REV. A

Information furnished by Analog Devices is believed to be accurate andreliable. However, no responsibility is assumed by Analog Devices for itsuse, nor for any infringements of patents or other rights of third parties thatmay result from its use. No license is granted by implication or otherwiseunder any patent or patent rights of Analog Devices.

aOP227

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700 www.analog.com

Fax: 781/326-8703 © Analog Devices, Inc., 2002

Dual, Low Noise, Low OffsetInstrumentation Operational Amplifier

PIN CONNECTIONS

NOTE DEVICE MAY BE OPERATED EVEN IF INSERTION

IS REVERSED; THIS IS DUE TO INHERENT SYMMETRYOF PIN LOCATIONS OF AMPLIFIERS A AND BV–(A) AND V–(B) ARE INTERNALLY CONNECTED VIASUBSTRATE RESISTANCE

1.

2.

NULL (A)

NULL (A)

–IN (A)

+IN (A)

V– (B)

OUT (B)

V+ (B)

1 V+ (A)

OUT (A)

V– (A)

+IN (B)

–IN (B)

NULL (B)

NULL (B)

A

B

2

3

4

5

6

7

14

13

12

11

10

9

8

FEATURES

Excellent Individual Amplifier Parameters

Low VOS, 80 �V Max

Offset Voltage Match, 80 �V Max

Offset Voltage Match vs. Temperature, 1 �V/�C Max

Stable VOS vs. Time, 1 �V/MO Max

Low Voltage Noise, 3.9 nV/÷Hz Max

Fast, 2.8 V/�s Typ

High Gain, 1.8 Million Typ

High Channel Separation, 154 dB Typ

GENERAL DESCRIPTIONThe OP227 is the first dual amplifier to offer a combination oflow offset, low noise, high speed, and guaranteed amplifier matchingcharacteristics in one device. The OP227, with a VOS match of25 mV typical, a TCVOS match of 0.3 mV/∞C typical and a 1/f cornerof only 2.7 Hz is an excellent choice for precision low noise designs.These dc characteristics, coupled with a slew rate of 2.8 V/mstypical and a small-signal bandwidth of 8 MHz typical, allow thedesigner to achieve ac performance previously unattainable withop amp based instrumentation designs.

When used in a three op amp instrumentation configuration, theOP227 can achieve a CMRR in excess of 100 dB at 10 kHz. Inaddition, this device has an open-loop gain of 1.5 M typical witha 1 kW load. The OP227 also features an IB of ± 10 nA typical,an IOS of 7 nA typical, and guaranteed matching of input currents

SIMPLIFIED SCHEMATIC

NONINVERTINGINPUT (+)

INVERTINGINPUT (–)

Q3

Q6

Q1A Q1B Q2B Q2A

R1*

R3

NULL

R4

R2*

*R1 AND R2 ARE PREMATURELY ADJUSTED AT WAFER TEST FOR MINIMUM OFFSET VOLTAGE.

Q21

Q11 Q12

Q27

C2

Q23 Q24

R23 R24

Q28

R5C3

R11 C4

R12

R9

Q22C1

Q20 Q19

Q26

Q45

Q46

OUTPUT

V-

V+

between amplifiers. These outstanding input current specificationsare realized through the use of a unique input current cancellationcircuit which typically holds IB and IOS to ± 20 nA and 15 nArespectively over the full military temperature range.

Other sources of input referred errors, such as PSRR and CMRR,are reduced by factors in excess of 120 dB for the individualamplifiers. DC stability is assured by a long-term drift applicationof 1.0 mV/month.

Matching between channels is provided on all critical param-eters including offset voltage, tracking of offset voltage versustemperature, noninverting bias current, CMRR, and powersupply rejection ratio. This unique dual amplifier allows theelimination of external components for offset nulling andfrequency compensation.

REV. A– 2 –

OP227–SPECIFICATIONSIndividual Amplifier Characteristics (VS = �15 V, TA = 25�C, unless otherwise noted.)

OP227E OP227GParameter Symbol Conditions Min Typ Max Min Typ Max Unit

INPUT OFFSET VOLTAGE VOS Note 1 20 80 60 180 mV

LONG-TERM VOS STABILITY VOS/Time Notes 2,4 0.2 1.0 0.4 2.0 mV/MO

INPUT OFFSET CURRENT IOS 7 35 12 75 nA

INPUT BIAS CURRENT IB ± 10 ± 40 ± 15 ± 80 nA

INPUT NOISE VOLTAGE en p-p 0.1 Hz to 10 Hz 0.08 0.20 0.09 0.28 mV p-pNotes 3,5

INPUT NOISE VOLTAGE DENSITY en fO = 10 Hz3 3.5 6.0 3.8 9.0 nV/�Hz

fO = 30 Hz3 3.1 4.7 3.3 5.9 nV/�HzfO = 1000 Hz3 3.0 3.9 3.2 4.6 nV/�Hz

INPUT NOISE DENSITY in fO = 10 Hz3, 6 1.7 4.5 1.7 pA/�HzfO = 30 Hz3, 6 1.0 2.5 1.0 pA/�HzfO = 1000 Hz3, 6 0.4 0.7 0.4 0.7 pA/�Hz

