US20040113692A1 - Opamp with infinite open loop gain - Google Patents
Opamp with infinite open loop gain Download PDFInfo
- Publication number
- US20040113692A1 US20040113692A1 US10/320,815 US32081502A US2004113692A1 US 20040113692 A1 US20040113692 A1 US 20040113692A1 US 32081502 A US32081502 A US 32081502A US 2004113692 A1 US2004113692 A1 US 2004113692A1
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- Prior art keywords
- operational amplifier
- current
- circuit according
- directional
- amplifier circuit
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- 230000015556 catabolic process Effects 0.000 claims abstract description 6
- 238000006731 degradation reaction Methods 0.000 claims abstract description 6
- 238000012358 sourcing Methods 0.000 claims description 8
- 238000001914 filtration Methods 0.000 claims 2
- 238000010586 diagram Methods 0.000 description 5
- 230000003071 parasitic effect Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 239000000872 buffer Substances 0.000 description 1
- 238000005094 computer simulation Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45479—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection
- H03F3/45632—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection in differential amplifiers with FET transistors as the active amplifying circuit
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
- H03F3/45179—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using MOSFET transistors as the active amplifying circuit
- H03F3/45183—Long tailed pairs
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2200/00—Indexing scheme relating to amplifiers
- H03F2200/261—Amplifier which being suitable for instrumentation applications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45676—Indexing scheme relating to differential amplifiers the LC comprising one cascode current mirror
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
- H03F2203/45—Indexing scheme relating to differential amplifiers
- H03F2203/45684—Indexing scheme relating to differential amplifiers the LC comprising one or more buffers or driving stages not being of the emitter respectively source follower type, between the output of the dif amp and the output stage
Definitions
- the present invention relates to an operational amplifier circuit, and to means, which enables an operational amplifier to exhibit a nearly infinite open loop gain without bandwidth degradation.
- Operational Amplifiers are used in many electronic applications requiring high sensitivity or accuracy such as instrumentation amplifiers and sensor or detection applications. For these applications, operational amplifier circuits are designed with high gain to provide high sensitivity or accuracy. Yet, as performance improvements in such electronics applications are desirable, so are improvements in the open loop gain of an operational amplifier are desirable.
- an operational amplifier circuit with a bi-directional cascode current amplifier.
- the bi-directional cascode current amplifier filters out the common-mode signal resulting in a nearly infinite open loop gain without bandwidth degradation.
- FIG. 1 shows a diagram of a typical amplifier with a push/pull output section
- FIG. 2 shows a diagram of an auto sensing directional current driver circuit
- FIG. 3 shows a diagram of the circuit of FIG. 1 connected to the circuit of FIG. 2 resulting in an operational amplifier circuit in accordance with the present invention
- FIG. 4 shows a graphical representation of the node voltages and branch currents of the sensing circuit versus current
- FIG. 5 is an enlarged graphical representation of FIG. 4.
- FIG. 6 is an enlarged graphical representation of FIG. 5.
- FIG. 1 shows a diagram of a typical amplifying circuit with a push/pull output section for use in the present invention.
- a typical push/pull operational amplifier has a gain defined by the following equation:
- Avol ( gm 1 +gm 2) ⁇ R 1 ⁇ R 2;
- (gm1+gm2) is the combined transconductance of the input source pair and R1 ⁇ R2 is the combined impedance at the output.
- Gm1, gm2 are the transconductance of M 1 24 , M 2 22 , respectively.
- R1 and R2 are the channel resistance of the transistors Mo 1 12 and Mo 2 26 , respecvtively with bias voltage 10 .
- Voltage gain occurs by an input voltage Vin getting converted by gm1 and gm2 into currents 1 ⁇ 2lb+gmVdm 28 and 1 ⁇ 2lb-gmVdm 30 which are mirrored to Mo 1 12 and Mo 2 26 and drawn through the channel resistances R2 and R1, respectively.
- Mo 2 26 For infinite gain to occur, Mo 2 26 must turn off if current from Mo 1 12 is flowing and Mo 1 12 must turn off if current from Mo 2 26 .
- a typical amplifier does not do this because at the quiescient point, the common mode portion of these current, 1 ⁇ 2lb, is non-zero, so Mo 1 12 and Mo 2 26 are on.
- the common-mode of the amplifier must be set such that the flow of current through Mo 1 12 and Mo 2 26 are mutually exclusive. Only one transistor may be on at any time. The other must be off to provide an infinity impedance. This occurs when the common mode signal is made zero.
- FIG. 2 there is shown a diagram of an auto sensing directional current driver circuit which provides mutually exclusive differential currents. If Vout of the typical amplifier is connected to the current input node of the current driver circuit, current Iin either flows out of Ma 36 and Mb 34 to be mirrorred to Mo 1 ′ 32 or flows into Mc 38 and Md 42 to be mirrorred to Mo 2 ′ 44 .
- Vb1 and Vb2 are chosen such that Vgs(Ma)+Vsg(Mc) is less than Vthn+Vthp, so current does not flow from Ma 36 to Mc 38 .
- Vgs(Ma) can become greater than Vthn or Vsg(Mc) to become greater than Vthp.
