a
Dual, Low Noise, Low Offset
Instrumentation Operational Amplifier
OP227
FEATURES
Excellent Individual Amplifier Parameters
Low VOS, 80 ␮V Max
Offset Voltage Match, 80 ␮V Max
Offset Voltage Match vs. Temperature, 1 ␮V/ⴗC Max
Stable VOS vs. Time, 1 ␮V/M O 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
PIN CONNECTIONS
NULL (A)
1
14
V+ (A)
NULL (A)
2
13
OUT (A)
–IN (A)
3
12
V– (A)
+IN (A)
4
11
+IN (B)
V– (B)
5
10
–IN (B)
OUT (B)
6
9
NULL (B)
V+ (B)
7
8
NULL (B)
A
B
NOTE
1. DEVICE MAY BE OPERATED EVEN IF INSERTION
IS REVERSED; THIS IS DUE TO INHERENT SYMMETRY
OF PIN LOCATIONS OF AMPLIFIERS A AND B
2. V–(A) AND V–(B) ARE INTERNALLY CONNECTED VIA
SUBSTRATE RESISTANCE
between amplifiers. These outstanding input current specifications
are realized through the use of a unique input current cancellation
circuit which typically holds IB and IOS to ± 20 nA and 15 nA
respectively over the full military temperature range.
GENERAL DESCRIPTION
The OP227 is the first dual amplifier to offer a combination of
low offset, low noise, high speed, and guaranteed amplifier matching
characteristics in one device. The OP227, with a VOS match of
25 mV typical, a TCVOS match of 0.3 mV/∞C typical and a 1/f corner
of 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/ms
typical and a small-signal bandwidth of 8 MHz typical, allow the
designer to achieve ac performance previously unattainable with
op amp based instrumentation designs.
Other sources of input referred errors, such as PSRR and CMRR,
are reduced by factors in excess of 120 dB for the individual
amplifiers. DC stability is assured by a long-term drift application
of 1.0 mV/month.
Matching between channels is provided on all critical parameters including offset voltage, tracking of offset voltage versus
temperature, noninverting bias current, CMRR, and power
supply rejection ratio. This unique dual amplifier allows the
elimination of external components for offset nulling and
frequency compensation.
When used in a three op amp instrumentation configuration, the
OP227 can achieve a CMRR in excess of 100 dB at 10 kHz. In
addition, this device has an open-loop gain of 1.5 M typical with
a 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
V+
Q6
R3
C2
R4
Q22
NULL
R1*
R2*
Q21
R23
Q46
C1
R24
Q20 Q19
Q23
Q24
R9
OUTPUT
R12
NON
INVERTING
INPUT (+)
INVERTING
INPUT (–)
Q1A Q1B
Q2B
Q2A
Q45
R5
Q3
Q11
C3
R11 C4
Q12
Q26
Q27
Q28
V-
*R1 AND R2 ARE PREMATURELY ADJUSTED AT WAFER TEST FOR MINIMUM OFFSET VOLTAGE.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
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
OP227–SPECIFICATIONS
Individual Amplifier Characteristics (V = ⴞ15 V, T = 25ⴗC, unless otherwise noted.)
S
A
Min
OP227E
Typ
Max
Symbol
Conditions
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
Notes 3,5
0.08
0.20
0.09
0.28
mV p-p
INPUT NOISE VOLTAGE
DENSITY
en
fO = 10 Hz3
fO = 30 Hz3
fO = 1000 Hz3
3.5
3.1
3.0
6.0
4.7
3.9
3.8
3.3
3.2
9.0
5.9
4.6
nV/Hz
nV/Hz
nV/Hz
INPUT NOISE DENSITY
in
fO = 10 Hz3, 6
fO = 30 Hz3, 6
fO = 1000 Hz3, 6
1.7
1.0
0.4
4.5
2.5
0.7
1.7
1.0
0.4
0.7
pA/Hz
pA/Hz
pA/Hz
INPUT RESISTANCE
Differential Mode
Common Mode
RIN
RINCM
INPUT VOLTAGE RANGE
IVR
COMMON-MODE
REJECTION RATIO
CMRR
VCM = ± 11 V
POWER SUPPLY
REJECTION RATIO
PSRR
VS = ± 4 V to
± 18 V
LARGE-SIGNAL
VOLTAGE GAIN
AVO
Note 7
RL ⱖ 2 kW,
VO = ± 10 V
RL ⱖ 600 kW,
VO = ± 10 V
Min
OP227G
Typ
Max
Parameter
Unit
1.3
6
3
0.7
4
2
MW
GW
± 11.0
± 12.3
± 11.0
± 12.3
V
114
126
100
120
dB
1
10
2
20
mV/V
1000
1800
700
1500
V/mV
800
1500
600
1500
V/mV
OUTPUT VOLTAGE SWING
VO
RL ⱖ 2 kW
RL ⱖ 600 W
± 12.0
± 10.0
± 13.8
± 11.5
± 11.5
± 10.0
± 13.5
± 11.5
V
V
SLEW RATE
SR
RL ⱖ 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 OUTPUT
RESISTANCE
RO
VO = 0, IO = 0
70
70
W
POWER CONSUMPTION
Pd
Each Amplifier
90
Rp = 10 kW
±4
OFFSET ADJUSTMENT
RANGE
140
100
±4
170
mW
mV
NOTES
1
Input offset voltage measurements are performed by automated test equipment approximately 0.5 seconds after application of power. E Grade specifications are
guaranteed fully warmed up.