INPUT RESISTANCEDifferential Mode RIN Note 7 1.3 6 0.7 4 MWCommon Mode RINCM 3 2 GW

INPUT VOLTAGE RANGE IVR ± 11.0 ± 12.3 ± 11.0 ± 12.3 V

COMMON-MODEREJECTION RATIO CMRR VCM = ± 11 V 114 126 100 120 dB

POWER SUPPLYREJECTION RATIO PSRR VS = ± 4 V to

± 18 V 1 10 2 20 mV/V

LARGE-SIGNALVOLTAGE GAIN AVO RL � 2 kW,

VO = ± 10 V 1000 1800 700 1500 V/mVRL � 600 kW,VO = ± 10 V 800 1500 600 1500 V/mV

OUTPUT VOLTAGE SWING VO RL � 2 kW ± 12.0 ± 13.8 ± 11.5 ± 13.5 VRL � 600 W ± 10.0 ± 11.5 ± 10.0 ± 11.5 V

SLEW RATE SR RL � 2 kW4 1.7 2.8 1.7 2.8 V/ms

GAIN BANDWIDTH PROD. GBW Note 4 5 8 5 8 MHz

OPEN-LOOP OUTPUTRESISTANCE RO VO = 0, IO = 0 70 70 W

POWER CONSUMPTION Pd Each Amplifier 90 140 100 170 mW

OFFSET ADJUSTMENTRANGE Rp = 10 kW ± 4 ± 4 mV

NOTES1Input offset voltage measurements are performed by automated test equipment approximately 0.5 seconds after application of power. E Grade specifications areguaranteed fully warmed up.

2Long term input offset voltage stability refers to the average trend line of VOS vs. time over extended periods after the first 30 days of operation. Excluding the initialhour of operation, changes in VOS during the first 30 days are typically 2.5 mV. Refer to the Typical Performance Curve.

3Sample tested.4Parameter is guaranteed by design.5See test circuit and frequency response curve for 0.1 Hz to 10 Hz tester.6See test circuit for current noise measurement.7Guaranteed by input bias current.

Specifications subject to change without notice.

REV. A – 3 –

OP227

SPECIFICATIONSIndividual Amplifier Characteristics (VS = �15 V, –25�C £ TA £ +85�C, unless otherwise noted.)

OP227E OP227GParameter Symbol Conditions Min Typ Max Min Typ Max Unit

INPUT OFFSETVOLTAGE VOS Note 1 40 140 85 280 mVAVERAGE INPUTOFFSET DRIFT TCVOS

TCVOSn Note 2 0.5 1.0 0.5 1.8 mV/�CINPUT OFFSETCURRENT IOS 10 50 20 135 nAINPUT BIASCURRENT IB ± 14 ± 60 ± 25 ± 150 nAINPUT VOLTAGERANGE IVR ± 10 ± 11.8 ± 10 ± 11.8 VCOMMON-MODEREJECTION RATIO CMRR VCM = ± 10 V 110 124 96 118 dBPOWER SUPPLYREJECTION RATIO PSRR VS = ± 4.5 V to

± 18 V 2 15 2 32 mV/VLARGE-SIGNALVOLTAGE GAIN AVO RL � 2 kW,

VO = ± 10 V 750 1500 450 1000 V/mVOUTPUT VOLTAGESWING VO RL � 2 kW ± 11.7 ± 13.6 ± 11.0 ± 13.3 V

Matching Characteristics (VS = ±15 V, TA = 25�C, unless otherwise noted.)

OP227E OP227GParameter Symbol Conditions Min Typ Max Min Typ Max Unit

INPUT OFFSETVOLTAGE MATCH �VOS 25 80 55 300 mVAVERAGENONINVERTING BiasCURRENT IB+

I

I IB

B A B B+ =+ + +

2

± 10 ± 40 ± 15 ± 90 nA

NONINVERTINGOFFSET CURRENT IOS+ IOS+ = IB+A-IB+B ± 12 ± 60 ± 20 ± 130 nAINVERTING OFFSETCURRENT IOS- IOS- = IB-A-IB-B ± 12 ± 60 ± 20 ± 130 nACOMMON-MODEREJECTION RATIOMATCH �CMRR VCM = ± 11 V 110 123 97 117 dBPOWER SUPPLYREJECTION RATIOMATCH �PSRR VS = ± 4 V to

± 18 V 2 10 2 20 mV/VCHANNELSEPARATION CS Note 1 126 154 126 154 dB

NOTES1Input Offset Voltage measurements are performed by automated equipment approximately 0.5 seconds after application of power.2The TCVOS performance is within the specifications unnulled or when nulled with RP = 8 kW to 20 kW, optimum performance is obtained with RP = 8 kW.3Sample tested.