- Iin can flow in only one direction at a time, tin cannot flow into both Ma 36 and Mc 38 , but only one or the other. So the current becomes only differential current, as the common-mode current is filtered out.
- an output section 60 without resistive input load is needed. Such circuits are common.
- the output section buffers the output node of the sensing current from possible resistive loads connected to the amplifiers output.
- the finished amplifier is in accordance with the present invention is shown in FIG. 3.
- FIGS. 4 through 6 there is shown graphical representations of computer simulation results of the sensing circuit shown in FIG. 3.
- FIG. 4 graphically illustrates the computer sources 70 into the V(in) node 54 the current “i in ” from ⁇ 10 uA to 10 uA. It repeats this ramp 11 ⁇ 's, one for each I(vio) nodal voltage of 0.0, 0.5, 1.0, 1.5 to 5.0V.
- the node voltages V($1n28) 50 , V($1n25) 52 , V(in) 54 and branch currents I(viop) and I(vion) 72 as shown in FIG. 4 are monitored.
- V($1n28) 50 indicates a non-zero Vsg for the PMOS current mirrors 48 .
- V($1n25) 52 indicates a non-zero Vgs for the NMOS current mirror.
- the output current I(vio) is the difference of the two currents, currents I(viop) and I(vion) which simulate as expected, ranging from 10 uA to 0 uA with no overlap or gap. Referring to FIG.
- This new current amplifier acts as an auto-direction sensing current driver that makes R1 ⁇ R2 to be infinite (open circuit) at the quiescent point, so the gain equals infinity, except for the effects of parasitics.
- the parasitic effects 80 can be seen in FIG. 6 were currents I(viop) and I(vion) are shown to have low levels of about 12 pA, within the range of source/drain reverse leakage currents.
Abstract
Description
- The present invention relates to an operational amplifier circuit, and to means, which enables an operational amplifier to exhibit a nearly infinite open loop gain without bandwidth degradation.
- Operational Amplifiers are used in many electronic applications requiring high sensitivity or accuracy such as instrumentation amplifiers and sensor or detection applications. For these applications, operational amplifier circuits are designed with high gain to provide high sensitivity or accuracy. Yet, as performance improvements in such electronics applications are desirable, so are improvements in the open loop gain of an operational amplifier are desirable.
- In accordance with the present invention, there is disclosed an operational amplifier circuit with a bi-directional cascode current amplifier. The bi-directional cascode current amplifier filters out the common-mode signal resulting in a nearly infinite open loop gain without bandwidth degradation.
- FIG. 1 shows a diagram of a typical amplifier with a push/pull output section;
- FIG. 2 shows a diagram of an auto sensing directional current driver circuit;
- FIG. 3 shows a diagram of the circuit of FIG. 1 connected to the circuit of FIG. 2 resulting in an operational amplifier circuit in accordance with the present invention;
- FIG. 4 shows a graphical representation of the node voltages and branch currents of the sensing circuit versus current;
- FIG. 5 is an enlarged graphical representation of FIG. 4; and
- FIG. 6 is an enlarged graphical representation of FIG. 5.
- Referring now to the drawings, FIG. 1 shows a diagram of a typical amplifying circuit with a push/pull output section for use in the present invention. A typical push/pull operational amplifier has a gain defined by the following equation:
- Avol=(gm1+gm2)×R1∥R2;
- where (gm1+gm2) is the combined transconductance of the input source pair and R1∥R2 is the combined impedance at the output. Gm1, gm2 are the transconductance of
M1 24,M2 22, respectively. R1 and R2 are the channel resistance of thetransistors Mo1 12 andMo2 26, respecvtively withbias voltage 10. Voltage gain occurs by an input voltage Vin getting converted by gm1 and gm2 into currents½lb+gmVdm 28 and½lb-gmVdm 30 which are mirrored toMo1 12 andMo2 26 and drawn through the channel resistances R2 and R1, respectively. - For infinite gain to occur,
Mo2 26 must turn off if current fromMo1 12 is flowing andMo1 12 must turn off if current fromMo2 26. A typical amplifier does not do this because at the quiescient point, the common mode portion of these current, ½lb, is non-zero, soMo1 12 andMo2 26 are on. To get the desired operation, the common-mode of the amplifier must be set such that the flow of current throughMo1 12 andMo2 26 are mutually exclusive. Only one transistor may be on at any time. The other must be off to provide an infinity impedance. This occurs when the common mode signal is made zero. - Referring to FIG. 2, there is shown a diagram of an auto sensing directional current driver circuit which provides mutually exclusive differential currents. If Vout of the typical amplifier is connected to the current input node of the current driver circuit, current Iin either flows out of
Ma 36 andMb 34 to be mirrorred to Mo1′ 32 or flows intoMc 38 andMd 42 to be mirrorred to Mo2′44. Vb1 and Vb2 are chosen such that Vgs(Ma)+Vsg(Mc) is less than Vthn+Vthp, so current does not flow fromMa 36 toMc 38. Furthermore, only a non-zero Iin current can cause Vgs(Ma) to become greater than Vthn or Vsg(Mc) to become greater than Vthp. As Iin can flow in only one direction at a time, tin cannot flow into bothMa 36 and Mc 38, but only one or the other. So the current becomes only differential current, as the common-mode current is filtered out. - All that is needed is to attach the
