U.S. patent application number 16/221552 was filed with the patent office on 2019-04-25 for apparatus with electronic circuitry having reduced leakage current and associated methods.
The applicant listed for this patent is Silicon Laboratories Inc.. Invention is credited to Essam Atalla, Nicholas M. Atkinson, Arnab Kumar Dutta.
Application Number | 20190123734 16/221552 |
Document ID | / |
Family ID | 62982507 |
Filed Date | 2019-04-25 |
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United States Patent
Application |
20190123734 |
Kind Code |
A1 |
Dutta; Arnab Kumar ; et
al. |
April 25, 2019 |
Apparatus with Electronic Circuitry Having Reduced Leakage Current
and Associated Methods
Abstract
An apparatus includes an integrated circuit (IC), which includes
complementary metal oxide semiconductor (CMOS) circuitry that
includes a pull-up network coupled to a supply voltage and at least
one input signal. The IC further includes a first metal oxide
semiconductor (MOS) transistor coupled to the pull-up network and
to a first bias voltage to reduce a gate-induced drain leakage
(GIDL) current of the CMOS circuitry.
Inventors: |
Dutta; Arnab Kumar; (Austin,
TX) ; Atalla; Essam; (Austin, TX) ; Atkinson;
Nicholas M.; (Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Silicon Laboratories Inc. |
Austin |
TX |
US |
|
|
Family ID: |
62982507 |
Appl. No.: |
16/221552 |
Filed: |
December 16, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15429690 |
Feb 10, 2017 |
10158354 |
|
|
16221552 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03K 17/162 20130101;
H03K 2017/066 20130101; H03K 2217/0036 20130101; H03K 17/161
20130101 |
International
Class: |
H03K 17/16 20060101
H03K017/16 |
Claims
1. An apparatus comprising: an integrated circuit (IC) comprising:
complementary metal oxide semiconductor (CMOS) circuitry comprising
a pull-up network coupled to a supply voltage and at least one
input signal; and a first metal oxide semiconductor (MOS)
transistor coupled to the pull-up network and to a first bias
voltage to reduce a gate-induced drain leakage (GIDL) current of
the CMOS circuitry.
2. The apparatus according to claim 1, wherein the IC further
comprises: a pull-down network coupled to a ground potential and to
the at least one input signal; and a second MOS transistor coupled
to the pull-down network and to a second bias voltage to reduce the
GIDL current of the CMOS circuitry.
3. The apparatus according to claim 1, wherein the first bias
voltage is applied to a gate of the first MOS transistor to reduce
a drain-bulk voltage of at least one transistor in the pull-up
network.
4. The apparatus according to claim 2, wherein the second bias
voltage is applied to a gate of the second MOS transistor to reduce
a drain-bulk voltage of at least one transistor in the pull-down
network.
5. The apparatus according to claim 2, wherein at least one of the
first and second bias voltages is variable.
6. The apparatus according to claim 1, wherein the first bias
voltage depends on a supply voltage of the CMOS circuitry.
7. The apparatus according to claim 2, wherein the second bias
voltage depends on a supply voltage of the CMOS circuitry.
8. An apparatus comprising: an integrated circuit (IC) comprising:
complementary metal oxide semiconductor (CMOS) circuitry comprising
a pull-down network coupled to a ground potential and at least one
input signal; and a first metal oxide semiconductor (MOS)
transistor coupled to the pull-down network and to first a bias
voltage to reduce a gate-induced drain leakage (GIDL) current of
the CMOS circuitry.
9. The apparatus according to claim 8, wherein the IC further
comprises: a pull-up network coupled to a supply voltage and to the
at least one input signal; and a second MOS transistor coupled to
the pull-up network and to a second bias voltage to reduce the GIDL
current of the CMOS circuitry.
10. The apparatus according to claim 8, wherein the first bias
voltage is applied to a gate of the first MOS transistor to reduce
a drain-bulk voltage of at least one transistor in the pull-down
network.
11. The apparatus according to claim 9, wherein the second bias
voltage is applied to a gate of the second MOS transistor to reduce
a drain-bulk voltage of at least one transistor in the pull-up
network.
12. The apparatus according to claim 9, wherein at least one of the
first and second bias voltages is variable.
13. The apparatus according to claim 8, wherein the first bias
voltage depends on a supply voltage of the CMOS circuitry.
14. The apparatus according to claim 9, wherein the second bias
voltage depends on a supply voltage of the CMOS circuitry.
15. A method of reducing a gate-induced drain leakage (GIDL)
current of at least one transistor in a complementary metal oxide
semiconductor (CMOS) circuit, the method comprising biasing a metal
oxide semiconductor (MOS) transistor coupled to the at least one
transistor by applying a bias voltage to a gate of the MOS
transistor so as to reduce a drain-bulk voltage of the at least one
transistor.
16. The method according to claim 15, wherein the at least one
transistor is included in a pull-up network of the CMOS
circuit.
17. The method according to claim 15, wherein the at least one
transistor is included in a pull-down network of the CMOS
circuit.
18. The method according to claim 15, wherein the bias voltage is
fixed.
19. The method according to claim 15, wherein the bias voltage is
variable.
20. The method according to claim 19, wherein the bias voltage
depends on a supply voltage of the CMOS circuit.
Description
TECHNICAL FIELD
[0001] The disclosure relates generally to electronic circuitry
with improved power consumption and, more particularly, to
integrated circuit (IC) apparatus with reduced power consumption,
and associated methods.
BACKGROUND
[0002] Modern ICs have helped to integrate electronic circuitry to
decrease size and cost. As a consequence, modern ICs can form
complex circuitry and systems. For example, virtually all of the
functionality of a system may be realized using one or a handful of
ICs. Such circuitry and systems may receive and operate on both
analog and digital signals, and may provide analog and digital
signals.
[0003] The result has been a growing trend to produce circuitry and
systems with increased numbers of transistors and similar devices.
The increased number of devices has also coincided with increased
power consumption of electronic circuits, such as ICs. Various
mechanisms, such as device leakage, underlie the increased power
consumption. Technologies such as complementary metal oxide
semiconductor (CMOS), which are used in a variety of IC devices,
use devices such as transistors with leakage currents.
[0004] The description in this section and any corresponding
figure(s) are included as background information materials. The
materials in this section should not be considered as an admission
that such materials constitute prior art to the present patent
application.
