U.S. patent application number 16/721919 was filed with the patent office on 2021-06-24 for operational transconductance amplifier and a method for converting a differential input voltage to a differential output current.
This patent application is currently assigned to Tower Semiconductors Ltd.. The applicant listed for this patent is Tower Semiconductors Ltd.. Invention is credited to Alon Blumenfeld, Danny Pollak, Erez Sarig.
Application Number | 20210194446 16/721919 |
Document ID | / |
Family ID | 1000005636475 |
Filed Date | 2021-06-24 |
United States Patent
Application |
20210194446 |
Kind Code |
A1 |
Sarig; Erez ; et
al. |
June 24, 2021 |
OPERATIONAL TRANSCONDUCTANCE AMPLIFIER AND A METHOD FOR CONVERTING
A DIFFERENTIAL INPUT VOLTAGE TO A DIFFERENTIAL OUTPUT CURRENT
Abstract
An operational transconductance amplifier, that may include a
first differential pair that comprises a first transistor and a
second transistor that are coupled to each other at a certain node;
wherein the first differential pair is configured to convert a
differential input voltage to first and second output currents; a
current source that is coupled to the certain node and may include
an adjustable current sources; and a feedback unit that is coupled
to the certain node and is configured to (a) receive the
differential input voltage, and maintain a voltage of the certain
node substantially fixed regardless of changes in the differential
input voltage.
Inventors: |
Sarig; Erez; (Migdal Haemek,
IL) ; Blumenfeld; Alon; (Migdal Haemek, IL) ;
Pollak; Danny; (Migdal Haemek, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tower Semiconductors Ltd. |
Migdal Haemek |
|
IL |
|
|
Assignee: |
Tower Semiconductors Ltd.
Migdal Haemek
IL
|
Family ID: |
1000005636475 |
Appl. No.: |
16/721919 |
Filed: |
December 20, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03F 2203/45114
20130101; H03F 3/45219 20130101 |
International
Class: |
H03F 3/45 20060101
H03F003/45 |
Claims
1. An operational transconductance amplifier with a boosted tail
current, comprising: a first differential pair that comprises a
first transistor and a second transistor that are coupled to each
other at a certain node; wherein the first differential pair is
configured to convert a differential input voltage to a first
output current and a second output current; a current source that
is coupled to the certain node and comprises an adjustable current
sources; wherein the current source is configured to output a
boosted tail current; a feedback unit that is coupled to the
certain node and is configured to (a) receive the differential
input voltage, and (b) maintain a voltage of the certain node
substantially fixed regardless of changes in the differential input
voltage.
2. The operational transconductance amplifier according to claim 1,
wherein a maximal value of a sum of the first and second output
currents is defined by a dimensions of the first differential pair
and the differential input voltages.
3. The operational transconductance amplifier according to claim 1,
wherein the feedback unit is configured to maintain the voltage of
the certain node substantially fixed by controlling the adjustable
current sources based on a higher valued input voltage out of of
the first and second input voltages.
4. The operational transconductance amplifier according to claim 1,
wherein the feedback unit is configured to maintain the voltage of
the certain node substantially fixed by controlling the adjustable
current sources based on the differential input voltage.
5. The operational transconductance amplifier according to claim 1
wherein the feedback unit comprises a first feedback sub-unit and a
second feedback sub-unit; wherein the first feedback sub-unit is
configured to (a) receive the first input voltage, and (b) control
a first adjustable current source of the adjustable current
sources, based on the first input voltage.
6. The operational transconductance amplifier according to claim 5,
wherein the second feedback sub-unit is configured to (a) receive
the second input voltage, and (b) control a second adjustable
current source of the adjustable current sources, based on the
second input voltage.
7. The operational transconductance amplifier according to claim 6,
wherein the first feedback sub-unit is configured to maintain the
voltage of the certain node substantially fixed regardless of an
increase in the second input voltage.
8. The operational transconductance amplifier according to claim 6,
wherein the second feedback sub-unit is configured to maintain the
voltage of the certain node substantially fixed regardless of an
increase in the first input voltage.
9. The operational transconductance amplifier according to claim 6,
wherein each one of the first feedback sub-unit and the second
feedback sub-unit comprises a folded cascode amplifier.
10. The operational transamplifier according to claim 1 wherein a
sum of the first and second output currents substantially equals
the boosted tail current.