2
Long term input offset voltage stability refers to the average trend line of V OS vs. time over extended periods after the first 30 days of operation. Excluding the initial
hour of operation, changes in V OS during the first 30 days are typically 2.5 mV. Refer to the Typical Performance Curve.
3
Sample tested.
4
Parameter is guaranteed by design.
5
See test circuit and frequency response curve for 0.1 Hz to 10 Hz tester.
6
See test circuit for current noise measurement.
7
Guaranteed by input bias current.
Specifications subject to change without notice.
–2–
REV. A
OP227
SPECIFICATIONS
Individual Amplifier Characteristics (V = ⴞ15 V, –25ⴗC £ T £ +85ⴗC, unless otherwise noted.)
S
Parameter
INPUT OFFSET
VOLTAGE
AVERAGE INPUT
OFFSET DRIFT
INPUT OFFSET
CURRENT
INPUT BIAS
CURRENT
INPUT VOLTAGE
RANGE
COMMON-MODE
REJECTION RATIO
POWER SUPPLY
REJECTION RATIO
LARGE-SIGNAL
VOLTAGE GAIN
OUTPUT VOLTAGE
SWING
A
OP227E
Typ
Symbol
Conditions
Min
VOS
Note 1
40
140
TCVOS
TCVOSn
Note 2
0.5
IOS
IB
IVR
CMRR
VCM = ± 10 V
PSRR
VS = ± 4.5 V to
± 18 V
AVO
VO
Max
Min
OP227G
Typ
Max
Unit
85
280
mV
1.0
0.5
1.8
mV/ⴗC
10
50
20
135
nA
± 14
± 60
± 25
± 150
nA
± 10
± 11.8
± 10
± 11.8
V
110
124
96
118
dB
2
15
2
mV/V
32
RL ⱖ 2 kW,
VO = ± 10 V
750
1500
450
1000
V/mV
RL ⱖ 2 kW
± 11.7
± 13.6
± 11.0
± 13.3
V
Matching Characteristics (V = ±15 V, T = 25ⴗC, unless otherwise noted.)
S
Parameter
INPUT OFFSET
VOLTAGE MATCH
AVERAGE
NONINVERTING
CURRENT
NONINVERTING
OFFSET CURRENT
INVERTING OFFSET
CURRENT
COMMON-MODE
REJECTION RATIO
MATCH
POWER SUPPLY
REJECTION RATIO
MATCH
CHANNEL
SEPARATION
Symbol
A
Conditions
Min
OP227E
Typ
Max
Min
OP227G
Typ
Max
Unit
⌬VOS
25
80
55
300
mV
IB +
± 10
± 40
± 15
± 90
Bias
nA
IB + =
I B + A +I B + B
2
IOS+
IOS+ = IB+A-IB+B
± 12
± 60
± 20
± 130
nA
IOS-
IOS- = IB-A-IB-B
± 12
± 60
± 20
± 130
nA
⌬CMRR
VCM = ± 11 V
⌬PSRR
VS = ± 4 V to
± 18 V
CS
Note 1
110
123
2
126
154
97
10
117
2
126
dB
20
154
NOTES
1
Input Offset Voltage measurements are performed by automated equipment approximately 0.5 seconds after application of power.
2
The TCVOS performance is within the specifications unnulled or when nulled with R P = 8 kW to 20 kW, optimum performance is obtained with R P = 8 kW.
3
Sample tested.
Specifications subject to change without notice.
REV. A
–3–
mV/V
dB
OP227–SPECIFICATIONS
Matching Characteristics (V = ⴞ15 V, T = -25ⴗC to +85ⴗC, unless otherwise noted.)
