Low Drift, 0.2 V/C
High Speed, 17 V/s Slew Rate
63 MHz Gain Bandwidth
Low Input Offset Voltage, 10 V
Excellent CMRR, 126 dB (Common-Voltage @ 11 V)
High Open-Loop Gain, 1.8 Million
Replaces 725, OP-07, SE5534 In Gains > 5
Available in Die Form
GENERAL DESCRIPTION
The OP37 provides the same high performance as the OP27,
but the design is optimized for circuits with gains greater than
five. This design change increases slew rate to 17 V/ms and
gain-bandwidth product to 63 MHz.
The OP37 provides the low offset and drift of the OP07
plus higher speed and lower noise. Offsets down to 25 mV and
a
3.5 nV/ @ 10 Hz), a low 1/f noise corner frequency of
(e
n
2.7 Hz,
and the high gain of 1.8 million, allow accurate
high-gain amplification of low-level signals.
The low input bias current of 10 nA and offset current of 7 nA
are achieved by using a bias-current cancellation circuit.
the military temperature range this typically holds I
to 20 nA and 15 nA respectively.
of 0.6 mV/∞C make the OP37 ideal for preci-
Over
and I
B
OS
Operational Amplifier (A
VCL
> 5)
OP37
The output stage has good load driving capability. A guaranteed
swing of 10 V into 600 W and low output distortion make the
OP37 an excellent choice for professional audio applications.
PSRR and CMRR exceed 120 dB. These characteristics, coupled
with long-term drift of 0.2 mV/month, allow the circuit
to achieve performance levels previously attained only by
discrete designs.
Low-cost, high-volume production of the OP37 is achieved
using on-chip zener-zap trimming. This reliable and stable
trimming scheme has proved its effectiveness over many
production history.
The OP37 brings low-noise instrumentation-type performance
such diverse applications as microphone, tapehead, and RIAA
phono preamplifiers, high-speed signal conditioning for data
acquisition systems, and wide-bandwidth instrumentation.
PIN CONNECTIONS
8-Lead Hermetic DIP
(Z Suffix)
Epoxy Mini-DIP
(P Suffix)
8-Lead SO
(S Suffix)
designer
by
offset
years of
to
SIMPLIFIED SCHEMATIC
V+
C2
Q21
Q23
Q27Q28
R23 R24
R5
Q24
Q22
C1
R9
R12
C3C4
Q20 Q19
Q26
Q46
OUTPUT
Q45
V–
NON-INVERTING
INPUT (+)
INVERTING
INPUT (–)
R1 AND R2 ARE PERMANENTLY
*
ADJUSTED AT WAFER TEST FOR
MINIMUM OFFSET VOLTAGE.
Q6
Q3
R1*
R3
18
ADJ.
V
OS
Q2B
R4
R2*
Q2AQ1A Q1B
Q11 Q12
REV. B
Information furnished by Analog Devices is believed to be accurate and
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.
reliable. However, no responsibility is assumed by Analog Devices for its
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 OP37 features proprietary ESD protection circuitry, permanent damage may occur on
devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions
are recommended to avoid performance degradation or loss of functionality.
Input Voltage
RangeIVR±11±12.3±11± 12.3±11±12.3V
Common Mode
Rejection Ratio
CMRRVCM = ±11 V114126106123100120dB
Power Supply
Rejection Ratio
PSSRVS = ±4 V110110220mV/ V
to ±18 V
Large Signal
Voltage GainA
VO
RL ≥ 2 kW,
= ±10 V10001800100018007001500V/mV
V
O
R
≥ 1 kW,
L
Vo = ±10 V800150080015004001500V/mV
R
≥ 600 W,
L
= ±1 V,
V
O
4
V
S
±4
250700250700200500V/mV
Output Voltage
SwingV
O
Slew RateSRR
Gain Bandwidth
ProductGBWf
RL ≥ 2 kW±12.0 ± 13.8± 12.0 ±13.8±11.5 ± 13.5V
≥ 600 W±10±11.5±10± 11.5±10±11.5V
R
L
L
= 10 kHz
O
= 1 MHz404040MHz
f
O
≥ 2k W
4
111711171117V/ms
4
456345634563MHz
Open-Loop
Output Resistance
R
O
VO = 0, IO = 0707070W
Power
ConsumptionP
d
VO = 09014090140100170mW
Offset Adjustment
RangeRP = 10 kW±4±4±4mV
NOTES
1
Input offset voltage measurements are performed by automated test equipment approximately 0.5 seconds after application of power. A/E grades guaranteed fully
warmed up.
