and accordingly the output
voltage of output node OD1 is made lowered in absolute value.
[0089] Control signal .phi.CP determining the voltage amplitude of
internal node ND2 is changed between power supply voltage VCC and
ground voltage GND. However, with the reference voltage being a
voltage Vr instead of ground voltage GND, and control signal
.phi.CP having a voltage amplitude V.phi., an output voltage VOUT
of output node OD1 can be expressed by the following relation
(1):
VOUT=Vr-V.phi. (1)
[0090] Generally, as in the above description of the operations,
reference voltage Vr is equal to ground voltage GND or 0 V, and
control signal .phi.CP is produced from a circuit using power
supply voltage VCC and ground voltage GND as operation power supply
voltages. Therefore, assuming that voltage amplitude V.phi. is
equal to power supply voltage VCC, the above relation (1) can be
modified into the following relation (2);
VOUT=-VCC (2)
[0091] In the above description, all control signals .phi.P,
.phi.CP and .phi.CT change between power supply voltage VCC and
ground voltage GND, and are the same voltage levels in the high
level and in the low level. However, the high levels of these
control signals .phi.P, .phi.CP and .phi.CT may be different in
voltage level from each other, and the low levels thereof may be
different in voltage level from each other, provided that MOS
transistors PQ1, PQ2, NQ1 and NQ2 are made non-conductive to
prevent current flow in a direction reverse to that of voltage
change upon the voltage change on internal nodes ND1, ND2 and
ND3.
[0092] According to the first embodiment of the invention, as
described above, the cross-coupled P-channel MOS transistors are
used, and the gate node potentials thereof are determined by the
charge pump operations of the capacitance elements. In addition,
the conduction/non-conduction states of the output transistor are
set by the control signal. Thus, it becomes possible to prevent
flow of an unnecessary current upon change of the potential of the
charge-accumulation node so that the voltage at an intended level
can be efficiently produced.
[0093] [Second Embodiment]
[0094] FIG. 3 shows a structure of a voltage generating circuit
according to a second embodiment of the invention. The voltage
generating circuit shown in FIG. 3 uses power supply voltage VCC as
a reference voltage, and generates a high voltage of 2.multidot.VCC
higher than power supply voltage VCC.
[0095] In FIG. 3, the voltage generating circuit includes an
N-channel MOS transistor NQ11 connected between a power supply node
(reference node) PW and an internal node (first internal node) ND11
and having a gate connected to an internal node (second internal
node) ND12, an N-channel MOS transistor NQ12 connected between a
power supply node PW and an internal node ND12 and having a gate
connected to internal node ND11, a capacitance element (first
capacitance element) C11 connected between a control signal input
node (first control signal input node) S11 receiving a first
control signal .phi.PZ and internal node ND11, and a capacitance
element (second capacitance element) C12 connected between a
control signal input node (second control signal input node) S12
receiving a control signal .phi.CPZ and internal node ND12.
[0096] Control signals .phi.PZ and .phi.CPZ each change between
power supply voltage VCC and ground voltage GND.
[0097] The voltage generating circuit further includes a P-channel
MOS transistor (third transistor) PQ11 connected between internal
node ND12 and an output node OD11 and having a gate connected to an
internal node (third internal node) ND13, a P-channel MOS
transistor (fourth transistor) PQ12 connected between internal node
ND13 and output node OD11 and having a gate connected to internal
node ND12, and a capacitance element (third capacitance element)
C13 connected between a control signal input node (third control
signal internal node) S13 receiving a control signal .phi.CTZ and
internal node ND13.
[0098] In the above description, parenthesized components
correspond to the elements in the claims. Control signal .phi.CTZ
changes between power supply voltage VCC and ground voltage
GND.
[0099] Output node OD11 is provided with a stabilizing capacitance
C14 for stabilizing a voltage on output node OD11. This stabilizing
capacitance C14 may not be provided if variation in load on output
node OD1 is small.
[0100] A voltage generating circuit shown in FIG. 3 is equivalent
to the voltage generating circuit shown in FIG. 1, provided that
the conductivity types of transistors are inverted, and the ground
node and the power supply node are replaced with each other.
Control signals .phi.PZ, .phi.CP and .phi.CT are complementary to
control signals .phi.P, .phi.CPZ and .phi.CTZ shown in FIG. 1.
[0101] FIG. 4 is a signal waveform diagram illustrating an
operation of the voltage generating circuit shown in FIG. 3. For
the sake of simplicity, FIG. 4 also illustrates signal waveforms in
the case when the output voltage is stable at the level of
2.multidot.VCC. Referring to FIG. 4, an operation of the voltage
generating circuit shown in FIG. 3 will now be described.
[0102] In the voltage generating circuit shown in FIG. 3, the
signal polarities as well as the conductivity types of transistors
in the circuit generating negative voltage -VCC shown in FIG. 1 are
inverted as described above. Therefore, similar operations are
performed. Thus, flow of an ineffective current can be
prevented.
[0103] At time t0, control signals .phi.PZ, .phi.CPZ and .phi.CTZ
are at the levels of power supply voltage VCC, ground voltage GND
and power supply voltage VCC, respectively. In this state, node
ND11 is at a high voltage level of 2.multidot.VCC, and node ND12 is
at a level of power supply voltage VCC (in the stable state). MOS
transistor NQ11 has a power supply node PW serving as a source, and
has gate and source at the same voltage level, and is made
non-conductive.
[0104] Even if MOS transistor NQ12 receives potential of high
voltage of 2.multidot.VCC at a gate, the voltage levels of node
ND12 and power supply node PW are equal to each other, so that no
current flows between the drain and source of MOS transistor
NQ12.
[0105] Node ND13 is at the level of high voltage of 2.multidot.VCC,
and MOS transistor PQ11 has a gate not lower in potential than the
source and drain, and maintains the non-conductive state. When the
output voltage is stable, node ND12 is at the level of power supply
voltage VCC, and therefore MOS transistor PQ12 is conductive. In
addition, the voltage levels of node ND13 and output node OD11 are
equal to each other, so that no current flows through MOS
transistor PQ12.
[0106] In a transition period such as a start of the charge pumping
operation, if the voltage of output node OD11 is lower than the
level of final voltage of 2.multidot.VCC, when the voltage level of
node ND12 is made lower than the voltage levels of node ND13 and
output node OD11, MOS transistor PQ12 is turned on to connect
electrically node ND13 to output node OD11. In this case, however,
a current flows in the direction of raising the voltage level of
output node OD11. Therefore, any ineffective current, which impedes
rising of the voltage of output node OD11, does not flow. In this
operation, the flow of current through MOS transistor PQ12 stops
when the voltage levels of output node OD11 and node ND13 become
equal to each other. In this state, since output node OD11 serves
as the source of MOS transistor PQ11, MOS transistor PQ11 has the
gate and source potentials made equal to each other, and maintains
the non-conductive state.
[0107] At time t1, control signal .phi.PZ falls from the level of
power supply voltage VCC to the level of ground voltage GND. MOS
transistor NQ11 turns non-conductive, and the charge pumping by
capacitance element C11 lowers the voltage level of node ND11 from
the high voltage of 2.multidot.VCC to power supply voltage VCC. In
this state, node ND12 is at the level of power supply voltage VCC,
and MOS transistor NQ12 is non-conductive. The potential of node
ND12 causes no change, and no ineffective current flows in this
state.
[0108] At time t2, control signal .phi.CPZ rises from the level of
ground voltage GND to the level of power supply voltage VCC, and
the voltage level of node ND12 rises from power supply voltage VCC
to the high voltage of 2.multidot.VCC. In this state, even when MOS
transistor NQ11 turns conductive, the voltage levels of node ND11
and power supply node PW are equal to each other, and therefore no
current flows. When internal node ND12 attains the level of high
voltage of 2.multidot.VCC, MOS transistor PQ12 has the gate set at
a potential not lower than the source and drain potentials, and is
reliably set to the non-conductive state. MOS transistor PQ11 has
the gate at the high voltage of 2.multidot.VCC. Even when the
voltage level of node ND12 is boosted to the high voltage of
2.multidot.VCC, MOS transistor PQ11 has node ND12 serving as the
source thereof, has the gate made equal in potential to the source,
and therefore, maintains the non-conductive state.
[0109] In the transition state where the voltage of output node
OD11 is lower than the final high voltage of 2.multidot.VCC, MOS
transistor PQ12 turns non-conductive due to the potential rising of
node ND12. Output node OD11 and internal node ND13 are already
connected electrically, and are set at the same voltage level. MOS
transistor PQ11 in this state has the gate-source voltage at most
at a level lower in absolute value than the threshold voltage
thereof, and maintains the non-conductive state.
[0110] MOS transistors NQ11, NQ12, PQ11 and PQ12 each are of the
enhancement type and turn non-conductive only when the gate-source
voltage thereof attains equal to or higher in absolute value than
the threshold voltage.
[0111] At time t3, control signal .phi.CTZ falls from the level of
power supply voltage VCC to the level of ground voltage GND. In
accordance with the falling of control signal .phi.CTZ, the charge
pumping by capacitance element C13 lowers the voltage level of node
ND13 from the high voltage of 2.multidot.VCC to power supply
voltage VCC, and MOS transistor PQ11 has the gate much lower in
potential than the source thereof, to turn conductive for coupling
electrically node ND12 to output node OD11.
[0112] When the voltage level of output node OD11 is lower than the
final voltage level of 2.multidot.VCC, positive charges are
supplied from internal node ND12 to output node OD11, and the
voltage level of output node OD11 rises. In this operation of
supplying charges to output node OD11, MOS transistor PQ12 has the
gate equal to or higher in potential than the source, and maintains
the non-conductive state. Therefore, no current flows.
[0113] At time t4, control signal .phi.CTZ rises from the level of
ground voltage GND to the level of power supply voltage VCC. The
charge pumping by capacitance element C13 raises the voltage level
of node ND13 from power supply voltage VCC to the high voltage of
2.multidot.VCC. MOS transistor PQ11 has the gate equal to or higher
in potential than the source thereof, and turns non-conductive.
[0114] In the transition period when the voltage level of output
node OD11 is lower than the high voltage of 2.multidot.VCC, MOS
transistor PQ12 turns conductive. Even in this state, however,
positive charges are supplied from node ND13 to output node OD11,
to raise the voltage level of output node OD11.
[0115] Particularly, when the voltage level of output node OD11 is
lower than the high voltage of 2.multidot.VCC in the transition
period of the initial stage of the charge pumping operation,
normally, the voltage level of node ND12 is lower than the high
voltage of 2.multidot.VCC, and output node OD11 is at a
substantially the same voltage level (the voltage level of node
ND13 is set to the same voltage level as the output node before the
transfer of charges). In this state, therefore, MOS transistor PQ12
of the enhancement type has the gate-source voltage not higher than
the absolute value of the threshold voltage, and maintains the
non-conductive state.
[0116] In this transition period, since MOS transistor PQ11 has the
gate equal to or higher in potential than the source (output node
OD11), and therefore maintains the non-conductive state. Thus, no
ineffective current flows from output node OD11 to internal node
ND12.
[0117] At time t5, control signal .phi.CPZ falls from the level of
power supply voltage VCC to the level of ground voltage GND. The
charge pumping by capacitance element C12 lowers the voltage level
of node ND12 from the high voltage of 2.multidot.VCC to power
supply voltage VCC. Node ND11 is at the level of power supply
voltage VCC. MOS transistor NQ12 has the source and gate equal in
potential to each other, and maintains the non-conductive
state.
[0118] The gate potential of MOS transistor PQ12 becomes lower than
the voltage level of its source (output node OD11), and MOS
transistor PQ12 is turns conductive to connect electrically output
node OD11 to internal node ND13. Through the connection of internal
node ND13 and output node OD11, MOS transistor PQ11 has the gate
and source made equal in potential to each other, and thus
maintains the non-conductive state. Therefore, even when internal
node ND13 is charged, only a current, which is required for
accurately transferring charges to the output node, flows and no
ineffective current flows.
[0119] In the transition period, even if the voltage level of node
ND13 becomes lower than the voltage level of internal node ND12 in
boosting of the voltage level of internal node ND12 through control
signal .phi.CPZ, MOS transistor PQ11 is held non-conductive (the
gate-source voltage is kept not higher than the absolute value of
the threshold voltage).
[0120] In the transition period, node ND12 may lower below power
supply voltage VCC when the voltage on output node OD11 has not yet
reached the final voltage level. In this state, node ND11 is at the
level of the power supply voltage, and node ND12 is held at the
voltage level lower than power supply voltage VCC by the threshold
voltage of MOS transistor NQ12. A current, which flows in this
state, is only supplied from power supply node PW through MOS
transistor 12, to compensate for the voltage level. No ineffective
current flows.