Specifications subject to change without notice.

REV. A– 4 –

OP227–SPECIFICATIONSMatching Characteristics (VS = �15 V, TA = -25�C to +85�C, unless otherwise noted.)

OP227E OP227GParameter Symbol Conditions Min Typ Max Min Typ Max Unit

INPUT OFFSETVOLTAGE MATCH �VOS 40 140 90 400 mVINPUT OFFSETTRACKING TC�VOS Nulled or Unnulled* 0.3 1.0 0.5 1.8 mV/�CAVERAGENONINVERTINGBIAS CURRENT IB+

I

I IB

B A B B+ =+ + +

2

± 14 ± 60 ± 25 ± 170 nA

AVERAGE DRIFT OFNONINVERTING BIASCURRENT TCIB+ 80 180 pA/�CNONINVERTINGOFFSET CURRENT IOS+ IOS+ = IB+A–IB+B ± 20 ± 90 ± 35 ± 250 nAAVERAGE DRIFT OFNONINVERTINGOFFSET CURRENT TCIOS+ 130 250 pA/�CINVERTING OFFSETCURRENT IOS– IOS– = IB–A–IB–B ± 20 ± 90 ± 35 ± 250 nACOMMON-MODEREJECTION RATIOMATCH �CMRR VCM = ± 10 V 106 120 90 112 dBPOWER SUPPLYREJECTION RATIOMATCH �PSRR VS = ± 4.5 V to ± 18 V 2 15 3 32 mV/V

NOTES*Sample tested.

Specifications subject to change without notice.

REV. A

OP227

– 5 –

ABSOLUTE MAXIMUM RATINGSSupply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 22 VInput Voltage1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 22 VOutput Short-Circuit Duration . . . . . . . . . . . . . . . . . IndefiniteDifferential Input Voltage2 . . . . . . . . . . . . . . . . . . . . . . . ± 0.7 VDifferential Input Current2 . . . . . . . . . . . . . . . . . . . . . ± 25 mAStorage Temperature Range . . . . . . . . . . . . . –65∞C to +150∞COperating Temperature Range

OP227E, OP227G . . . . . . . . . . . . . . . . . . . . –25∞C to +85∞CLead Temperature (Soldering 60 sec) . . . . . . . . . . . . . . 300∞CNOTES1For supply voltages less than ± 22 V, the absolute maximum input voltage is equal

to the supply voltage.2The OP227 inputs are protected by back-to-back diodes. Current limiting resistors

are not used in order to achieve low noise. If differential input voltage exceeds ± 0.7V, the input current should be limited to 25 mA.

3�JA is specified for worst-case mounting conditions, i.e., �JA is specified for devicein socket for CERDIP package.

CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readilyaccumulate on the human body and test equipment and can discharge without detection. Althoughthe OP227 features propriety ESD protection circuitry, permanent damage may occur on devicessubjected to high energy electrostatic discharges. Therefor, proper ESD precautions arerecommended to avoid performance degradation or loss of functionality.

WARNING!

ESD SENSITIVE DEVICE

ORDERING GUIDE

TA = 25�C Hermetic OperatingVOS MAX (�V) DIP 14-Lead Temperature Range

80 OP227EY IND180 OP227GY IND

THERMAL CHARACTERISTICSThermal Resistance

14-Lead CERDIP�JA

3 = 106∞C/W�JC = 16∞C/W

For military processed devices, please refer to the StandardMicrocircuit Drawing (SMD) available atwww.dscc.dla.mil/programs/milspec/default.asp.

SMD Part Number ADI Equivalent

5962-8688701CA* OP227AYMDA

*Not recommended for new design, obsolete April 2002.

