U.S. patent application number 10/034969 was filed with the patent office on 2002-06-27 for detector of range of supply voltage in an integrated circuit.
This patent application is currently assigned to STMicroelectronics S.A.. Invention is credited to Degoirat, Hubert, Lisart, Mathieu.
Application Number | 20020079933 10/034969 |
Document ID | / |
Family ID | 9493028 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020079933 |
Kind Code |
A1 |
Degoirat, Hubert ; et
al. |
June 27, 2002 |
Detector of range of supply voltage in an integrated circuit
Abstract
The disclosure relates to detectors of the level of supply
voltage in an integrated circuit. The disclosed detector is
designed to detect the crossing of low levels of supply voltage. It
comprises a first arm to define a first reference voltage and a
second arm to define a second reference voltage, these two
reference voltages varying differently as a function of the supply
voltage and their curves of variation intersecting for a value of
the supply voltage located close to a desired threshold. A
comparator receives the two reference voltages. The first arm has a
resistive divider bridge, an intermediate connector of which
constitutes the first reference voltage. The second arm comprises a
resistor series-connected with a native P type MOS transistor, the
point of junction of this resistor and this transistor constituting
the second reference voltage. A non-linear element may be
parallel-connected to the resistor which constitutes the first
reference voltage.
Inventors: |
Degoirat, Hubert; (Nice,
FR) ; Lisart, Mathieu; (Aix en Provence, FR) |
Correspondence
Address: |
James H. Morris
Wolf, Greenfield & Sacks, P.C.
Federal Reserve Plaza
600 Atlantic Avenue
Boston
MA
02210
US
|
Assignee: |
STMicroelectronics S.A.
29, Boulevard Romain Rolland
Montrouge
FR
92120
|
Family ID: |
9493028 |
Appl. No.: |
10/034969 |
Filed: |
December 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10034969 |
Dec 21, 2001 |
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09665794 |
Sep 20, 2000 |
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09665794 |
Sep 20, 2000 |
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08876282 |
Jun 12, 1997 |
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Current U.S.
Class: |
327/81 |
Current CPC
Class: |
G01R 19/16519 20130101;
G01R 19/1659 20130101 |
Class at
Publication: |
327/81 |
International
Class: |
H03K 005/153 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 1996 |
FR |
96/07368 |
Claims
What is claimed is:
1. A detector of the level of supply voltage Vcc of an integrated
circuit, comprising a first arm to define a first reference voltage
and a second arm to define a second reference voltage, these two
reference voltages varying differently as a function of a supply
voltage and their curves of variation intersecting for a value of
the supply voltage close to a desired threshold, and a comparator
receiving the two reference voltages, wherein the first arm has a
resistive divider bridge, of which an intermediate connector
constitutes the first reference voltage and the second arm
comprises a resistor series-connected with a native P type MOS
transistor, the point of junction of this resistor and this
transistor constituting the second reference voltage, the native
transistor in the arm that defines the second reference voltage, in
combination with the resistive divider bridge in the arm that
defines the first reference voltage, provides high stability of the
threshold value of supply voltage Vcc that is to be detected, the
resistive divider bridge, providing very efficient control, by a
simple choice of relative values of resistance, of the zone of
intersection of the curves of the first and second reference
voltages as a function of a supply voltage Vcc, and wherein the two
arms are joined by a connector defining a common potential for the
base of the two arms.
2. A detector according to claim 1, wherein the first arm
comprises, between the base and the resistive divider bridge, one
or more series-connected transistors, with their drain connected to
their gate.
3. A detector according to claim 1, wherein at least one additional
transistor having its gate connected to its drain is
series-connected in each of the arms, between a supply whose level
is to be detected and the point that defines each of the reference
voltages.
4. A detector according to claim 1 comprising, between the common
conductor forming the base of the arms and a ground, several
assemblies of transistors making it possible to set up, as desired,
different voltage drops between the ground and the common base of
the two arms, so as to enable an adjustment of the voltage levels
that the detector may detect, the placing of the different
assemblies in a state of conduction being activated by individual
selection, according to the desired voltage drop.