S
Parameter
INPUT OFFSET
VOLTAGE MATCH
INPUT OFFSET
TRACKING
AVERAGE
NONINVERTING
BIAS CURRENT
AVERAGE DRIFT OF
NONINVERTING BIAS
CURRENT
NONINVERTING
OFFSET CURRENT
AVERAGE DRIFT OF
NONINVERTING
OFFSET CURRENT
INVERTING OFFSET
CURRENT
COMMON-MODE
REJECTION RATIO
MATCH
POWER SUPPLY
REJECTION RATIO
MATCH
Symbol
A
Conditions
Min
⌬VOS
TC⌬VOS
IB +
Nulled or Unnulled*
IB + =
I B + A +I B + B
2
TCIB+
IOS+
OP227E
Typ
Max
Min
90
400
mV
0.3
1.0
0.5
1.8
mV/ⴗC
± 14
± 60
± 25
± 170
nA
180
± 90
± 35
130
± 20
IOS–
IOS– = IB–A–IB–B
⌬CMRR
VCM = ± 10 V
⌬PSRR
VS = ± 4.5 V to ± 18 V
106
Unit
140
± 20
TCIOS+
Max
40
80
IOS+ = IB+A–IB+B
OP227G
Typ
± 250
250
± 90
120
2
pA/ⴗC
± 35
90
15
pA/ⴗC
± 250
112
3
nA
nA
dB
32
mV/V
NOTES
*Sample tested.
Specifications subject to change without notice.
–4–
REV. A
OP227
ABSOLUTE MAXIMUM RATINGS
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 22 V
Input Voltage1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 22 V
Output Short-Circuit Duration . . . . . . . . . . . . . . . . . Indefinite
Differential Input Voltage2 . . . . . . . . . . . . . . . . . . . . . . . ± 0.7 V
Differential Input Current2 . . . . . . . . . . . . . . . . . . . . . ± 25 mA
Storage Temperature Range . . . . . . . . . . . . . –65∞C to +150∞C
Operating Temperature Range
OP227E, OP227G . . . . . . . . . . . . . . . . . . . . –25∞C to +85∞C
Lead Temperature (Soldering 60 sec) . . . . . . . . . . . . . . 300∞C
NOTES
1
For supply voltages less than ± 22 V, the absolute maximum input voltage is equal
to the supply voltage.
2
The 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 ± 0.7
V, the input current should be limited to 25 mA.
3
␪JA is specified for worst-case mounting conditions, i.e., ␪JA is specified for device
in socket for CERDIP package.
THERMAL CHARACTERISTICS
Thermal Resistance
14-Lead CERDIP
␪JA3 = 106∞C/W
␪JC = 16∞C/W
ORDERING GUIDE
TA = 25ⴗC
VOS MAX (␮V)
Hermetic
DIP 14-Lead
Operating
Temperature Range
80
180
OP227EY
OP227GY
IND
IND
For military processed devices, please refer to the Standard
Microcircuit Drawing (SMD) available at
www.dscc.dla.mil/programs/milspec/default.asp.
SMD Part Number
ADI Equivalent
5962-8688701CA*
OP227AYMDA
*Not recommended for new design, obsolete April 2002.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the OP227 features propriety ESD protection circuitry, permanent damage may occur on devices
subjected to high energy electrostatic discharges. Therefor, proper ESD precautions are
recommended to avoid performance degradation or loss of functionality.
REV. A
–5–
WARNING!
ESD SENSITIVE DEVICE
OP227–Typical Performance Characteristics
BACK-TO-BACK
47␮F
0.1␮F
100k⍀
1 SEC / DIV
120
10⍀
2k⍀
5␮F
VOLTAGE GAIN
= 50,000
4.3k⍀
23.5␮F
OP12
100k⍀
SCOPE
X 1
RIN = 1M⍀
2.35␮F
0.1␮F
110k⍀
24.3k⍀
100
VOLTAGE NOISE – nV
D.U.T.