2
Long 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 initial
hour of operation, changes in VOS during the first 30 days are typically 2.5 mV—refer to typical performance curve.
3
Sample tested.
4
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.
REV. B
–3–
Page 4
OP37–SPECIFICATIONS
Electrical Characteristics
( VS = 15 V, –55C < TA < +125C, unless otherwise noted.)
OP37AOP37C
ParameterSymbolConditionsMinTypMaxMinTypMaxUnit
Input Offset
VoltageV
OS
Note 1102530100mV
Average Input
Offset DriftTCV
TCV
OS
OSN
Note 2
Note 30.20.60.41.8mV/∞C
Input Offset
CurrentI
OS
155030135nA
Input Bias
CurrentI
B
±20± 60±35±150nA
Input Voltage
RangeIVR±10.3± 11.5±10.2± 11.5V
Common Mode
Rejection RatioCMRRV
= ±10 V10812294116dB
CM
Power Supply
Rejection RatioPSRRV
= ±4.5 V to
S
±18 V216451mV/ V
Large-Signal
Voltage GainA
VO
RL ≥ 2 kW,
V
= ±10 V6001200300800V/mV
O
Output Voltage
SwingV
O
RL ≥ 2 kW±11.5±13.5± 10.5±13.0V
(VS = 15 V, –25C < TA < +85C for OP37EZ/FZ, 0C < TA < 70C for OP37EP/FP, and –40C < T
Electrical Characteristics
< +85C for OP37GP/GS/GZ, unless otherwise noted.)
±14±60±18±95± 25±150nA
Input Voltage
RangeIVR±10.5 ± 11.8±10.5 ±11.8±10.5 ±11.8V
Common Mode
Rejection RatioCMRRV
= ±10 V10812210011994116dB
CM
Power Supply
Rejection RatioPSRRV
= ±4.5 V to
S
±18 V215216432mV/ V
Large-Signal
Voltage GainA
VO
RL ≥ 2 kW,
= ±10 V750150070013004501000V/mV
VO
Output Voltage
SwingV
NOTES
1
Input offset voltage measurements are performed by automated test equipment approximately 0.5 seconds after application of power. A/E grades guaranteed fully
warmed up.
2
The TC
3
Guaranteed by design.
performance is within the specifications unnulled or when nulled withRP = 8 kW to 20 kW. TC
VOS
O
RL ≥ 2 kW±11.7 ± 13.6±11.4 ±13.5±11±13.3V
is 100% tested for A/E grades, sample tested for F/G grades.
VOS
A
–4–
REV. B
Page 5
OP37
BINDING DIAGRAM
1. NULL
8
7
2. (–) INPUT
3. (+) INPUT
4. V–
6. OUTPUT
7. V+
8. NULL
1
1990
1427U
2
3
4
6
(VS = 15 V, TA = 25C for OP37N, OP37G, and OP37GR devices; TA = 125C for OP37NT and OP37GT devices,
±60± 40± 95±55± 80nA MAX
Input Voltage
RangeIVR±10.3±11± 10.3± 11± 11V MIN
Common Mode
Rejection RatioCMRRV
= ±11 V108114100106100 dB MIN
CM
Power Supply
Rejection RatioPSRRT
= 25∞C,
A
V
= ±4 V to
S
±18 V1010101020mV/V MAX
= 125∞C,
T
A
V
= ±4.5 V to
S
±18 V1620mV/V MAX
Large-Signal
Voltage GainA
VO
RL ≥ 2 kW,
= ±10 V60010005001000700V/mV MIN
V
O
R
≥ 1 kW,
L
V
= ±10 V800800V/mV MIN
O
Output Voltage
SwingV
O
RL ≥ 2 kW±11.5±12± 11±12±11.5V MIN
R
≥ 600 kW±10±10±10V MIN
L
Power
ConsumptionP
NOTES
For 25∞C characterlstics of OP37NT and OP37GT devices, see OP 37N and OP37G characteristics, respectively.
Electrical tests are performed at wafer probe to the limits shown. Due to variations in assembly methods and normal yield loss, yield after packaging is not guaranteed
for standard product dice. Consult factory to negotiate specifications based on dice lot qualification through sample lot assembly and testing.