[0121] At time t6, control signal .phi.PZ rises from the level of
ground voltage GND to the level of power supply voltage VCC. The
charge pumping by capacitor element C11 raises the voltage level of
node ND11 from power supply voltage VCC to the high voltage level
of 2.multidot.VCC so that MOS transistor NQ12 is turned on, and
node ND12 is reliably set to the level of power supply voltage
VCC.
[0122] Therefore, no ineffective current flows during the periods
of precharging to the power supply voltage VCC, charging to the
high voltage 2.multidot.VCC and transferring of the accumulated
charges to the output node, on the internal node ND12 serving as
the charge accumulation node, in accordance with control signals
.phi.PZ, .phi.CPZ and .phi.CTZ, respectively. Therefore, the
charges can be effectively utilized to produce the high voltage of
2.multidot.VCC.
[0123] In the construction of the voltage generation circuit shown
in FIG. 3, the presence of a parasitic capacitance at node ND12 is
neglected. If an innegligible parasitic capacitance is present at
internal node ND12, the amplitude of the voltage at internal node
ND12 is made smaller than the power supply voltage VCC. Thus, the
output voltage at output node OD11 is resultantly at a level lower
than the high voltage of 2.multidot.VCC.
[0124] Assuming generally that control signal .phi.CPZ has the
amplitude of V.phi. similarly to the foregoing embodiment and that
power supply node PW is at a voltage VPW, output voltage VOUT from
output node OD11 is represented by the following relation (3):
VOUT=VPW+V (3)
[0125] Therefore, the amplitude of control signal .phi.CPZ is
determined in accordance with a required voltage level. In the
structure shown in FIG. 3, power supply node PW is at a level of
power supply voltage VCC, and control signal .phi.CPZ has the
amplitude of power supply voltage VCC so that output voltage VOUT
can be represented by the following relation (4):
VOUT=2.multidot.VCC (4)
[0126] It is not necessary that control signals .phi.PZ, .phi.CPZ
and .phi.CTZ are equal in voltage to each other in the high level
and in the low level. The high levels and the low levels of control
signals .phi.PZ, .phi.CPZ and .phi.CTZ may be different from each
other, provided that the precharging of internal node ND12,
supplying of charges and transferring of the charges can be
performed while ensuring the on/off states of MOS transistors NQ11,
NQ12, PQ11 and PQ12.
[0127] According to the second embodiment of the invention, as
described above, the N-channel MOS transistors are cross-coupled,
the charging of the charge-accumulation node is performed by
utilizing the charge pump operation of the capacitance element. The
charges can be supplied to the charge-accumulation node after the
MOS transistors are turned non0-conductive. Thus, flow of an
ineffective current can be prevented, and a positive high voltage
can be efficiently generated.
[0128] [Third Embodiment]
[0129] FIG. 5 schematically shows a structure of an internal
voltage generating circuit according to a third embodiment of the
invention. In FIG. 5, the internal voltage generating circuit
includes a control signal generating circuit 1 for producing
control signals .phi.P, .phi.CP and .phi.CT in accordance with a
repetition signal .phi.0, a negative voltage generating circuit 10
for generating a negative voltage -VCC in accordance with control
signals .phi.P, .phi.CP and .phi.CT received from control signal
generating circuit 1, an inverting circuit 15 for inverting control
signals .phi.P, .phi.CP and .phi.CT to produce control signals
.phi.PZ, .phi.CPZ and .phi.CTZ, respectively, and a positive
voltage generating circuit 20 for producing a positive voltage of
2.multidot.VCC in accordance with control signals .phi.PZ, .phi.CPZ
and .phi.CTZ applied from inverting circuit 15.
[0130] Negative voltage generating circuit 10 has a construction
similar to that of the voltage generating circuit shown in FIG. 1,
and positive voltage generating circuit 20 has a construction
similar to that of the voltage generating circuit shown in FIG. 3.
Control signal generating circuit 1 is provided commonly to
negative and positive voltage generating circuits 10 and 20. The
internal voltages at intended levels of-VCC and 2.multidot.VCC can
be efficiently produced with a reduced occupation area.
[0131] FIG. 6 schematically shows a construction of control signal
generating circuit 1 shown in FIG. 5. In FIG. 6, control signal
generating circuit 1 includes cascaded delay circuits 30a-30d of
four stages for receiving repetition signal .phi.0, an inverter 32a
receiving an output signal .phi.1 of delay circuit 30a, an inverter
32b receiving an output signal .phi.3 of delay circuit 30c, and an
OR circuit 33 receiving the output signal of inverter 32a and an
output signal .phi.4 of delay circuit 30d to produce control signal
.phi.CP, and an AND circuit 34 receiving output signal .phi.2 of
delay circuit 30b and the output signal of inverter 32b to produce
control signal .phi.CT.
[0132] Each of delay circuits 30a-30d is formed of an even number
of stages of cascaded inverters, and has a delay time DT.
[0133] FIG. 7 is a signal waveform diagram illustrating an
operation of control signal generating circuit 1 shown in FIG. 6.
Referring to FIG. 7, the operation of control signal generating
circuit 1 shown in FIG. 6 will now be described.
[0134] Repetition signal .phi.0 has a constant period, and is used
also as control signal .phi.P for precharging. Delay circuits
30a-30d delay the received signals by a predetermined time DT to
produce delayed signals .phi.1-.phi.4, respectively.
[0135] OR circuit 33 receives the output signal of inverter 32a and
output signal .phi.4 of delay circuit 30d to produce control signal
.phi.CP for accumulating charges. Therefore, the period in which
control signal .phi.CP is at an L level (logical low level), is
provided by the period in which output signal .phi.4 of delay
circuit 30d is at an L level and output signal .phi.1 of delay
circuit 30a is at an H level (logical high level). Therefore,
control signal .phi.CP falls to the L level when output signal
.phi.1 of delay circuit 30a rises to the H level, and rises to the
H level when output signal .phi.4 of delay circuit 30a rises to the
H level. Accordingly, control signal .phi.P is maintained at the L
level for a time period of 3.multidot.DT.
[0136] Control signal .phi.CT applied from AND circuit 34 for the
charge transfer is at the H level when output signal .phi.2 of
delay circuit 30b is at the H level and the output signal of
inverter 32b is at the H level. Therefore, control signal .phi.CT
attains the H level when output signal .phi.2 of delay circuit 30b
rises to the H level, and attains the L level when output signal
.phi.3 of delay circuit 30c attains the H level. Control signal
.phi.CT is maintained at the H level for the period of DT.
[0137] The high levels of output signals .phi.1-.phi.4 of delay
circuits 30a-30d are at the level of power supply voltage VCC, and
the low levels thereof are at the level of ground voltage GND. In
this case, as for control signals .phi.P, .phi.CP and .phi.CT, the
high level is at the level of power supply voltage VCC and the low
level is at a level of ground voltage GND. By changing the level of
the operation power supply voltage of control signal generating
circuit 1, it is possible to change the amplitudes, and the voltage
levels of the high level and the low level of control signals
.phi.P, .phi.CP and .phi.CT.
[0138] Repetition signal .phi.0 may be produced from an internal
oscillator circuit, or may be formed of a clock signal externally,
repetitively supplied for the signal transfer, setting of operation
cycles and others.
[0139] Positive voltage generating circuit 20 operates in
accordance with control signals .phi.PZ, .phi.CPZ and .phi.CTZ
produced by inverting control signals .phi.P, .phi.CP and .phi.CT,
respectively. By utilizing these control signals, it is possible to
achieve the phase relationships between the control signals in the
timing charts of FIGS. 2 and 4. Thus, after turning off the MOS
transistors, the charge pump operation can be performed to
accumulate the charges for generating an internal voltage, and then
the MOS transistors for transferring the charges can be made
conductive.
[0140] In the construction of control signal generating circuit 1
shown in FIG. 6, delay circuits 30a-30d have the same delay time
DT. Delay circuits 30a-30d may have different delay times from each
other, provided that the following control signal generation
sequence is satisfied. When a predetermined time elapses after the
change in voltage level of control signal .phi.P for the
precharging, control signal .phi.CP for precharging changes. When a
predetermined time elapses thereafter, the voltage level of control
signal .phi.CT for the charge transfer changes to perform the
charge transfer. When control signal .phi.CT for the charge
transfer turns inactive, the logical level of control signal
.phi.CP for the charge accumulation changes, and thereafter the
voltage level of precharging control signal .phi.CP changes and the
precharging is performed. Such sequence is required to be
achieved.
[0141] The internal voltage generating circuit shown in FIG. 5
includes negative and positive voltage generating circuits 10 and
20 for producing negative voltage -VCC and positive voltage of
2.multidot.VCC, respectively. However, even in the case where only
one of negative and positive voltage generating circuits 10 and 20
is employed, the internal voltage at an intended level can be
efficiently generated by utilizing the control signal generating
circuit 1. The internal voltage generated may be at a level
different from -VCC and 2.multidot.VCC.
[0142] According to the third embodiment of the invention, as
described above, the delay circuits are cascaded, and the signals
in an intended phase relationship are logically processed to
produce the control signals for the charge precharging, charging
and transferring. Therefore, the control signals for the charge
pump operation for generating the internal voltages can be easily
produced with a simple circuit construction.
[0143] [Fourth Embodiment]
[0144] FIG. 8 shows a structure of a voltage generating circuit
according to a fourth embodiment of the invention. The voltage
generating circuit shown in FIG. 8 differs from the voltage
generating circuit shown in FIG. 1 in that a voltage drive stage 40
for increasing an absolute value of a produced internal voltage is
further arranged between output node OD1 and a final output node
FOD.
[0145] The construction of the negative voltage generating portion
upstream to output node OD1 is the same as that in the voltage
generating circuit shown in FIG. 1. Corresponding portions are
allotted with the same reference numerals, and description thereof
will not be repeated.
[0146] A voltage drive stage 40 includes a capacitance element C20
connected between a control signal input node S31 receiving control
signal .phi.P and output node OD1, an N-channel MOS transistor NQ31
connected between internal output node OD1 and final output node
FOD and having a gate connected to an internal node ND30, an
N-channel MOS transistor NQ32 connected between internal node ND30
and final output node FOD and having a gate connected to internal
output node OD1, and a capacitance element C21 connected between a
control signal input node S32 receiving a control signal .phi.CTF
and internal node ND30.
[0147] Final output node FOD is provided with a stabilizing
capacitance C4, similarly to the first embodiment. However,
stabilizing capacitance C4 may be eliminated if variation in output
load is small.
[0148] Control signal .phi.CTF turns active when negative charges
are to be supplied from final output node FOD to internal output
node OD1. Control signals .phi.P, .phi.CP and .phi.CT are the same
as those in the first embodiment.
[0149] FIG. 9 is a timing diagram illustrating an operation of the
voltage generating circuit shown in FIG. 8. Referring to FIG. 9,
description will now be given on the operation of the voltage
generating circuit shown in FIG. 8. FIG. 9 illustrates also signal
waveforms in the stable state over a time period of 2.multidot.T.
The following description will be given on the operation in the
stable state. In a transition period in the initial stage of the
charge pumping operation, an operation is performed as in the
stable state although the respective nodes attain different voltage
levels.
[0150] Control signals .phi.P, .phi.CP and .phi.CT are the same as
those in the first embodiment, and therefore, the operation itself
of the circuitry upstream to output node OD1 is substantially the
same as that in the first embodiment. However, the voltage
amplitude of internal output node OD1 is different from that in the
first embodiment so that the voltage change on internal node ND3 is
different from that in the first embodiment.
[0151] At a time t10, control signals .phi.P and .phi.CT are set to
the L level, and control signal .phi.CP is set to the H level. In
this state, node ND1 is at the level of negative voltage -VCC, and
output node OD1 is at the negative voltage level of
-2.multidot.VCC. Therefore, node ND1 is driven to the level of
negative voltage -VCC, and node ND2 is precharged to the level of
ground voltage GND. Further, internal output node OD1 is at the
negative voltage of -2.multidot.VCC, MOS transistor NQ2 is
conductive, and internal node ND3 is electrically connected to
internal output node OD1, and is held at the same voltage
level.
[0152] By holding internal node ND3 and internal output node OD1 at
the same voltage level, MOS transistor NQ1 is maintained in the
non-conductive state.
[0153] At time t11, control signal .phi.P rises from the level of
ground voltage GND to the level of power supply voltage VCC.
Responsively, capacitance element C1 drives node ND1 to the level
of ground voltage GND, and the precharge operation on node ND2 is
completed. In this state, a capacitance element C20 raises the
voltage level of output node OD1 from -2.multidot.VCC to -VCC. In
this state, node ND2 is at the level of ground voltage GND, and MOS
transistor NQ2 maintains the conductive state so that internal node
ND3 attains the same voltage level as internal output node OD1, and
attains the level of negative voltage -VCC.