REV. A

OP227

– 6 –

FREQUENCY – Hz

VOLT

AG

E N

OIS

E D

EN

SIT

Y –

nV

/ H

z

11 10 100 1k

2

3

4

5

6789

10

TA = 25�C

l/f CORNER= 2.7Hz

VS = �15V

TPC 3. Voltage Noise Density vs.Frequency

SOURCE RESISTANCE – �

TOTA

L N

OIS

E –

nV

/ H

z

100

100

10

11k 10k

RESISTOR NOISE ONLY

TA = 25�CVS = �15V

AT 10Hz

AT 1kHZ

R1

R2

RS = 2R1

TPC 6. Total Noise vs. SourceResistance

FREQUENCY – Hz

VOLT

AG

E N

OIS

E –

nV

/ H

z

100

1

10

1010 100 1k

741

l/f CORNERLOW NOISEAUDIOOP AMP

l/f CORNEROP227

l/f CORNER2.7 Hz

INSTRUMENTATIONRANGE, TO DC

AUDIO RANGETO 20 kHz

TPC 4. Comparison of Op Amp VoltageNoise Spectra

TEMPERATURE – �C

VOLT

AG

E N

OIS

E D

EN

SIT

Y –

nV

/ H

z

5

–50

4

3

2

1–25 0 25 50 75 100 125

AT 10Hz

AT 1kHz

VS = �15V

TPC 7. Voltage Noise Density vs.Temperature

BANDWIDTH – Hz

rms

VO

LTA

GE

NO

ISE

– �

V

10

100

1

0.1

0.011k 10k 100k

TA = 25�CVS = �15V

TPC 5. Input Wideband Noise vs. Band-width (0.1 Hz to Frequency Indicated)

FREQUENCY – Hz

CU

RR

EN

T N

OIS

E –

pA

/ H

z

10.0

10

1.0

0.1100 1k 10k

l/f CORNER= 140Hz

TPC 8. Current Noise Density vs.Frequency

10

0%

100

90

1 SEC / DIV

0.1Hz TO 10Hz PEAK-TO-PEAK NOISE�

0

40

80

120

–40

–80

–120

VO

LTA

GE

NO

ISE

– n

V

TPC 2. Low Frequency Noise(Observation Must Be Limited to 10Seconds to Ensure 0.1 Hz Cutoff)

10�

0.1�F

100k�

D.U.T.

VOLTAGE GAIN= 50,000

2k�

5�F OP12

24.3k�

0.1�F

100k�

4.3k�

2.35�F

23.5�F

SCOPEX 1

RIN = 1M�

110k�

BACK-TO-BACK10�F

BACK-TO-BACK4.7�F

BACK-TO-BACK47�F

TPC 1. Voltage Noise Test Circuit(0.1 Hz to 10 Hz p-p)

–Typical Performance Characteristics

REV. A – 7 –

OP227

TOTAL SUPPLY VOLTAGE – V

SU

PP

LY C

UR

RE

NT

– m

A(B

OT

H A

MP

LIF

IER

S O

N)

10

25

9

6

5

4

3

8

7

10 15 20 25 30 35 40 45

TA = +25�C

TA = +125�C

TA = –55�C

TPC 9. Supply Current vs. SupplyVoltage

TIME AFTER POWER ON – MINUTES

CH

AN

GE

IN IN

PU

T O

FF

SE

T V

OLT

AG

E –

�V

10

00 1 52 3 4

5

TA = 25�CVS = �15V

OP227G

TPC 12. Warm-Up Drift

TEMPERATURE – �C

INP

UT

OF

FS

ET

CU

RR

EN

T –

nA

50

0–75

40

30

20

10

–50 –25 0 25 50 75 100 125

VS = �15V

TPC 15. Input Offset Current vs.Temperature

TEMPERATURE – �C

OF

FS

ET

VO

LTA

GE

– �

V

120

–75–55–35–15 5 25 45 65 85 105125145165

100

80

60

40

20

0

–20

–40

–60

–80

–100

TPC 10. Offset Voltage Drift ofRepresentative Units

TIME – Sec

AB

SO

LU

TE

CH

AN

GE

IN IN

PU

T O

FF

SE

TVO

LTA

GE

– �

V

30

0–20

25

20

15

10

5

0 20 40 60 80 100

THERMALSHOCKRESPONSEBAND

DEVICE IMMERSEDIN 70� C OIL BATH

VS = �15V

TA = 25�C TA = 70�C

TPC 13. Offset Voltage Change Due toThermal Shock

FREQUENCY – Hz

OP

EN

-LO

OP

GA

IN –

dB

130

1

110

90

70

50

30

10

–1010 100 1k 10k 100k 1M 10M 100M

TPC 16. Open-Loop Gain vs. Frequency

TIME – MONTHS

OF

FS

ET

VO

LTA

GE

DR

IFT

WIT

H T

IME

– �

V

5

0 2 3 4 5 6 7 8 9 10

4

–1

3

1

2

0

–2

–3

–4

–51 11 12

0.2�V/MO.

0.2�V/MO.

0.2�V/MO.