8080130130180pA/∞C
Average Input
Bias Current
DriftTCI
B
100100160160200pA/∞C
Input Noise
Voltage Densitye
n
fO = 10 Hz3.53.53.53.53.8nV/÷Hz
= 30 Hz3.13.13.13.13.3nV/÷Hz
f
O
f
= 1000 Hz3.03.03.03.03.2nV/÷Hz
O
Input Noise
Current Density i
n
fO = 10 Hz1.71.71.71.71.7pA/÷ Hz
= 30 Hz1.01.01.01.01.0pA/÷ Hz
f
O
f
= 1000 Hz0.40.40.40.40.4pA/÷ Hz
O
Input Noise
Voltagee
n p-p
0.1 Hz to
10 Hz0.080.080.080.080.09mV p-p
Slew RateSRR
≥ 2k W1717171717V/ms
L
Gain Bandwidth
ProductGBWfO = 10 kHz6363636363MHz
–6–
REV. B
Page 7
Typical Performance Characteristics–
OP37
100
90
80
70
60
GAIN – dB
50
TEST TIME OF 10sec MUST BE USED
TO LIMIT LOW FREQUENCY
40
(<0.1Hz) GAIN.
30
0.01
0.1110100
FREQUENCY – Hz
TPC 1. Noise-Tester Frequency
Response (0.1 Hz to 10 Hz)
10
TA = 25C
= 15V
V
S
1
0.1
RMS VOLTAGE NOISE – V
0.01
1001k10k
BANDWIDTH – Hz
100k
TPC 4. Input Wideband Voltage Noise
vs. Bandwidth (0.1 Hz to Frequency
Indicated)
10
9
8
7
6
5
4
3
I/F CORNER = 2.7Hz
2
VOLTA GE NOISE – nV/ Hz
1
1
101001k
FREQUENCY – Hz
TA = 25C
= 15V
V
S
TPC 2. Voltage Noise Density vs.
Frequency
100
TA = 25C
= 15V
V
S
10
AT 10Hz
TOTAL NOISE – nV/ Hz
AT 1kHz
1
RESISTOR NOISE ONLY
SOURCE RESISTANCE –
R
R1
R2
S
– 2R1
10k1001k
TPC 5. Total Noise vs. Source Resistance
100
741
10
I/F CORNER =
2.7Hz
VOLTA GE NOISE – nV/ Hz
INSTRUMENTATION
1
1
I/F CORNER
LOW NOISE
OP37
I/F CORNER
RANGE TO DC
101001k
FREQUENCY – Hz
AUDIO OP AMP
AUDIO RANGE
TO 20kHz
TPC 3. A Comparison of Op Amp
Voltage Noise Spectra
5
4
3
2
VOLTA GE NOISE – nV/ Hz
1
–50 –250255075100 125
AT 10Hz
AT 1kHz
TEMPERATURE – C
VS = 15V
TPC 6. Voltage Noise Density vs.
Temperature
5
T
= 25C
A
4
3
2
VOLTA GE NOISE – nV/ Hz
1
01040
TOTA L SUPPLY VOLTAGE (V+ – V–) – Volts
AT 10Hz
AT 1kHz
2030
TPC 7. Voltage Noise Density vs.
Supply Voltage
REV. B
10.0
1.0
CURRENT NOISE – pA/ Hz
0.1
I/F CORNER = 140Hz
1010k
1001k
FREQUENCY – Hz
TPC 8. Current Noise Density vs.