80
90
40
0
–40
–80
10
0%
–120
BACK-TO-BACK
10␮F
BACK-TO-BACK
4.7␮F
0.1Hz TO 10Hz PEAK-TO-PEAK NOISE
3
l/f CORNER
= 2.7Hz
10
100
FREQUENCY – Hz
1
INSTRUMENTATION
RANGE, TO DC
10
AUDIO RANGE
TO 20 kHz
100
1k
TPC 4. Comparison of Op Amp Voltage
Noise Spectra
5
RS = 2R1
10
AT 10Hz
AT 1kHZ
RESISTOR NOISE ONLY
1k
SOURCE RESISTANCE – ⍀
1
0.1
0.01
100
10k
TPC 6. Total Noise vs. Source
Resistance
1k
10k
BANDWIDTH – Hz
100k
TPC 5. Input Wideband Noise vs. Bandwidth (0.1 Hz to Frequency Indicated)
10.0
R1
VOLTAGE NOISE DENSITY – nV/ Hz
TOTAL NOISE – nV/ Hz
1
TA = 25ⴗC
VS = ⴞ15V
FREQUENCY – Hz
R2
1
100
10
1k
TPC 3. Voltage Noise Density vs.
Frequency
TA = 25ⴗC
VS = ⴞ15V
10
VS = ⴞ15V
CURRENT NOISE – pA/ Hz
2
l/f CORNER
LOW NOISE
AUDIO
OP AMP
l/f CORNER
2.7 Hz
l/f CORNER
OP227
rms VOLTAGE NOISE – ␮V
4
100
10
741
TA = 25ⴗC
VS = ⴞ15V
5
1
TPC 2. Low Frequency Noise
(Observation Must Be Limited to 10
Seconds to Ensure 0.1 Hz Cutoff)
100
10
9
8
7
6
VOLTAGE NOISE – nV/ Hz
VOLTAGE NOISE DENSITY – nV/ Hz
TPC 1. Voltage Noise Test Circuit
(0.1 Hz to 10 Hz p-p)
4
AT 10Hz
3
AT 1kHz
2
1
–50
–25
0
25
50
75
100
125
TEMPERATURE – ⴗC
TPC 7. Voltage Noise Density vs.
Temperature
–6–
1.0
l/f CORNER
= 140Hz
0.1
10
100
1k
FREQUENCY – Hz
10k
TPC 8. Current Noise Density vs.
Frequency
REV. A
OP227
5
OFFSET VOLTAGE DRIFT WITH TIME – ␮V
120
100
9
OFFSET VOLTAGE – ␮V
SUPPLY CURRENT – mA
(BOTH AMPLIFIERS ON)
80
8
TA = +25ⴗC
7
TA = +125ⴗC
6
5
TA = –55ⴗC
4
60
40
20
0
–20
–40
–60
3
2
–80
5
10
15
20
25 30
35
40
TOTAL SUPPLY VOLTAGE – V
45
TPC 10. Offset Voltage Drift of
Representative Units
OP227G
5
0
2
3
4
1
TIME AFTER POWER ON – MINUTES
15
10
THERMAL
SHOCK
RESPONSE
BAND
5
0
20
40
60
TIME – Sec
VS = ⴞ15V
OPEN-LOOP GAIN – dB
30
20
90
70
50
30
10
10
0
0
25
50
75
–75 –50 –25
TEMPERATURE – ⴗC
–10
100 125
TPC 15. Input Offset Current vs.
Temperature
REV. A
0.2␮V/MO.
–3
–4
0
1
2
3
4 5 6 7 8
TIME – MONTHS
9 10 11 12
40
30
20
10
100
110
40
–2
0
80
130
50
–1
VS = ⴞ15V
DEVICE IMMERSED
IN 70ⴗ C OIL BATH
TPC 13. Offset Voltage Change Due to
Thermal Shock
TPC 12. Warm-Up Drift
INPUT OFFSET CURRENT – nA
TA = 25ⴗC TA = 70ⴗC
20
0
–20
5
0
VS = ⴞ15V
25
1
10
100
1k 10k 100k 1M 10M 100M
FREQUENCY – Hz
TPC 16. Open-Loop Gain vs. Frequency
–7–
–50 –25
0
25 50 75 100 125 150
TEMPERATURE – ⴗC
TPC 14. Input Bias Current vs.
Temperature
SLEW RATE – V/␮s PHASE MARGIN – DEG
0
0.2␮V/MO.
1
50
INPUT BIAS CURRENT – nA
10
2
TPC 11. Offset Voltage Stability
with Time
30
TA = 25ⴗC
VS = ⴞ15V
0.2␮V/MO.