SUMMARY
[0005] A variety of apparatus and associated methods are
contemplated according to exemplary embodiments. According to one
exemplary embodiment, an apparatus includes an IC, which includes
CMOS circuitry that includes a pull-up network coupled to a supply
voltage and at least one input signal. The IC further includes a
first metal oxide semiconductor (MOS) transistor coupled to the
pull-up network and to a first bias voltage to reduce a
gate-induced drain leakage (GIDL) current of the CMOS
circuitry.
[0006] According to another exemplary embodiment, an apparatus
includes an IC, which includes CMOS circuitry that includes a
pull-down network coupled to a ground potential and at least one
input signal. The IC further includes a first MOS transistor
coupled to the pull-down network and to a first bias voltage to
reduce a GIDL current of the CMOS circuitry.
[0007] According to another exemplary embodiment, a method of
reducing a GIDL current of at least one transistor in a CMOS
circuit includes biasing a MOS transistor coupled to the at least
one transistor by applying a bias voltage to a gate of the MOS
transistor so as to reduce a drain-bulk voltage of the at least one
transistor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The appended drawings illustrate only exemplary embodiments
and therefore should not be considered as limiting the scope of the
application or the claims. Persons of ordinary skill in the art
will appreciate that the disclosed concepts lend themselves to
other equally effective embodiments. In the drawings, the same
numeral designators used in more than one drawing denote the same,
similar, or equivalent functionality, components, or blocks.
[0009] FIG. 1 illustrates a leakage mechanism in one state of a
CMOS inverter.
[0010] FIG. 2 depicts a leakage mechanism in another state of a
CMOS inverter.
[0011] FIG. 3 shows a plot of leakage current as a function of the
drain-bulk voltage of a transistor.
[0012] FIG. 4 depicts a circuit arrangement for an inverter with
reduced leakage current according to an exemplary embodiment.
[0013] FIG. 5 illustrates one state of a circuit arrangement for an
inverter with reduced leakage current according to an exemplary
embodiment.
[0014] FIG. 6 depicts another state of a circuit arrangement for an
inverter with reduced leakage current according to an exemplary
embodiment.
[0015] FIG. 7 illustrates a plot of leakage current as a function
of bias voltage according to an exemplary embodiment.
[0016] FIG. 8 shows a circuit arrangement for an inverter with
reduced leakage current according to an exemplary embodiment.
[0017] FIG. 9 illustrates a circuit arrangement for a CMOS circuit
with reduced leakage current according to an exemplary
embodiment.
[0018] FIG. 10 depicts a circuit arrangement for a NAND gate with
reduced leakage current according to an exemplary embodiment.
[0019] FIG. 11 shows a circuit arrangement for a NOR gate with
reduced leakage current according to an exemplary embodiment.
[0020] FIGS. 12-15 illustrate leakage mechanisms in various states
of a CMOS transmission gate.
[0021] FIG. 16 depicts a transmission gate with reduced leakage
current according to an exemplary embodiment.
[0022] FIG. 17 shows a circuit arrangement for a level shifter
according to an exemplary embodiment.
[0023] FIG. 18 illustrates a circuit arrangement for a level
shifter according to another exemplary embodiment.
[0024] FIG. 19 depicts a circuit arrangement for reducing leakage
current according to an exemplary embodiment.
[0025] FIG. 20 shows a block diagram of an IC according to another
exemplary embodiment.
DETAILED DESCRIPTION
[0026] The disclosed concepts relate generally to improving the
performance of electronic circuitry. More specifically, the
disclosed concepts provide apparatus and methods for reducing the
leakage and, thus, improving or reducing the power consumption of,
electronic circuitry, such as ICs. Rather than modifying the
semiconductor fabrication process, the techniques according to the
disclosure use circuit-based approaches to reducing the leakage
current of CMOS circuitry, as described below in detail.
[0027] CMOS circuitry, such as an inverter, can have several
leakage mechanisms. For example, considering an inverter 10, as
shown in FIG. 1, the gates of transistor 13 and transistor 16 tend
to leak current. In other words, the oxide layer used to construct
the gates of the transistors is not a perfect insulator, which
results in some leakage current. Generally, reverse-biased PN
junctions will also leak a certain amount of current and therefore
increase the overall leakage current of inverter 10.
[0028] Inverter 10 in FIG. 1 also exhibits other leakage
mechanisms. For instance, gate-induced drain leakage (GIDL) current
may constitute a relatively large or substantial part of the total
leakage current for CMOS circuits such as inverter 10. More
specifically, GIDL may contribute a relatively large or substantial
amount to the overall leakage of CMOS circuits employing
lightly-doped drain (LDD) transistors designed for operation with
relatively high supply voltages (V.sub.DD), say, greater than 3
volts.
[0029] Generally, the GIDL mechanism and the effects of LDD are
known to, and understood by, persons of ordinary skill in the art.
A brief summary is provided below.
[0030] GIDL is a phenomenon where current flows between the bulk
and the drain regions of a metal-oxide-semiconductor field effect
transistor (MOSFET) because of the bulk-drain junction getting
modulated by the gate-drain voltage. The GIDL phenomenon is
sometimes associated with higher than normal operating voltages
(for example, write voltages used to write date to flash memory
cells). The GIDL phenomenon, however, can also happen at regular or
nominal operating voltages in CMOS circuits where LDD transistors
are used. LDD transistors are typically used to allow or tolerate
higher voltages across the bulk-drain PN-junctions of transistors.
Leakage because of the GIDL phenomenon is independent of
temperature.
[0031] GIDL is typically a relatively strong function of the
drain-bulk voltage (V.sub.DB) when the MOSFET is in the off state
(i.e., the gate-source voltage, V.sub.GS, is 0 or below the
threshold voltage, V.sub.T). This condition is common in CMOS
circuits. Consequently, GIDL can constitute a relatively large or
even dominant leakage mechanism at room temperature for CMOS
circuits.
[0032] Referring again to FIG. 1, inverter 10 includes P-channel
MOS (PMOS) transistor 13 and N-channel MOS (NMOS) transistor 16.
Assuming that transistor 13 and transistor 16 constitute LDD
transistors, when the input voltage has a logic 1 value, transistor
16 is on, and transistor 13 is off. The drain of transistor 13 is
at or nearly at ground potential (VSS) (because transistor 16 is
on, thus pulling the output (OUT) to the ground potential, or logic
0), and the drain of transistor 13 is coupled to the supply
voltage.
[0033] Consequently, the drain-bulk voltage (V.sub.DB) of
transistor 13 is relatively large, which leads to leakage because
of GIDL. Path 18 shows the path through which the leakage current
flows. Specifically, current flows from the supply source through
transistor 13, through transistor 16, and finally to the ground
node.