Frequency
–7–
5.0
4.0
TA = +125C
3.0
TA = –55C
2.0
SUPPLY CURRENT – mA
1.0
TA = +25C
5
15253545
TOTA L SUPPLY VOLTAGE – Volts
TPC 9. Supply Current vs. Supply
Voltage
Page 8
OP37
60
50
40
30
20
10
0
–10
–20
–30
OFFSET VOLTAGE – V
–40
TRIMMING WITH
10k POT DOES
–50
NOT CHANGE
–60
TCV
OS
–70
–50 –25 0 25 50 75 100 125 150 175
–75
TEMPERATURE – C
OP37C
OP37B
OP37A
OP37B
OP37A
OP37A
OP37B
OP37C
TPC 10. Offset Voltage Drift of Eight
Representative Units vs. Temperature
30
25
TA =
25C
20
15
10
OPEN-LOOP GAIN – dB
5
0
–20
= 70C
T
A
DEVICE IMMERSED
IN 70C OIL BATH
02040
TIME – Seconds
THERMAL SHOCK
RESPONSE BAND
VS = +15V
6080
100
6
4
2
0
–2
–4
–6
6
4
2
0
–2
CHANGE IN OFFSET VOLTAGE – V
–4
–6
0
1234567
TIME – MONTHS
TPC 11. Long-Term Offset Voltage
Drift of Six Representative Units
50
40
30
20
INPUT BIAS CURRENT – nA
10
0
OP37C
OP37B
–50
–25 025 50 75 100 125 150
TEMPERATURE – C
VS = +15V
OP37A
TA = 25C
= 15V
V
S
10
OP37C/G
OP37F
5
CHANGE IN INPUT OFFSET VOLTAGE – V
1
014
TIME AFTER POWER ON – MINUTES
23
OP37A/E
5
TPC 12. Warm Up Offset Voltage Drift
50
40
30
20
OP37C
10
OP37B
INPUT OFFSET CURRENT – nA
0
–75
–50 –25 025 50 75 100 125
OP37A
TEMPERATURE – C
VS = 15V
TPC 13. Offset Voltage Change Due
to Thermal Shock
140
120
100
80
60
40
20
OPEN-LOOP VOLTAGE GAIN – dB
0
10
1
2103104105106107108
10
FREQUENCY – Hz
TA = 25C
= 15V
V
S
2k
R
L
TPC 16. Open-Loop Gain vs. Frequency
TPC 14. Input Bias Current vs. Temperature
80
75
70
65
60
PHASE MARGIN – DEG
55
30
25
20
15
SLEW RATE – V/s
10
–50
–250255075100 125
M
GBW
SLEW
TEMPERATURE – C
VS = 15V
90
85
80
75
70
65
60
55
50
GAIN-BANDWIDTH PRODUCT – MHz
45
40
F = 10kHz
TPC 17. Slew Rate, Gain Bandwidth
Product, Phase Margin vs. Temperature
TPC 15. Input Offset Current vs.
Temperature
60
50
40
30
20
GAIN – dB
10
0
–10
100k1M10M100M
MARGIN
FREQUENCY – Hz
PHASE
= 71
TA = 25C
= 15V
V
S
–80
–100
–120
–140
–160
AV = 5
–180
–200
–220
TPC 18. Gain, Phase Shift vs. Frequency
PHASE SHIFT – Degrees
–8–
REV. B
Page 9
OP37
20mV
200ns
+50mV
0V
–50mV
TA = 25C
V
S
= 15V
A
V
= +5
(1k, 250)
2.5
TA = 25C
2.0
RL = 2k
1.5
RL = 1k
1.0
OPEN-LOOP GAIN – V/V
0.5
0
01040
TOTA L SUPPLY VOLTAGE – Volts
2030
50
TPC 19. Open-Loop Voltage Gain vs.
Supply Voltage
80
60
40
PEAK-TO-PEAK AMPLITUDE – Volts
28
24
20
16
12
8
4
0
4
10
5
10
FREQUENCY – Hz
6
10
TA = 25C
= 15V
V
S
7
10
TPC 20. Maximum Output Swing vs.
Frequency
5V
+10V
0V
1µs
18
16
POSITIVE
MAXIMUM OUTPUT – Volts
14
12
10
8
6
4
2
0
–2
100
SWING
NEGATIVE
SWING
LOAD RESISTANCE –
1k10k
TA = 25C
= 15V
V
S
TPC 21. Maximum Output Voltage
vs. Load Resistance
PERCENT OVERSHOOT
20
0
05002000
VS = 15V
= 20mV
V
IN
= +5 (1k, 250)
A
V
10001500
CAPACITIVE LOAD – pF
TPC 22. Small-Signal Overshoot vs.