[0154] MOS transistor NQ1 has the gate (node ND3) and source
(internal output node OD1) set to the same potential, and maintains
the non-conductive state.
[0155] At a time t12, control signal .phi.CP falls from the level
of power supply voltage VCC to the level of ground voltage GND, and
node ND12 is driven to the level of negative voltage -VCC so that
N-channel MOS transistor NQ2 turns non-conductive. In this state,
node ND2 is at the level of negative voltage -VCC, and all the
gate, source and drain of MOS transistor NQ1 are at the same
potential in the stable state, so that MOS transistor NQ1 maintains
the non-conductive state. In a transition period, MOS transistor
NQ1 has the gate-source voltage not exceeding the threshold voltage
as in the first embodiment, and maintains the non-conductive
state.
[0156] At time t13, control signal .phi.CT rises from the level of
ground voltage GND to the level of power supply voltage VCC, and
the voltage level of node ND3 rises from negative voltage -VCC to
ground voltage GND. MOS transistor NQ1 turns conductive to connect
electrically node ND2 to output node OD1, and internal node ND2 and
internal output node OD1 are made the same in voltage level.
However, in the steady state, internal output node OD1 is already
precharged to the level of negative voltage -VCC, and the drain
potential and source potential of MOS transistor NQ1 are made equal
to each other so that a current does not flow therethrough in the
steady state.
[0157] At time t14, control signal .phi.CT falls from the level of
power supply voltage VCC to the level of ground voltage GND, and
the voltage level of node ND3 lowers from ground voltage GND to
negative voltage -VCC. Responsively, MOS transistor NQ1 turns
non-conductive to isolate node ND2 from internal output node OD1.
In the stable state, MOS transistor NQ2 have the gate, drain and
source set at the same potential, and does not pass a current.
[0158] At time t15, control signal .phi.CP rises from the level of
ground voltage GND to the level of power supply voltage VCC, and
the voltage level of node ND2 rises from the negative voltage -VCC
to ground voltage GND. In accordance with the rising of voltage
level of node ND2, MOS transistor PQ1 is turned off for preparing
for a next precharge operation.
[0159] Further, MOS transistor NQ2 is turned on to connect
electrically internal node ND3 and internal output node OD1, and
internal node ND3 attains the same voltage level as that on
internal output node OD1, i.e., the level of negative voltage -VCC
so that MOS transistor NQ1 has the gate and source set at the same
voltage, and is kept non-conductive.
[0160] At time t16, control signal .phi.P falls from the level of
power supply voltage VCC to the level of ground voltage GND, and
responsively the voltage on node ND1 lowers from the level of
ground voltage GND to the level of negative voltage -VCC. In
addition, capacitance element C20 lowers internal output node OD1
from the level of the shallow negative voltage -VCC to the level of
the deep negative voltage of -2.multidot.VCC. Node ND2 is at the
level of ground voltage GND, and MOS transistor NQ2 is in a
conductive state so that node ND3 and internal output node OD1 are
at the same voltage level, and MOS transistor NQ1 is kept off.
Therefore, even if node ND2 is at the level of ground voltage GND,
internal output node OD1 lowers to of the deep negative voltage
level of -2.multidot.VCC, and node ND3 also lowers to the deep
negative voltage level of -2.multidot.VCC.
[0161] In this case, since MOS transistor NQ1 has the source
electrically coupled to the gate through MOS transistor NQ2, MOS
transistor NQ1 rapidly turns non-conductive, so that an ineffective
current hardly flows, and internal output node OD1 reliably lowers
to the negative voltage level of -2.multidot.VCC.
[0162] In a transition period and other, the voltage level of
internal node ND30 may possibly exceed the voltage level of
internal output node OD1. However, internal node ND30 is once
connected electrically to final output node FOD, and a difference
in voltage level between internal node ND30 and internal output
node OD1 is small in such a state. Therefore, MOS transistor NQ1
maintains the non-conductive state owing to its threshold
voltage.
[0163] At time t17, control signal .phi.CTF rises from the level of
ground voltage GND to the level of power supply voltage VCC, and
the voltage level of node ND30 rises from the deep negative voltage
of -2.multidot.VCC to the shallow negative voltage -VCC.
Responsively, MOS transistor NQ31 turns conductive to couple
electrically output node OD1 to final output node FOD. When the
voltage level of final output node FOD is higher than the deep
negative voltage of -2.multidot.VCC, negative charges are supplied
from internal output node OD1 to final output node FOD. In this
charge transfer operation, MOS transistor NQ2 has the gate and the
source (final output node FOD) set to the same potential, and
maintains the non-conductive state. Thus, the charges are
efficiently transferred from internal output node OD1 to final
output node FOD.
[0164] At time t18, control signal .phi.P rises from the level of
ground voltage GND to the level of power supply voltage VCC.
Responsively, node ND1 returns from the level of the shallow
negative voltage -VCC to the level of ground voltage GND, and
output node OD1 rises from the level of deep negative voltage of
-2.multidot.VCC to the level of the shallow negative voltage -VCC.
In this state, node ND2 is at the ground voltage level, and node
ND3 rises in voltage level from the deep negative voltage of
-2.multidot.VCC to negative voltage -VCC, similarly to output node
OD1.
[0165] At time t19 and subsequently, the operations described above
are repeated.
[0166] When output node OD1 lowers to the level of the deep
negative voltage of -2.multidot.VCC to lower the voltage level of
node ND3 to the level of deep negative voltage of -2.multidot.VCC,
the voltage level of node ND3 can be reliably and rapidly changed
in accordance with the voltage level of output node OD1 with
capacitance element C20 having the capacitance value much larger
than that of capacitance element C3.
[0167] In the initial period at start of the charge pumping
operation, the voltage of final output node FOD lowers to
-2.multidot.VCC after the voltage on output node OD1 changes
between -VCC and -2.multidot.VCC. The operation of voltage drive
stage 40 in this transition period is similar to that of the
voltage generating circuit previously described in connection with
the first embodiment.
[0168] Voltage drive stage 40 has a structure similar to that of an
output stage (charge transfer stage) of a circuit generating the
negative voltage -VCC and arranged in -VCC generating circuit at
the preceding stage. Therefore, the deep negative voltage of
-2.multidot.VCC can be efficiently generated without causing an
ineffective current flow.
[0169] According to the fourth embodiment of the invention, as
described above, the output stage of the circuit generating shallow
negative voltage -VCC is further connected to the charge pump
capacitance of the output node, and the output stage (charge
transfer stage) of the same structure as the output stage of the
-VCC generating circuit is arranged to form the voltage drive
stage. Thereby, the charges can be efficiently utilized to generate
the negative voltage of -2.multidot.VCC with low power
consumption.
[0170] [Fifth Embodiment]
[0171] FIG. 10A schematically shows a construction of a voltage
generating circuit according to a fifth embodiment of the
invention. The voltage generating circuit shown in FIG. 10A
includes charge transfer stages XFN1, XFN2, . . . and XFNn cascaded
between node ND2 and output node FOD.
[0172] P-channel MOS transistors PQ1 and PQ2 are cross-coupled and
arranged between the ground node and nodes ND1 and ND2. Node ND1
receives control signal .phi.P for precharging via capacitance
element C1, and node ND2 receives control signal .phi.CP for
producing charges via capacitance element C2. MOS transistors PQ1
and PQ2 as well as capacitance elements C1 and C2 have the same
structures as those shown in FIGS. 1 and 8, and nodes ND1 and ND2
are changed in voltage level between ground voltage GND and
negative voltage -VCC in accordance with control signals .phi.P and
.phi.CP.
[0173] Capacitance elements CK1-CKn-1 are connected to output nodes
OD1-ODn-1 of charge transfer stages XFN1-XFNn-1, respectively. In
charge transfer stages XFN1, XFN3, . . . and XFNn-1 at odd-numbered
stages, capacitance elements CQ1 . . . CQn-1 arranged at respective
output nodes OD1, OD3, . . . and ODn-1 receive control signal
.phi.P via control signal input nodes S1. In charge transfer stages
XFN2 . . . at even-numbered stages, capacitance elements CQ2 . . .
arranged at respective output nodes OD2 . . . receive control
signal .phi.CP via control signal input nodes S2. Charge transfer
stages XFN1-XFNn alternately receive control signals .phi.CT and
.phi.CTF. The charge transfer stage and the capacitance element
arranged at a respective input node (i.e., the output node of the
upstream charge transfer stage) form the voltage drive stage.
[0174] Final output node FOD is connected to stabilizing
capacitance element C4. If the voltage on final output node FOD is
stable, stabilizing capacitance element C4 may not be provided.
[0175] FIG. 10B shows a construction of charge transfer stages
XFN1-XFNn. Charge transfer stages XFN1-XFNn have the same
structure, and FIG. 10B shows charge transfer stage XFN generally
representing charge transfer stages XFN1-XFNn.
[0176] Charge transfer stage XFN includes an N-channel MOS
transistor NQa connected between an input node NDI and an output
node NDO, an N-channel MOS transistor NQb connected between output
node NDO and an internal node NDA and having a gate connected to
input node NDI, and a capacitance element Ca connected between
control signal input node Sa and internal node NDA.
[0177] Charge transfer stage XFN is equivalent in construction to
voltage drive stage 40 shown in FIG. 8 other than capacitance
element C20. Control signal input node Sa receives control signal
.phi.CT or .phi.CTF for controlling the charge transfer. The
precharging of input node NDI and the charge transfer are
alternately performed in charge transfer stages XFN1-XFNn, so that
a voltage drop by -VCC can be caused in each of charge transfer
stages XFN1-XFNn, and a voltage of -n.multidot.VCC can be generated
on final output node FOD.
[0178] FIG. 11 is a timing chart representing an operation of the
voltage generating circuit shown in FIGS. 10A and 10B. FIG. 11
illustrates signal waveforms on the output and input nodes of
charge transfer stages XFNi-1, XFNi and XFNi+1. Capacitance
elements Ca of charge transfer stages XFNi-1, XFNi and XFNi+1 are
supplied with control signals .phi.CTF, .phi.CT and .phi.CTF,
respectively. Referring to FIG. 11, description will now be given
on the operation of the voltage generating circuit shown in FIGS.
10A and 10B.
[0179] When control signal .phi.P rises from ground voltage GND to
power supply voltage VCC, the voltage level of input node NDIi-1 of
charge transfer stage XFNi-1 is raised by the charge pump operation
of corresponding capacitance element CKi-2. In this case, the
voltage level changes from a negative voltage of
-(i-1).multidot.VCC to a negative voltage of -(i-2).multidot.VCC.
In this state, internal node NDAi-1 is at the voltage of
-(i-1).multidot.VCC, and MOS transistor NQa in charge transfer
stage XFNi-1 maintains the non-conductive state.
[0180] In charge transfer stage XFNi+1, the charge pump operation
is likewise effected on input node NDIi+1 in accordance with
control signal .phi.P, and the voltage level thereof changes from
-(i+1).multidot.VCC to -i.multidot.VCC. Input node NDIi+1 of charge
transfer stage XFNi+1 corresponds to output node ODi of charge
transfer stage XFNi. In this case, MOS transistor NQb in charge
transfer stage XFNi is in a conductive state, and accordingly the
level of node NDIi changes from a voltage of -(i+1).multidot.VCC to
-i.multidot.VCC. Even in this state, MOS transistor NQa in charge
transfer stage XFNi has the gate lower in potential than its
source, and therefore maintains the non-conductive state.
[0181] When control signal .phi.CP falls from the level of power
supply voltage VCC to the level of ground potential GND,
capacitance element CKi in charge transfer stage XFNi performs the
charge pumping operation to change the voltage on input node NDIi
from -(i-1).multidot.VCC to -i.multidot.VCC. In this operation, in
charge transfer stage XFNi-1, node NDIi-1 is at the voltage level
of -(i-2).multidot.VCC and MOS transistor NQb is in a conductive
state, so that node NDAi-1 rises from the voltage level of
-(i-1).multidot.VCC to the voltage level of -i.multidot.VCC.
[0182] When a predetermined period elapses, control signal .phi.CT
is driven to the level of power supply voltage VCC. In charge
transfer stage XFNi, the charge pumping by capacitance element Ca
raises the voltage level of input node NDAi from
-(i+1).multidot.VCC to -i.multidot.VCC, and MOS transistor NQa
turns conductive. Accordingly, the charges are driven via MOS
transistor NQa in charge transfer stage XFNi. In this state, node
NDIi+1 is at the voltage level of -i.multidot.VCC, and the voltage
level of input node NDIi in charge transfer stage XFNi is made
equal to the voltage level of input node NDIi+1 in charge transfer
stage XFNi+1.