[0034] A similar phenomenon causes GIDL current when the input
voltage has a logic 0 value. FIG. 2 shows this situation. Referring
to FIG. 2, transistor 13 is on and, thus, conducting. Conversely,
transistor 16 is off, as its gate-source voltage is below its
threshold voltage.
[0035] Even though it is in the off state, transistor 16 has a
relatively large drain-bulk voltage (V.sub.DB). More specifically,
the drain of transistor 16 has a relatively large voltage, i.e., at
or near the supply voltage, as transistor 13 is on and pulls up the
output node towards the supply voltage. The bulk of transistor 16,
however, is coupled to the ground potential. As a result,
transistor 16 has a relatively large drain-bulk voltage (V.sub.DB),
which leads to leakage because of GIDL. Path 18 shows the path
through which the leakage current flows. Specifically, current
flows from the supply source through transistor 13, through
transistor 16, and finally to the ground node through the bulk or
bulk region of transistor 16.
[0036] As noted, GIDL current of a transistor is a function of the
drain-bulk voltage (V.sub.DB) of the transistor. FIG. 3 shows a
plot 20 of leakage current in a CMOS transistor as a function of
the drain-bulk voltage. Specifically, the horizontal axis shows
increasing values of the drain-bulk voltage, from about 3 volts to
about 3.9 volts. The vertical axis shows GIDL current with the
transistor in the off state (e.g., V.sub.GS is zero or nearly
zero), and the source-bulk voltage (V.sub.SB) also zero or nearly
zero. The numbers on the vertical axis are relative to a drain-bulk
voltage of 3 volts.
[0037] As curve 23 of the GIDL current shows, decreasing the
drain-bulk voltage (V.sub.DB) results in a corresponding decrease
in the GIDL current. For example, as curve 23 illustrates,
decreasing the drain-bulk voltage even by .about.500 mV can
decrease GIDL substantially, say, by a factor of nearly 10. This
property may be used to improve the GIDL current of various CMOS
circuits, such as inverters, logic gates, level shifters,
transmission gates, etc., as described below in detail.
[0038] Generally speaking, CMOS circuits according to exemplary
embodiments employ techniques to reduce the drain-bulk voltage
(V.sub.DB) seen by or applied to a leaking device, such as an LDD
PMOS or NMOS transistor. In some embodiments, an additional PMOS
transistor is coupled to a pull-up transistor (e.g., the pull-up
PMOS transistor of a CMOS inverter). FIG. 4 depicts a circuit
arrangement 30 for an inverter with reduced leakage current
according to an exemplary embodiment.
[0039] Specifically, the inverter in FIG. 4 includes pull-up PMOS
transistor 33 and pull-down NMOS transistor 36. In addition, the
inverter includes GIDL current reduction PMOS transistor 39,
coupled between transistor 33 and the output node (OUT) of the
inverter. More specifically, the source of transistor 39 is coupled
to the drain of transistor 33, whereas the drain of transistor 39
is coupled to the output node of the inverter.
[0040] Transistor 39 acts to reduce the effective drain-bulk
voltage (V.sub.DB) of transistor 33 (the drain-bulk voltage seen by
transistor 33 when it is in the off state). To facilitate this
operation, the bulk or body of transistor 39 is coupled to the
supply voltage (V.sub.DD) and the gate of transistor 39 is coupled
to a bias voltage (V.sub.bias). The bias voltage is selected so as
to cause a voltage drop across transistor 39, thus reducing the
effective drain-bulk voltage of transistor 33. The reduction of the
drain-bulk voltage of transistor 33 causes a reduction in the GIDL
current attributable to transistor 33.
[0041] Note that, in some embodiments, rather than including
transistor 39 in series with transistor 33, a GIDL current
reduction NMOS transistor may be added in series with transistor
36. The gate of such a transistor would be coupled to a bias source
of appropriate value in order to decrease the drain-bulk voltage of
transistor 36. The reduction in the drain-bulk voltage of
transistor 36 would cause a reduction in the GIDL current
attributable to transistor 36. Furthermore in some embodiments,
both a GIDL current reduction PMOS transistor and a GIDL current
reduction NMOS transistor may be used, as described below, for
example, in connection with FIG. 8.
[0042] One aspect of the disclosure relates to generation of the
bias voltage used to reduce leakage current, such as V.sub.bias
shown in FIG. 4. FIG. 5 illustrates one state of a circuit
arrangement 40 for providing a bias voltage to a CMOS logic circuit
(an inverter, in the example shown). Circuit arrangement 40
includes an inverter 43 coupled in cascade with an inverter 46.
Inverter 43 and inverter 46 receive supply voltage from a voltage
source labeled "V.sub.BIAS." Thus, for CMOS inverters, the output
voltages of inverter 43 and inverter 46 varies in the range of
V.sub.SS (typically ground potential) and the supply voltage,
V.sub.BIAS.
[0043] FIG. 5 illustrates the situation where the input voltage has
a logic 1 value (IN=1). In this case, the output of inverter 43 has
a logic 0 value, which results in the output of inverter 46 having
a logic 1 value (labeled "V.sub.BIAS"). The output of inverter 46
provides the bias voltage to GIDL current reduction PMOS transistor
39. Thus, for a logic 1 input value, inverter 46 provides a bias
voltage of V.sub.BIAS.
[0044] FIG. 6 shows the situation where the input voltage has a
logic 0 value (IN=0). In this situation, the output of inverter 43
has a logic 1 value, which results in the output of inverter 46
having a logic 0 value (labeled "0"). The output of inverter 46
provides the bias voltage to GIDL current reduction PMOS transistor
39. Thus, for a logic 0 input value, inverter 46 provides a bias
voltage of 0 volts (ground potential).
[0045] As FIGS. 5-6 illustrate, using inverter 43 and inverter 46
provides a mechanism for providing a bias voltage that varies in
response to the input signal to a CMOS logic circuit. In other
words, the bias voltage provided is adaptive, in that it adapts in
response to the values of the input voltage applied to the CMOS
logic circuit. Note that a similar arrangement may be applied to
situations where a GIDL current reduction NMOS transistor is added
in series with transistor 36 (described above), or in the case
where both a GIDL current reduction PMOS transistor and a GIDL
current reduction NMOS transistor are used (described above).