Capacitive Load
60
TA = 25C
= 15V
V
S
50
40
30
20
SHORT-CIRCUIT CURRENT – mA
10
014
TIME FROM OUTPUT SHORTED TO
I
(+)
SC
I
(–)
SC
235
GROUND – MINUTES
TPC 25. Short-Circuit Current vs. Time
–10V
TA = 25C
= 15V
V
S
= +5 (1k, 250)
A
V
TPC 23. Large-Signal Transient
Response
140
120
100
80
CMRR – dB
60
40
1k
10k100k1M10M
FREQUENCY – Hz
VS = 15V
= 25C
T
A
= 10V
V
CM
TPC 26. CMRR vs. Frequency
TPC 24. Small-Signal Transient
Response
16
12
8
4
0
–4
–8
COMMON-MODE RANGE – Volts
–12
–16
05
TA = +25C
SUPPLY VOLTAGE – Volts
TA = –55C
TA = +125C
TA = –55C
TA = +25C
= +125C
T
A
101520
TPC 27. Common-Mode Input Range
vs. Supply Voltage
REV. B
–9–
Page 10
OP37
0.1F
100k
OP37
10
D.U.T.
VOLTA G E
GAIN
= 50,000
4.7F
2k
OP12
100k
0.1F
24.3k
4.3k
2.2F
22F
SCOPE 1
= 1M
R
IN
110k
TPC 28. Noise Test Circuit (0.1 Hz to
10 Hz)
160
140
120
100
80
60
40
20
POWER SUPPLY REJECTION RATIO – dB
0
1
NEGATIVE
SWING
POSITIVE
SWING
10 100 1k 10k 100k 1M 10M 100M
FREQUENCY – Hz
TA = 25C
TPC 31. PSRR vs. Frequency
1 SEC/DIV
TPC 29. Low-Frequency Noise
19
TA = 25C
= 15V
V
S
= 5
A
V
18
= 20V p-p
V
O
V
17
SLEW RATE – V/
16
15
1001k10k100k
LOAD RESISTANCE –
TPC 32. Slew Rate vs. Load
2.4
TA = 25C
2.2
= 15V
V
S
2.0
1.8
1.6
1.4
1.2
1.0
0.8
OPEN-LOOP VOLTAGE GAIN – V/V
0.6
0.4
1001k10k100k
LOAD RESISTANCE –
TPC 30. Open-Loop Voltage Gain vs.
Load Resistance
20
TA = 25C
A
VCL
15
10
5
VOLTA GE NOISE – V/s
0
3
RISE
= 5
FA LL
6912 15 1821
SUPPLY VOLTAGE – Volts
TPC 33. Slew Rate vs. Supply Voltage
–10–
REV. B
Page 11
OP37
R7
100k
C1
100pF
R1
5k
0.1%
R3
390
R2
100
R4
5k
0.1%
INPUT (+)
INPUT (–)
R5
500
0.1%
R6
500
0.1%
R8
20k
0.1%
R9
19.8k
R10
500
V
OUT
NOTES:
TRIM R2 FOR A
VCL
= 1000
TRIM R10 FOR dc CMRR
TRIM R7 FOR MINIMUM V
OUT
AT VCM = 20V p-p, 10kHz
+
–
OP37
+
–
OP37
+
–
OP37
APPLICATIONS INFORMATION
OP37 Series units may be inserted directly into 725 and OP07
sockets with or without removal of external compensation or
nulling components. Additionally, the OP37 may be fitted to
unnulled 741type sockets; however, if
circuitry is in use, it should be modified
conventional 741 nulling
or removed to ensure
Noise Measurements
To measure the 80 nV peak-to-peak noise specification of the
OP37 in the 0.1 Hz to 10 Hz range, the following precautions
must be observed:
∑ The device has to be warmed-up for at least five minutes. As
correct OP37 operation. OP37 offset voltage may be nulled to
zero (or other desired setting) using a potentiometer (see figure 1).
The OP37 provides stable operation with load capacitances of
up to 1000 pF and ±10 V swings; larger capacitances should be
decoupled with a 50 W resistor inside the feedback loop. Closed
∑ For similar reasons, the device has to be well-shielded from
loop gain must be at least five. For closed loop gain between five
to ten, the designer should consider both the OP27 and the OP37.
∑ Sudden motion in the vicinity of the device can also
For gains above ten, the OP37 has a clear advantage over the
unity stable OP27.
∑ The test time to measure 0.1 Hz to l0 Hz noise should not
Thermoelectric voltages generated by dissimilar metals at the input
terminal contacts can degrade the drift performance. Best
operation will be obtained when both input contacts are maintained at the same temperature.
∑ A noise-voltage-density test is recommended when measuring
10k R
P
V+
–
OP37
+
OUTPUT
Optimizing Linearity
Best linearity will be obtained by designing for the minimum
V–
Figure 1. Offset Nulling Circuit
Offset Voltage Adjustment
The input offset voltage of the OP37 is trimmed at wafer level.