11. A method for converting a differential input voltage to a first
and second output currents, the method comprises: receiving, by a
first differential pair, the differential input voltage; wherein
the differential input voltage is a difference between a first
input voltage and a second input voltage; converting, by the first
differential pair, the differential input voltage to the first and
second output currents; wherein the first differential pair
comprises a first transistor and a second transistor that are
coupled to each other at a certain node; wherein the tail current
includes the first current and the second current; feeding, by a
current source that is coupled to the certain node, the first
differential pair with a boosted tail current; wherein the boosted
tail current is a sum of current outputted by the adjustable
current sources; receiving, by a feedback unit that is coupled to
the certain node, the differential input voltage; and maintaining,
by the feedback unit, a voltage of the certain node substantially
fixed regardless of changes in the differential input voltage.
12. The method according to claim 11 wherein a maximal value of the
first and second output currents is defined by a dimensions of the
first differential pair.
13. The method according to claim 11, comprising maintaining the
voltage of the certain node substantially fixed by controlling the
adjustable current sources based on a higher valued input voltage
out of the first and second input voltages.
14. The method according to claim 11, wherein the maintaining of
the voltage of the certain node comprises controlling, by the
feedback unit, the adjustable current sources based on the
differential input voltage.
15. The method according to claim 14, wherein the feedback unit
comprises a first feedback sub-unit and a second feedback sub-unit;
wherein the method further comprises: receiving, by the first
feedback sub-unit, the first input voltage; and controlling, by the
first feedback sub-unit, a first adjustable current source of the
adjustable current sources, based on the first input voltage.
16. The method according to claim 15, comprising receiving, by the
second feedback sub-unit, the second input voltage; and
controlling, by the second feedback sub-unit, a second adjustable
current source of the adjustable current sources, based on the
second input voltage.
17. The method according to claim 16, comprising maintaining, by
the first feedback sub-unit, the voltage of the certain node
substantially fixed regardless of an increase in the second input
voltage.
18. The method according to claim 16, comprising maintaining, by
the second feedback sub-unit, the voltage of the certain node
substantially fixed regardless of an increase in the first input
voltage.
19. The method according to claim 16, wherein each one of the first
feedback sub-unit and the second feedback sub-unit comprises a
folded cascode amplifier.
20. The method according to claim 11 wherein a sum of the first and
second output currents substantially equals the boosted tail
current.
Description
BACKGROUND OF THE INVENTION
[0001] Operational amplifier that require a responds to large input
signals usually use some slew rate boosting techniques. Most
operational amplifiers uses a differential input stage constructed
with an input pair transistors and a tail current. The current of a
differential input stages is defined by its tail current. In the
event of a step response, the maximum current the differential pair
can drive is limited by the tail current. Common methods to
mitigate this challenge is known as current boosting or slew rate
enhancement. There are many different slew rate boosting
techniques. In general they are divided in to two groups.
[0002] Techniques which enhance the output driving current (such as
class AB output stage) and ones which boost the input differential
pair tail current. Most of the techniques to boost tail current are
based on a feedback current branches or voltage nodes further along
the signal path of the amplifier. Such techniques defines the
amplifier architecture.
SUMMARY
[0003] According to an embodiment of the invention there may be
provided an operational transconductance amplifier and a
method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The subject matter regarded as the invention is particularly
pointed out and distinctly claimed in the concluding portion of the
specification. The invention, however, both as to organization and
method of operation, together with objects, features, and
advantages thereof, may best be understood by reference to the
following detailed description when read with the accompanying
drawings in which:
[0005] FIG. 1 is example of an operational transconductance
amplifier;
[0006] FIG. 2 is example of an operational transconductance
amplifier;
[0007] FIG. 3 is example of a method; and
[0008] FIG. 4 is an example of a comparison of relationships
between differential input voltage and tail current.
[0009] It will be appreciated that for simplicity and clarity of
illustration, elements shown in the figures have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements may be exaggerated relative to other elements for clarity.
Further, where considered appropriate, reference numerals may be
repeated among the figures to indicate corresponding or analogous
elements.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] In the following detailed description, numerous specific
details are set forth in order to provide a thorough understanding
of the invention. However, it will be understood by those skilled
in the art that the present invention may be practiced without
these specific details. In other instances, well-known methods,
procedures, and components have not been described in detail so as
not to obscure the present invention.