5. A detector according to claim 1 for application to the detection
of high voltage levels wherein, between each of the points defining
the reference voltage levels wherein, between each of the points
defining the reference voltages and the corresponding input of the
comparator, there is provided a voltage level transposition stage
comprising a transistor and a resistor series-connected with this
transistor between a main low-voltage supply source and a ground,
the first and second reference voltages being connected to the gate
of this transistor, the respective input of the comparator being
connected to the drain and to the resistor, the source of the
transistor being connected to the ground.
6. A detector of the level of supply voltage of an integrated
circuit, comprising: a comparator having a first input receiving a
first reference voltage and a second input receiving a second
reference voltage, the two reference voltages varying differently
as a function of a supply voltage to form curves of variation which
intersect at a value of supply voltage which is located close to a
desired threshold, the comparator further having an output which
switches from a first state to a second state when the supply
voltage crosses the threshold; a resistive divider bridge supplied
with the supply voltage, having an intermediate connector of which
constitutes the first reference voltage; and a resistor
series-connected with a native P type MOS transistor, supplied with
the supply voltage, a point of junction of the resistor and the
transistor constituting the second reference voltage.
7. A detector according to claim 6, wherein the native P type
transistor has a gate, source and drain, where the gate is
connected to the drain.
8. A detector according to claim 7, wherein the gate and the drain
are connected to the ground and the resistor which is
series-connected with the transistor is connected between the
source of the transistor and the supply voltage.
9. A detector according to claim 6, wherein a non-linear element
with relatively low conduction threshold voltage is
parallel-connected to a resistor of the divider bridge.
10. A detector according to claim 9, wherein the non-linear element
is parallel-connected to the resistor of the divider bridge at the
terminals of which the first reference voltage is taken.
11. A detector according to claim 9, wherein the non-linear element
has conduction threshold characteristics that vary as a function of
the temperature in such a way that the curve of variation of the
first reference voltage has substantially similar temperature
dependency as the curve of variation of the second reference
voltage such that the first and second curves intersect at a value
which is substantially independent of the temperature.
12. A detector according to 9, wherein the p type native transistor
has a first conduction threshold voltage and wherein the non-linear
element has a second conduction threshold voltage lower than the
first conduction threshold voltage.
13. A detector according to one of the claim 9, wherein the
non-linear element comprises a series assembly of an N channel
transistor and a P channel transistor.
14. A detector according to claim 13, wherein the N channel
transistor is a native type of transistor.
15. A detector according to claim 6, wherein the resistive divider
bridge comprises a bridge resistor having means to short circuit
the bridge resistor as a function of the output of the comparator,
in order to introduce hysteresis in the desired threshold.
16. A detector of the level of supply voltage of an integrated
circuit, comprising: a device for comparing having a first input
receiving a first reference voltage and a second input receiving a
second reference voltage, the two reference voltages varying
differently as a function of a supply voltage to form curves of
variation which intersect at a value of supply voltage which is
located close to a desired threshold, the device for comparing
further having an output which switches from a first state to a
second state when the supply voltage crosses the threshold; a
resistive divider bridge, supplied with the supply voltage, having
an intermediate connector which supplies the first reference
voltage; and a resistor series-connected with a first nonlinear
element, the series-connection being supplied with the supply
voltage, the point of junction of the resistor and the first
non-linear element supplies the second reference voltage.
17. A detector as in claim 16, wherein the non-linear element is a
MOS transistor which has no channel doping.
18. A detector as in claim 16, wherein the resistive divider bridge
comprises three series connected bridge resistors, the first bridge
resistor is connected to the supply voltage, the third bridge
resistor is connected to a ground and the second bridge resistor is
connected between the first and third bridge resistors, the
intermediate connector which provides the first reference voltage
being connected between the second and third resistors.
19. A detector as in claim 18, wherein the second bridge resistor
has short circuit means activated by the output of the comparator
in order to lower the threshold voltage for which the comparator
switches from the first state to the second state.
20. A detector as in claim 16, wherein the first nonlinear element
has a first conduction threshold voltage, and wherein a second
nonlinear element, connected across the third bridge resistor, has
a second conduction threshold voltage smaller than the first
conduction threshold voltage.
21. A detector as in claim 20, wherein the second nonlinear element
varies the first reference voltage as a function of temperature to
compensate for the variations of the second reference voltage as a
function of temperature, such that the curves of variation
intersect at a value of supply voltage substantially independent of
the temperature.
22. A detector as in claim 16, wherein respective values of the
bridge resistors and the resistor which is series-connected with
the first nonlinear element determine the value of the supply
voltage for which the curves of variation intersect.