3
–5
–100
–75–55–35–15 5 25 45 65 85 105125145165
TEMPERATURE – ⴗC
ABSOLUTE CHANGE IN INPUT OFFSET
VOLTAGE – ␮V
CHANGE IN INPUT OFFSET VOLTAGE – ␮V
TPC 9. Supply Current vs. Supply
Voltage
4
70
10
⌽M
VS = ⴞ15V
9
60
GBW
50
4
8
7
3
SLEW
2
0
25
50
75
–75 –50 –25
TEMERATURE – ⴗC
GAINBANDWIDTH PRODUCT – MHz
10
8
100 125
TPC 17. Slew Rate, Gain Bandwidth
Product, Phase Margin vs. Temperature
OP227
80
GAIN
120
10
140
PHASE
MARGIN
= 70ⴗ
5
160
180
0
14
2.0
RL = 1k⍀
TA = 25ⴗC
1.5
1.0
10
1M
220
100M
10M
FREQUENCY – Hz
TPC 18. Gain, Phase Shift vs.
Frequency
28
0
10
20
30
40
TOTAL SUPPLY VOLTAGE – V
PERCENT OVERSHOOT
16
12
8
60
40
VS = 615V
VIN = 100mV
AV = +1
20
10k
100k
1M
FREQUENCY – Hz
0
10M
TPC 21. Maximum Undistorted Output
vs. Frequency
8
6
4
10k
60
4
0
1k
NEGATIVE
SWING
10
TPC 20. Output Swing vs. Resistive
Load
100
80
20
POSITIVE
SWING
0 TS = 25ⴗC
VS = ⴞ15V
–2
1k
100
LOAD RESISTANCE – ⍀
50
TPC 19. Open-Loop Gain vs. Supply
Voltage
TA = 25ⴗC
VS = ⴞ15V
24
0.0
12
2
0.5
200
–5
PEAK-TO-PEAK OUTPUT VOLTAGE – V
16
100
SHORT-CIRCUIT CURRENT – mA
GAIN – dB
15
RL = 2k⍀
OPEN-LOOP GAIN – V/␮V
20
18
2.5
PHASE SHIFT – DEG
TA = 25ⴗC
VS = ⴞ15V
OUTPUT SWING – V
25
0
500
1000
1500
2000
CAPACITIVE LOAD – pF
50
lSC(–)
40
30
lSC(+)
20
20
2500
TPC 22. Small-Signal Overshoot vs.
Capacitive Load
TA = ⴞ25ⴗ
VS = ⴞ15V
0
2
3
4
1
TIME FROM OUTPUT SHORTED TO
GROUND – MINUTES
5
TPC 23. Short-Circuit Current vs. Time
140
20mV
500ns
+50mV
2␮s
2V
+5V
100
90
90
0V
120
⌬CMMR – dB
100
0V
10
10
0%
0%
–50mV
100
80
–5V
AVCL = +1, CL= 15pF
VS = ⴞ15V
TA = 25ⴗC
TPC 24. Small-Signal Transient
Response
60
1k
AVCL = +1
VS = ⴞ15V
TA = 25ⴗC
TPC 25. Large-Signal Transient
Response
–8–
10k
100k
1M
FREQUENCY – Hz
10M
TPC 26. Matching Characteristic
CMRR Match vs. Frequency
REV. A
OP227
2.4
16
TA = +125ⴗC
4
0
TA = –55ⴗC
–4
–8
TA = +125ⴗC
TA = +25ⴗC
–12
–16
0
ⴞ5
ⴞ10
ⴞ15
SUPPLY VOLTAGE – V
1.8
1.6
1.4
1.2
1.0
0.8
0.4
100
NONINVERTING BIAS CURRENT – ⴞnA
OFFSET VOLTAGE MATCH – ␮V
40
20
0
–20
–40
–60
–80
–100
TPC 30. Matching Characteristic:
Drift of Offset Voltage Match of
Representative Units
CHANNEL SEPARATION – dB
⌬ CMRR – dB
115
110
5 25 45 65 85 105 125
TEMPERATURE – ⴗC
TPC 33. Matching Characteristic:
CMRR Match vs. Temperature
REV. A
30
20
10
5 25 45 65 85 105 125
TEMPERATURE – ⴗC
180
120
PSRR (–)
60
20
1
100k
TPC 31. Matching Characteristic:
Average Noninverting Bias Current
vs. Temperature
125
PSRR (+)
140
120
100
80
60
100
10
100
1k
10k
FREQUENCY – Hz
100k
1M
TPC 29. PSRR and ⌬PSRR vs.
Frequency
50
0
–55 –35 –15
–120
–75 –55–35–15 5 25 45 65 85 105125145165
TEMPERATURE – ⴗC
105
–55 –35 –15
1k
10k
LOAD RESISTANCE – ⍀
40
60
80
⌬ PSRR (+)
40
TPC 28. Open-Loop Voltage Gain vs.
Load Resistance
100
80
100
0.6
ⴞ20
TPC 27. Common-Mode Input Range
vs. Supply Voltage
⌬ PSRR (–)
120
2.0
OFFSET CURRENT – ⴞnA
8
TA = –55ⴗC
PSRR AND ⌬ PSSR – dB
TA = +25ⴗC
OPEN-LOOP VOLTAGE GAIN – V/␮V
COMMON-MODE RANGE – V
12
140
TA = 25ⴗC
VS = ⴞ15V
2.2
1k
10k
100k
FREQUENCY – Hz
1M
10M
TPC 34. Channel Separation vs.
Frequency
–9–
40
30
20
10
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE – ⴗC
TPC 32. Matching Characteristic:
Average Offset Current vs. Temperature (Inverting or Noninverting)
OP227
∑ A noise-voltage-density test is recommended when measuring
noise on a large number of units. A 10 Hz noise-voltagedensity measurement will correlate well with a 0.1 Hz to 10 Hz
peak-to-peak noise reading, since both results are determined
by the white noise and the location of the 1/f corner frequency.
BASIC CONNECTIONS
V+(A)
10k⍀
2
1
14
Instrumentation Amplifier Applications of the OP227
(–)
INPUTS
(+)
The excellent input characteristics of the OP227 make it ideal
for use in instrumentation amplifier configurations where low
level differential signals are to be amplified. The low noise, low
input offsets, low drift, and high gain, combined with excellent
CMR provide the characteristics needed for high performance
instrumentation amplifiers. In addition, CMR versus frequency
is very good due to the wide gain bandwidth of these op amps.
3
13
A
OUT (A)
4
12
V–(A)
The circuit of Figure 2 is recommended for applications where
the common-mode input range is relatively low and differential
gain will be in the range of 10 to 1000. This two op amp
instrumentation amplifier features independent adjustment of
common-mode rejection and differential gain. Input impedance is very high since both inputs are applied to non-inverting
op amp inputs.
OP227
5
(+)
INPUTS
(–)
V–(B)
11
6
B
OUT (B)
10
R0
9
8
7
10k⍀
R1
R2
A1
V+(A)
VCM – 1/2Vd
R4
V1
R3
Figure 1. Offset Nulling Circuit
A2
VO
VCM + 1/2Vd
APPLICATIONS INFORMATION
Noise Measurements
VO = R4
R3
To measure the 80 nV peak-to-peak noise specification of the
OP227 in the 0.1 Hz to 10 Hz range, the following precautions
must be observed:
+ R3 + R2 + R3 ] V
[1+ 12 (R2
R0
R1 R4 )
R4
d + R3
– R2 V
(R3
R4 R1 )
CM
Figure 2. Two Op Amp Instrumentation Amplifier Configuration
• The device must be warmed up for at least five minutes. As
shown in the warm-up drift curve, the offset voltage typically
changes 4 mV due to increasing chip temperature after power-up.
In the 10-second measurement interval, these temperatureinduced effects can exceed tens-of-nanovolts.
The output voltage VO, assuming ideal op amps, is given in
Figure 2. the input voltages are represented as a common-mode
input, VCM, plus a differential input, Vd. The ratio R3/R4 is
made equal to the ratio R2/R1 to reject the common mode input
VCM. The differential signal VO is then amplified according to:
Ê
ˆ
VO = R 4 Á1 + R3 + R2 + R3 ˜ V d , where R3 = R2
R3 Ë
R4
RO ¯
R 4 R1
∑ For similar reasons, the device must be well shielded from air
currents. Shielding minimizes thermocouple effects.
∑ Sudden motion in the vicinity of the device can also “feedthrough” to increase the observed noise.
∑ The test time to measure 0.1 Hz to 10 Hz noise should not
exceed 10-seconds. As shown in the noise-tester frequencyresponse curve, the 0.1 Hz corner is defined by only one zero
to eliminate noise contributions from the frequency band
below 0.1 Hz.
Note that gain can be independently varied by adjusting RO.
From considerations of dynamic range, resistor tempco matching, and matching of amplifier response, it is generally best to
make R1, R2, R3, and R4 approximately equal. Designing R1,
R2, R3, and R4 as RN allows the output equation to be further
simplified:
V
–10–
O
Ê
R ˆ
= 2Á 1 + N ˜ Vd , where RN = R1 = R2 = R3 = R4
R ¯
Ë
O
REV. A
OP227
Dynamic range is limited by A1 as well as A2. The output of A1
is:
Ê
R ˆ
V1 = – Á1 + N ˜ V d + 2 V CM
RO ¯
Ë
If the instrumentation amplifier was designed for a gain of 10
and maximum Vd of ± 1 V, then RN/RO would need to be four
and VO would be a maximum of ± 10 V. Amplifier A1 would have
a maximum output of ± 5 V plus 2 VCM, thus a limit of ± 10 V
on the output of A1 would imply a limit of ± 2.5 V on VCM. A
nominal 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 range
of 10 to 1000. The current through RO is Vd/RO, so the amplifiers
must supply ± 10 mV/20 W (or ± 0.5 mA) when the gain is at the
maximum value of 1000 and Vd is at ± 10 mV.
Rejecting common-mode inputs is important in accurately
amplifying low level differential signals. Two factors determine
the CMR in this instrumentation amplifier configuration (assuming
infinite gain):
∑ CMR of the op amps
For Ad/A01 < 1, this simplifies to (2Ad/A01) 3 VCM. If the op amp
gain is 700 V/mV, VCM is 2.5 V, and Ad is set to 700, then the
error at the output due to this effect will be approximately 5 mV.
A compete instrumentation amplifier designed for a gain of 100
is shown in Figure 3. It has provision for trimming of input
offset voltage, CMR, and gain. Performance is excellent due to
the high gain, high CMR, and low noise of the individual amplifiers combined with the tight matching characteristics of the
OP227 dual.
Ad
1
,
<1
Ad
2 AO1 AO1
1+
AO 2
where Ad is the instrumentation amplifier differential gain and
AO2 is the open loop gain of op amp A2. This analysis assumes
equal values of R1, R2, R3, and R4. For example, consider an
OP227 with AO2 of 700 V/mV. Id the differential gain Ad were
set to 700, then the gain error would be 1/1.001, which is
approximately 0.1%.
REV. A
1
14
9.95k⍀
3
13
4
VCM – 1/2Vd
12
2.5k⍀
V–
OP227
7
191⍀
V+
10
6
VCM – 1/2Vd
VO = 100Vd
11
5
V–
10k⍀, 0.1%
10k⍀, 0.1%
Figure 3. Two Op Amp Instrumentation Amplifier Using
OP227 Dual
A three op amp instrumentation amplifier configuration using
the OP227 and OP27 is recommended for applications requiring high accuracy over a wide gain range. This circuit provides
excellent CMR over a wide frequency range. As with the two op
amp instrumentation amplifier circuits, the tight matching of the
two op amps within the OP227 package provides a real boost in
performance. Also, the low noise, low offset, and high gain of
the 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 without
amplifying the common-mode voltage VCM. The output stage
then rejects the common-mode input. With ideal op amps and
no resistor matching errors, the outputs of each amplifier will
be:
Another effect of finite op amp gain is undesired feedthrough of
common-mode input. Defining AO1 as the open-loop gain of op
amp A1, then the common-mode error (CME) at the output
due to this effect would be approximately:
CME 2
GAIN
In this instrumentation amplifier configuration error due to CMR
effect 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 a
common-mode input range of ± 2.5 V indicates a peak inputreferred error of only ± 25 mV. Resistor matching is the other
factor affecting CMR. Defining Ad as the differential gain of the
instrumentation amplifier and assuming that R1, R2, R3, and R4
are approximately equal (RN will be the nominal value), then CMR
for this instrumentation amplifier configuration will be approximately Ad divided by 4⌬R/RN. CMR at differential gain of 100
would be 88 dB with resistor matching of 0.01%. Trimming R1
to make the ratio R3/R4 equal to R2/R1 will raise the CMR
until limited by linearity and resistor stability considerations.
Gain Error ADJUST
10k⍀
10k⍀
0.1%
50⍀
∑ Matching of the resistor network ratios (R3/R4 = R2/R1)
The high open-loop gain of the OP227 is very important to
achieving high accuracy in the two op amp instrumentation
amplifier configuration. Gain error can be approximated by:
OFFSET
V+
CMR
Ê
ˆV
V1 = – Á1 + 2R1˜ d + V CM
RO ¯ 2
Ë
Ê
ˆV
V2 = – Á1 + 2R1˜ d + V CM
RO ¯ 2
Ë
2 Ad
, 1 V CM
Ad
AO1
1+
AO 2
Ê
ˆ
VO = V2 – V1 = Á1 + 2R1˜ V d
R
Ë
O ¯
–11–
VO = Ad V d
OP227
The differential gain Ad is 1 + 2R1/R0 and the common-mode
input VCM is rejected.