[0011] The subject matter regarded as the invention is particularly
pointed out and distinctly claimed in the concluding portion of the
specification. The invention, however, both as to organization and
method of operation, together with objects, features, and
advantages thereof, may best be understood by reference to the
following detailed description when read with the accompanying
drawings.
[0012] Because the illustrated embodiments of the present invention
may for the most part, be implemented using electronic components
and circuits known to those skilled in the art, details will not be
explained in any greater extent than that considered necessary as
illustrated above, for the understanding and appreciation of the
underlying concepts of the present invention and in order not to
obfuscate or distract from the teachings of the present
invention.
[0013] FIG. 1 illustrates an example of operational
transconductance amplifier 10.
[0014] The operational transconductance amplifier is configured to
drive large current with respect to its input voltage and it may be
limited only by the dimensions of the differential input pair.
[0015] The suggested operational transconductance amplifier may
provide a simple input stage architecture which is insensitive to
the type of load it drives or the amplifier architecture. In
addition, the operational transconductance amplifier doesn't
interfere a differential pair operation, doesn't change its
characteristics (including voltage swing, noise or offset).
[0016] The operational transconductance amplifier 10 may
include:
[0017] A differential input pair 30 that includes a first
transistor (M1 31) and a second transistor (M2 32) that are coupled
to each other at a certain node (at node 90) together with a
current tail (40). The differential input pair is configured to
convert a differential input voltage (which equals the difference
between first input voltage VIN1 21 and second input voltage VIN2
22) to a first output current I1 11 and a second output current I2
12.
[0018] A current source that is coupled to the certain node and may
include a fixed tail current source (ITAIL 40) and adjustable
current sources (third transistor M3 33 and fourth transistor M4
34). The combination of the fixed tail current from the fixed
current source and the currents outputted from the adjustable
current sources is a boosted tail current which is driven to the
output current (IL 11 I2 12) according to the input voltages.
[0019] In contrary to a common differential pair (in which the
maximum output current in either of the current outputs is limited
to the fixed current tail current)--the suggested operational
transconductance amplifier provides a much higher output
current.
[0020] Feedback unit (70) that is coupled to the certain node and
is configured to (a) receive the differential input voltage, (b)
maintain a voltage (VCM 91) of the certain node 90 substantially
fixed regardless of changes in the differential input voltage, and
(c) control the adjustable current sources (third transistor M3 33
and fourth transistor M4 34) based on the differential input
voltage.
[0021] The feedback unit 70 may include first feedback sub-unit 71
and second feedback sub-unit 72.
[0022] First feedback sub-unit 71 is configured to (a) receive a
first input voltage (VIN1 21), and (b) control a first adjustable
current source (M3 33) of the adjustable current sources, based on
the first input voltage.
[0023] Second feedback sub-unit 72 is configured to (a) receive a
second input voltage (VIN2 22), and (b) control a second adjustable
current source (M4 34) of the adjustable current sources, based on
the second input voltage.
[0024] First feedback sub-unit 71 is configured to maintain the
voltage (VCM 91) of the certain node substantially fixed regardless
of an increase in the second input voltage (VIN2 22).
[0025] Second feedback sub-unit 72 is configured to maintain the
voltage (VCM 91) of the certain node substantially fixed regardless
of an increase in the first input voltage (VIN1 21).
[0026] Each one of the first feedback sub-unit and the second
feedback sub-unit could be comprises a folded cascode
amplifier.
[0027] FIG. 1 illustrates the first feedback sub-unit 71 as
including a first amplifier 61 and a first voltage source 51 that
virtually adds a threshold voltage Vth to VCM 91 (voltage of node
90). The first voltage source is coupled to a non-inventing input
of the first amplifier 61. An inverting input of the first
amplifier is fed by the first input voltage VIN1 21.
[0028] FIG. 1 illustrates the second feedback sub-unit 72 as
including second amplifier 62 and a second voltage source 52 that
virtually adds a threshold voltage Vth the VCM 91 of node 90. The
second voltage source 52 is coupled to a non-inventing input of the
second amplifier 62. An inverting input of the second amplifier 62
is fed by the second input voltage VIN2 22.