[0046] One aspect of the disclosure relates to providing one or
more variable (or configurable or adjustable or programmable) bias
voltages to one or more CMOS logic circuits in order to reduce GIDL
current. FIG. 7 illustrates a plot 50 of leakage current as a
function of bias voltage according to an exemplary embodiment. Plot
50 includes curve 53, which shows results of simulation of GIDL
current as a function of bias voltage (labeled "V.sub.BIAS"). More
specifically, curve 53 provides the results for a CMOS inverter
with a supply voltage of 3.8 volts, and is normalized to a regular
CMOS inverter (i.e., with no GIDL current reduction) when
V.sub.BIAS is swept between the ground potential (0 volts) and the
supply voltage (V.sub.DD).
[0047] As FIG. 7 illustrates, GIDL current is optimized when the
bias voltage has a value close to half of the supply voltage, i.e.,
V.sub.BIAS.apprxeq.1/2V.sub.DD. Thus, in some embodiments, a bias
voltage is used with a value of half the supply voltage, or near
half of the supply voltage (e.g., substantially equal to half the
supply voltage, for example, within 5%, 10%, or 20% of the supply
voltage, etc.). Note that such bias voltages may be applied to GIDL
current reduction PMOS transistor(s) and/or GIDL current reduction
NMOS transistor(s), as desired.
[0048] For basic logic gates, such as an inverter, a simpler option
is to use fixed bias voltages. For instance, in some embodiments, a
bias voltage of 0 volts (ground potential) is used for GIDL current
reduction PMOS transistor(s), and/or the supply voltage (VDD) is
used as a bias voltage GIDL current reduction NMOS transistor(s).
This scheme provides a tradeoff between circuit complexity and
performance, for instance, compared to bias voltages with arbitrary
or variable values.
[0049] As noted above, in some embodiments, both GIDL current
reduction PMOS transistor(s) and GIDL current reduction NMOS
transistor(s) are used. FIG. 8 shows a circuit arrangement 60 for a
CMOS inverter that uses this configuration.
[0050] More specifically, the inverter in FIG. 8 includes pull-up
PMOS transistor 33 and pull-down NMOS transistor 36. The inverter
also includes GIDL current reduction PMOS transistor 39, coupled
between transistor 33 and the output node (OUT) of the inverter.
More specifically, the source of transistor 39 is coupled to the
drain of transistor 33, whereas the drain of transistor 39 is
coupled to the output node of the inverter.
[0051] Transistor 39 acts to reduce the effective drain-bulk
voltage (V.sub.DB) of transistor 33 (the drain-bulk voltage seen by
transistor 33 when it is in the off state). To facilitate this
operation, the bulk or body of transistor 39 is coupled to the
supply voltage (V.sub.DD) and the gate of transistor 39 is coupled
to a bias voltage which, in the embodiment shown, is ground
potential. The bias voltage is selected so as to reduce the
effective drain-bulk voltage of transistor 33. The reduction of the
drain-bulk voltage of transistor 33 causes a reduction in the GIDL
current attributable to transistor 33.
[0052] The inverter also includes GIDL current reduction NMOS
transistor 63, coupled between transistor 36 and the output node
(OUT) of the inverter. More specifically, the source of transistor
63 is coupled to the drain of transistor 36, whereas the drain of
transistor 63 is coupled to the output node of the inverter.
[0053] Transistor 63 acts to reduce the effective drain-bulk
voltage (V.sub.DB) of transistor 36 (the drain-bulk voltage seen by
transistor 36 when it is in the off state). To facilitate this
operation, the bulk or body of transistor 63 is coupled to the
ground potential and the gate of transistor 63 is coupled to a bias
voltage which, in the embodiment shown, is the supply voltage
(V.sub.DD). The bias voltage is selected so as to reduce the
effective drain-bulk voltage of transistor 36. The reduction of the
drain-bulk voltage of transistor 36 causes a reduction in the GIDL
current attributable to transistor 36.
[0054] Note that, as discussed above, circuit arrangement 60 uses
fixed bias voltages, i.e., ground potential coupled to the gate of
transistor 39, and the supply voltage coupled to the gate of
transistor 63. In other embodiments, however, the bias voltage
applied to transistor 39 and/or the bias voltage applied to
transistor 63 may be variable (or configurable or adjustable or
programmable), as discussed above.
[0055] The use of GIDL current reduction PMOS transistor 39 and/or
GIDL current reduction NMOS transistor 63 may be applied generally
to various CMOS circuits. FIG. 9 illustrates a circuit arrangement
70 for a CMOS circuit with reduced leakage current according to an
exemplary embodiment. The bulk or body nodes of PMOS transistors
and the bulk and body nodes of NMOS transistors in circuit
arrangement 70 are coupled to the supply voltage (V.sub.DD) and
ground potential (V.sub.SS), respectively.
[0056] Circuit arrangement 70 includes pull-up network 73, which is
coupled to receive the supply voltage (V.sub.DD) and one or more
inputs (labeled "IN") of the CMOS circuit. Note that not all
transistors in pull-up network 73 are necessarily coupled to the
supply voltage or the input(s). Pull-up network 73 typically
includes one or more PMOS transistors.
[0057] Similar to the inverter shown in FIG. 8, GIDL current
reduction PMOS transistor 39 in FIG. 9 is coupled between pull-up
network 73 and the output node (labeled "OUT") of the CMOS circuit.
The bulk or body of transistor 39 is coupled to the supply voltage
(V.sub.DD). The gate of transistor 39 is coupled to a bias voltage
V.sub.BIASP, which may be fixed or variable (or configurable or
adjustable or programmable), as described above.
[0058] Furthermore, the CMOS circuit in FIG. 9 includes a pull-down
network, which is coupled to the ground potential and to one or
more inputs (labeled "IN") of the CMOS circuit. Note that not all
transistors in pull-down network 76 are necessarily coupled to the
ground potential or the input(s).
[0059] Similar to the inverter shown in FIG. 8, GIDL current
reduction NMOS transistor 63 in FIG. 9 is coupled between pull-down
network 76 and the output node (labeled "OUT") of the CMOS circuit.
The bulk or body of transistor 63 is coupled to the ground
potential or V.sub.SS. The gate of transistor 63 is coupled to a
bias voltage V.sub.BIASN, which may be fixed or variable (or
configurable or adjustable or programmable), as described
above.
[0060] Note that in some embodiments, the bias voltages V.sub.BIASP
and V.sub.BIASN might be the same, for example, one half of the
supply voltage, as described above. In other embodiments, however,
the bias voltages V.sub.BIASP and V.sub.BIASN might different
values.
[0061] The use of GIDL current reduction PMOS transistor 39 and
GIDL current reduction NMOS transistor 63 reduces the drain-bulk
voltage (V.sub.DB) seen by or applied to the transistor(s) in
pull-up network 73 and/or pull-down network 76, as described above.
As a result, the GIDL current in the CMOS circuit is reduced.