23. A detector as in claim 16, wherein an increased value of the
resistor which is series-connected with the first nonlinear element
and/or changes in size of the nonlinear element provide a detector
which detects relatively lower voltages.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to detectors of the level of supply
voltage Vcc of an integrated circuit.
[0003] These detectors are incorporated into the integrated circuit
and can be useful for various applications such as:
[0004] detecting that the supply voltage is in a specified range
for which the circuit is designed and prohibiting operation if the
voltage is in another range;
[0005] detecting the range in which the supply voltage is located
if there are several possible ranges, and changing the
configuration of operation of the integrated circuit as a function
of the detected range;
[0006] ascertaining that the supply voltage has reached a specified
threshold before permitting the operation of the integrated
circuit.
[0007] Thus, for example, it may be sought to make a voltage level
detector that finds out whether or not the voltage level is greater
than about 2 volts and another detector that finds out whether or
not it is greater than about 4 volts. These two detectors may be
used simultaneously in one and the same integrated circuit which
could work for several ranges of supply voltages that are
different, such as for example a range of 2.7 to 3.3 volts and a
range of 4.5 to 5.5 volts. The combination of information elements
given by the two detectors indicates the range in which the supply
voltage is located.
[0008] 2. Description of the Prior Art
[0009] Such a detector, shown in FIG. 1, consists of a comparator
having as input two reference voltages, Vref1 and Vref2, that vary
differently as a function of the supply voltage, VCC, and that vary
in such a way that their curves of variation intersect when the
supply voltage reaches a specified threshold (FIG. 2). The
comparator compares these two references and switches over in one
direction or another depending on whether the supply voltage Vcc
crosses this threshold or not. The output of the comparator may be
applied through a buffer amplifier to the rest of the integrated
circuit in order to modify, permit or prohibit its operation
depending on the desired application.
[0010] There are two main difficulties, which affect the detection
of low supply voltage levels (the detection of a threshold of 2.5
volts for example). First, it is difficult to make a comparator
that works accurately even when it is supplied with a low value of
supply voltage (far below the threshold to be detected). Second, it
is difficult to make reference voltages that meet the above
conditions (regarding different variations as a function of Vcc,
and threshold value of intersection of their variation curves)
because each reference voltage varies as a function of Vcc which
depends firstly on the operating temperature of the integrated
circuit and secondly on the variations of parameters of the method
of manufacture of this
[0011] Consequently, whereas it is sought to have reference
voltages whose curves of variation intersect at a well-defined
point that corresponds to a desired threshold value Vs, it is
observed in reality that it is necessary to plot a quadruple
network of curves that intersect in a zone of threshold values
which may be very extensive. This quadruple network consists of two
networks of curves for the first reference voltage Vref1 and two
networks for the second reference Vref2. For each reference, a
network of curves may be plotted as a function of the possible
variations of the manufacturing method and another may be plotted
as a function of the operating temperature of the circuit.
[0012] It can be easily understood that, with this quadruple
network, the variation of the threshold voltage as a function of
manufacture and as a function of the temperature becomes great and
makes the detector of little use and of little reliability.
[0013] This is all the truer as the curves of variation of the
reference voltages intersect with a narrower acute angle. For, the
greater the manufacturing and temperature variations, the more
variable will be the position of the intersection.
[0014] FIG. 3 gives an exemplary illustration of the different
points of intersection of a curve Vref2 with several curves Vref1
corresponding to a certain degree of variation of manufacturing
parameters and/or a variation of operating temperature. The result
thereof is uncertainty in regard to the significance of the output
information from the comparator for it corresponds to a crossing of
a threshold Vs which may vary within a fairly broad range.
[0015] There is therefore need for a detector whose detection
threshold is as stable as possible despite variations in
manufacture and despite variations in operating temperature. This
detector must be simple and must consume little current.
SUMMARY OF THE INVENTION
[0016] The invention proposes a detector of this kind to detect the
level of supply voltage Vcc of an integrated circuit, this detector
comprising a first arm to define a first reference voltage Vref1
and a second arm to define a second reference voltage Vref2 these
two reference voltages varying differently as a function of the
supply voltage Vcc and their curves of variation intersecting for a
value of Vcc located close to a desired threshold Vs, and a
comparator receiving the two reference voltages, wherein the first
arm has a resistive divider bridge, of which an intermediate
connector constitutes the first reference voltage Vref1 and the
second arm comprises a resistor series-connected with a native P
type MOS transistor, the point of junction of this resistor and
this transistor constituting the second reference voltage.