[0029] The first and second amplifiers (61 and 62) are configured
to detect changes in the first and second input voltages (minus
Vth) in reference to the VCM 91 (of node 90).
[0030] When one of the first and second input voltages drops below
(VCM 91+VTN) the corresponding amplifier drives its output high
turning on the respective adjustable current source out of third
and fourth transistors (M3 33 or M4 34) so as to driver additional
tail current to the outputs of M1 31 or M2 32 (for outputting first
output current I1 and second output current, I2).
[0031] The selective operation of the adjustable current sources
creates a low impedance on node 90 enabling first and second
transistors M1 31 and M2 32 to behave as a common source NMOS with
no limit current. This allows a user to connect any load to the
terminal over which the first and second output currents (I1 and
I2) are supplied.
[0032] FIG. 2 illustrates an example of operational
transconductance amplifier 10'.
[0033] The first feedback sub-unit 71 includes seventh transistor
M7 37 and serially coupled elements that include (a) first
additional fixed current source I3 43, (b) fifth transistor M5 35.
and (c) second additional fixed current source I5 45.
[0034] The gates of the seventh transistor M7 37 and the first
transistor M1 31 receive the first input voltage VIN1 21.
[0035] Fifth transistor M5 35 and eighth transistor M8 38 may act
as cascode stages.
[0036] The second feedback sub-unit 72 includes eighth transistor
M8 38 and serially coupled elements that include (a) third
additional fixed current source I4 44, (b) sixth transistor M6 36,
and (c) fourth additional fixed current source I6 46.
[0037] The gates of the eighth transistor M8 38 and the second
transistor M2 32 receive the second input voltage VIN2 22.
[0038] Seventh transistor M7 37 and eighth transistor M8 38 are in
a folded cascade connection which allows the wide input swing
option. With this architecture, each one of the first and second
input voltages can swing between VTH+VDS (drain source voltage) as
in a standard differential N-type pair to as high as VDD-VDS (VDD
being the voltage supply). To decrease offset and noise of this
topology the value of the tail current can be adjust to place the
amplifiers at saturation level up to certain differential input
level.
[0039] This method and device allows to be used in any amplifier
design that requires a differential input stage.
[0040] The suggested operational transconductance amplifier
improves the driving capability of the differential pair with no
effect to its other parameters such as input voltages, noise and
offset. This concept can be implemented also for a PMOS type
differential pair.
[0041] FIG. 3 is an example of method 100.
[0042] Method 100 is for converting a differential input voltage to
an amplifier tail current.
[0043] Method 100 may start by steps 110, 120 and 130.
[0044] Step 110 may include receiving, by a first differential
pair, the differential input voltage. The differential input
voltage is a difference between a first input voltage and a second
input voltage. The first differential pair may include a first
transistor and a second transistor that are coupled to each other
at a certain node.
[0045] Step 110 may be followed by step 115 of converting, by the
first differential pair, the differential input voltage to two
output currents.
[0046] Step 120 may include feeding, by a current source that is
coupled to the certain node, the first differential pair with a
boosted tail current. The current source may include an adjustable
current sources and may include a fixed tail current source. The
boosted tail current is a sum of currents outputted by the first
tail current source and the adjustable current sources.
[0047] Step 130 may include receiving, by a feedback unit that is
coupled to the certain node, the differential input voltage.
[0048] Step 130 may be followed by step 135.
[0049] Step 135 may include maintaining, by the feedback unit, a
voltage of the certain node substantially fixed regardless of
changes in the differential input voltage. This may be achieved by
controlling, by the feedback unit, the adjustable current sources
based on the differential input voltage.
[0050] The feedback unit may include a first feedback sub-unit and
a second feedback sub-unit.
[0051] Step 130 may include receiving, by the first feedback
sub-unit, the first input voltage, and receiving, by the second
feedback sub-unit, the second input voltage.
[0052] Step 135 may include at least one of the following:
a. Controlling, by the first feedback sub-unit, a first adjustable
current source of the adjustable current sources, based on the
first input voltage. b. Controlling, by the second feedback
sub-unit, a second adjustable current source of the adjustable
current sources, based on the second input voltage. c. Maintaining,
by the first feedback sub-unit, the voltage of the certain node
substantially fixed regardless of an increase in the second input
voltage. d. Maintaining, by the second feedback sub-unit, the
voltage of the certain node substantially fixed regardless of an
increase in the first input voltage.