TPC 11. Offset Voltage Stabilitywith Time

TEMPERATURE – �CIN

PU

T B

IAS

CU

RR

EN

T –

nA

50

–50

40

30

20

10

0–25 0 25 50 75 100 125 150

VS = �15V

TPC 14. Input Bias Current vs.Temperature

TEMERATURE – �C

SL

EW

RAT

E –

V/�

sP

HA

SE

MA

RG

IN –

DE

G 70

–75

60

50

4

3

2

–50 –25 0 25 50 75 100 125

10

9

8

7

8

GA

INB

AN

DW

IDT

H P

RO

DU

CT

– M

Hz�M

GBW

SLEW

VS = �15V

�

TPC 17. Slew Rate, Gain BandwidthProduct, Phase Margin vs. Temperature

REV. A

OP227

–8–

FREQUENCY – Hz

GA

IN –

dB

25

1M

0

20

15

10

5

–5

1010M 100M

GAIN

PHASEMARGIN

= 70�

TA = 25�CVS = �15V

PH

AS

E S

HIF

T –

DE

G

80

100

120

140

160

180

200

220

TPC 18. Gain, Phase Shift vs.Frequency

FREQUENCY – Hz

PE

AK

-TO

-PE

AK

OU

TP

UT

VO

LTA

GE

– V

28

1k

24

20

16

12

8

4

010k 100k 1M 10M

TA = 25�CVS = �15V

TPC 21. Maximum Undistorted Outputvs. Frequency

500ns

10

0%

100

90

20mV

AVCL = +1, CL= 15pFVS = �15VTA = 25�C�

+50mV

0V

–50mV

TPC 24. Small-Signal TransientResponse

TOTAL SUPPLY VOLTAGE – V

OP

EN

-LO

OP

GA

IN –

V/�

V

2.5

0 10 20 30 40 50

2.0

1.5

1.0

0.5

0.0

TA = 25�C

RL = 2k�

RL = 1k�

TPC 19. Open-Loop Gain vs. SupplyVoltage

CAPACITIVE LOAD – pF

PE

RC

EN

T O

VE

RS

HO

OT

100

0

80

60

40

20

0500 1000 1500 2000 2500

VS = 615VVIN = 100mVAV = +1

TPC 22. Small-Signal Overshoot vs.Capacitive Load

2�s

10

0%

100

90

2V

AVCL = +1VS = �15VTA = 25�C�

+5V

0V

–5V

TPC 25. Large-Signal TransientResponse

LOAD RESISTANCE – �

OU

TP

UT

SW

ING

– V

18

100

0

16

14

12

10

8

6

4

2

–21k 10k

POSITIVESWING

NEGATIVESWING

TS = 25�CVS = �15V

TPC 20. Output Swing vs. ResistiveLoad

TIME FROM OUTPUT SHORTED TOGROUND – MINUTES

SH

OR

T-C

IRC

UIT

CU

RR

EN

T –

mA

60

0 1 52 3 4

50

40

30

20

20

lSC(–)

lSC(+)

TA = �25�VS = �15V

TPC 23. Short-Circuit Current vs. Time

FREQUENCY – Hz

�C

MM

R –

dB

140

1k

120

100

80

6010k 100k 1M 10M

TPC 26. Matching CharacteristicCMRR Match vs. Frequency

REV. A – 9 –

OP227

SUPPLY VOLTAGE – V

CO

MM

ON

-MO

DE

RA

NG

E –

V

16

0

12

8

4

0

–4

–8

–12

–16�5 �10 �15 �20

TA = –55�CTA = +125�C

TA = –55�C

TA = +125�CTA = +25�C

TA = +25�C

TPC 27. Common-Mode Input Rangevs. Supply Voltage

TEMPERATURE – �C

OF

FS

ET

VO

LTA

GE

MAT

CH

– �

V

100

–75

80

60

40

20

0

–20

–40

–60

–80

–100

–120–55–35–15 5 25 45 65 85 105125145165

TPC 30. Matching Characteristic:Drift of Offset Voltage Match ofRepresentative Units

TEMPERATURE – �C

� C

MR

R –

dB

125

–55

120

115

110

105–35 –15 5 25 45 65 85 105 125

TPC 33. Matching Characteristic:CMRR Match vs. Temperature

LOAD RESISTANCE – �

OP

EN

-LO

OP

VO

LTA

GE

GA

IN –

V/�

V

100

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.41k 10k 100k

TA = 25�CVS = �15V

TPC 28. Open-Loop Voltage Gain vs.Load Resistance

TEMPERATURE – �C

NO

NIN

VE

RT

ING

BIA

S C

UR

RE

NT

– �

nA

40

–55

30

20

10

0–35 –15 5 25 45 65 85 105 125

TPC 31. Matching Characteristic:Average Noninverting Bias Currentvs. Temperature

FREQUENCY – Hz

CH

AN

NE

L S

EPA

RAT

ION

– d

B

180

100

140

120

100

80

601k 10k 100k 1M 10M

TPC 34. Channel Separation vs.Frequency

FREQUENCY – Hz

PS

RR

AN

D �

PS

SR

– d

B

140

1

120

100

80

60

40

2010 100 1k 10k 100k 1M

� PSRR (–)