[0183] When control signal .phi.CT falls to the ground voltage
level again, the voltage level of input node NDAi in charge
transfer stage XFNi is lowered by power supply voltage VCC to
attain the voltage level of -i.multidot.VCC, and MOS transistor NQa
in charge transfer stage XFNi turns non-conductive.
[0184] Then, control signal .phi.CP rises from the level of ground
voltage GND to the level of power supply voltage VCC, and the
voltage level of input node NDIi of charge transfer stage XFNi
rises. Responsively, internal node NDAi-1 in charge transfer stage
XFNi-1 is raised in voltage level through MOS transistor NQb in
accordance with the voltage level of node NDIi, and is set to the
voltage level of -(i-1).multidot.VCC.
[0185] In accordance with control signal .phi.CP, the voltage level
of internal node NDAi+1 in charge transfer stage XFNi+1 likewise
lowers, to render corresponding MOS transistor NQa non-conductive
when the voltage level of the output node ODi+1 lowers.
[0186] When a predetermined time elapses, control signal .phi.P
falls from the level of power supply voltage VCC to the level of
ground voltage GND. Responsively, the capacitance element in charge
transfer stage XFNi+1 performs the charge pump operation on input
node NDIi+1, and the voltage level thereof lowers from
-i.multidot.VCC to -(i+1).multidot.VCC. This voltage drop is
transmitted to internal node NDAi of charge transfer stage XFNi via
MOS transistor NQb, and this MOS transistor NQb is reliably made
non-conductive.
[0187] After a predetermined time further elapses, control signal
.phi.CTF attains and maintains the level of power supply voltage
VCC for a predetermined period, and the voltage levels of internal
nodes NDAi-1 and NDAi+1 in charge transfer stages XFNi-1 and XFNi+1
are raised by power supply voltage VCC so that corresponding MOS
transistors NQa turns conductive to transfer the charges.
[0188] In the above operation, as for charge transfer stage XFNi,
the voltage level of internal node NDAi is equal to the voltage
level of input node NDIi+1 of charge transfer stage XFNi+1, and
therefore to the voltage level of output node ODi of charge
transfer stage XFNi, and thus MOS transistor NQa maintains the
non-conductive state to prevent backflow of a current in charge
transfer stage XFNi.
[0189] Accordingly, by cascading charge transfer stages XFN1-XFNn,
and by alternately performing the precharging of the input nodes
and the charging of the associated internal nodes in accordance
with phase-controlled control signals in these charge transfer
stages, the backflow of the current can be reliably prevented from
occurring, and the generated voltages can be decreased by the
voltage VCC in the charge transfer stages. In the structure of
charge transfer stages XFN1-XFNn of n stages, a voltage of
-n.multidot.VCC is produced on output node FOD. Thus, it is
possible to generate a negative voltage at an intended voltage
level, and a required voltage level can be stably generated with
low power consumption even under a low power supply voltage
condition.
[0190] FIG. 12 schematically shows a construction of a circuit for
generating the control signals used in the voltage generating
circuit shown in FIGS. 10A and 10B. In addition to the components
of the control signal generating circuit shown in FIG. 6, the
control signal generating circuit shown in FIG. 12 includes an AND
circuit 45 receiving output signal .phi.4 of delay circuit 30d and
the output signal of inverter 32b to produce control signal
.phi.CTF. Other components of the control signal generating circuit
shown in FIG. 12 are the same as those of the control signal
generating circuit shown in FIG. 6. Corresponding portions are
allotted with the same reference numerals, and description thereof
will not be repeated.
[0191] According to the construction of the control signal
generating circuit shown in FIG. 12, AND circuit 45 generates
control signal .phi.CTF at the H level when output signal .phi.4 of
delay circuit 30d is at the H level and the output signal of
inverter 32b is at the H level. As shown in FIG. 13, therefore,
control signal .phi.CTF is at the H level when output signals
.phi.3 and .phi.4 of delay circuits 30c and 30d are at the L- and H
levels, respectively. Other control signals .phi.P, .phi.CP and
.phi.CT are generated from the same components as those in the
circuit shown in FIG. 6, and have the same timing relationship. By
utilizing the control circuit shown in FIG. 12, for each charge
transfer stage, when the negative charges are supplied on its input
node to be ready for transferring the charges, the control signal
for charge transfer can be applied accurately to transfer the
charges to the output node. In addition, the backflow of the
current can be prevented.
[0192] According to the fifth embodiment of the invention, as
described above, the plurality of charge transfer stages are
cascaded, and the charge transferring and the precharging of the
input node are alternately performed in the respective charge
transfer stages, so that a deep negative voltage can be produced
with low power consumption.
[0193] [Sixth Embodiment]
[0194] FIG. 14 shows a construction of a voltage generating circuit
according to a sixth embodiment of the invention. In addition to
the components of the voltage generating circuit shown in FIG. 3,
the voltage generating circuit shown in FIG. 14 further includes a
voltage drive stage 50 for transmitting charges of output node OD11
to final output node FOD in accordance with control signals .phi.PZ
and .phi.CTFZ.
[0195] Voltage drive stage 50 includes a capacitance element CC
performing a charge pump operation on internal output node OD11 in
accordance with control signal .phi.PZ, and a charge transfer stage
XFP transmitting the charged electric charges in capacitance
element CC to final output node FOD in accordance with control
signal .phi.CTFZ.
[0196] Charge transfer stage XFP includes a P-channel MOS
transistor PQa connected between internal output node OD11 and
final output node FOD and having a gate connected to an internal
node NDB, a P-channel MOS transistor PQb connected between internal
node NDB and final output node FOD and having a gate connected to
internal output node OD11, and a capacitance element Cb connected
between a control signal input node S52 receiving control signal
.phi.CTFZ and internal node NDB. Charge transfer stage XFP has an
input node PDI connected to internal output node OD11, and an
output node POD connected to final output node FOD.
[0197] In the voltage generating circuit shown in FIG. 14, a
circuit, arranged upstream to output node OD11 for generating a
voltage of 2.multidot.VCC, is formed of a portion for generating
the voltage boosting charges and a portion for transferring the
voltage boosting charges. These charge generating portion and the
charge transferring portion have the same constructions as those in
the circuit shown in FIG. 1. Corresponding components are allotted
with the same reference numbers, and description thereof will not
be repeated.
[0198] FIG. 15 is a signal waveform diagram showing an operation in
the stable state of the voltage generating circuit shown in FIG.
14. Referring to FIG. 15, an operation in the stable state of the
voltage generating circuit shown in FIG. 14 will now be
described.
[0199] The voltage generating circuit shown in FIG. 14 is the same
as the voltage generating circuit shown in FIG. 8, provided that
the conductivities of the transistors, polarities of the control
signals and polarities of the voltages are exchanged. Basically, in
the voltage generating circuit shown in FIG. 14, the charge pump
operation for the charges of node ND12 is the same as that of the
circuit shown in FIG. 3, and capacitance element C12 changes the
voltage level of node ND12 between power supply voltage VCC and the
high voltage of 2.multidot.VCC in accordance with control signal
.phi.CPZ. Capacitance element CC changes the voltage level of
internal output node OD11 through the charge pumping operation in
accordance with control signal .phi.PZ. Therefore, internal output
node OD11 changes between the voltages of 2.multidot.VCC and
3.multidot.VCC. Since the voltage level of internal output node
OD11 changes up to 3.multidot.VCC, the voltage level of internal
node ND13 changes between power supply voltage VCC and the high
voltages of 2.multidot.VCC and 3.multidot.VCC over three
stages.
[0200] At time t11, control signal .phi.PZ falls from power supply
voltage VCC to ground voltage GND. Responsively, output node OD11
is set to the voltage level of 2.multidot.VCC by the charge pumping
operation of capacitance element CC. In this operation, node ND12
is at the level of power supply voltage VCC, and MOS transistor
PQ12 is in a conductive state, so that node ND13 attains the
voltage level of 2.multidot.VCC similarly to internal output node
OD11. Accordingly, MOS transistor PQ11 has gate and the source at
the same potential, and turns non-conductive.
[0201] At time t12, control signal .phi.CPZ rises to the level of
power supply voltage VCC. Responsively, the voltage level of node
ND12 attains the level of high voltage of 2.multidot.VCC, so that
MOS transistor PQ12 is turned off. In this state, MOS transistor
PQ11 has the gate, drain and source set at the same voltage level,
and maintains off.
[0202] In voltage drive stage 50, control signal .phi.CTFZ is at
the level of power supply voltage VCC, node NDB is at the level of
3.multidot.VCC and MOS transistor PQa is in an off state. Since
internal output node OD11 is at the voltage level of
2.multidot.VCC, MOS transistor PQb maintains the conductive state,
but a current does not flow through MOS transistor PQb because node
NDB and final output node FOD are at the same voltage level.
[0203] At a time t13, control signal .phi.CTZ falls from the level
of power supply voltage VCC to the level of ground voltage GND.
Responsively, the voltage level of node ND13 lowers from the
voltage of 2.multidot.VCC to power supply voltage VCC so that MOS
transistor PQ11 turns conductive, to transfer the charges between
internal output node OD1 and internal node ND12. This charge
transfer operation completes when internal node ND12 and output
node OD11 attain the same potential level.
[0204] In the charge transfer operation, MOS transistor PQ12
maintains the non-conductive state because its gate and source are
set to the same voltage level. In this charge transfer operation,
node NDB is at the voltage level of 3.multidot.VCC, internal output
node OD11 is at the voltage level of 2.multidot.VCC, and P-channel
MOS transistor PQa for the charge transfer maintains the
non-conductive state.
[0205] At a time t14, control signal .phi.CPZ rises from the level
of ground voltage to the level of power supply voltage VCC, and
responsively the voltage level of node ND13 rises from power supply
voltage VCC to the high voltage of 2.multidot.VCC, so that MOS
transistor PQ11 turns non-conductive. In this operation, MOS
transistor PQ12 maintains the non-conductive state owing to its
threshold voltage because node ND12 is at the voltage level of
2.multidot.VCC At time t15, control signal .phi.CPZ falls from
power supply voltage VCC to ground voltage GND. Responsively, the
charge pumping by capacitance element C12 lowers the voltage level
of node ND12 from the high voltage of 2.multidot.VCC to power
supply voltage VCC. When the voltage level of node ND12 lowers to
the level of power supply voltage VCC to turn on P-channel MOS
transistor PQ12, for electrically connecting nodes ND13 and OD11
together, node ND13 and internal output node OD11 are at the equal
voltage level of 2.multidot.VCC, and a current does not flow in the
stable state. MOS transistor PQ11 maintains the non-conductive
state because its gate and source are at the same potential
level.
[0206] At time t16, control signal .phi.PZ rises from the level of
ground voltage GND to the level of power supply voltage VCC, and
responsively, node ND11 is raised to the level of power supply
voltage VCC so that node ND12 is reliably precharged to the level
of power supply voltage VCC.
[0207] When control signal .phi.PZ rises, capacitance element CC
performs the charge pump operation to raise output node OD1 from
the level of 2.multidot.VCC to the level of 3.multidot.VCC. When
the voltage level of output node OD11 rises to the voltage level of
3.multidot.VCC, node ND12 is at the level of power supply voltage
VCC, and MOS transistor PQ12 is rendered conductive, so that node
ND13 rises to the voltage level of 3.multidot.VCC, and MOS
transistor PQ11 maintains the non-conductive state.
[0208] At time t17, control signal .phi.CTFZ falls from the level
of power supply voltage VCC to the level of ground voltage GND.
Responsively, the charge pumping by capacitance element Cb lowers
the voltage level of node NDB from the voltage of 3-VCC to the
voltage of 2.multidot.VCC, and MOS transistor PQa is turned on to
transfer the charges from output node OD11 to final output node FOD
so that final output node FOD is reliably kept at the voltage level
of 3.multidot.VCC. In this charge transfer operation, node NDB is
at the voltage level of 2.multidot.VCC, and output node OD11 and
final output node FOD are at the same voltage level higher than
that of node NDB. Thus, MOS transistor PQb maintains the
non-conductive state.
[0209] At time t18, control signal .phi.CTFZ rises from the level
of ground voltage GND to the level of power supply voltage VCC
again. Responsively, the charge pumping by capacitance element Cb
raises the voltage level of node NDB to the voltage of
3.multidot.VCC, and MOS transistor PQa turns non-conductive.
[0210] At time t19, control signal .phi.PZ falls from the level of
power supply voltage VCC to the level of ground voltage GND so that
the voltage level of output node OD11 lowers to 2.multidot.VCC. In
this operation, MOS transistor PQ12 is in an on-state, so that the
voltage level of node ND13 lowers from 3.multidot.VCC to
2.multidot.VCC. Subsequently, the above operations are
repeated.