[0053] Each one of the first feedback sub-unit and the second
feedback sub-unit may include a folded cascode amplifier or any
other eligible amplifier.
[0054] FIG. 4 is an example of a comparison of relationships
between differential input voltage and output currents I1 and
I2.
[0055] Curves 201 and 202 represent the relationship between I1 and
I2 (respectively) and the input differential voltage of a prior art
circuit.
[0056] Curves 211 and 212 represent the relationship between I1 and
I2 (respectively) and the input differential voltage of the
operational transconductance amplifier of FIGS. 1-2.
[0057] Any reference to any of the terms "comprise", "comprises",
"comprising" "including", "may include" and "includes" may be
applied to any of the terms "consists", "consisting", "consisting
essentially of". For example--any of the rectifying circuits
meaning illustrated in any figure may include more components that
those illustrated in the figure, only the components illustrated in
the figure or substantially only the components illustrated in the
figure.
[0058] In the foregoing specification, the invention has been
described with reference to specific examples of embodiments of the
invention. It will, however, be evident that various modifications
and changes may be made therein without departing from the broader
spirit and scope of the invention as set forth in the appended
claims. Moreover, the terms "front," "back," "top," "bottom,"
"over," "under" and the like in the description and in the claims,
if any, are used for descriptive purposes and not necessarily for
describing permanent relative positions. It is understood that the
terms so used are interchangeable under appropriate circumstances
such that the embodiments of the invention described herein are,
for example, capable of operation in other orientations than those
illustrated or otherwise described herein.
[0059] Those skilled in the art will recognize that the boundaries
between logic blocks are merely illustrative and that alternative
embodiments may merge logic blocks or circuit elements or impose an
alternate decomposition of functionality upon various logic blocks
or circuit elements. Thus, it is to be understood that the
architectures depicted herein are merely exemplary, and that in
fact many other architectures can be implemented which achieve the
same functionality. Any arrangement of components to achieve the
same functionality is effectively "associated" such that the
desired functionality is achieved. Hence, any two components herein
combined to achieve a particular functionality can be seen as
"associated with" each other such that the desired functionality is
achieved, irrespective of architectures or intermedial components.
Likewise, any two components so associated can also be viewed as
being "operably connected," or "operably coupled," to each other to
achieve the desired functionality.
[0060] Furthermore, those skilled in the art will recognize that
boundaries between the above described operations merely
illustrative. The multiple operations may be combined into a single
operation, a single operation may be distributed in additional
operations and operations may be executed at least partially
overlapping in time. Moreover, alternative embodiments may include
multiple instances of a particular operation, and the order of
operations may be altered in various other embodiments.
[0061] Also for example, in one embodiment, the illustrated
examples may be implemented as circuitry located on a single
integrated circuit or within a same device. Alternatively, the
examples may be implemented as any number of separate integrated
circuits or separate devices interconnected with each other in a
suitable manner.
[0062] However, other modifications, variations and alternatives
are also possible. The specifications and drawings are,
accordingly, to be regarded in an illustrative rather than in a
restrictive sense.
[0063] In the claims, any reference signs placed between
parentheses shall not be construed as limiting the claim. The word
`comprising` does not exclude the presence of other elements or
steps then those listed in a claim. Furthermore, the terms "a" or
"an," as used herein, are defined as one or more than one. Also,
the use of introductory phrases such as "at least one" and "one or
more" in the claims should not be construed to imply that the
introduction of another claim element by the indefinite articles
"a" or "an" limits any particular claim containing such introduced
claim element to inventions containing only one such element, even
when the same claim includes the introductory phrases "one or more"
or "at least one" and indefinite articles such as "a" or "an." The
same holds true for the use of definite articles. Unless stated
otherwise, terms such as "first" and "second" are used to
arbitrarily distinguish between the elements such terms describe.
Thus, these terms are not necessarily intended to indicate temporal
or other prioritization of such elements.
[0064] While certain features of the invention have been
illustrated and described herein, many modifications,
substitutions, changes, and equivalents will now occur to those of
ordinary skill in the art. It is, therefore, to be understood that
the appended claims are intended to cover all such modifications
and changes as fall within the true spirit of the invention.
* * * * *