[0017] It may be recalled that a native transistor, as opposed to a
depleted or enhanced transistor, is a transistor formed in a doped
semiconductor region, the channel of which has not undergone any
surface depletion (P type doping for a PMOS transistor) or surface
enhancement (N type doping for a PMOS transistor). The channel is
therefore formed directly on the surface of the doped region
without the performance of an ion implantation or diffusion after
the formation of the well. In the present case, the native
transistor is a P type transistor and it is generally formed in an
N type well diffused in a P type substrate.
[0018] The use of such a native transistor in the arm that defines
the voltage Vref2 in combination with the use of a resistive
divider bridge in the arm that defines Vref1, leads to high
stability of the threshold value Vs of supply voltage Vcc that is
to be detected. One of the reasons for this stability is the fact
that the absence of doping of the channel eliminates a factor of
variation of characteristics in the manufacturing method.
Furthermore, the use of a resistive divider bridge, alone or
complemented by a non-linear element, enables the very efficient
control, by a simple choice of relative values of resistance, of
the zone of intersection of the curves of Vref1 and Vref2 as a
function of Vcc.
[0019] The native P type transistor is, in principle, mounted as a
diode, namely with its gate connected to its drain. The gate and
the drain are then connected to the ground, while the resistor
series-connected with the transistor is connected between the
source of the transistor and the supply Vcc.
[0020] In a particularly useful embodiment for making a detector
with a low threshold level (about 2.5 volts), a non-linear element
with low conduction threshold voltage is connected in parallel to a
resistor of the divider bridge (in practice the non-linear element
is connected in parallel to the resistor at the terminals of which
the voltage Vref1 is taken). The non-linear element is chosen so
that the variation of Vref1 as a function of the temperature
compensates for the variation of Vref2 as a function of the
temperature, so that the curves Vref1 and Vref2 intersect for a
value of supply voltage substantially independent of the
temperature.
[0021] The non-linear element is preferably a series-connected
assembly of a PMOS transistor and an NMOS transistor (preferably
native) mounted as a diode. The sum of their threshold voltages is
preferably lower than the threshold voltage of the native P type
transistor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Other characteristics and advantages of the invention shall
appear from the following detailed description, made with reference
to the appended drawings, of which:
[0023] FIG. 1, already described, shows the general principle of a
voltage supply level detector;
[0024] FIG. 2 shows the curves of variation of Vref1 and Vref2 as a
function of Vcc, intersecting for a threshold voltage Vs to be
detected;
[0025] FIG. 3 shows the variation of the threshold voltage
detected;
[0026] FIG. 4 shows a diagram of a detector according to the
invention;
[0027] FIG. 5 shows a more detailed diagram;
[0028] FIG. 6 shows the curves of variation of Vref1 and Vref2 as a
function of time when a linearly increasing and then stable voltage
Vcc is applied;
[0029] FIG. 7 shows a variant of an embodiment for the detection of
a threshold of about 2.5 volts;
[0030] FIG. 8 shows the corresponding curves of variation for Vref1
and Vref2;
[0031] FIG. 9 shows a diagram of a comparator that can be used in
the detector according to the invention.
[0032] FIG. 10 shows a more complex embodiment of the invention,
designed to detect higher voltage supply levels.
DETAILED DESCRIPTION
[0033] The general schematic drawing of the invention is shown in
FIG. 4. The detector has two arms supplied with the voltage Vcc,
one used to define a reference voltage Vref1 having a first type of
variation as a function of Vcc and the other used to define a
reference voltage Vref2 having a second type of variation as a
function of Vcc. The two types of variation are different in order
that the curves of variation may intersect. The first arm has a
divider bridge of resistors (R1, R2, R3) while the second arm has a
resistor (R4) series-connected with a native P channel transistor
T1. An intermediate connector of the divider bridge of the first
arm defines the reference Vref1. The point of junction of the
resistor and the transistor of the second arm defines the reference
Vref2. These two reference voltages are applied to the inputs of a
comparator COMP which gives a logic signal at an output S. The
signal at the output S has a first level (for example a high level)
when Vref2 is greater than Vref1, which occurs if Vcc is below a
threshold Vs. If not, it has a second level (low level).