[0062] Note that, rather than using both GIDL current reduction
PMOS transistor 39 and GIDL current reduction NMOS transistor 63,
in some embodiments one or the other transistor is used to reduce
GIDL current in the CMOS circuit. More specifically, in some
embodiments, the CMOS circuit includes pull-up network 73 coupled
to GIDL current reduction PMOS transistor 39, and a pull-down
network 76 (in other words, GIDL current reduction NMOS transistor
63 is omitted). Conversely, in some embodiments, the CMOS circuit
includes pull-down network 76 coupled to GIDL current reduction
NMOS transistor 63, and a pull-up network 73 (in other words, GIDL
current reduction PMOS transistor 39 is omitted).
[0063] Referring again to FIG. 9, as persons of ordinary skill in
the art will understand, pull-up network 73 and pull-down network
76 include one or more MOSFETs. More specifically, in exemplary
embodiments, pull-up network 73 includes one or more PMOS
transistors. Conversely, pull-down network 76 includes one or more
NMOS transistors.
[0064] The configuration of the transistors in pull-up network 73
and pull-down network 76 determines the overall logic function that
the CMOS circuit performs. For example, FIG. 10 depicts a circuit
arrangement 90 for a NAND gate with reduced leakage current
according to an exemplary embodiment.
[0065] The pull-up network in the NAND gate includes transistor 93
coupled to receive input IN2 and transistor 96 coupled to receive
input IN1 of the NAND gate. GIDL current reduction PMOS transistor
39 is coupled between transistor 96 and the output node (labeled
"OUT") of the NAND gate. The gate of transistor 39 is biased by the
ground potential, although other bias voltages may be used, as
described above.
[0066] Conversely, the pull-down network in the NAND gate includes
transistor 105 coupled to receive input IN1 and transistor 108
coupled to receive input IN2 of the NAND gate. GIDL current
reduction NMOS transistor 63 is coupled between transistors 105 and
108 and the output node (labeled "OUT") of the NAND gate. The gate
of transistor 63 is biased by the supply voltage (V.sub.DD),
although other bias voltages may be used, as described above.
[0067] FIG. 11 shows a circuit arrangement 120 for a NOR gate with
reduced leakage current according to an exemplary embodiment. The
pull-up network in the NOR gate includes transistor 126 coupled to
receive input IN1 and transistor 123 coupled to receive input IN2
of the NOR gate. GIDL current reduction PMOS transistor 39 is
coupled between transistors 123 and 126 and the output node
(labeled "OUT") of the NOR gate. The gate of transistor 39 is
biased by the ground potential, although other bias voltages may be
used, as described above.
[0068] Conversely, the pull-down network in the NOR gate includes
transistor 135 coupled to receive input IN1 and transistor 138
coupled to receive input IN1 of the NOR gate. GIDL current
reduction NMOS transistor 63 is coupled between transistor 135 and
the output node (labeled "OUT") of the NOR gate. The gate of
transistor 63 is biased by the supply voltage (V.sub.DD), although
other bias voltages may be used, as described above.
[0069] One aspect of the disclosure relates to reducing GIDL
current in CMOS transmission gates. FIGS. 12-15 illustrate leakage
mechanisms in various states of a CMOS transmission gate 150.
Transmission gate 150 includes NMOS transistor 153 and PMOS
transistor 156, coupled to the input (labeled "IN") and output
(labeled "OUT") nodes. In response to the enable signal (labeled
"EN") and the logical complement of the enable signal (labeled
"ENB"), transistor 153 either couple the input to the output (when
transmission gate 150 is on) or isolate the input from the output
(when transmission gate 150 is off).
[0070] Transmission gate 150 includes multiple paths where GIDL
currents flow when EN=0 (i.e., ENB=1, and transmission gate 150 is
off), depending on the state of the input and output signals, i.e.,
"IN" and "OUT." FIGS. 12-15 show paths 18 through which the leakage
current flows, depending on the states of the input and output
signals, as Table 1 below indicates:
TABLE-US-00001 TABLE 1 FIG. EN ENB IN OUT 12 0 1 0 0 13 0 1 1 0 14
0 1 0 1 15 0 1 1 1
[0071] GIDL current reduction transistors may be used to reduced
the leakage current of CMOS transmission gates. FIG. 16 depicts a
circuit arrangement 180 for a transmission gate with reduced
leakage current according to an exemplary embodiment. The
transmission gate includes transistor 153, driven by the EN signal,
and transistor 156, driven by the ENB signal.
[0072] In addition, the transmission gates includes GIDL current
reduction NMOS transistors 183 and 186. Transistor 183 is coupled
between the input of the transmission gate and transistor 153.
Conversely, transistor 186 is coupled between the output of the
transmission gate and transistor 153. The gates of transistors 183
and 186 are coupled to a bias voltage, V.sub.DD, in the example
shown, although other bias voltage values may be used, as discussed
above.
[0073] The transmission gate further includes GIDL current
reduction PMOS transistors 189 and 192. Transistor 189 is coupled
between the input of the transmission gate and transistor 156.
Conversely, transistor 192 is coupled between the output of the
transmission gate and transistor 156. The gates of transistors 189
and 192 are coupled to a bias voltage, the ground potential in the
example shown, although other bias voltage values may be used, as
discussed above.
[0074] The bulk or body regions of the NMOS transistors in the
transmission gate are coupled to the ground potential. The bulk or
body regions of the PMOS transistors in the transmission gate are
coupled to the supply voltage (V.sub.DD).
[0075] One aspect of the disclosure relates reducing GIDL current
in CMOS level shifters. FIG. 17 shows a circuit arrangement 210 for
a level shifter according to an exemplary embodiment. The level
shifter constitutes a low-to-high level shifter, and includes GIDL
current reduction circuitry.
[0076] The level shifter includes inverter 231 coupled in cascade
with inverter 234. The cascade of the two inverters buffers the
input voltage (labeled "IN"). The output of inverter 231 (labeled
"INB") drives the gate of transistor 228. The output of inverter
234 (labeled "INX") drives the gate of transistor 225.
[0077] Transistor 225 is cross-coupled with transistor 216. More
specifically, the drain of transistor 225 is coupled to the gate of
transistor 216. Similarly, transistor 228 is cross-coupled with
transistor 213. Thus, the drain of transistor 228 is coupled to the
gate of transistor 216.