[0211] Accordingly, since one voltage drive stage 50 is arranged
for precharging the output node to transfer the charges in the
operation of precharging the internal node, the voltage on this
output node can be raised by voltage VCC, and the voltage of
3.multidot.VCC can be produced on final output node FOD.
[0212] For the simplicity reason, no description is given on the
operation in the transition period of the initial charge pump
operation. However, an operation is performed similarly to that in
the circuit generating the negative voltage of -2.multidot.VCC in
the fourth embodiment, and the threshold voltages of the
transistors of the enhancement type are utilized to raise gradually
the voltage level of the final output voltage while preventing the
occurrence of an ineffective current flow.
[0213] Stabilizing capacitance C4 provided at final output node FOD
may be removed if the load variation of final output node FOD is
small.
[0214] Control signals .phi.PZ, .phi.CPZ, .phi.CTZ and .phi.CTFZ
can be produced by inverting the output signals of the control
signal generating circuits shown in FIG. 12.
[0215] Similarly to the second embodiment, therefore, control
signals .phi.PZ, .phi.CPZ, .phi.CTZ and .phi.CTFZ are not required
to change between ground voltage GND and power supply voltage VCC,
and may be replaced with signals changing between any intended
voltages, provided that the on/off conditions of the MOS
transistors of the components are met.
[0216] According to the sixth embodiment, as described above, the
capacitance element for the charge pump is arranged at the output
node of the circuit generating the voltage of 2.multidot.VCC, and
one stage of charge transfer stage is further arranged in which the
on/off of charge transferring transistor PQa is controlled by the
capacitance element and the MOS transistor detecting the potential
of the output node. Accordingly, flow of ineffective charges is
prevented, and the charges can be efficiently used to generate the
high voltage of 3.multidot.VCC.
[0217] [Seventh Embodiment]
[0218] FIG. 16 schematically shows a construction of a voltage
generating circuit according to a seventh embodiment of the
invention. In FIG. 16, charge transfer stages XFP1-XFPn are
cascaded between internal node ND12 and final output node FOD. Each
of charge transfer stages XFP1-XFPn is the same in configuration as
charge transfer stage XFP shown in FIG. 14.
[0219] Capacitance elements CC1 to CCn-1 are arranged corresponding
to input nodes ODP1-ODPn-1 of charge transfer stages XFP2-XFPn,
respectively. Capacitance elements CC1 to CCn-1 are alternately
supplied with control signals .phi.PZ and .phi.CPZ through control
signal input nodes S11 and S12. Charge transfer stages XFP1-XFPn
are alternately supplied with control signals .phi.CTZ and
.phi.CTFZ through control signal input nodes S13 and S52. Thus,
charge transfer stages IFX1, XFP3, . . . and XFPn-1 in odd-numbered
stages are supplied with control signal .phi.CTZ through control
signal input nodes S13 to transfer the charges, and charge transfer
stages XFP2, . . . and XFPn in even-numbered stages are supplied
with control signal .phi.CTFZ through control signal input nodes
S52 and has the charge transfer controlled.
[0220] Each of charge transfer stages XFP1-XFPn raises the received
voltage by power supply voltage VCC. Therefore, a voltage of
(n+1).multidot.VCC is produced on final output node FOD.
[0221] For controlling the operation of accumulating the charges on
node ND12, cross-coupled N-channel MOS transistors NQ11 and NQ12
are arranged, and capacitance elements C11 and C12 performing the
charge pump operation on nodes ND11 and ND 12 in accordance with
control signal .phi.PZ and .phi.CPZ are arranged. The circuit
portion performing the charge pump operation on node ND12 is the
same in configuration as that shown in FIGS. 3 and 14, and
therefore the voltage on node ND12 changes between voltage VCC and
the high voltage of 2.multidot.VCC.
[0222] FIG. 17 is a timing chart illustrating an operation of the
voltage generating circuit shown in FIG. 16 in the stable state.
Referring to FIGS. 17 and 14, description will now be given on the
operation of the voltage generating circuit shown in FIG. 16 in the
stable state.
[0223] FIG. 17 illustrates waveforms of voltages on the input and
internal nodes of charge transfer stages XFPi-1, XFPi and XFPi+1.
Charge transfer stages XFPi-1 and XFPi+1 are supplied with control
signal .phi.CTF, and charge transfer stage XFPi is supplied with
control signal .phi.CT. Input node NDIj of charge transfer stage
XFPj is connected to internal output node ODPj-1 of charge transfer
stage XFPj-1 at the preceding stage. FIG. 17 illustrates internal
output nodes ODIi-1 and ODIi corresponding to input nodes NDIi and
NDIi+1, respectively. The potentials of the input nodes of the
respective charge transfer stages will now be described due to the
reference to FIG. 14.
[0224] When control signal .phi.PZ falls to the level of ground
voltage GND, input node NDIi-1 of charge transfer stage XFPi-1
lowers from a voltage level of i.multidot.VCC to a voltage level of
(i-1).multidot.VCC. In charge transfer stage XFPi+1, the voltage of
its input node NDIi+1 lowers from the voltage level of
(i+1).multidot.VCC to the voltage level of (i+1).multidot.VCC. In
these charge transfer stages XFPi-1 and XFPi+1, since MOS
transistor PQb is in an conductive state, internal nodes NDBi-1 and
NDBi+1 are set to the voltage levels corresponding to the voltage
levels of the subsequent charge transfer stages XFPi and XFPi+2,
respectively.
[0225] When input node NDIi+1 of the charge transfer stage XFPi+1
subsequent to charge transfer stage XFPi lowers to the voltage
level of (i+1).multidot.VCC, the voltage level of output node NDBi
of charge transfer stage XFPi lowers from (i+2).multidot.VCC to
(i+1).multidot.VCC because MOS transistor PQd is conductive.
[0226] When control signal .phi.CPZ rises from the level of ground
voltage GND to the level of power supply voltage VCC, in charge
transfer stage XFPi, the charge pumping by corresponding
capacitance element CCi raises the voltage level of input node NDIi
from the voltage of i.multidot.VCC to the voltage of
(i+1).multidot.VCC. Since MOS transistor PQb in charge transfer
stage XFPi-1 is in a conductive state, such boosted voltage of node
NDIi raises the voltage level of node NDBi-1 to (i+1).multidot.VCC,
and corresponding MOS transistor PQa is kept off.
[0227] Likewise, in charge transfer stage XFPi+1, the voltage level
of internal node NDBi+1 rises to the voltage of (i+3).multidot.VCC,
and corresponding P-channel MOS transistor PQa is kept off.
[0228] When control signal .phi.CTZ falls from power supply voltage
VCC to ground voltage GND, in charge transfer stage XFPi, internal
node NDBi attains the voltage level of i.multidot.VCC, MOS
transistor PQa turns conductive to transmit the voltage of
(i+1).multidot.VCC on internal node NDIi to input node NDIi+1 at
the subsequent or downstream charge transfer stage XFPi+1. In this
charge transfer, backflow of charges is prevented in charge
transfer stages XFPi-1 and XFPi+1 because MOS transistors PQa are
in an off (non-conductive state).
[0229] When control signal .phi.CPZ rises to the level of power
supply voltage VCC, the voltage level of internal node NDBi in
charge transfer stage XFPi rises from the voltage of i.multidot.VCC
to the voltage of (i+1).multidot.VCC, and the gate potential of
corresponding P-channel MOS transistor PQa becomes equal to or
higher than its source potential so that MOS transistor PQa is
turned off.
[0230] When control signal .phi.PZ rises from ground voltage GND to
power supply voltage VCC, capacitance elements CCi-1 and CCi+1 in
charge transfer stages XFPi-1 and XFPi+1 perform the charge pump
operations to raise the voltage levels of the corresponding input
nodes by power supply voltage VCC, respectively. Thus, input node
NDIi-1 of charge transfer stage XFPi-1 attains the voltage level of
i.multidot.VCC, and input node NDIi+1 of charge transfer stage
XFPi+1 attains the voltage level of (i+2).multidot.VCC.
[0231] In such state, in charge transfer stage XFPi, MOS transistor
PQb turns conductive because the gate potential thereof is lower
than the source potential thereof, and internal node NDBi rises to
the level of the voltage of (i+2).multidot.VCC equal to that of
input node NDIi+1 of charge transfer stage XFPi+1, and MOS
transistor PQa is kept off to prevent backflow of charges.
[0232] In this state, control signal .phi.CTZF falls from power
supply voltage VCC to ground voltage GND, and in charge transfer
stages XFPi-1 and XFPi+1, the voltage levels of internal nodes
NDBi-1 and NDBi+1 are lowered by power supply voltage VCC, and
corresponding MOS transistors PQa are rendered conductive.
Consequently, the charges are transferred from input node NDIi-1 to
output node ODPi-1 (NDIi), and also the charges are supplied from
input node NDIi+1 to the output node in charge transfer stage
XFPi+1.
[0233] Subsequently, the above operations are repeated so that
charge transfer stages XFP1-XFPn alternately perform the charge
pump operation to boost the received voltages by the power supply
voltage VCC, and can finally produce the voltage of
(n+1).multidot.VCC on final output node FOD.
[0234] In the high voltage generating circuit, in the transition
period of the initial period of the charge pumping operation, as in
the sixth embodiment, the threshold voltage of an MOS transistor is
utilized to control the setting of the non-conductive state of the
MOS transistor to prevent the occurrence of an ineffective current
and each node is raised in voltage level gradually to attain the
final stable voltage level.
[0235] In this seventh embodiment, control signals .phi.PZ,
.phi.CPZ, .phi.CTZ and .phi.CTFZ each may be different in the high
level voltage and the low level voltage from the others.
[0236] According to the seventh embodiment of the invention, as
described above, a plurality of charge transfer stages are
cascaded, the capacitance elements are used to perform the charge
pump operation on the input nodes of the respective charge transfer
stages, and the charge transfer operations are performed in an
alternate manner. Accordingly, the internal voltage at an intended
level can be produced with reduced current consumption.
[0237] Control signals .phi.PZ, .phi.CPZ, .phi.CTZ and .phi.CTFZ
can be produced by inverting all the output signals of the control
signal generating circuitry shown in FIG. 12.
[0238] [Eighth Embodiment]
[0239] FIG. 18 shows a construction of a voltage generating circuit
according to an eighth embodiment of the invention. The voltage
generating circuit shown in FIG. 18 differs in configuration from
the voltage generating circuit shown in FIG. 1 in the following
points. Cross-coupled P-channel MOS transistors PQ1 and PQ2 in FIG.
1 are replaced with N-channel MOS transistors NQQ1 and NQQ2 forming
a charge transfer stage. N-channel MOS transistor NQQ1 is connected
between a precharge voltage supply node NDD2 and internal node ND2,
and has a gate (control electrode) connected to an internal node
(first internal node) NDD1. Precharge voltage supply node NDD2 is
connected to ground node GG supplying ground voltage GND of the
reference voltage.
[0240] N-channel MOS transistor NQQ2 is connected between internal
nodes NDD1 and NDD2, and has a gate coupled to control signal input
node S1 receiving control signal .phi.P. Internal node NDD1 is
coupled via capacitance element CQ1 to input node S32 receiving
control signal .phi.CTF.
[0241] The construction of the charge transfer stage arranged
between input node ND2 and output node OD1 is the same as that
shown in FIG. 1. Corresponding elements are allotted with the same
reference numerals, and description thereof will not be
repeated.
[0242] Control signals .phi.CTF, .phi.P, .phi.CP and .phi.CT each
change between ground voltage GND and power supply voltage VCC, and
are produced from the control circuit shown in FIG. 12.
[0243] MOS transistors NQQ1 and NQQ2 correspond to the claimed
first and second transistors, respectively, and capacitance element
CQ1 correspond to the claimed first capacitance element. Control
signal .phi.CTF corresponds to the first control signal, and
control signal .phi.P corresponds to the second control signal in
the claim recitation. MOS transistors NQ1 and NQ2 correspond to the
claimed third and fourth transistors, respectively, and capacitance
elements C2 and C3 correspond to the claimed second and third
capacitance elements, respectively. Control signals .phi.CP and
.phi.CT correspond to the claimed third and fourth control signals,
respectively. All the MOS transistors are each of the enhancement
type.
[0244] FIG. 19 is a signal waveform diagram illustrating an
operation of the voltage generating circuit shown in FIG. 18.
Referring to FIG. 19, description will now be given on the
operation of the voltage generating circuit shown in FIG. 18. FIG.
19 illustrates signal waveforms in the case when negative voltage
-VCC is produced on output node OD1.