input 54 of the circuit of FIG. 2 into the output of the typical opamp in FIG. 1, as shown in FIG. 3. The output current of the sensor is either sinking or sourcing, without any overlap or gap between the sinking and sourcing currents. The currents are thus mutually exclusive and when one is flowing, it is being drawn through an off transistor, an infinite impedance, creating an infinite gain except for the possible effects of some parasitics. - To finish the infinite gain opamp, an
output section 60 without resistive input load is needed. Such circuits are common. The output section buffers the output node of the sensing current from possible resistive loads connected to the amplifiers output. The finished amplifier is in accordance with the present invention is shown in FIG. 3. - Referring to FIGS. 4 through 6 there is shown graphical representations of computer simulation results of the sensing circuit shown in FIG. 3. FIG. 4 graphically illustrates the
computer sources 70 into the V(in)node 54 the current “iin” from −10 uA to 10 uA. It repeats this ramp 11×'s, one for each I(vio) nodal voltage of 0.0, 0.5, 1.0, 1.5 to 5.0V. The node voltages V($1n28) 50, V($1n25) 52, V(in) 54 and branch currents I(viop) and I(vion) 72 as shown in FIG. 4 are monitored. For negative input currents, V($1n28) 50 indicates a non-zero Vsg for the PMOScurrent mirrors 48. Similarly, V($1n25) 52 indicates a non-zero Vgs for the NMOS current mirror. V(in)'s transition at Iin=0 is the circuit switching from one current mirror to the other. The output current I(vio) is the difference of the two currents, currents I(viop) and I(vion) which simulate as expected, ranging from 10 uA to 0 uA with no overlap or gap. Referring to FIG. 5, thegraphical representation 75 zooms in on −1nA<Iin<1nA, and shows that there is no discontinuity of the voltage V(in) or the current I(vio)=I(viop) I(vion). Hence there is no “dead zone” despite the overlap of Vsg(Ma) an Vgs(Mc). This new current amplifier acts as an auto-direction sensing current driver that makes R1∥R2 to be infinite (open circuit) at the quiescent point, so the gain equals infinity, except for the effects of parasitics. Theparasitic effects 80 can be seen in FIG. 6 were currents I(viop) and I(vion) are shown to have low levels of about 12 pA, within the range of source/drain reverse leakage currents. - It should be noted that numerous changes in details of construction and the combination and arrangement of elements may be resorted to without departing from the true spirit and scope of the invention as hereinafter claimed.
Claims (20)
Priority Applications (1)
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US10/320,815 US6750714B1 (en) | 2002-12-16 | 2002-12-16 | Opamp with infinite open loop gain |
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US10/320,815 US6750714B1 (en) | 2002-12-16 | 2002-12-16 | Opamp with infinite open loop gain |
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US6750714B1 US6750714B1 (en) | 2004-06-15 |
US20040113692A1 true US20040113692A1 (en) | 2004-06-17 |
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US10/320,815 Expired - Fee Related US6750714B1 (en) | 2002-12-16 | 2002-12-16 | Opamp with infinite open loop gain |
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Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
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US8289796B2 (en) * | 2010-01-26 | 2012-10-16 | Micron Technology, Inc. | Sense amplifier having loop gain control |
US8705304B2 (en) | 2010-03-26 | 2014-04-22 | Micron Technology, Inc. | Current mode sense amplifier with passive load |
US8283950B2 (en) | 2010-08-11 | 2012-10-09 | Micron Technology, Inc. | Delay lines, amplifier systems, transconductance compensating systems and methods of compensating |
US8810281B2 (en) | 2011-07-26 | 2014-08-19 | Micron Technology, Inc. | Sense amplifiers including bias circuits |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5146179A (en) * | 1991-11-29 | 1992-09-08 | Carnegie Mellon University | Fully differential operational amplifier having frequency dependent impedance division |
US6018267A (en) * | 1998-03-10 | 2000-01-25 | Information Storage Devices, Inc. | High output swing operational amplifier using low voltage devices |
US6028479A (en) * | 1998-01-07 | 2000-02-22 | Plato Labs, Inc. | Low voltage transmission line driver |
-
2002
- 2002-12-16 US US10/320,815 patent/US6750714B1/en not_active Expired - Fee Related
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5146179A (en) * | 1991-11-29 | 1992-09-08 | Carnegie Mellon University | Fully differential operational amplifier having frequency dependent impedance division |
US6028479A (en) * | 1998-01-07 | 2000-02-22 | Plato Labs, Inc. | Low voltage transmission line driver |
US6018267A (en) * | 1998-03-10 | 2000-01-25 | Information Storage Devices, Inc. | High output swing operational amplifier using low voltage devices |
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Owner name: XEROX CORPORATION, CONNECTICUT Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:MCINTYRE, HARRY JONATHAN;REEL/FRAME:013597/0600 Effective date: 20021213 |
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