� PSRR (+)

PSRR (+)

PSRR (–)

TPC 29. PSRR and �PSRR vs.Frequency

TEMPERATURE – �CO

FF

SE

T C

UR

RE

NT

– �

nA

50

–55

40

30

20

10–35 –15 5 25 45 65 85 105 125

TPC 32. Matching Characteristic:Average Offset Current vs. Temper-ature (Inverting or Noninverting)

REV. A

OP227

– 1 0 –

BASIC CONNECTIONS

OUT (A)

V–(A)

V–(B)

OUT (B)

(–)

(+)

(+)

(–)

3

4

11

10

9 8 7

2 1 14

13

12

5

6

10k�

10k�

V+(A)

V+(A)

INPUTS

INPUTS A

B

OP227

Figure 1. Offset Nulling Circuit

APPLICATIONS INFORMATIONNoise MeasurementsTo measure the 80 nV peak-to-peak noise specification of theOP227 in the 0.1 Hz to 10 Hz range, the following precautionsmust be observed:

• The device must be warmed up for at least five minutes. Asshown in the warm-up drift curve, the offset voltage typicallychanges 4 mV due to increasing chip temperature after power-up.In the 10-second measurement interval, these temperature-induced effects can exceed tens-of-nanovolts.

∑ For similar reasons, the device must be well shielded from aircurrents. Shielding minimizes thermocouple effects.

∑ Sudden motion in the vicinity of the device can also “feed-through” to increase the observed noise.

∑ The test time to measure 0.1 Hz to 10 Hz noise should notexceed 10-seconds. As shown in the noise-tester frequency-response curve, the 0.1 Hz corner is defined by only one zeroto eliminate noise contributions from the frequency bandbelow 0.1 Hz.

∑ A noise-voltage-density test is recommended when measuringnoise on a large number of units. A 10 Hz noise-voltage-density measurement will correlate well with a 0.1 Hz to 10 Hzpeak-to-peak noise reading, since both results are determinedby the white noise and the location of the 1/f corner frequency.

Instrumentation Amplifier Applications of the OP227The excellent input characteristics of the OP227 make it idealfor use in instrumentation amplifier configurations where lowlevel differential signals are to be amplified. The low noise, lowinput offsets, low drift, and high gain, combined with excellentCMR provide the characteristics needed for high performanceinstrumentation amplifiers. In addition, CMR versus frequencyis very good due to the wide gain bandwidth of these op amps.

The circuit of Figure 2 is recommended for applications wherethe common-mode input range is relatively low and differentialgain will be in the range of 10 to 1000. This two op ampinstrumentation amplifier features independent adjustment ofcommon-mode rejection and differential gain. Input imped-ance is very high since both inputs are applied to non-invertingop amp inputs.

R0

R2R1

R4

R3V1A1

A2

VCM – 1/2Vd

VCM + 1/2Vd

VO

VO =R4R3

1+ 12

R2R1

R3R4

+ R2 + R3R0

VdR4R3

R3R4

– R2R1

VCM[ ( )+ ] + ( )

Figure 2. Two Op Amp Instrumentation Amplifier Configuration

The output voltage VO, assuming ideal op amps, is given inFigure 2. the input voltages are represented as a common-modeinput, VCM, plus a differential input, Vd. The ratio R3/R4 ismade equal to the ratio R2/R1 to reject the common mode inputVCM. The differential signal VO is then amplified according to:

V R

RRR

R RR

V where RR

RRO

Od= + + +Ê

ËÁˆ¯̃

=43

1 34

2 3 34

21

,

Note that gain can be independently varied by adjusting RO.From considerations of dynamic range, resistor tempco match-ing, and matching of amplifier response, it is generally best tomake R1, R2, R3, and R4 approximately equal. Designing R1,R2, R3, and R4 as RN allows the output equation to be furthersimplified:

VRR

V where R R R R RO

N

O

d N= +Ê

ËÁ

ˆ

¯˜ = = = =2 1 1 2 3 4,

REV. A

OP227

– 1 1 –

Dynamic range is limited by A1 as well as A2. The output of A1is:

V

RR

V VN

Od CM1 1 2= +

ÊËÁ

ˆ¯̃

+–

If the instrumentation amplifier was designed for a gain of 10and maximum Vd of ± 1 V, then RN/RO would need to be fourand VO would be a maximum of ± 10 V. Amplifier A1 would havea maximum output of ± 5 V plus 2 VCM, thus a limit of ± 10 Von the output of A1 would imply a limit of ± 2.5 V on VCM. Anominal value of 10 kW for RN is suitable for most applications.A range of 20 W to 2.5 kW for RO will then provide a gain rangeof 10 to 1000. The current through RO is Vd/RO, so the amplifiersmust supply ± 10 mV/20 W (or ± 0.5 mA) when the gain is at themaximum value of 1000 and Vd is at ± 10 mV.