However, if further adjustment of V
potentiometer may be used. TCV
is necessary, a 10 kW trim
OS
is not degraded (see offset
OS
nulling circuit). Other potentiometer values from 1 kW to 1 MW
can be used with a slight degradation (0.1 mV/∞C to 0.2 mV/∞C) of
. Trimming to a value other than zero creates a drift of
TCV
OS
approximately (VOS/300) mV/∞C. For example, the change in TCV
will be 0.33 mV/∞C if VOS is adjusted to 100 mV. The offset voltage
adjustment range with a 10 kW potentiometer is ±4 mV. If smaller
adjustment range is required, the nulling sensitivity can be reduced
by using a smaller pot in conjunction with fixed resistors. For
output current required for the application. High gain and
excellent linearity can be achieved by operating the op amp with
a peak output current of less than ±10 mA.
Instrumentation Amplifier
A three-op-amp instrumentation amplifier, shown in figure 4,
provides high gain and
circuit below is 4.9 nV/÷Hz.
25 and the gain of the second
The amplifier bandwidth of 800 kHz is extraordinarily good for
a precision instrumentation amplifier. Set to a gain of 1000, this
OS
yields a
bandwidth
R7 provides quadrature
amplifier’s ac common-
example, the network shown in figure 2 will have a ±280 mV adjustment range.
shown in the warm-up drift curve, the offset voltage typically
changes 4 mV due to increasing chip temperature after power up.
In the ten second measurement interval, these temperatureinduced effects can exceed tens of nanovolts.
air currents. Shielding minimizes thermocouple effects.
“feedthrough” to increase the observed noise.
exceed 10 seconds. As shown in the noise-tester frequency
response curve, the 0.1 Hz corner is defined by only one zero.
The test time of ten seconds acts as an additional zero to eliminate
noise contributions from the frequency band below 0.1 Hz.
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.
wide bandwidth. The input noise of the
The gain of the input stage is set at
stage is 40; overall gain is 1000.
gain bandwidth product of 800 MHz. The full-power
for a 20 V p-p output is 250 kHz. Potentiometer
trimming to optimize the instrumentation
mode rejection.
Figure 2. Offset Voltage Adjustment
REV. B
1
V+
Figure 3. Burn-In Circuit
+18V
OP37
–18V
84.7k4.7k1k POT
Figure 4a. Instrumentation Amplifier
–11–
Page 12
OP37
140
120
100
80
CMRR – dB
60
40
10
1k UNBALANCED
1001k10k100k1M
RS = 0
RS = 100,
FREQUENCY – Hz
Figure 4b. CMRR vs. Frequency
Comments on Noise
The OP37 is a very low-noise monolithic op amp. The outstanding
input voltage noise characteristics of the OP37 are achieved
mainly by operating the input stage at a high quiescent current.
The input bias and offset currents, which would normally increase,
are held to reasonable values by the input bias current cancellation
circuit. The OP37A/E has IB and IOS of only ±40 nA and 35 nA
respectively at 25∞C. This is particularly important when the input
has a high source resistance. In addition, many audio amplifier
designers prefer to use direct coupling. The high I
TA = 25C
= 15V
V
S
= 20V p-p
V
CM
AC TRIM @ 10kHz
= 0
R
S
RS = 1k
BALANCED
. TCVOS of
B
Figure 6. Peak-to-Peak Noise (0.1 Hz to 10 Hz) vs. Source
Resistance (Includes Resistor Noise)
At RS < 1 kW key the OP37’s low voltage noise is maintained.
With R
resistor noise rather than current or voltage noise. It is only
beyond Rs of 20 kW that current noise starts to dominate. The
argument can be made that current noise is not important for
applications with low to-moderate source resistances.
crossover
in the 15 kW to 40 kW region.
previous designs have made direct coupling difficult, if not
impossible, to use.
Voltage noise is inversely proportional to the square-root of bias
current, but current noise is proportional to the square-root of
bias current. The OP37’s noise advantage disappears when high
source-resistors are used. Figures 5, 6, and 7 compare OP-37
observed total noise with the noise performance of other devices
in different circuit applications.