[0245] At time t0, control signals .phi.P, .phi.CT and .phi.CTF are
at the L level, and control signal .phi.CP is at the H level. In
this state, internal node ND2 is at the level of ground voltage GND
through the charge pump operation of capacitance element C2
receiving control signal .phi.CP. Internal node ND3 attains the
level of negative voltage -VCC through the charge pump operation of
capacitance element C3. In the stable state, when internal node ND2
is at the level of ground voltage GND, MOS transistor NQ2 is turned
on (output node OD1 is at the level of negative voltage -VCC), and
internal node ND3 is set to the same voltage level as that of
output node OD1.
[0246] Internal node NDD1 is at the level of ground voltage GND
through the charge pump operation of capacitance element CQ1.
Control signal .phi.P is at the L level of the ground voltage, and
MOS transistor NQQ2 is in a non-conductive state.
[0247] At time t1, control signal .phi.P rises to the H level of
power supply voltage VCC. In response to this rising of control
signal .phi.P, MOS transistor NQQ2 is turned on, so that internal
nodes NDD1 and ND2 are electrically coupled together, to attain the
same voltage level (set to the ground voltage level).
[0248] At time t2, while control signal .phi.P is at the H level,
control signal .phi.CP falls to the L level of ground voltage GND.
In response to the falling of control signal .phi.CP, the charge
pumping by capacitance element C2 lowers the voltage level of node
ND2. Since MOS transistor NQQ2 is in a conductive state, the charge
pumping by capacitance element C2 lowers the voltage levels of
nodes NDD1 and ND2 from the ground voltage to negative voltage
-VCC. By making capacitance element C2 to have a capacitance value
much larger than that of capacitance element CQ1, both internal
nodes NDD1 and ND2 can be lowered from the level of ground voltage
GND to the level of negative voltage -VCC.
[0249] When the voltage level of internal node ND2 lowers to the
level of negative voltage -VCC, MOS transistor NQ2 in the output
charge transfer stage turns off, so that internal node ND3 is
isolated from output node OD1, and enters into an electrically
floating state.
[0250] In this state, control signal .phi.CT is raised from the
level of ground voltage GND to the level of power supply voltage
VCC at time t3. In response to the rising of control signal
.phi.CT, the charge pumping by capacitance element C3 raises the
voltage level of node ND3 from negative voltage -VCC to the level
of ground voltage GND, and MOS transistor NQ1 is turned on to
couple electrically internal node ND2 to output node OD1. When
output node OD1 is at a higher voltage level than internal node
ND2, positive charges move from output node OD1 to internal node
ND2 so that the voltage level of output node OD1 lowers.
[0251] Internal node ND3 is at the level of ground voltage GND. In
the steady state, the gate-source voltage of MOS transistor NQ1 is
equal to power supply voltage VCC, and the charges can be
transferred between internal node ND2 and output node OD1 without
an influence by the threshold voltage of MOS transistor NQ1.
[0252] When MOS transistor NQ1 is turned on to move the charges
between internal node ND2 and output node OD1, the gate and source
of MOS transistor NQ2 attain the same potential level. In this
state, MOS transistor NQ2 is of the enhancement type, and maintains
the non-conductive state due to its threshold voltage.
[0253] At time t4, control signal .phi.CT falls from the H level to
the L level. Responsively, the charge pumping by capacitance
element C3 lowers the voltage level of internal node ND3 to
negative voltage -VCC again, and MOS transistor NQ1 turns
non-conductive.
[0254] When the charges move between internal node ND2 and output
node OD1, MOS transistor NQQ2 is in a conductive state to couple
electrically internal nodes NDD1 and ND2, and can supply negative
charges from internal node ND2 to internal node NDD1 so that the
charges can be efficiently transferred. In the above operation, MOS
transistor NQQ1 maintains the non-conductive state because internal
nodes NDD1 and ND2 are at substantially equal potentials, and the
gate-source voltage thereof is lower than the threshold
voltage.
[0255] At time t5, control signal .phi.CP is raised from the L
level of ground voltage GND to the H level of power supply voltage
VCC. In response to the rising of control signal .phi.CP, the
charge pumping by capacitance element C2 raises the potential of
internal node ND2 from the level of negative voltage -VCC. In this
state, control signal .phi.P is at the level of power supply
voltage VCC, and MOS transistor NQQ2 is in a conductive state, so
that the voltage levels of both internal nodes NDD1 and ND2 rise to
ground voltage GND.
[0256] At time t6, control signal .phi.P falls to the L level, and
MOS transistor NQQ2 is turned off, and internal nodes ND2 and NDD1
are electrically isolated from each other.
[0257] At time t7, control signal .phi.CTF rises to the H level.
Thereby, the charge pump operation of capacitance element CQ1
raises the voltage level of internal node NDD1 from ground voltage
GND to power supply voltage VCC (MOS transistor NQQ2 is off). In
accordance with this rising of the potential level of internal node
NDD1, MOS transistor NQQ1 is turned on to precharge internal node
ND2 to the level of ground voltage GND.
[0258] At time t8, control signal .phi.CTF falls to the L level.
Responsively, the charge pumping by capacitance element CC1 lowers
the potential of internal node NDD1 to the level of ground voltage
GND again, and MOS transistor NQQ1 is turned off (node ND2 is at
the ground voltage level).
[0259] Subsequently, the operations performed from time t0 to time
t8 are repeated so that negative voltage -VCC corresponding to the
potential amplitude of internal node ND2 is produced on output node
OD1. A stabilizing capacitance element 4 stably maintains negative
voltage -VCC on output node OD1.
[0260] In the transition period before the voltage level of output
node OD1 becomes stable, node NDD1 attains the level of power
supply voltage VCC in accordance with the H level of control signal
.phi.CTF in the period between times t7 and t8, to turn MOS
transistor NQ1 conductive, so that internal node ND2 is coupled to
the ground node to be set to the ground voltage level. After MOS
transistor NQQ1 is turned off, control signal .phi.CP is lowered
from the H level to the L level. According to such control
procedure, internal node ND2 attains the level of negative voltage
-VCC, and positive charges flow from output node OD1 into internal
node ND2 (negative charges flow from internal node ND2 into output
node OD1) when MOS transistor NQ1 is conductive, and the voltage
level of output node OD1 gradually lowers.
[0261] Even when the charges moves in the transition state,
internal node ND2 is at the level of negative voltage -VCC, and MOS
transistor NQ2 has the gate potential not exceeding the source and
drain potentials, and maintains the non-conductive state. In this
state, MOS transistor NQ1 can be kept conductive in accordance with
control signal .phi.CT. In the transition period, therefore, the
negative charges can be reliably supplied to output node OD1 to
lower its potential level gradually.
[0262] In the construction of the voltage generating circuit shown
in FIG. 18, only N-channel MOS transistors are employed. Therefore,
it is not necessary to provide a region for isolating a P-channel
MOS transistor from an N-channel MOS transistor, and the circuit
occupation area can be reduced. Further, steps for forming the
P-channel MOS transistor are not necessary so that the number of
manufacturing steps and the manufacturing cost can be reduced.
[0263] The gate potentials of MOS transistors NQ1, NQ2, NQQ1 and
NQQ2 are individually controlled by control signals .phi.CT,
.phi.CP, .phi.CTF and .phi.P, respectively. Therefore, by
appropriately setting the timing of these control signals, the
charges can be transferred after cutting off a path of flow of
ineffective charges, and the flow of ineffective charges can be
prevented so that the negative charges can be efficiently
transferred to output node OD1 to produce negative voltage
-VCC.
[0264] Similarly to the construction of the first embodiment shown
in FIG. 1, the construction shown in FIG. 18 can set the voltage
level produced from output node OD1 at any intended level by
appropriately setting the amplitudes of control signals .phi.CT,
.phi.CP, .phi.P and .phi.CTF, and the level of voltage applied to a
ground node OGG serving as the precharge voltage supply node
coupled to MOS transistor NQQ1.
[0265] According to the eighth embodiment of the invention, as
described above, the charge transfer stages are cascaded, these
charge transfer stages alternately perform the charge transfer, and
the precharging and the charge accumulation are alternately
performed on the internal nodes connected to these charge transfer
stages. Thus, the charges can be efficiently utilized to produce
the negative voltage at an intended voltage level. Further, the
circuits are formed of the MOS transistors of the same conductivity
type, and therefore a region for isolating the PMOS and NMOS
transistors from each other is not required. In addition, the
number of manufacturing steps can be reduced, and therefore, the
manufacturing cost can be reduced.
[0266] [Ninth Embodiment]
[0267] FIG. 20 shows a construction of a voltage generating circuit
according to a ninth embodiment of the invention. The voltage
generating circuit shown in FIG. 20 differs in construction from
the voltage generating circuit shown in FIG. 3 in the following
points. Cross-coupled N-channel MOS transistors NQ11 and NQ12 shown
in FIG. 3 are replaced with P-channel MOS transistors PQQ1 and
PQQ2. P-channel MOS transistor PQQ1 is connected between a
precharge voltage supply node NDD12 and internal node ND12, and has
a gate connected to an internal node NDD13.
[0268] Precharge voltage supply node NDD12 is connected to power
supply node PW supplying power supply voltage VCC, and supplies
charges for precharging internal node ND12 to the level of power
supply voltage VCC. Internal node NDD13 is coupled via a
capacitance element CQ13 to input node S52 receiving control signal
.phi.CTFZ. The high voltage 2.multidot.VCC (equal to
2.multidot.VCC) is produced on output node OD11.
[0269] P-channel MOS transistor PQQ2 is connected between internal
nodes ND12 and NDD13, and has a gate connected to input node S11
receiving control signal .phi.PZ.
[0270] A charge transfer stage transferring charges between
internal node ND12 and output node OD11 has the same construction
as that shown in FIG. 3. Corresponding elements are allotted with
the same reference numerals, and description thereof will not be
repeated.
[0271] Internal node ND12 is coupled to input node S12 receiving
control signal .phi.CPZ via capacitance element C12.
[0272] These control signals .phi.PZ, .phi.CPZ, .phi.CTZ and
.phi.CTFZ are produced by inverting control signals .phi.P,
.phi.CP, .phi.CT and .phi.CTF generated from the control signal
generating circuits.
[0273] In the structure shown in FIG. 20, for correlation with the
claimed elements, MOS transistors PQQ1 and PQQ2 correspond to the
first and second transistors, and MOS transistors PQ11 and PQ12
correspond to the third and fourth transistors, respectively.
Control signals .phi.CTFZ, .phi.PZ, .phi.CPZ and .phi.CTZ
correspond to the first, second, third and fourth control signals,
respectively. Capacitance elements CQ13, C12 and C13 correspond to
the first, second and third capacitance elements, respectively.
[0274] FIG. 21 is a signal waveform diagram illustrating an
operation of the voltage generating circuit shown in FIG. 20. The
voltage generating circuit shown in FIG. 20 generates a voltage of
2.multidot.VCC on output node OD11 on the basis of the voltage VCC
applied to power supply node PW. Accordingly, the operation
waveforms of the voltage generating circuit shown in FIG. 20 can be
obtained by inverting voltage polarities of the signals and nodes
of the voltage generating circuit shown in FIG. 18, and measuring
the voltages on the respective nodes with reference to power supply
voltage VCC. Therefore, the operation of the voltage generating
circuit shown in FIG. 20 will now be described briefly with
reference to FIG. 21.
[0275] At time t0, control signals .phi.PZ, .phi.CTZ and .phi.CTFZ
are at the H level of power supply voltage VCC, and control signal
.phi.CPZ is at the L level of ground voltage GND. In this state,
node ND12 is at the level of power supply voltage VCC, and node
ND13 is at the level of power supply voltage VCC. MOS transistor
PQQ2 is in a non-conductive state, and MOS transistor PQQ1 is also
in a non-conductive state. Through the charge pump operation of
capacitance element C13, node ND13 is at the level of high voltage
2.multidot.VCC, similarly to the second embodiment, and MOS
transistor PQ11 is in an off state (non-conductive state). MOS
transistor PQ12 is an on state (conductive state), and internal
node ND13 is electrically coupled to output node OD11.
[0276] At time t1, control signal .phi.PZ falls from the H level of
power supply voltage VCC to the L level of ground voltage GND, and
MOS transistor PQQ2 turns conductive to couple electrically
internal node NDD13 to internal node ND12. MOS transistor PQQ1
maintains the non-conductive state because the gate, source and
drain potentials thereof are equal to each other.
[0277] At time t2, control signal .phi.CPZ rises from the L level
to the H level. In response to the rising of control signal
.phi.CPZ, the charge pumping by capacitance element C12 raises the
voltage level of node ND12 from power supply voltage VCC to high
voltage 2.multidot.VCC by an amplitude VCC of control signal
.phi.CPZ. In this operation, MOS transistor PQQ2 is conductive so
that the voltage level of node NDD13 rises to high voltage
2.multidot.VCC. With capacitance element C12 much larger in
capacitance value than capacitance element CQ13, node NDD13 can be
charged to the level of high voltage 2.multidot.VCC, similarly to
the charging operation of node NDD12. In accordance with the rising
of the potential level of node NDD13, MOS transistor PQQ1 turns
non-conductive.