[0078] Inverter 231 and inverter 234 use a power supply voltage
V.sub.DDL. Transistors 213 and 216 are coupled to a supply voltage
V.sub.DDH. The supply voltage V.sub.DDH has a larger value than the
supply voltage V.sub.DDL. Thus, the output of the level shifter, at
the drain of transistor 228, can drive follow-on circuitry (not
shown) supplied by supply voltage V.sub.DDH.
[0079] Note that the gates of transistors 225 and 228 are driven by
inverters 231 and 234, respectively, which are supplied power from
V.sub.DDL, a relatively low supply voltage (compared to V.sub.DDH).
With respect to transistor 213 and transistor 216, the level
shifter includes additional circuitry to reduce the GIDL current of
transistors 213 and 216. More specifically, the level shifter
includes GIDL current reduction PMOS transistor 39A, coupled
between transistor 213 and transistor 225. The source of transistor
39A is coupled to the drain of transistor 213. The drain of
transistor 39A is coupled to the drain of transistor 225.
[0080] The gate of transistor 39A is coupled to the ground
potential. The addition of transistor 39A reduces the drain-bulk
voltage (V.sub.DB) seen by or applied to transistor 213 in its off
state. As a result, the GIDL current contribution from transistor
213 is reduced.
[0081] Similarly, the level shifter includes GIDL current reduction
PMOS transistor 39B, coupled between transistor 216 and transistor
228. The source of transistor 39B is coupled to the drain of
transistor 216. The drain of transistor 39B is coupled to the drain
of transistor 228.
[0082] The gate of transistor 39B is coupled to the ground
potential. The addition of transistor 39B reduces the drain-bulk
voltage (V.sub.DB) seen by or applied to transistor 216 in its off
state. As a result, the GIDL current contribution from transistor
216 is reduced.
[0083] The bulk or body regions of NMOS transistors 225 and 228 are
coupled to ground potential. The bulk or body regions of PMOS
transistors 213, 216, 39A, and 39B are coupled to the supply
voltage V.sub.DDH.
[0084] FIG. 18 illustrates a circuit arrangement 220 for a level
shifter according to another exemplary embodiment. The level
shifter in FIG. 18 is similar to and operates similarly to the
level shifter in FIG. 17, with the exception of the bias voltages
applied to transistors 39A and 39B. The level shifter in FIG. 18,
however, uses an intermediate voltage (V.sub.DDL) available in the
circuit in order to further reduce the GIDL current.
[0085] More specifically, the gate of transistor 39A is coupled to
the voltage "INX" (described above) i.e., the voltage "INX" serves
as a bias voltage for transistor 39A. Similarly, the gate of
transistor 39B is coupled to the voltage "INB" (described above)
i.e., the voltage "INB" serves as a bias voltage for transistor
39B.
[0086] When the input voltage (IN) has a logic 1 value, the output
voltage also has a logic 1 value. Transistor 213 is in the off
state in this scenario. Given that the voltage "INX" has the same
(or nearly same, accounting for non-ideal characteristics of a
practical implementation) voltage as the supply voltage V.sub.DDL,
the drain of transistor 213 is maintained at a voltage level of
V.sub.DDL plus the threshold voltage of transistor 39A, thus
reducing the drain-bulk voltage (V.sub.DB) of transistor 213 and,
hence, its GIDL current contribution.
[0087] A similar analysis applies to transistors 39B and 216. In
this case, the gate of transistor 39B is biased by the voltage
"INB" which, similar to the voltage "INX," has the same (or nearly
same, accounting for non-ideal characteristics of a practical
implementation) voltage as the supply voltage V.sub.DDL.
Consequently, the drain-bulk voltage (V.sub.DB) of transistor 216
and, hence, its GIDL current contribution are reduced.
[0088] The circuitry and techniques described above can be used to
reduce the GIDL current of various CMOS circuitry. Simulation has
shown that the GIDL current reduction may range 2 to 15 times in
exemplary embodiments, depending on supply voltage, the bias
voltage(s) used, and the type of logic gate.
[0089] One aspect of the disclosure relates to the generation of
bias voltages in response to variables such as supply voltage. FIG.
19 depicts a circuit arrangement 300 for reducing leakage current
according to an exemplary embodiment.
[0090] Circuit arrangement 300 includes an IC 305, which receives a
supply voltage V.sub.DD. The supply voltage V.sub.DD is provided to
bias voltage generator 310. As noted above, the magnitude of the
GIDL current for a given CMOS circuit depends in part on the supply
voltage used. In response to the level of the supply voltage
V.sub.DD, generates a bias voltage V.sub.BIASP for GIDL current
reduction PMOS transistor(s) (not shown) in the IC. Similarly, in
response to the level of the supply voltage V.sub.DD, generates a
bias voltage V.sub.BIASN for GIDL current reduction PMOS
transistor(s) (not shown) in the IC. The bias voltages V.sub.BIASP
and V.sub.BIASN are used in CMOS circuitry (not shown) in the IC to
reduce GIDL current, as described above.
[0091] Optionally, bias voltage generator 310 may respond to one or
more input signals 315. More specifically, bias voltage generator
310 in some embodiments generates the bias voltages V.sub.BIASP and
V.sub.BIASN depending on the level or type of input signal(s) 315.
In some embodiments, one or more signals may be used to control the
level of bias voltage(s) that bias voltage generator 310
generates.
[0092] For example, one or more signals may be used to control
whether bias voltage generator 310 generates fixed or variable bias
voltage(s). As another example, one or more signals may be used to
control the level of change in the bias voltage(s) in response to a
given amount of change in one or more variables, for instance, the
amount of change in the supply voltage V.sub.DD. As another
example, one or more control signals may be used to control whether
one or another set of fixed bias voltages is used (for instance,
V.sub.DD and ground potential are used as V.sub.BIASP and
V.sub.BIASN, respective, or 1/2VDD is used for both V.sub.BIASP and
V.sub.BIASN). As another example, one or more control signals may
be used to control whether one or both of bias voltages V.sub.BIASP
and V.sub.BIASN is variable (e.g., one fixed bias voltage and one
variable bias voltage, both fixed bias voltages, or both variable
bias voltages).
[0093] Other variations in the configuration and control of bias
voltage generator 310 are possible and contemplated, as persons of
ordinary skill in the art will understand. The choice of
configuration and control of bias voltage generator 310 in a given
implementation depends on a variety of factors, as persons of
ordinary skill in the art will understand. Such factors include
design specifications, performance specifications, the level of
GIDL current reduction desired, circuit complexity, cost, IC or
device area, available technology, such as semiconductor
fabrication technology, target markets, target end-users, etc.