Rejecting common-mode inputs is important in accuratelyamplifying low level differential signals. Two factors determinethe CMR in this instrumentation amplifier configuration (assuminginfinite gain):

∑ CMR of the op amps

∑ Matching of the resistor network ratios (R3/R4 = R2/R1)

In this instrumentation amplifier configuration error due to CMReffect is directly proportional to the CMR match of the op amps.For the OP227, this DCMR is a minimum of 97 dB for the “G”and 110 dB for the “E” grades. A DCMR value of 100 dB and acommon-mode input range of ± 2.5 V indicates a peak input-referred error of only ± 25 mV. Resistor matching is the otherfactor affecting CMR. Defining Ad as the differential gain of theinstrumentation amplifier and assuming that R1, R2, R3, and R4are approximately equal (RN will be the nominal value), then CMRfor this instrumentation amplifier configuration will be approxi-mately Ad divided by 4�R/RN. CMR at differential gain of 100would be 88 dB with resistor matching of 0.01%. Trimming R1to make the ratio R3/R4 equal to R2/R1 will raise the CMRuntil limited by linearity and resistor stability considerations.

The high open-loop gain of the OP227 is very important toachieving high accuracy in the two op amp instrumentationamplifier configuration. Gain error can be approximated by:

Gain ErrorAA

AA Ad

O

d

O O

� 1

12

1

2

1 1+<,

where Ad is the instrumentation amplifier differential gain andAO2 is the open loop gain of op amp A2. This analysis assumesequal values of R1, R2, R3, and R4. For example, consider anOP227 with AO2 of 700 V/mV. Id the differential gain Ad wereset to 700, then the gain error would be 1/1.001, which isapproximately 0.1%.

Another effect of finite op amp gain is undesired feedthrough ofcommon-mode input. Defining AO1 as the open-loop gain of opamp A1, then the common-mode error (CME) at the outputdue to this effect would be approximately:

CMEAAA

AVd

d

O

OCM�

2

1

1

2

1+,

For Ad/A01 < 1, this simplifies to (2Ad/A01) 3 VCM. If the op ampgain is 700 V/mV, VCM is 2.5 V, and Ad is set to 700, then theerror at the output due to this effect will be approximately 5 mV.

A compete instrumentation amplifier designed for a gain of 100is shown in Figure 3. It has provision for trimming of inputoffset voltage, CMR, and gain. Performance is excellent due tothe high gain, high CMR, and low noise of the individual ampli-fiers combined with the tight matching characteristics of theOP227 dual.

3

4

10

11

2 1 14

13

12

7

6

10k�

OFFSETV+

V–

V+

VO = 100Vd

V–5

ADJUST

CMR

50�

9.95k�

2.5k�

191�

10k�0.1%

VCM – 1/2Vd

GAIN

VCM – 1/2Vd

10k�, 0.1%

10k�, 0.1%

OP227

Figure 3. Two Op Amp Instrumentation Amplifier UsingOP227 Dual

A three op amp instrumentation amplifier configuration usingthe OP227 and OP27 is recommended for applications requir-ing high accuracy over a wide gain range. This circuit providesexcellent CMR over a wide frequency range. As with the two opamp instrumentation amplifier circuits, the tight matching of thetwo op amps within the OP227 package provides a real boost inperformance. Also, the low noise, low offset, and high gain ofthe individual op amps minimize errors.

A simplified schematic is shown in Figure 4. The input stage(A1 and A2) serves to amplify the differential input Vd withoutamplifying the common-mode voltage VCM. The output stagethen rejects the common-mode input. With ideal op amps andno resistor matching errors, the outputs of each amplifier willbe:

V RR

VV

V RR

VV

V V V RR

V

V A V

O

dCM

O

dCM

OO

d

O d d

1

2

2 1

1 2 12

1 2 12

1 2 1

= +ÊËÁ

ˆ¯̃

+

= +ÊËÁ

ˆ¯̃

+

= = +ÊËÁ

ˆ¯̃

=

–

–

–

REV. A

OP227

–12–

The differential gain Ad is 1 + 2R1/R0 and the common-modeinput VCM is rejected.

While output error due to input offsets and noise are easilydetermined, the effects of finite gain and common-mode rejec-tion are more subtle. CMR of the complete instrumentationamplifier is directly proportioned to the match in CMR of theinput op amps. This match varies from 97 dB to 110 dB mini-mum for the OP227. Using 100 dB, then the output response toa common-mode input VCM would be:

V A VO

CMd CM[ ] = ¥ 10 5–

CMRR of the instrumentation amplifier, which is defined as20 log10Ad/ACM, is simply equal to the �CMRR of the OP227.While this �CMRR is already high, overall CMRR of thecomplete amplifier can be raised by trimming the output stageresistor network.