[0278] In accordance with the rising of the potential level of
internal node ND12, MOS transistor PQ12 turns non-conductive
(output node OD11 is at the potential level of voltage
2.multidot.VCC), and internal node ND13 is isolated from output
node OD11.
[0279] At time t3, control signal .phi.CTZ falls from the H level
to the L level, and the charge pumping by capacitance element C13
lowers the potential level of internal node ND13 from the high
voltage 2.multidot.VCC to power supply voltage VCC. When the
potential of internal node ND13 lowers to the level of power supply
voltage VCC, MOS transistor PQ11 turns conductive to transfer the
charges between internal node ND12 and output node OD11. Since the
absolute value of threshold voltage of MOS transistor PQ11 is much
smaller than power supply voltage VCC, the charges can be
transferred between internal node ND12 and output node OD11 without
an influence of the threshold voltage of MOS transistor PQ1. When
the voltage level of output node OD11 is lower than the voltage of
2.multidot.VCC, positive charges are supplied from internal node
ND12 to output node OD11, and the voltage level of output node OD11
rises.
[0280] At time t4, control signal .phi.CTZ rises from the L level
to the H level, and the charge pumping by capacitance element C13
raises the potential level of internal node ND13 to the high
voltage 2.multidot.VCC again. Accordingly, MOS transistor PQ11
turns non-conductive, and the charge transfer operation completes.
In this state, the potential level of internal node ND12 is lower
than the potential level of internal node ND13, and the positive
charges move from internal node ND13 to output node OD11 via MOS
transistor PQ12 even when MOS transistor PQ12 is in a conductive
state. Responsively, the voltage level of output node OD11 rises so
that the flow-out charges are effectively utilized, and no
ineffective current flows. This is the same as in the second
embodiment.
[0281] At time t5, control signal .phi.CPZ falls from the H level
to the L level, and responsively the charge pumping by capacitance
element C12 lowers the voltage level of internal node ND12 from
high voltage 2.multidot.VCC to power supply voltage VCC. When
internal node ND12 attains the level of power supply voltage VCC,
MOS transistor PQ12 is turned on to make node ND13 and output node
OD11 equal in potential to each other, and accordingly MOS
transistor PQ11 is turned off, and internal node ND13 is isolated
from output node OD11 (in the case where the voltage level of
output node OD11 is higher than power supply voltage VCC).
[0282] Since MOS transistor PQQ2 is conductive, the voltage level
of internal node NDD13 lowers from the positive high voltage
2.multidot.VCC to power supply voltage VCC in accordance with the
potential change on internal node ND12. In this state, MOS
transistor PQQ1 of the enhancement type has the gate and source set
at equal potential, and maintains the non-conductive state so that
no charges flow from internal node ND12 to power supply node
PW.
[0283] At time t6, control signal .phi.PZ rises from the L level to
the H level. Responsively, MOS transistor PQQ2 has the gate and
source set to the potential equal to each other, and turns
non-conductive to isolate electrically internal node NDD13 from
internal node ND12.
[0284] At time t7, control signal .phi.CTFZ lowers from the H level
to the L level. Responsively, the charge pumping by capacitance
element CQ13 lowers the voltage level of internal node NDD13 from
power supply voltage VCC to ground voltage GND, and MOS transistor
PQQ1 turns conductive to couple internal node ND12 to power supply
node PW, and internal node ND12 is precharged to the level of power
supply voltage VCC.
[0285] At time t8, control signal .phi.CTFZ rises from the L level
to the H level again, and the charge pump operation of capacitance
element CQ13 changes the voltage level of internal node NDD13 to
power supply voltage VCC again. Responsively, MOS transistor PQQ1
is turned off, and the precharging operation of internal node ND12
completes.
[0286] Subsequently, the operations from time t0 to time t8 are
repeated so that high voltage 2.multidot.VCC can be produced on
output node OD1.
[0287] In the transition period before the voltage on output node
OD1 reaches high voltage 2.multidot.VCC, control signal .phi.CTFZ
lowers to the L level of ground voltage GND in a period between
times t7 and t8, and responsively MOS transistor PQQ1 is turned on
to precharge internal node ND12 to the level of power supply
voltage VCC. When the voltage level of output node OD11 is lower
than power supply voltage VCC, MOS transistor PQ12 is reliably
maintained non-conductive. When control signal .phi.CPZ rises to
the level of power supply voltage VCC, internal node ND12 attains
the level of high voltage 2.multidot.VCC. Responsively, MOS
transistor PQQ1 turns non-conductive, and the flow of current from
internal node ND12 to power supply node PW is suppressed. In
addition, MOS transistor PQ12 has the gate potential higher than
its source and drain potentials, and is reliably turned off.
[0288] When control signal .phi.CTZ is at the L level, internal
node ND13 lowers to or below the level of power supply voltage VCC
in a transition period, and MOS transistor PQ11 has the gate
potential lower than its source potential, and is turned on.
Therefore, the positive charges can be supplied from internal node
ND12 to output node OD1, and the voltage level of output node OD11
rises.
[0289] In this transition state, the voltage level of node ND13
changes between power supply voltage VCC and high voltage
2.multidot.VCC. Before the voltage on output node OD11 lowers to or
below power supply voltage VCC, MOS transistor PQ12 maintains the
non-conductive state. In this state, the voltage level of internal
node ND13 changes between power supply voltage VCC and ground
voltage GND, and MOS transistor PQ11 is turned on when internal
node ND13 is set to the ground voltage level in accordance with
control signal .phi.CPZ. Consequently, the positive charges are
supplied to output node OD11 to raise its voltage level.
[0290] When MOS transistor PQ12 starts to be conductive in
accordance with rising of the voltage level of output node OD11 to
or above power supply voltage VCC, the voltage level of internal
node ND13 rises similarly to the voltage level of output node OD11,
and the voltage level of internal node ND13 rises in accordance
with the voltage level of output node OD11. In this case, the
charges flowing from output node OD11 to internal node ND13 are
utilized to raise the potential level of internal node ND13, for
setting the MOS transistors PQ12 and PQ11 to the
conductive/non-conductiv- e states in accordance with control
signals .phi.CTZ and .phi.CPZ. Therefore, no ineffective current
flows.
[0291] Similarly to the eighth embodiment, the voltage generating
circuit shown in FIG. 20 can efficiently transfer the charges
without causing any ineffective current, and thereby can produce
high voltage 2.multidot.VCC on output node OD11.
[0292] In the voltage generating circuit shown in FIG. 20, only the
P-channel MOS transistors are employed. Similarly to the eighth
embodiment, therefore, it is not necessary to manufacture both the
P- and N-channel MOS transistors, so that the area occupied by the
circuitry and the number of manufacturing steps can be reduced, and
accordingly, the manufacturing cost can be reduced.
[0293] In the ninth embodiment, control signals .phi.PZ, .phi.CPZ,
.phi.CTZ and .phi.CTFZ have the amplitudes of power supply voltage
VCC, and a high voltage 2.multidot.VCC higher by this amplitude
than the reference voltage being power supply voltage VCC. However,
the voltage applied to the power supply node (precharge voltage
supply node) may be at the level different from power supply
voltage VCC, and control signals .phi.PZ, .phi.CPZ, .phi.CTZ and
.phi.CTFZ may have the amplitudes different from power supply
voltage VCC. In this case, the voltage supplied to the reference
precharge voltage supply node (power supply node PW) can be used as
a reference voltage, and a high voltage higher by the amplitude of
control signal .phi.CPZ can be produced on output node OD11 on the
basis of such reference voltage.
[0294] According to the ninth embodiment, as described above, the
PMOS transistor is utilized to accumulate and transfer the charges
by controlling the gate voltage, and the positive high voltage, at
an intended level can be produced without causing an ineffective
current.
[0295] [Tenth Embodiment]
[0296] FIG. 22 shows a structure of a voltage generating circuit
according to a tenth embodiment of the invention. In the voltage
generating circuit shown in FIG. 22, precharge voltage supply node
NDD2 is coupled to input node S1 receiving control signal .phi.P.
Other construction of the voltage generating circuit shown in FIG.
22 is the same as that of the voltage generating circuit shown in
FIG. 18. Corresponding portions are allotted with the same
reference numerals, and description thereof will not be
repeated.
[0297] MOS transistor NQQ1 is provided for reliably precharging
internal node ND2 to the level of ground voltage GND in accordance
with control signal .phi.CTF. When control signal .phi.CTF attains
the H level of power supply voltage VCC, control signal .phi.P is
at the L level of ground voltage GND (FIG. 19). Therefore, when MOS
transistor NQQ1 is conductive, internal node ND2 can be precharged
to the ground voltage level in accordance with control signal
.phi.P.
[0298] When control signal .phi.P is at the H level of power supply
voltage VCC, control signal .phi.CTF is at the L level of ground
voltage GND. In this state, MOS transistor NQQ2 is in a conductive
state to electrically couple internal nodes NDD1 and ND2.
Accordingly, MOS transistor NQQ1 have the gate and source made
equal in potential to each other, and maintains the non-conductive
state. Therefore, such a situation can be reliably prevented that a
current flows from control signal input node S1 to internal node
ND2 when the potential level of internal node ND2 lowers.
[0299] Operation waveforms of the voltage generating circuit shown
in FIG. 22 are the same as those in FIG. 19 for the voltage
generating circuit shown in FIG. 18. It is not necessary to use
ground voltage GND for generating negative voltage -VCC, and the
circuit configuration and layout can be made simple. Stabilizing
capacitance 4 merely has the other electrode coupled to ground node
GG, and therefore can be arranged in any position. Accordingly, the
voltage generating circuit is not subject to restriction by the
interconnection layout of the power supply line and ground line,
and the restrictions on the circuit arrangement positions are
mitigated, which improves the freedom degree in arrangement
position of the voltage generating circuit in the semiconductor
device incorporating the voltage generating circuit.
[0300] [Eleventh Embodiment]
[0301] FIG. 23 shows a structure of a voltage generating circuit
according to an eleventh embodiment of the invention. The voltage
generating circuit shown in FIG. 23 differs in configuration from
the voltage generating circuit shown in FIG. 20 in the following
points. Specifically, precharge voltage supply node NDD12 coupled
to P-channel MOS transistor PQQ1 is coupled to control signal input
node S11 receiving control signal .phi.PZ. Other configuration of
the voltage generating circuit shown in FIG. 23 is the same as in
the voltage generating circuit shown in FIG. 20. Corresponding
portions are allotted with the same reference numerals, and
description thereof will not be repeated.
[0302] MOS transistor PQQ1 is provided for precharging internal
node ND12 to the level of power supply voltage VCC. Control signal
.phi.PZ is at the H level of power supply voltage VCC when control
signal .phi.CTZF turning on MOS transistor PQQ1 is at the L level.
When MOS transistor PQQ1 is conductive, therefore, control signal
.phi.PZ can precharge internal node ND12 to the level of power
supply voltage VCC. Accordingly, the operation waveforms of the
voltage generating circuit shown in FIG. 23 are provided by the
operation waveforms corresponding to those illustrated in FIG. 21,
and the same operations as the voltage generating circuit shown in
FIG. 20 can be implemented.
[0303] When control signal .phi.PZ is at the L level, control
signal .phi.CTFZ is at the H level, and MOS transistor PQQ2
electrically couples internal nodes NDD13 and ND12. Therefore, MOS
transistor PQQ1 has the equal potential at its gate and source
(internal node 12), and therefore maintains the non-conductive
state so that the flow of a current from internal node ND12 to
input node S11 can be reliably suppressed.
[0304] By using the voltage generating circuit shown in FIG. 23,
therefore, high positive voltage 2.multidot.VCC can be produced,
similarly to the voltage generating circuit shown in FIG. 20.
[0305] The voltage generating circuit shown in FIG. 23 does not
utilize power supply voltage VCC for producing high voltage
2.multidot.VCC. Therefore, the circuit configuration can be made
simple, and the interconnection layout can also be made simple.
Since the voltage generating circuit does not utilize the power
supply voltage VCC, the voltage generating circuit can be arranged
without a restriction by the interconnection layout of power supply
voltage VCC (if it is arranged as an internal circuit of a
semiconductor integrated circuit). This voltage generating circuit
may be arranged in a structure such as a system LSI as a macro of
one circuit block.
[0306] According to the eleventh embodiment of the invention, as
described above, the control signals are utilized for precharging
the internal node, and a power supply voltage is not required so
that the circuit configuration can be made simple.