[0034] In the embodiment described in FIG. 4, designed to detect
any passage of the supply voltage beyond a threshold of about 4
volts, the native transistor P has its gate connected to the
ground, its source connected to the resistor R4 and its drain
connected to the ground. The source is connected to the well in
which, in a standard way, there is formed the transistor
(integrated circuit on P type substrate, N type well for the P
channel transistors, and this well does not undergo any surface
implantation of depletion or enhancement).
[0035] The divider bridge here is formed by three series-connected
resistors, R1 connected to Vcc, R3 connected to the ground and R2
connected between R1 and R3. The intermediate connector defining
Vref1 is the junction point of R2 and R3 The resistor R2 may be
short-circuited by a switch activated by the output of the
comparator. It is used to set up hysteresis in changing the value
of the division ratio set up by the divider bridge depending on
whether the comparator switches over in one direction or the other.
Here, when Vcc is below the threshold Vs, the resistor R2 is
short-circuited, the division ratio is R3/(R1+R3). If Vcc goes
beyond the threshold (which depends on this division ratio), the
comparator switches over and sets up the series connection of the
resistor R2, making the division ratio go to R3/(R1+R2+R3). This
tends to lower the threshold Vs for which the comparator switches
over. Thus, the instabilities when the voltage Vcc is close to the
threshold are avoided.
[0036] The sum R1+R2+R3 is any sum that is low enough so as to
avoid excess consumption of current, for current consumption is a
major factor to be watched in the designing of an integrated
circuit.
[0037] Owing to the fact that Vref1 is set up, in this embodiment,
only by the divider bridge to whose terminals the supply voltage
Vcc is applied, the reference voltage Vref1 varies linearly as a
function of Vcc. The slope of this variation is R3/(R1+R3) or
R3/(R1+R2+R3). Such a slope depends very little on the method of
manufacture for it does not depend on the value of the resistors
(which are subject to high variations of manufacture) but only on
their ratio (which undergoes very small variations).
[0038] The ratio R3/(R1+R3) is chosen so as to set up a slope of
variation of Vref1 as a function of Vcc which intersects the curve
of variation of Vref2 for a value of Vcc equal to a desired
threshold Vs, which in this case is in the range of 4 volts. The
slope to be chosen for the curve Vref1 as a function of Vcc to
obtain this threshold depends of course on the curve of variation
of Vref2 and this curve depends on the resistor R4 and the
transistor T1. By a process of empirical definition, it is possible
to find values of R1, R3 and R4 that are appropriate for obtaining
a given threshold.
[0039] The transistor T1 has a threshold voltage Vtp0 of the order
of 1.6 volts. So long as Vcc remains below this value, the
transistor remains off and the voltage Vref2 remains at the same
value as Vcc. As Vcc increases, the transistor gradually becomes
conductive and the current in the resistor R4 increases essentially
linearly with Vcc such that the voltage Vref2 increases
substantially logarithmically with Vcc. The logarithmic curve
obtained depends on the value of R4 and the geometrical dimension
(channel width/length ratio W/L) of the transistor.
[0040] In practice, the detector shown schematically in FIG. 4 may
have other accessory elements. By way of an example, FIG. 5 shows a
practical embodiment in which there has been added a circuit
designed to prevent the consumption of current when the integrated
circuit is in a state of standby. An input terminal STBY transmits
a standby signal which, when it is at the high logic level,
interrupts the consumption of current in the two arms of the
detector by means of the transistors T2 and T3 and inhibits the
consumption of current and the working of the comparator COMP (by
cancelling the signal for authorizing operation AMP_ON). The
transistor T3 is inserted between the transistor T1 and the ground,
and the transistor T2 is inserted between the resistor R3 and the
ground. Their influence on the working of the detector is
negligible.
[0041] The switch which short-circuits the resistor R2 for the
hysteresis may be formed in a standard way by an N type transistor
T4 parallel-connected with a P type transistor T5, one of these
transistors being controlled by the same logic level as that coming
out of the comparator and the other being controlled by the
complementary logic level.