Finite gain of the input op amps causes a scale factor error and asmall degradation in CMR. Designating the open-loop gain ofop amp A1 as AO1, and op amp A2 as AO2, then the followingequation approximates output:

VRR A A

A VR

R A AV

O

O O

d dO O

CM�

1

110

1 1

2 10

1 1

1 2

1 2+ +Ê

ËÁ

ˆ

¯˜

+Ê

ËÁ

ˆ

¯˜

Ê

ËÁÁ

ˆ

¯˜̃–

This can be simplified by defining AO as the nominal open-loopgain and �A0 as the differential open-loop gain. Then:

VRR A

A V RR

A

AVO

O

d dO

O

CM� 11 1

01

2 10 2

++

Ê

ËÁ

ˆ

¯˜

D

The high open-loop gain of each amplifier within the OP227(700,000 minimum at 25∞C in RL ≥ 2 kW) assures good gainaccuracy even at high values of Ad. The effect of finite open-loop gain on CMR can be approximated by:

CMRR

AAO

O

�2

D

If �AO/AO were 6% and AO were 600,000, then the CMRR due tofinite gain of the input op amps would be approximately 140 dB.

R1

R1

R2

R2

A3

A1

A2

R2

R0

VCM – 1/2Vd

VCM + 1/2Vd

V1

V2

1/2OP227

VO

OP27

VO = (1 + 2R1 ) VdR0

R2

1/2OP227

Figure 4. Three Op Amp Instrumentation Amplifier UsingOP227 and OP27

The unity-gain output stage contributes negligible error to theoverall amplifier. However, matching of the four resistor R2network is critical to achieving high CMR. Consider a worst-case situation where each R2 resistor had an error of ± �R2. Ifthe resistor ratio is high on one side and low on the other, thenthe common-mode gain will be 2�R2/2�R2. Since the outputstage gain is unity, CMRR will then be R2/2�R2. It is commonpractice to maximize overall CMRR for the total instrumenta-tion amplifier circuit.

REV. A

OP227

– 1 3 –

A1 A2

C130pF

D11N914

R1*1k�

2N4393

R32k�

D2

V1

VO

* MATCHED

A1, A2: OP27

R2*1k�

Figure 5. High Speed Precision Rectifier

High Speed Precision RectifierThe low offsets and excellent load driving capability of the OP27are key advantages in this precision rectifier circuit. The summingimpedances can be as low as 1 kW which helps to reduce theeffects of stray capacitance.

For positive inputs, D2 conducts and D1 is biased OFF. Ampli-fiers A1 and A2 act as a follower with output-to-output feedbackand the R1 resistors are not critical. For negative inputs, D1conducts and D2 is biased OFF. A1 acts as a follower and A2serves as a precision inverter. In this mode, matching of the twoR1 resistors is critical to gain accuracy.

Typical component values are 30 pF for C1 and 2 kW for R3.The drop across D1 must be less than the drop across the FETdiode D2. A 1N914 for D1 and a 2N4393 for the JFET wereused successfully.

The circuit provides full-wave rectification for inputs of up to± 10 V and up to 20 kHz in frequency. To assure frequency stability,be sure to decouple the power supply inputs and minimize anycapactive loading. An OP227, which is two OP27 amplifiers in asingle package, can be used to improve packaging density.

REV. A

OP227

– 1 4 –

OUTLINE DIMENSIONS

14-Lead Ceramic Dip – Glass Hermetic Seal [CERDIP](Q-14)

Dimensions shown in inches and (millimeters)

14

1 7

80.310 (7.87)0.220 (5.59)

PIN 1

0.005 (0.13) MIN 0.098 (2.49) MAX

0.100 (2.54) BSC

15 0

0.320 (8.13)0.290 (7.37)

0.015 (0.38)0.008 (0.20)

SEATINGPLANE

0.200 (5.08)MAX

0.785 (19.94) MAX

0.150(3.81)MIN

0.200 (5.08)0.125 (3.18)

0.023 (0.58)0.014 (0.36)

0.070 (1.78)0.030 (0.76)

0.060 (1.52)0.015 (0.38)

CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETERS DIMENSIONS(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FORREFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN

REV. A

OP227

–15–

Revision HistoryLocation Page

10/02—Data Sheet changed from REV. 0 to REV. A.

Edits to GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

OP227A and OP227F deleted from Individual Amplifier Characteristics section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

OP227A and OP227F deleted from Matching Characteristics section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Edits to ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Edits to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

– 1 6 –

C02

685–

0–10

/02(

A)

PR

INT

ED

IN U

.S.A

.