[0094] Note that in some embodiments, rather than providing two
bias voltages, bias voltage generator 310 may generate one bias
voltage. For example, in some embodiments, generator 310 may
generate V.sub.BIASP but not V.sub.BIASN. As another example, in
some embodiments, generator 310 may generate V.sub.BIASN but not
V.sub.BIASP. The choice of the number of bias voltages depends on
whether GIDL current reduction PMOS transistor(s), GIDL current
reduction NMOS transistor(s), or both are used in a CMOS
circuit.
[0095] Bias voltage generator 310 may be implemented in a variety
of ways. In some embodiments, a control circuit may be used to
control the operation of bias voltage generator 310. In some
embodiments, an analog circuit (e.g., an amplifier or scaling
circuit) may be used to implement the generation of bias voltage(s)
in response to the level of the supply voltage V.sub.DD. Generally,
either analog circuitry or mixed-signal circuitry may be used to
implement bias voltage generator 310, depending on factors such as
design specifications, performance specifications, the level of
GIDL current reduction desired, circuit complexity, cost, IC or
device area, available technology, such as semiconductor
fabrication technology, target markets, target end-users, etc., as
persons of ordinary skill in the art will understand.
[0096] As noted, GIDL current reduction circuitry according to
various embodiments may be used in a variety of circuitry, such as
ICs. FIG. 20 shows a block diagram of an IC 550 according to
another exemplary embodiment. In the particular example shown, IC
550 includes or constitutes a microcontroller unit (MCU), although
other types of circuitry or IC may be used, as persons of ordinary
skill in the art will understand.
[0097] Referring to FIG. 20, IC 550, which constitutes or includes
an MCU. IC 550 includes a number of blocks (e.g., processor(s) 565,
data converter 605, I/O circuitry 585, etc.) that communicate with
one another using a link 560. In exemplary embodiments, link 560
may constitute a coupling mechanism, such as a bus, a set of
conductors or semiconductors for communicating information, such as
data, commands, status information, and the like.
[0098] IC 550 may include link 560 coupled to one or more
processors 565, clock circuitry 575, and power management circuitry
or PMU 580. In some embodiments, processor(s) 565 may include
circuitry or blocks for providing computing functions, such as
central-processing units (CPUs), arithmetic-logic units (ALUs), and
the like. In some embodiments, in addition, or as an alternative,
processor(s) 565 may include one or more DSPs. The DSPs may provide
a variety of signal processing functions, such as arithmetic
functions, filtering, delay blocks, and the like, as desired.
[0099] Clock circuitry 575 may generate one or more clock signals
that facilitate or control the timing of operations of one or more
blocks in IC 550. Clock circuitry 575 may also control the timing
of operations that use link 560. In some embodiments, clock
circuitry 575 may provide one or more clock signals via link 560 to
other blocks in IC 550.
[0100] In some embodiments, PMU 580 may reduce an apparatus's
(e.g., IC 550) clock speed, turn off the clock, reduce power, turn
off power, or any combination of the foregoing with respect to part
of a circuit or all components of a circuit. Further, PMU 580 may
turn on a clock, increase a clock rate, turn on power, increase
power, or any combination of the foregoing in response to a
transition from an inactive state to an active state (such as when
processor(s) 565 make a transition from a low-power or idle or
sleep state to a normal operating state).
[0101] Link 560 may couple to one or more circuits 600 through
serial interface 595. Through serial interface 595, one or more
circuits coupled to link 560 may communicate with circuits 600.
Circuits 600 may communicate using one or more serial protocols,
e.g., SMBUS, I.sup.2C, SPI, and the like, as person of ordinary
skill in the art will understand.
[0102] Link 560 may couple to one or more peripherals 590 through
I/O circuitry 585. Through I/O circuitry 585, one or more
peripherals 590 may couple to link 560 and may therefore
communicate with other blocks coupled to link 560, e.g.,
processor(s) 365, memory circuit 625, etc.
[0103] In exemplary embodiments, peripherals 590 may include a
variety of circuitry, blocks, and the like. Examples include I/O
devices (keypads, keyboards, speakers, display devices, storage
devices, timers, etc.). Note that in some embodiments, some
peripherals 590 may be external to IC 550. Examples include
keypads, speakers, and the like.
[0104] In some embodiments, with respect to some peripherals, I/O
circuitry 585 may be bypassed. In such embodiments, some
peripherals 590 may couple to and communicate with link 560 without
using I/O circuitry 585. Note that in some embodiments, such
peripherals may be external to IC 550, as described above.
[0105] Link 560 may couple to analog circuitry 620 via data
converter 605. Data converter 405 may include one or more ADCs 605B
and/or one or more DACs 605A. The ADC(s) 615 receive analog
signal(s) from analog circuitry 620, and convert the analog
signal(s) to a digital format, which they communicate to one or
more blocks coupled to link 560.
[0106] Analog circuitry 620 may include a wide variety of circuitry
that provides and/or receives analog signals. Examples include
sensors, transducers, and the like, as person of ordinary skill in
the art will understand. In some embodiments, analog circuitry 620
may communicate with circuitry external to IC 550 to form more
complex systems, sub-systems, control blocks, and information
processing blocks, as desired.
[0107] Control circuitry 570 couples to link 560. Thus, control
circuitry 570 may communicate with and/or control the operation of
various blocks coupled to link 560. In addition, control circuitry
570 may facilitate communication or cooperation between various
blocks coupled to link 560.
[0108] In some embodiments, control circuitry 570 may initiate or
respond to a reset operation. The reset operation may cause a reset
of one or more blocks coupled to link 560, of IC 550, etc., as
person of ordinary skill in the art will understand. For example,
control circuitry 570 may cause PMU 580 to reset to an initial
state. In some embodiments, the functionality and/or circuitry (or
part thereof) of bias voltage generator 310 may be included in
control circuitry 570, as desired.
[0109] In exemplary embodiments, control circuitry 570 may include
a variety of types and blocks of circuitry. In some embodiments,
control circuitry 570 may include logic circuitry, finite-state
machines (FSMs), or other circuitry to perform a variety of
operations, such as the operations described above.
[0110] Communication circuitry 640 couples to link 560 and also to
circuitry or blocks (not shown) external to IC 550. Through
communication circuitry 640, various blocks coupled to link 560 (or
IC 550, generally) can communicate with the external circuitry or
blocks (not shown) via one or more communication protocols.
Examples include USB, Ethernet, and the like. In exemplary
embodiments, other communication protocols may be used, depending
on factors such as specifications for a given application, as
person of ordinary skill in the art will understand.
[0111] As noted, memory circuit 625 couples to link 560.