[0042] In an exemplary embodiment for which curves of variation of
Vref1 and Vref2 have been plotted in FIG. 6, the following values
have been chosen for the resistors and the transistor T1, with a
view to obtaining a threshold voltage of about 4 volts: R1=52
kiloohms, R2=5 kiloohms, R3=200 kiloohms, R4=57 kiloohms and
W/L=4.5/5.7 (micrometers) for T1.
[0043] The curves plotted in FIG. 6 show the variations of Vref1
and Vref2 as a function of time while Vcc varies linearly as a
function of time and stabilizes at a value of 7 volts. This
indirectly amounts to a depiction of Vref1 and Vref2 as a function
of Vcc.
[0044] Since Vref1 in practice does not at all depend on the
parameters of the method of manufacture or the operating
temperature of the integrated circuit, a single curve Vref1 has
been plotted. However, since Vref2 depends on the variation of the
parameters of the method of manufacture and also depends on the
operating temperature, two extreme curves Vref2a and Vref2b have
been plotted, representing the maximum variation of the curve
Vref2.
[0045] The intersection of the curve Vref1 and of the curve Vref2a
corresponds to a first value of Vcc substantially equal to 4.6
volts. The intersection of Vref1 and Vref2b corresponds to a second
value of Vcc, substantially equal to 3.3 volts.
[0046] Consequently, the comparator switches over and the detector
gives a logic signal pertaining to a crossing of a threshold when
Vcc exceeds 4 volts, but with a margin of error of about 0.6 volts
due to the variations of manufacture and due to the temperature.
This margin of error is acceptable in an application where it is
sought to find out if the supply voltage is rather in the
2.7-to-3.3 volt range or rather in the 4.5-to-5.5 volt range.
[0047] With this same principle, but with a slightly modified
embodiment, it is possible to detect a far lower threshold of
supply voltage, substantially equal to 2 volts for example, with a
smaller margin of error.
[0048] To detect a supply voltage of approximately 2 volts, the
value of the resistor R4 and the size of the transistor T1 are
increased to achieve an overall reduction of the voltage Vref2
which stabilizes swiftly in the neighborhood of the threshold
voltage of the transistor T1 (about 1.6 volts). This results in a
curve Vref2a and a curve Vref2b which can be seen in FIG. 8
pertaining to a case where the resistor R4 is equal to 500 kiloohms
and the geometry of the transistor is W/L=20/2 micrometers. The
variation of the curve Vref2 comes above all from the operating
temperature of the integrated circuit.
[0049] The intersection of the curves Vref2a and Vref2b with a
single straight line Vref1 as in FIG. 6 gives varied threshold
values as explained above, both for a detector of a threshold of
about 4 volts and for the detector of a threshold of about 2.5
volts.
[0050] However, this threshold variation can be reduced by adopting
an additional measurement, used in FIG. 7, consisting of the
parallel connection, to the resistor R3, of a non-linear element
that plays no role so long as Vcc is low enough, but then
attenuates the slope of the straight line Vref1 in a non-linear
way. This attenuation must depend on the parameters of the method
of manufacture as well as on the operating temperature of the
integrated circuit, somewhat in the same way as the dependence of
Vref2, so as to restrict the effective zone of intersection of the
curves Vref1 and Vref2.
[0051] In examining FIG. 8, it can be seen that a curve Vref1a has
been plotted, representing a limit of variation of Vref1 as a
function of the manufacturing parameters. This curve intersects the
corresponding curve Vref2a (for the same extreme parameters of
manufacture) at a point corresponding to Vcc=2.4 volts. And the
curve Vref1b intersects the curve Vref2b (for the other extreme of
manufacturing parameters,) at another point corresponding almost
exactly to the same value 2.4 volts for Vcc.
[0052] Consequently, it will be understood that the range of error
on the threshold can be reduced to a very large extent, while at
the same time enabling an easy choice of the value of this
threshold.
[0053] In the embodiment shown in FIG. 7, with reference to a 2.5
volt detector, the non-linear element parallel-connected to the
resistor R3 is a series-connected assembly of two transistors
mounted as a diode (with the gate connected to the drain), one
being a P channel transistor T6 and the other being a native N
channel transistor T7. These transistors may be series-connected
with a transistor T8 controlled like the transistors T2 and T3 so
as to be off in the standby mode. The sum of the threshold voltages
of the transistors T6 and T7 is smaller than the threshold voltage
of the transistor T1, so that the straight line Vref1 with a slope
R3/(R3+R1) as a function of Vcc becomes curved (by the gradual
placing of T6 and T7 in a state of conduction) in the region of
intersection of the curves Vref1 and Vref2 namely for a value of
Vref2 similar to the threshold voltage of T1 (1.6 volts in the
example given). For example, where the sum of the threshold
voltages T6 and T7 is about 1 volt to 1.3 volts (with a high
dependence depending on the temperature of the circuit), the
dependence of Vref1 on the temperature is fairly similar to the
temperature dependence of Vref2.