[0307] [Twelfth Embodiment]
[0308] FIG. 24 shows a construction of a voltage generating circuit
according to a twelfth embodiment of the invention. The voltage
generating circuit shown in FIG. 24 differs in configuration from
the voltage generating circuit shown in FIG. 10A in the following
points. The negative charge producing stage is not formed of
cross-coupled P-channel MOS transistors PQ1 and PQ2 in FIG. 10A,
but is formed of MOS transistors NQQ1 and NQQ2 as well as
capacitance elements CQ1 and CQ2 shown in FIG. 18.
[0309] Between internal node ND2 and final output node FOD, a
plurality of charge transfer stages XFN1-XFNn are connected in
series, similarly to the construction shown in FIG. 10A. The
construction arranged between internal node ND2 and final output
node FOD is the same as that shown in FIG. 10A. Corresponding
portions are allotted with the same reference numerals, and
description thereof will not be repeated. Each of charge transfer
stages XFN1-XFNn has the same configuration as in charge transfer
stage XFN shown in FIG. 10B.
[0310] In the voltage generating circuit shown in FIG. 24, the
voltage level of internal node ND2 changes between ground voltage
GND and negative voltage -VCC, and charge transfer stage XFN1
supplies negative charges to internal output node OD1 from internal
node ND2. In the operation of transferring the negative charges
from internal node ND2 to internal output node OD1, control signal
.phi.P is at the H level, and internal output node OD1 has been
precharged to negative voltage -VCC (in the stable operation), so
that internal output node OD1 is reliably set to the level of
negative voltage -VCC in accordance with transfer control signal
.phi.CT. In the charge transfer operation, MOS transistor NQ2 is
non-conductive, and internal node ND3 is set to the ground voltage
level in response to control signal .phi.CT, and accordingly, MOS
transistor NQ1 turns conductive, so that the negative charges can
be transferred between node ND2 and OD1.
[0311] When control signal .phi.CP attains the H level, internal
node ND2 attains the ground voltage level, and MOS transistor NQ2
is turned on to connect electrically internal output node OD1 to
internal node ND3 so that MOS transistor NQ1 is reliably turned
on.
[0312] When control signal .phi.P falls from the H level to the L
level, the voltage level of internal output node OD1 lowers from
negative voltage -VCC to the negative voltage of -2.multidot.VCC.
In this state, MOS transistor NQ2 is conductive, and MOS transistor
NQ1 has the source and drain made equal in potential to each other,
and maintains the non-conductive state. Therefore, backflow of the
negative charges does not occur.
[0313] Similarly to the construction shown in FIG. 10A, the voltage
drop equal to the amplitude of VCC of control signals .phi.CP and
.phi.P is caused in each of charge transfer stages XFN2-XFNn.
Therefore, the potential of output node ODn-1 of charge transfer
stage XFNn-1 changes between the negative voltage of -(n-1)VCC and
the negative voltage of -n.multidot.VCC. Last charge transfer stage
XFNn supplies the negative voltage to final output node FOD in
accordance with control signal .phi.CTF. Therefore, the negative
voltage of -n.multidot.VCC is generated on final output node FOD
similarly to the structure shown in FIG. 10A.
[0314] In the construction of the voltage generating circuit shown
in FIG. 24, capacitance element C2 is provided for internal node
ND2, and negative voltage of -n.multidot.VCC is produced on final
output node FOD. By using this capacitance element C2, the negative
potential of internal node ND2 is changed between ground voltage
GND and negative voltage -VCC, and accordingly, charge transfer
stage XFN1 can reliably transfer negative voltage -VCC to internal
output node OD1 when internal MOS transistor (NQ1) for charge
transfer is turned on in response to control signal ACT. When
internal node ND2 restores to the level of ground voltage GND, the
charge transfer transistor (NQ1) can be made non-conductive in
charge transfer stage XFN1. In charge transfer stage XFN1,
therefore, the charge transfer operation can be controlled in
accordance with control signal .phi.CT, and therefore, the voltage
drop by the amplitude of VCC can be caused in each of charge
transfer stages XFN1-XFNn without causing an ineffective current
flow.
[0315] The operation waveforms of the voltage generating circuit
shown in FIG. 24 are represented by the signal waveforms
illustrated in FIG. 11.
[0316] Accordingly, charge transfer stages XFN1-XFNn in the voltage
generating circuit shown in FIG. 24 are each formed of N-channel
MOS transistors, and the basic negative charge producing stage
producing the basic negative charges on internal node ND2 is formed
of N-channel MOS transistors NQQ1 and NQQ2. In this voltage
generating circuit, therefore, each stage is formed of the
N-channel MOS transistors, and the negative voltage of
-n.multidot.VCC at an intended level can be produced with a small
circuit occupation area and reduced current consumption.
[0317] [Modification]
[0318] FIG. 25 shows a construction of a voltage generating circuit
of a modification of the twelfth embodiment of the invention. The
voltage generating circuit shown in FIG. 25 differs in
configuration from the voltage generating circuit shown in FIG. 24
in the following points. Precharge voltage supply node NDD2 of
N-channel MOS transistor NQQ1 is connected to input node S1
receiving control signal .phi.P. Other configuration of the voltage
generating circuit shown in FIG. 25 is the same as that of the
voltage generating circuit shown in FIG. 24. Corresponding portions
are allotted with the same reference numerals, and description
thereof will not be repeated.
[0319] In the construction of the voltage generating circuit shown
in FIG. 25, the voltage level of internal node ND2 changes between
ground voltage GND (corresponding to the L level of control signal
.phi.P) and negative voltage -VCC. Therefore, the negative voltage
of -n.multidot.VCC is generated on final output node FOD.
[0320] The operation waveforms of the voltage generating circuit
shown in FIG. 25 are represented by those illustrated in FIG. 11.
In the voltage generating circuit shown in FIG. 25, ground voltage
GND is not used for generating the negative voltage, so that the
circuit configuration can be made simple as in the tenth
embodiment, and thus, the manufacturing cost can be reduced.
[0321] According to the twelfth embodiment of the invention, as
described above, a plurality of charge transfer stages are cascaded
to produce the final negative voltage on the final output node, and
the negative voltage at an intended voltage level can be easily
produced. Since each charge transfer stage is formed of the
N-channel MOS transistors, the circuit configuration can be made
simple. Also, the circuit layout area can be reduced, and the
manufacturing cost can be made low.
[0322] [Thirteenth Embodiment]
[0323] FIG. 26 shows a construction of a voltage generating circuit
according to a thirteenth embodiment of the invention. The voltage
generating circuit shown in FIG. 26 differs in configuration from
the voltage generating circuit shown in FIG. 16 in the following
points. For a circuit supplying the positive charges to internal
node ND12, the voltage generating circuit shown in FIG. 26 employs
P-channel MOS transistors PQQ1 and PQQ2 as well as capacitance
elements CQ13 and C12, as in the construction shown in FIG. 20.
Precharge voltage supply node NDD12 of MOS transistor PQQ1 is
coupled to power supply node PW, and receives power supply voltage
VCC. The circuit configuration for supplying the positive charges
to internal node ND12 is the same as the configuration shown in
FIG. 20. Corresponding portions are allotted with the same
reference numerals, and description thereof will not be
repeated.
[0324] Similarly to the construction of the voltage generating
circuit shown in FIG. 6, charge transfer stages XFP1-XFPn of n
stages are cascaded between internal node ND12 and final output
node FOD. In addition, capacitance elements CC1-CCn-1 are connected
to internal output nodes ODP1-ODPn-1 of charge transfer stages
XFP1-XFPn-1, respectively. The connection and operation of these
charge transfer stages XFP1-XFPn and capacitance elements CC1 to
CCn-1 are the same as those of the voltage generating circuit shown
in FIG. 18, and corresponding portions are allotted with the same
reference numerals. Accordingly, charge transfer stages XFP1-XFPn
alternately perform the precharging of the internal nodes and the
charge transfer operation, and capacitance elements CC1 to CCn-1
alternately perform the precharging and the boosting of
corresponding internal output nodes ODP1-ODPn-1.
[0325] Internal node ND12 changes in potential between power supply
voltage VCC and high voltage 2.multidot.VCC, similarly to the
construction of the voltage generating circuit shown in FIG. 20.
After charge transfer stage XFP1 transmits high voltage
2.multidot.VCC to internal output node ODP1 (OD11), capacitance
element CC1 further raises the voltage level of internal output
node ODP1 by voltage VCC in accordance with control signal .phi.PZ.
Therefore, charge transfer stages XFP1 to XFPn-1 produce on their
respective output nodes the voltages boosted by the voltage VCC
relative to the output node voltages in the preceding stages. The
voltage level of output node ODPn-1 of charge transfer stage
XFP(n-1) changes between the voltage of n.multidot.VCC and
(n+1).multidot.VCC. Therefore, charge transfer stage XFPn in the
last stage produces the high voltage of (n+1).multidot.VCC on final
output node FOD.
[0326] The operation waveforms of voltage generating circuit shown
in FIG. 26 are represented by those of the voltage generating
circuit shown in FIG. 19, and the high voltage of
(n+1).multidot.VCC can likewise be produced from power supply
voltage VCC.
[0327] By arranging the capacitance element C12 for internal node
ND12, and changing the potential of internal node ND12 between
power supply voltage VCC and high voltage 2.multidot.VCC, the
following operation is reliably implemented in charge transfer
stage XFP1. The MOS transistor for the transfer (MOS transistor
PQ11) is maintained in a non-conductive state to prevent the
backflow of positive charges when control signal .phi.CPZ attains
the H level. In addition, the positive charges can be transferred
from node ND12 to internal output node ODP1 through charge transfer
stage XFP1 in accordance with control signal .phi.CTZ.
[0328] Charge transfer stages XFP1 to XFPn are each formed of the
P-channel MOS transistors, and the stage for supplying positive
charges to internal node ND12 is likewise formed of P-channel MOS
transistors PQQ1 and PQQ2, or of the MOS transistors of the same
conductivity type. Therefore, the positive high voltage of
(n+1).multidot.VCC at any voltage level can be produced with the
circuit of simplified configuration.
[0329] [Modification]
[0330] FIG. 27 shows a construction of a voltage generating circuit
of a modification of the thirteenth embodiment of the invention.
The voltage generating circuit shown in FIG. 27 differs in
configuration from the voltage generating circuit shown in FIG. 26
in the following points. Precharge voltage supply node NDD12 is
coupled to input node S11 receiving control signal .phi.PZ. Other
configuration of the voltage generating circuit shown in FIG. 27 is
the same as that of the voltage generating circuit shown in FIG.
26. Corresponding portions are allotted with the same reference
numerals, and description thereof will not be repeated.
[0331] According to the construction of the voltage generating
circuit shown in FIG. 27, a voltage changing between voltages of
VCC and 2.multidot.VCC is produced on internal node ND12. Similarly
to the voltage generating circuit shown in FIG. 26, the high
positive voltage at the level of (n+1).multidot.VCC is generated
from final output node FOD, similarly to the voltage generating
circuit shown in FIG. 26.
[0332] The voltage generating circuit shown in FIG. 27 does not use
power supply voltage VCC for generating the high voltage of
(n+1).multidot.VCC. Therefore, the circuit configuration can be
made simple.
[0333] The operation waveforms of the voltage generating circuit
shown in FIG. 27 are represented by those shown in FIG. 19,
similarly to the voltage generating circuit shown in FIG. 26.
[0334] According to the thirteenth embodiment of the invention, as
described above, a plurality of charge transfer stages are cascaded
between the internal node and the final output node, and these
charge transfer stages alternately perform the precharging of the
output node and the charge transferring. In addition, all the
transistor elements are formed of the P-channel MOS transistors,
and the charges can be efficiently transferred to produce a
positive high voltage. Further, the circuit occupation area and the
manufacturing cost can be reduced.
[0335] The voltage generating circuit according to the invention
can be applied to a general LSI (Large Scale Integrated Circuit) as
an embedded circuit producing an internal voltage. In addition, the
present invention can be generally applied to semiconductor device
requiring a voltage at a level different from the power supply
voltage and/or the ground voltage. Further, the voltage generating
circuit according to the invention can be utilized for driving
liquid crystal elements in a liquid crystal display device
requiring positive and negative voltages. By utilizing the voltage
generating circuit according to the invention, it is possible to
reduce costs of the parts and/or a final product, and also to
reduce the power consumption.
[0336] According to the invention, as described above, the gate
potential of each transistor is controlled by the charge pump
operation of the capacitance element to generate the charges for
generating an internal voltage, and conduction/non-conduction
states of the transistors are individually and accurately
controlled to produce the charges for generating the internal
voltage. Thus, flow of an ineffective current can be suppressed,
and the charges can be efficiently used to generate an internal
voltage at an intended level with reduced power consumption.
[0337] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *