www.docs.chipfind.ru
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.
a
OP227
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 Offset
Instrumentation Operational Amplifier
PIN CONNECTIONS
NOTE
DEVICE MAY BE OPERATED EVEN IF INSERTION
IS REVERSED; THIS IS DUE TO INHERENT SYMMETRY
OF PIN LOCATIONS OF AMPLIFIERS A AND B
V(A) AND V(B) ARE INTERNALLY CONNECTED VIA
SUBSTRATE 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 V
OS
, 80 V Max
Offset Voltage Match, 80 V Max
Offset Voltage Match vs. Temperature, 1 V/ C Max
Stable V
OS
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
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 V
OS
match of
25
mV typical, a TCV
OS
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.
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 k
W load. The OP227 also features an I
B
of
10 nA typical,
an I
OS
of 7 nA typical, and guaranteed matching of input currents
SIMPLIFIED SCHEMATIC
NON
INVERTING
INPUT (+)
INVERTING
INPUT ()
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
R5
C3
R11 C4
R12
R9
Q22
C1
Q20 Q19
Q26
Q45
Q46
OUTPUT
V-
V+
between amplifiers. These outstanding input current specifications
are realized through the use of a unique input current cancellation
circuit which typically holds I
B
and I
OS
to
20 nA and 15 nA
respectively 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 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 param-
eters 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.
REV. A
2
OP227SPECIFICATIONS
Individual Amplifier Characteristics
(V
S
= 15 V, T
A
= 25 C, unless otherwise noted.)
OP227E
OP227G
Parameter
Symbol
Conditions
Min
Typ
Max
Min
Typ
Max
Unit
INPUT OFFSET VOLTAGE
V
OS
Note 1
20
80
60
180
mV
LONG-TERM V
OS
STABILITY
V
OS
/Time
Notes 2,4
0.2
1.0
0.4
2.0
mV/M
O
INPUT OFFSET CURRENT
I
OS
7
35
12
75
nA
INPUT BIAS CURRENT
I
B
10
40
15
80
nA
INPUT NOISE VOLTAGE
e
n p-p
0.1 Hz to 10 Hz
0.08
0.20
0.09
0.28
mV p-p
Notes 3,5
INPUT NOISE VOLTAGE
DENSITY
e
n
f
O
= 10 Hz
3
3.5
6.0
3.8
9.0
nV/
Hz
f
O
= 30 Hz
3
3.1
4.7
3.3
5.9
nV/
Hz
f
O
= 1000 Hz
3
3.0
3.9
3.2
4.6
nV/
Hz
INPUT NOISE DENSITY
i
n
f
O
= 10 Hz
3, 6
1.7
4.5
1.7
pA/
Hz
f
O
= 30 Hz
3, 6
1.0
2.5
1.0
pA/
Hz
f
O
= 1000 Hz
3, 6
0.4
0.7
0.4
0.7
pA/
Hz
INPUT RESISTANCE
Differential Mode
R
IN
Note 7
1.3
6
0.7
4
M
W
Common Mode
R
INCM
3
2
G
W
INPUT VOLTAGE RANGE
IVR
11.0 12.3
11.0 12.3
V
COMMON-MODE
REJECTION RATIO
CMRR
V
CM
=
11 V
114
126
100
120
dB
POWER SUPPLY
REJECTION RATIO
PSRR
V
S
=
4 V to
18 V
1
10
2
20
mV/V
LARGE-SIGNAL
VOLTAGE GAIN
A
VO
R
L
2 k
W,
V
O
=
10 V
1000
1800
700
1500
V/mV
R
L
600 k
W,
V
O
=
10 V
800
1500
600
1500
V/mV
OUTPUT VOLTAGE SWING
V
O
R
L
2 k
W
12.0 13.8
11.5 13.5
V
R
L
600
W
10.0 11.5
10.0 11.5
V
SLEW RATE
SR
R
L
2 k
W
4
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
R
O
V
O
= 0, I
O
= 0
70
70
W
POWER CONSUMPTION
P
d
Each Amplifier
90
140
100
170
mW
OFFSET ADJUSTMENT
RANGE
R
p
= 10 k
W
4
4
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.
REV. A
3
OP227
SPECIFICATIONS
Individual Amplifier Characteristics
(V
S
= 15 V, 25 C
T
A
+85 C, unless otherwise noted.)
OP227E
OP227G
Parameter
Symbol
Conditions
Min
Typ
Max
Min
Typ
Max
Unit
INPUT OFFSET
VOLTAGE
V
OS
Note 1
40
140
85
280
mV
AVERAGE INPUT
OFFSET DRIFT
TCV
OS
TCV
OSn
Note 2
0.5
1.0
0.5
1.8
mV/ C
INPUT OFFSET
CURRENT
I
OS
10
50
20
135
nA
INPUT BIAS
CURRENT
I
B
14
60
25
150
nA
INPUT VOLTAGE
RANGE
IVR
10
11.8
10
11.8
V
COMMON-MODE
REJECTION RATIO
CMRR
V
CM
=
10 V
110
124
96
118
dB
POWER SUPPLY
REJECTION RATIO
PSRR
V
S
=
4.5 V to
18 V
2
15
2
32
mV/V
LARGE-SIGNAL
VOLTAGE GAIN
A
VO
R
L
2 k
W,
V
O
=
10 V
750
1500
450
1000
V/mV
OUTPUT VOLTAGE
SWING
V
O
R
L
2 k
W
11.7 13.6
11.0 13.3
V
Matching Characteristics
(V
S
=
15 V, T
A
= 25 C, unless otherwise noted.)
OP227E
OP227G
Parameter
Symbol
Conditions
Min
Typ
Max
Min
Typ
Max
Unit
INPUT OFFSET
VOLTAGE MATCH
V
OS
25
80
55
300
mV
AVERAGE
NONINVERTING
Bias
CURRENT
I
B
+
I
I
I
B
B
A
B
B
+ =
+ + +
2
10
40
15
90
nA
NONINVERTING
OFFSET CURRENT
I
OS
+
I
OS
+ = I
B
+
A
-I
B+B
12
60
20
130
nA
INVERTING OFFSET
CURRENT
I
OS
-
I
OS
- = I
B
-
A
-I
B
-
B
12
60
20
130
nA
COMMON-MODE
REJECTION RATIO
MATCH
CMRR
V
CM
=
11 V
110
123
97
117
dB
POWER SUPPLY
REJECTION RATIO
MATCH
PSRR
V
S
=
4 V to
18 V
2
10
2
20
mV/V
CHANNEL
SEPARATION
CS
Note 1
126
154
126
154
dB
NOTES
1
Input Offset Voltage measurements are performed by automated equipment approximately 0.5 seconds after application of power.
2
The TCV
OS
performance is within the specifications unnulled or when nulled with R
P
= 8 k
W to 20 kW, optimum performance is obtained with R
P
= 8 k
W.
3
Sample tested.
Specifications subject to change without notice.
REV. A
4
OP227SPECIFICATIONS
Matching Characteristics
(V
S
= 15 V, T
A
= -25 C to +85 C, unless otherwise noted.)
OP227E
OP227G
Parameter
Symbol
Conditions
Min
Typ
Max
Min
Typ
Max
Unit
INPUT OFFSET
VOLTAGE MATCH
V
OS
40
140
90
400
mV
INPUT OFFSET
TRACKING
TC V
OS
Nulled or Unnulled
*
0.3
1.0
0.5
1.8
mV/ C
AVERAGE
NONINVERTING
BIAS CURRENT
I
B
+
I
I
I
B
B
A
B
B
+ =
+ + +
2
14
60
25
170
nA
AVERAGE DRIFT OF
NONINVERTING BIAS
CURRENT
TCI
B
+
80
180
pA/ C
NONINVERTING
OFFSET CURRENT
I
OS
+
I
OS
+ = I
B
+
A
I
B
+
B
20
90
35
250
nA
AVERAGE DRIFT OF
NONINVERTING
OFFSET CURRENT
TCI
OS
+
130
250
pA/ C
INVERTING OFFSET
CURRENT
I
OS
I
OS
= I
B
A
I
B
B
20
90
35
250
nA
COMMON-MODE
REJECTION RATIO
MATCH
CMRR
V
CM
=
10 V
106
120
90
112
dB
POWER SUPPLY
REJECTION RATIO
MATCH
PSRR
V
S
=
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 RATINGS
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22 V
Input Voltage
1
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22 V
Output Short-Circuit Duration . . . . . . . . . . . . . . . . . Indefinite
Differential Input Voltage
2
. . . . . . . . . . . . . . . . . . . . . . .
0.7 V
Differential Input Current
2
. . . . . . . . . . . . . . . . . . . . .
25 mA
Storage Temperature Range
. . . . . . . . . . . . . 65
C to +150C
Operating Temperature Range
OP227E, OP227G . . . . . . . . . . . . . . . . . . . . 25
C to +85C
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.
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.
WARNING!
ESD SENSITIVE DEVICE
ORDERING GUIDE
T
A
= 25 C
Hermetic
Operating
V
OS
MAX ( V)
DIP 14-Lead
Temperature Range
80
OP227EY
IND
180
OP227GY
IND
THERMAL CHARACTERISTICS
Thermal Resistance
14-Lead CERDIP
JA
3
= 106
C/W
JC
= 16
C/W
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.
REV. A
OP227
6
FREQUENCY Hz
VO
LTA
GE NOISE DENSITY nV/
Hz
1
1
10
100
1k
2
3
4
5
6
7
8
9
10
T
A
= 25 C
l/f CORNER
= 2.7Hz
V
S
= 15V
TPC 3. Voltage Noise Density vs.
Frequency
SOURCE RESISTANCE
TOT
A
L
N
O
I
SE nV/
Hz
100
100
10
1
1k
10k
RESISTOR NOISE ONLY
T
A
= 25 C
V
S
= 15V
AT 10Hz
AT 1kHZ
R1
R2
R
S
= 2R1
TPC 6. Total Noise vs. Source
Resistance
FREQUENCY Hz
VO
LTA
G
E
N
OISE nV/
Hz
100
1
10
10
10
100
1k
741
l/f CORNER
LOW NOISE
AUDIO
OP AMP
l/f CORNER
OP227
l/f CORNER
2.7 Hz
INSTRUMENTATION
RANGE, TO DC
AUDIO RANGE
TO 20 kHz
TPC 4. Comparison of Op Amp Voltage
Noise Spectra
TEMPERATURE C
VO
LTA
GE NOISE DENSITY nV/
Hz
5
50
4
3
2
1
25
0
25
50
75
100
125
AT 10Hz
AT 1kHz
V
S
= 15V
TPC 7. Voltage Noise Density vs.
Temperature
BANDWIDTH Hz
rms
V
O
L
T
A
GE NOISE
V
10
100
1
0.1
0.01
1k
10k
100k
T
A
= 25 C
V
S
= 15V
TPC 5. Input Wideband Noise vs. Band-
width (0.1 Hz to Frequency Indicated)
FREQUENCY Hz
CURRENT NOISE pA/
Hz
10.0
10
1.0
0.1
100
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
G
E
NOISE nV
TPC 2. Low Frequency Noise
(Observation Must Be Limited to 10
Seconds 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
SCOPE
X 1
R
IN
= 1M
110k
BACK-TO-BACK
10 F
BACK-TO-BACK
4.7 F
BACK-TO-BACK
47 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
SUPPL
Y CURRENT mA
(BO
TH AMPLIFIERS ON)
10
2
5
9
6
5
4
3
8
7
10
15
20
25
30
35
40
45
T
A
= +25 C
T
A
= +125 C
T
A
= 55 C
TPC 9. Supply Current vs. Supply
Voltage
TIME AFTER POWER ON MINUTES
CHANGE IN INPUT OFFSET
V
O
L
T
A
GE
V
10
0
0
1
5
2
3
4
5
T
A
= 25 C
V
S
= 15V
OP227G
TPC 12. Warm-Up Drift
TEMPERATURE C
INPUT OFFSET CURRENT nA
50
0
75
40
30
20
10
50 25
0
25
50
75
100 125
V
S
= 15V
TPC 15. Input Offset Current vs.
Temperature
TEMPERATURE C
OFFSET V
O
L
T
A
GE
V
120
75553515 5 25 45 65 85 105125145165
100
80
60
40
20
0
20
40
60
80
100
TPC 10. Offset Voltage Drift of
Representative Units
TIME Sec
ABSOLUTE CHANGE IN INPUT OFFSET
VO
LTA
G
E
V
30
0
20
25
20
15
10
5
0
20
40
60
80
100
THERMAL
SHOCK
RESPONSE
BAND
DEVICE IMMERSED
IN 70 C OIL BATH
V
S
= 15V
T
A
= 25 C T
A
= 70 C
TPC 13. Offset Voltage Change Due to
Thermal Shock
FREQUENCY Hz
OPEN-LOOP GAIN dB
130
1
110
90
70
50
30
10
10
10
100
1k
10k 100k 1M 10M 100M
TPC 16. Open-Loop Gain vs. Frequency
TIME MONTHS
OFFSET V
O
L
T
A
GE
DRIFT WITH
TIME
V
5
0
2
3
4
5
6
7
8
9 10
4
1
3
1
2
0
2
3
4
5
1
11 12
0.2 V/MO.
0.2 V/MO.
0.2 V/MO.
TPC 11. Offset Voltage Stability
with Time
TEMPERATURE C
INPUT BIAS CURRENT nA
50
50
40
30
20
10
0
25
0
25
50
75
100 125 150
V
S
= 15V
TPC 14. Input Bias Current vs.
Temperature
TEMERATURE C
SLEW RA
TE
V/
s
PHASE MARGIN DEG
70
75
60
50
4
3
2
50 25
0
25
50
75
100 125
10
9
8
7
8
GAINB
AND
WIDTH PR
ODUCT MHz
M
GBW
SLEW
V
S
= 15V
TPC 17. Slew Rate, Gain Bandwidth
Product, Phase Margin vs. Temperature
REV. A
OP227
8
FREQUENCY Hz
GAIN dB
25
1M
0
20
15
10
5
5
10
10M
100M
GAIN
PHASE
MARGIN
= 70
T
A
= 25 C
V
S
= 15V
PHASE SHIFT DEG
80
100
120
140
160
180
200
220
TPC 18. Gain, Phase Shift vs.
Frequency
FREQUENCY Hz
PEAK-T
O-PEAK OUTPUT
V
OL
T
A
GE
V
28
1k
24
20
16
12
8
4
0
10k
100k
1M
10M
T
A
= 25 C
V
S
= 15V
TPC 21. Maximum Undistorted Output
vs. Frequency
500ns
10
0%
100
90
20mV
A
VCL
= +1, C
L
= 15pF
V
S
= 15V
T
A
= 25 C
+50mV
0V
50mV
TPC 24. Small-Signal Transient
Response
TOTAL SUPPLY VOLTAGE V
OPEN-LOOP GAIN
V/
V
2.5
0
10
20
30
40
50
2.0
1.5
1.0
0.5
0.0
T
A
= 25 C
R
L
= 2k
R
L
= 1k
TPC 19. Open-Loop Gain vs. Supply
Voltage
CAPACITIVE LOAD pF
PERCENT O
VERSHOO
T
100
0
80
60
40
20
0
500
1000
1500
2000
2500
V
S
= 615V
V
IN
= 100mV
A
V
= +1
TPC 22. Small-Signal Overshoot vs.
Capacitive Load
2 s
10
0%
100
90
2V
A
VCL
= +1
V
S
= 15V
T
A
= 25 C
+5V
0V
5V
TPC 25. Large-Signal Transient
Response
LOAD RESISTANCE
OUTPUT SWING
V
18
100
0
16
14
12
10
8
6
4
2
2
1k
10k
POSITIVE
SWING
NEGATIVE
SWING
T
S
= 25 C
V
S
= 15V
TPC 20. Output Swing vs. Resistive
Load
TIME FROM OUTPUT SHORTED TO
GROUND MINUTES
SHOR
T
-CIRCUIT CURRENT mA
60
0
1
5
2
3
4
50
40
30
20
20
l
SC
()
l
SC
(+)
T
A
= 25
V
S
= 15V
TPC 23. Short-Circuit Current vs. Time
FREQUENCY Hz
CMMR dB
140
1k
120
100
80
60
10k
100k
1M
10M
TPC 26. Matching Characteristic
CMRR Match vs. Frequency
REV. A
9
OP227
SUPPLY VOLTAGE V
COMMON-MODE RANGE
V
16
0
12
8
4
0
4
8
12
16
5
10
15
20
T
A
= 55 C
T
A
= +125 C
T
A
= 55 C
T
A
= +125 C
T
A
= +25 C
T
A
= +25 C
TPC 27. Common-Mode Input Range
vs. Supply Voltage
TEMPERATURE C
OFFSET
V
O
L
T
A
GE MA
TCH
V
100
75
80
60
40
20
0
20
40
60
80
100
120
553515 5 25 45 65 85 105125145165
TPC 30. Matching Characteristic:
Drift of Offset Voltage Match of
Representative Units
TEMPERATURE C
CMRR 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
OPEN-LOOP
V
O
L
T
A
GE GAIN
V/
V
100
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
1k
10k
100k
T
A
= 25 C
V
S
= 15V
TPC 28. Open-Loop Voltage Gain vs.
Load Resistance
TEMPERATURE C
NONINVER
TING BIAS CURRENT
nA
40
55
30
20
10
0
35 15
5
25
45
65
85 105 125
TPC 31. Matching Characteristic:
Average Noninverting Bias Current
vs. Temperature
FREQUENCY Hz
CHANNEL SEP
ARA
TION dB
180
100
140
120
100
80
60
1k
10k
100k
1M
10M
TPC 34. Channel Separation vs.
Frequency
FREQUENCY Hz
PSRR AND
PSSR dB
140
1
120
100
80
60
40
20
10
100
1k
10k
100k
1M
PSRR ()
PSRR (+)
PSRR (+)
PSRR ()
TPC 29. PSRR and PSRR vs.
Frequency
TEMPERATURE C
OFFSET CURRENT
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 INFORMATION
Noise Measurements
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:
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 temperature-
induced effects can exceed tens-of-nanovolts.
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 "feed-
through" 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 frequency-
response curve, the 0.1 Hz corner is defined by only one zero
to eliminate noise contributions from the frequency band
below 0.1 Hz.
A noise-voltage-density test is recommended when measuring
noise on a large number of units. A 10 Hz noise-voltage-
density 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.
Instrumentation Amplifier Applications of the OP227
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.
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 imped-
ance is very high since both inputs are applied to non-inverting
op amp inputs.
R0
R2
R1
R4
R3
V1
A1
A2
V
CM
1/2V
d
V
CM
+ 1/2V
d
V
O
V
O
= R4
R3
1+ 1
2
R2
R1
R3
R4
+
R2 + R3
R0
V
d
R4
R3
R3
R4
R2
R1
V
CM
[
(
)
+
]
+
(
)
Figure 2. Two Op Amp Instrumentation Amplifier Configuration
The output voltage V
O
, assuming ideal op amps, is given in
Figure 2. the input voltages are represented as a common-mode
input, V
CM
, plus a differential input, V
d
. The ratio R3/R4 is
made equal to the ratio R2/R1 to reject the common mode input
V
CM
. The differential signal V
O
is then amplified according to:
V
R
R
R
R
R
R
R
V
where R
R
R
R
O
O
d
=
+
+
+
^
~
=
4
3
1
3
4
2
3
3
4
2
1
,
Note that gain can be independently varied by adjusting R
O
.
From considerations of dynamic range, resistor tempco match-
ing, 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 R
N
allows the output equation to be further
simplified:
V
R
R
V
where R
R
R
R
R
O
N
O
d
N
=
+
^
~
=
=
=
=
2 1
1
2
3
4
,
REV. A
OP227
1 1
Dynamic range is limited by A1 as well as A2. The output of A1
is:
V
R
R
V
V
N
O
d
CM
1
1
2
=
+
^
~
+
If the instrumentation amplifier was designed for a gain of 10
and maximum V
d
of
1 V, then R
N
/R
O
would need to be four
and V
O
would be a maximum of
10 V. Amplifier A1 would have
a maximum output of
5 V plus 2 V
CM
, thus a limit of
10 V
on the output of A1 would imply a limit of
2.5 V on V
CM
. A
nominal value of 10 k
W for R
N
is suitable for most applications.
A range of 20
W to 2.5 kW for R
O
will then provide a gain range
of 10 to 1000. The current through R
O
is V
d
/R
O
, so the amplifiers
must supply
10 mV/20 W (or 0.5 mA) when the gain is at the
maximum value of 1000 and V
d
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
Matching of the resistor network ratios (R3/R4 = R2/R1)
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 input-
referred error of only
25 mV. Resistor matching is the other
factor affecting CMR. Defining A
d
as the differential gain of the
instrumentation amplifier and assuming that R1, R2, R3, and R4
are approximately equal (R
N
will be the nominal value), then CMR
for this instrumentation amplifier configuration will be approxi-
mately A
d
divided by 4 R/R
N
. 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.
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:
Gain Error
A
A
A
A A
d
O
d
O
O
1
1
2
1
2
1
1
+
<
,
where A
d
is the instrumentation amplifier differential gain and
A
O2
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 A
O2
of 700 V/mV. Id the differential gain A
d
were
set to 700, then the gain error would be 1/1.001, which is
approximately 0.1%.
Another effect of finite op amp gain is undesired feedthrough of
common-mode input. Defining A
O1
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
A
A
A
A
V
d
d
O
O
CM
2
1
1
2
1
+
,
For A
d
/A
01
< 1, this simplifies to (2A
d
/A
01
) 3 V
CM
. If the op amp
gain is 700 V/mV, V
CM
is 2.5 V, and A
d
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 ampli-
fiers combined with the tight matching characteristics of the
OP227 dual.
3
4
10
11
2
1
14
13
12
7
6
10k
OFFSET
V+
V
V+
V
O
= 100V
d
V
5
ADJUST
CMR
50
9.95k
2.5k
191
10k
0.1%
V
CM
1/2V
d
GAIN
V
CM
1/2V
d
10k , 0.1%
10k , 0.1%
OP227
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 requir-
ing 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 V
d
without
amplifying the common-mode voltage V
CM
. 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:
V
R
R
V
V
V
R
R
V
V
V
V
V
R
R
V
V
A V
O
d
CM
O
d
CM
O
O
d
O
d
d
1
2
2
1
1
2 1
2
1
2 1
2
1
2 1
=
+
^
~
+
=
+
^
~
+
=
= +
^
~
=
REV. A
OP227
12
The differential gain A
d
is 1 + 2R1/R0 and the common-mode
input V
CM
is rejected.
While output error due to input offsets and noise are easily
determined, the effects of finite gain and common-mode rejec-
tion 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 mini-
mum for the OP227. Using 100 dB, then the output response to
a common-mode input V
CM
would be:
V
A V
O
CM
d
CM
[ ]
=
10
5
CMRR of the instrumentation amplifier, which is defined as
20 log10A
d
/A
CM
, 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.
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 A
1
as A
O1
, and op amp A
2
as A
O2
, then the following
equation approximates output:
V
R
R
A
A
A V
R
R
A
A
V
O
O
O
d
d
O
O
CM
1
1
1
0
1
1
2 1
0
1
1
1
2
1
2
+
+
^
~
+
^
~
^
~
~
This can be simplified by defining A
O
as the nominal open-loop
gain and A0 as the differential open-loop gain. Then:
V
R
R
A
A V
R
R
A
A
V
O
O
d
d
O
O
CM
1
1
1
0
1
2 1
0
2
+
+
^
~
D
The high open-loop gain of each amplifier within the OP227
(700,000 minimum at 25
C in R
L
2 kW) assures good gain
accuracy even at high values of A
d
. The effect of finite open-
loop gain on CMR can be approximated by:
CMRR
A
A
O
O
2
D
If A
O
/A
O
were 6% and A
O
were 600,000, then the CMRR due to
finite gain of the input op amps would be approximately 140 dB.
R1
R1
R2
R2
A3
A1
A2
R2
R0
V
CM
1/2V
d
V
CM
+ 1/2V
d
V1
V2
1/2
OP227
V
O
OP27
V
O
= (1 +
2R1
) Vd
R0
R2
1/2
OP227
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 worst-
case 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 instrumenta-
tion amplifier circuit.
REV. A
OP227
1 3
A1
A2
C
1
30pF
D
1
1N914
R
1
*
1k
2N4393
R
3
2k
D
2
V
1
V
O
*
MATCHED
A1, A2: OP27
R
2
*
1k
Figure 5. High Speed Precision Rectifier
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 k
W which helps to reduce the
effects 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 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 k
W 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.
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
8
0.310 (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)
SEATING
PLANE
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 FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
REV. A
OP227
15
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
1 6
C02685010/02(A)
PRINTED IN U.S.A.
Document Outline
- FEATURES
- GENERAL DESCRIPTION
- PIN CONNECTIONS
- SIMPLIFIED SCHEMATIC
- SPECIFICATIONS
- ABSOLUTE MAXIMUM RATINGS
- THERMAL CHARACTERISTICS
- ORDERING GUIDE
- Typical Performance Characteristics
- BASIC CONNECTIONS
- APPLICATIONS INFORMATION
- Noise Measurements
- Instrumentation Amplifier Applications of the OP227
- High Speed Precision Rectifier
- OUTLINE DIMENSIONS
- Revision History
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