[0054] Two additional transistors T9 and T10, activated by the
standby signal STBY, have been designed to place Vref2 initially at
Vcc, in order to ensure, unambiguously, that the operation of the
circuit will start in a condition where Vref2 is greater than
Vref1.
[0055] One example of the numerical values that may be used to make
a level detector of about 2.5 volts, leading to the curves shown in
FIG. 8, is given here below:
[0056] R1=80 kiloohms, R2=20 kiloohms, R3=450 kiloohms,
[0057] R4=500 kiloohms,
[0058] geometry of T1: W/L=20/2
[0059] geometry of T6: W/L=15/2.4
[0060] geometry of T7: W/L=5/2.4.
[0061] FIG. 9 shows an example of a diagram of a comparator that
can be used in the circuits of these above figures. This comparator
can work even for very low supply voltages of less than 2 volts.
This comparator is put into operation only outside standby periods,
by means of a signal AMP_ON (the logic complement of the standby
setting signal STBY). The signal AMP_ON permits or prohibits the
passage of current in the different arms of the comparator.
[0062] The integrated circuit may simultaneously include a detector
such as the one shown in FIG. 5 for the detection of a four-volt
threshold and a detector such as that of FIG. 7 for the detection
of a 2.5-volt threshold. The logic combination of the output
indications from these two detectors enables, for example, the very
simple determination of the range of supply voltages in which Vcc
is located, when it is known in advance that the possible ranges
are the following:
[0063] below 2.5 volts,
[0064] in the nominal range of 2.7 to 3.3 volts,
[0065] in the nominal range of 4.5 to 5.5 volts.
[0066] In a more complex embodiment, shown in FIG. 10, different
improvements are provided. These improvements can be used
separately or together, and seek above all to adapt the circuit to
the detection of higher supply voltage levels.
[0067] In particular, in integrated circuits comprising
electrically programmable non-programmable memories, there is need
for supply voltages in the range of 15 or 18 volts for the write
circuits of the memory. These supply voltages are not given
directly from the exterior of the integrated circuit but are
generally given by a so-called <<load pump >> circuit,
present in the integrated circuit itself and operating through the
one and only supply Vcc of the integrated circuit. It may be
necessary to detect the level of the high supply voltage Hiv given
by the load pump.
[0068] The circuit of FIG. 10 enables this detection to be made. It
has different parts, some of which receive the voltage Hiv to be
detected while others are supplied with the ordinary voltage Vcc (3
volts or 5 volts for example).
[0069] The modifications of the circuit with respect to the
schematic drawing of FIG. 4 are as follows: first of all, the two
arms used to define the voltage references Vref1 and Vref2 are
joined by a common conductor, constituting a base for the two arms,
this common conductor representing a fictitious ground MF for which
it will be seen that its potential may be carried to the true
ground of the circuit or to a higher potential that may be chosen
at will.
[0070] The resistors R1, R3 of the divider bridge of the first arm
are made in the form of two P channel transistors Q6, Q7 whose
gates are connected to the fictitious ground. The point of junction
between these two transistors is the one that defines the reference
voltage Vref1. A series of diode-mounted transistors (with the
drain connected to the source), in this case a series constituted
by P channel transistors Q2, Q3, Q4, Q5, is interposed in the first
arm, between the fictitious ground and the resistive divider bridge
Q6, Q7. These transistors Q2 to Q5 are used to set up a desired
voltage drop between the fictitious ground and the resistive
divider bridge. Their presence and their number depends on the
application that is specifically envisaged.
[0071] Furthermore, it has been planned that there will be several
P channel native transistors T1a, T1b, T1c series-connected in the
first arm and not just one native transistor T1.
[0072] In the second arm, the resistor R4 of the circuit of FIG. 4
is formed by a P channel transistor Q1 whose gate is connected to
the fictitious ground.