2
CMRR While output error due to input offsets and noise are easily
determined, the effects of finite gain and common-mode rejection are more subtle. CMR of the complete instrumentation
amplifier is directly proportioned to the match in CMR of the
input op amps. This match varies from 97 dB to 110 dB minimum for the OP227. Using 100 dB, then the output response to
a common-mode input VCM would be:
[V ]
O
CM
If ⌬AO/AO were 6% and AO were 600,000, then the CMRR due to
finite gain of the input op amps would be approximately 140 dB.
R1
= Ad V CM ¥ 10–5
O
VO Ê
ˆ
DAO
1
Ad V d + 2R1
V CM ˜
Á
2
R0 A
1 + R1 1 Ë
¯
O
R0 AO
R2
R2
V1
VCM – 1/2Vd
OP27
R0
A3
R1
VO
1/2
Ê
ˆ
2R1 Ê 1
1 ˆ
V
–
ÁA V +
˜
Á
˜
Á d d
R0 Ë A
A ¯ CM ˜¯
R1 Ê 1
1 ˆ Ë
O1
O2
+
1+
Á
˜
R0 Ë A
A ¯
O1
O2
This can be simplified by defining AO as the nominal open-loop
gain and ⌬A0 as the differential open-loop gain. Then:
R0
A1
OP227
Finite gain of the input op amps causes a scale factor error and a
small degradation in CMR. Designating the open-loop gain of
op amp A1 as AO1, and op amp A2 as AO2, then the following
equation approximates output:
1
VO = (1 + 2R1 ) Vd
1/2
OP227
CMRR of the instrumentation amplifier, which is defined as
20 log10Ad/ACM, is simply equal to the ⌬CMRR of the OP227.
While this ⌬CMRR is already high, overall CMRR of the
complete amplifier can be raised by trimming the output stage
resistor network.
V AO
DAO
R2
A2
VCM + 1/2Vd
V2
R2
Figure 4. Three Op Amp Instrumentation Amplifier Using
OP227 and OP27
The unity-gain output stage contributes negligible error to the
overall amplifier. However, matching of the four resistor R2
network is critical to achieving high CMR. Consider a worstcase situation where each R2 resistor had an error of ± ⌬R2. If
the resistor ratio is high on one side and low on the other, then
the common-mode gain will be 2⌬R2/2⌬R2. Since the output
stage gain is unity, CMRR will then be R2/2⌬R2. It is common
practice to maximize overall CMRR for the total instrumentation amplifier circuit.
The high open-loop gain of each amplifier within the OP227
(700,000 minimum at 25∞C in RL ≥ 2 kW) assures good gain
accuracy even at high values of Ad. The effect of finite openloop gain on CMR can be approximated by:
–12–
REV. A
OP227
High Speed Precision Rectifier
The low offsets and excellent load driving capability of the OP27
are key advantages in this precision rectifier circuit. The summing
impedances can be as low as 1 kW which helps to reduce the
effects of stray capacitance.
For positive inputs, D2 conducts and D1 is biased OFF. Amplifiers A1 and A2 act as a follower with output-to-output feedback
and the R1 resistors are not critical. For negative inputs, D1
conducts and D2 is biased OFF. A1 acts as a follower and A2
serves as a precision inverter. In this mode, matching of the two
R1 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 FET
diode D2. A 1N914 for D1 and a 2N4393 for the JFET were
used 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 any
capactive loading. An OP227, which is two OP27 amplifiers in a
single package, can be used to improve packaging density.
R1*
1k⍀
C1
30pF
R2*
1k⍀
D1
1N914
* MATCHED
D2
A1
2N4393
V1
A1, A2: OP27
R3
2k⍀
Figure 5. High Speed Precision Rectifier
REV. A
–13–
A2
VO
OP227
OUTLINE DIMENSIONS
14-Lead Ceramic Dip – Glass Hermetic Seal [CERDIP]
(Q-14)
Dimensions shown in inches and (millimeters)
0.005 (0.13) MIN
14
0.098 (2.49) MAX
8
PIN 1
1
7
0.310 (7.87)
0.220 (5.59)
0.320 (8.13)
0.290 (7.37)
0.100 (2.54) BSC
0.785 (19.94) MAX
0.200 (5.08)
MAX
0.200 (5.08)
0.125 (3.18)
0.023 (0.58)
0.014 (0.36)
0.060 (1.52)
0.015 (0.38)
0.150
(3.81)
MIN
0.070 (1.78) SEATING 15
PLANE
0
0.030 (0.76)
0.015 (0.38)
0.008 (0.20)
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETERS DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
–14–
REV. A
OP227
Revision History
Location
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
REV. A
–15–
–16–
PRINTED IN U.S.A.
C02685–0–10/02(A)