Consequently, memory circuit 625 may communicate with one or more
blocks coupled to link 560, such as processor(s) 365, control
circuitry 570, I/O circuitry 585, etc. Memory circuit 625 provides
storage for various information or data in IC 550, such as
operands, flags, data, instructions, and the like, as persons of
ordinary skill in the art will understand. Memory circuit 625 may
support various protocols, such as double data rate (DDR), DDR2,
DDR3, and the like, as desired. In some embodiments, the memory
read and/or write operations involve the use of one or more blocks
in IC 550, such as processor(s) 565. A direct memory access (DMA)
arrangement (not shown) allows increased performance of memory
operations in some situations. More specifically, the DMA (not
shown) provides a mechanism for performing memory read and write
operations directly between the source or destination of the data
and memory circuit 625, rather than through blocks such as
processor(s) 565.
[0112] Memory circuit 625 may include a variety of memory circuits
or blocks. In the embodiment shown, memory circuit 625 includes
non-volatile (NV) memory 635. In addition, or instead, memory
circuit 625 may include volatile memory (not shown). NV memory 635
may be used for storing information related to performance or
configuration of one or more blocks in IC 550. For example, NV
memory 635 may store configuration information related to the
operation of bias voltage generator 310, such as the degree of
change in the level of bias voltage(s) in response to change, for
example, in the level of the supply voltage, as described
above.
[0113] IC 550 also includes bias voltage generator 310. As
discussed above, bias voltage generator 310 operates in response to
the supply voltage V.sub.DD and, optionally, to input signal(s)
315. Bias voltage generator 310 generates bias voltage V.sub.BIASP
and/or V.sub.BIASN. The bias voltage(s) may be used to bias GIDL
current reduction PMOS transistor(s) and/or GIDL current reduction
NMOS transistor(s) used to reduce GIDL current, as described above.
More specifically, the bias voltage(s) may be used to reduce GIDL
current in one or more of the blocks of circuitry shown in IC 550
(or other desired circuitry), as described above.
[0114] Various circuits and blocks described above and used in
exemplary embodiments may be implemented in a variety of ways and
using a variety of circuit elements or blocks. For example, part of
bias generator 310, pull-up network 73, and pull-down network 76
may generally be implemented using digital circuitry. The digital
circuitry may include circuit elements or blocks such as gates,
digital multiplexers (MUXs), latches, flip-flops, registers, finite
state machines (FSMs), processors, programmable logic (e.g., field
programmable gate arrays (FPGAs) or other types of programmable
logic), arithmetic-logic units (ALUs), standard cells, custom
cells, etc., as desired, and as persons of ordinary skill in the
art will understand. In addition, analog circuitry or mixed-signal
circuitry or both may be included, for instance, power converters,
discrete devices (transistors, capacitors, resistors, inductors,
diodes, etc.), and the like, as desired. The analog circuitry may
include bias circuits, decoupling circuits, coupling circuits,
supply circuits, current mirrors, current and/or voltage sources,
filters, amplifiers, converters, signal processing circuits (e.g.,
multipliers), detectors, transducers, discrete components
(transistors, diodes, resistors, capacitors, inductors), analog
MUXs and the like, as desired, and as persons of ordinary skill in
the art will understand. The mixed-signal circuitry may include
analog to digital converters (ADCs), digital to analog converters
(DACs), etc.) in addition to analog circuitry and digital
circuitry, as described above, and as persons of ordinary skill in
the art will understand. The choice of circuitry for a given
implementation depends on a variety of factors, as persons of
ordinary skill in the art will understand. Such factors include
design specifications, performance specifications, cost, IC or
device area, available technology, such as semiconductor
fabrication technology), target markets, target end-users, etc.
[0115] Various other circuits and blocks described above and used
in exemplary embodiments may be implemented in a variety of ways
and using a variety of circuit elements or blocks. For example,
part of bias generator 310 or other mixed-signal circuitry (e.g.,
in IC 550 in FIG. 20) may generally be implemented using analog
circuitry. The analog circuitry may include bias circuits,
decoupling circuits, coupling circuits, supply circuits, current
mirrors, current and/or voltage sources, filters, amplifiers,
converters, signal processing circuits (e.g., multipliers), sensors
or detectors, transducers, discrete components (transistors,
diodes, resistors, capacitors, inductors), analog MUXs, and the
like, as desired, and as persons of ordinary skill in the art will
understand. In addition, digital circuitry or mixed-signal
circuitry or both may be included. The digital circuitry may
include circuit elements or blocks such as gates, digital
multiplexers (MUXs), latches, flip-flops, registers, finite state
machines (FSMs), processors, programmable logic (e.g., field
programmable gate arrays (FPGAs) or other types of programmable
logic), arithmetic-logic units (ALUs), standard cells, custom
cells, etc., as desired, and as persons of ordinary skill in the
art will understand. The mixed-signal circuitry may include analog
to digital converters (ADCs), digital to analog converters (DACs),
etc.) in addition to analog circuitry and digital circuitry, as
described above, and as persons of ordinary skill in the art will
understand. The choice of circuitry for a given implementation
depends on a variety of factors, as persons of ordinary skill in
the art will understand. Such factors include design
specifications, performance specifications, cost, IC or device
area, available technology, such as semiconductor fabrication
technology), target markets, target end-users, etc.
[0116] Referring to the figures, persons of ordinary skill in the
art will note that the various blocks shown might depict mainly the
conceptual functions and signal flow. The actual circuit
implementation might or might not contain separately identifiable
hardware for the various functional blocks and might or might not
use the particular circuitry shown. For example, one may combine
the functionality of various blocks into one circuit block, as
desired. Furthermore, one may realize the functionality of a single
block in several circuit blocks, as desired. The choice of circuit
implementation depends on various factors, such as particular
design and performance specifications for a given implementation.
Other modifications and alternative embodiments in addition to the
embodiments in the disclosure will be apparent to persons of
ordinary skill in the art. Accordingly, the disclosure teaches
those skilled in the art the manner of carrying out the disclosed
concepts according to exemplary embodiments, and is to be construed
as illustrative only. Where applicable, the figures might or might
not be drawn to scale, as persons of ordinary skill in the art will
understand.
[0117] The particular forms and embodiments shown and described
constitute merely exemplary embodiments. Persons skilled in the art
may make various changes in the shape, size and arrangement of
parts without departing from the scope of the disclosure. For
example, persons skilled in the art may substitute equivalent
elements for the elements illustrated and described. Moreover,
persons skilled in the art may use certain features of the
disclosed concepts independently of the use of other features,
without departing from the scope of the disclosure.
* * * * *