[0073] To obtain a drop in potential between the level of the
supply voltage Hiv and the junction point that defines the first
reference voltage Vref1 (the junction between the source of Q6 and
the drain of Q7 in the diagram of FIG. 10), there is provided, in
the first arm, between this point and the supply voltage Hiv, an
element capable of causing a drop in potential, preferably a P
channel transistor Q8 having its gate connected to its drain and
having high internal resistance (for example, with a length 50
times greater than its width). The drop in voltage may thus have a
value of several volts. The transistor Q8 may be located between
the transistor Q6 and the supply Hiv or between the transistor Q6
and the junction point that defines the reference Vref1.
[0074] A similar arrangement may be adopted in the second arm, with
a transistor Q9 that brings about a drop of several volts in the
voltage between the supply Hiv and the junction point that defines
the second reference Vref2. The transistor Q9 may be located
between the transistor Q1 and the voltage Hiv or between the
transistor Q1 and the reference Vref2.
[0075] With this type of arrangement, the reference voltages Vref1
and Vref2 may be in the range of 7 to 8 volts. These voltage are
however far too high to enable an operation of the comparator COMP.
For, this comparator COMP is powered at a voltage Vcc of about 3 to
5 volts.
[0076] It is therefore preferably provided that the voltage Vref1
and the voltage Vref2 will be converted, by stages of transposition
of voltage level, into two other auxiliary reference voltages
Vref'1 and Vref'2, of a lower level (about 1.5 volts), and it is
these auxiliary references that are effectively applied to the
inputs of the comparator COMP.
[0077] For this purpose, the voltage Vref1 is applied to the gate
of a highly resistive N channel transistor Q10, whose source is at
the electrical ground (and not at the fictitious ground MF) and
whose drain is connected by a resistor R5 to the low supply voltage
Vcc. The auxiliary reference voltage Vref'2 is taken at the
junction of the transistor Q10 and the resistor R5.
[0078] Similarly, the voltage Vref2 is applied to the gate of a
highly resistive N channel transistor Q11, whose source is at the
electrical ground and whose drain is connected by a resistor R6 to
the low supply voltage Vcc. The auxiliary reference voltage Vref'2
is taken at the junction of the transistor Q10 and the resistor
R5.
[0079] Finally, to enable, if desired, an adaptation of the
detector to the various ranges of possible values of voltage levels
to be detected, it is provided that the potential of the fictitious
ground MF may be offset with respect to the ground of the
integrated circuit, through a set of arms that can selectively
connect the fictitious ground to the ground under the control of a
selection circuit. The different arms set up different voltage
drops when they are put into operation. A selected arm will be put
into operation by the operation of turning on a transistor located
at the foot of this arm (transistors Q20 to Q25 in the diagram of
FIG. 10 which has six possible arms). A selection signal SEL
activates the operation of turning on a selected arm (in principle
only one arm at a time).
[0080] The different voltage drops are set up by different
transistors mounted in these arms (it is assumed that the base
transistor introduces no voltage drop or a very low and identical
voltage drop in all the arms). In the example shown, designed for
the precise adjustment of the voltage level detected, there are
provided six arms in which the voltage drops introduced are due to
one or more series-connected N channel transistors that are
diode-mounted. These arms are the following:
[0081] arm A: direct link to place the fictitious ground MF at the
real ground;
[0082] arm B: drop in voltage of a native transistor Q26;
[0083] arm C: drop in voltage of an enhanced transistor Q27;
[0084] arm D: drop in voltage of an enhanced transistor Q28
series-connected with a native transistor Q29;
[0085] arm E: drop in voltage of two enhanced transistors Q30 and
Q31;
[0086] arm F: drop in voltage of two enhanced transistors Q32 and
Q33 and one native transistor Q34 or two native transistors and one
enhanced transistor;
[0087] and so on and so forth, other arms could be planned, with
the parallel connection of several arms itself possibly providing
for greater precision of adjustment of the levels to be
detected.
[0088] Having thus described at least one illustrative embodiment
of the invention, various alterations, modifications, and
improvements will readily occur to those skilled in the art. Such
alterations, modifications, and improvements are intended to be
within the spirit and scope of the invention. Accordingly, the
foregoing description is by way of example only and is not intended
as limiting. The invention is limited only as defined in the
following claims and the equivalents thereto.
* * * * *