Total noise = [( Voltage noise)2 + (current noise ⫻ RS)2 +
(resistor noise_]1/2
Figure 5 shows noise versus source resistance at 1000 Hz. The
same plot applies to wideband noise. To use this plot, just multiply
the picture is less favorable; resistor noise is negligible, current
noise becomes important because it is inversely proportional to
the square-root of frequency. The crossover with the OP07
occurs in the 3 kW to 5 kW range depending on whether balanced or unbalanced source resistors are used (at 3 kW the I
I
OS
Therefore, for low-frequency applications, the OP07 is better
than the OP27/37 when Rs > 3 kW. The only exception is when
gain error is important. Figure 7 illustrates the 10 Hz noise. As
expected, the results are between the previous two figures.
For reference, typical source resistances of some signal sources
are listed in Table I.
the vertical scale by the square-root of the bandwidth.
1k
OP08/108
500
5534
OP07
100
OP27/37
p-p NOISE – nV
50
REGISTER
10
5010k
< 1 kW, total noise increases, but is dominated by the
S
NOISE ONLY
10050k
RS – SOURCE RESISTANCE –
1
2
1 RS UNMATCHED
e.g. RS = RS1 = 10k, RS2 = 0
MATCHED
2 R
S
= 10k, RS1 = RS2 = 5k
e.g. R
S
500 1k5k
R
S1
R
S2
between the OP37 and OP07 and OP08 noise occurs
100
50
OP08/108
OP07
10
5534
5
TOTAL NOISE – nV/ Hz
OP27/37
REGISTER
1
5010k
NOISE ONLY
10050k
500 1k5k
RS – SOURCE RESISTANCE –
1 RS UNMATCHED
= RS1 = 10k, RS2 = 0
e.g. R
S
2 R
MATCHED
S
= 10k, RS1 = RS2 = 5k
e.g. R
S
1
2
R
S1
R
S2
error also can be three times the VOS spec.).
The
.
B
–12–
REV. B
Page 13
OP37
Table I.
Source
DeviceImpedanceComments
Straln Gauge<500 WTypically used in low-
frequency
by only 0.7 dB. With a 1 kW source, the circuit noise measures
63 dB below a 1 mV reference level, unweighted, in a 20 kHz
noise bandwidth.
Gain (G) of the circuit at 1 kHz can be calculated by the expression:
applications.
Magnetic<1500 W
Tapehead
Magnetic<1500 WSimilar need for low I
Phonograph
Cartridges
Linear Variable <1500 WUsed in rugged servo-feedback
Differential
Transformeris 400 Hz to 5 kHz.
Audio Applications
The following applications information has been abstracted from
a PMI article in the 12/20/80 issue of Electronic Design magazine
and updated.
Low IB very important to reduce
set-magnetization problems when
direct coupling is used. OP37
I
can be neglected.
B
in direct
B
coupled applications. OP37 will not
introduce any self-magnetization
problem.
applications. Bandwidth of interest
C4 (2)
220F
++
R5
100k
For the values shown, the gain is just under 100 (or 40 dB).
Lower gains can be accommodated by increasing R3, but gains
higher than 40 dB will show more equalization errors because of
the 8 MHz gain bandwidth of the OP27.
This circuit is capable of very low distortion over its entire range,
generally below 0.01% at levels up to 7 V rms. At 3 V output
levels,
at frequencies up to 20 kHz.
Capacitor C3 and resistor R4 form a simple –6 dB per octave
rumble filter, with a corner at 22 Hz. As an option, the switch
selected shunt capacitor C4, a nonpolarized electrolytic, bypasses
the low-frequency rolloff. Placing the rumble filter’s high-pass
action after the preamp has the desirable result of discriminating
against the RIAA amplified low frequency noise components
and pickup-produced low-frequency disturbances.
A preamplifier for NAB tape playback is similar to an RIAA
MOVING MAGNET
CARTRIDGE INPUT
Ra
47.5k
Ca
150pF
A1
OP27
R1
97.6k
R3
100
LF ROLLOFF
C3
0.47F
R2
7.87k
G = 1kHz GAIN
= 0.101 ( )
= 98.677 (39.9dB) AS SHOWN
C1
0.03F
C2
0.01F
1 +
OUT IN
R4
75k
R1
R3
OUTPUT
phono preamp, though more gain is typically demanded, along
with equalization requiring a heavy low-frequency boost. The
circuit In Figure 8 can be readily modified for tape use, as
shown by Figure 9.
Figure 8. Phono Pre-Amplifier Circuit
Figure 8 is an example of a phono pre-amplifier circuit using the
OP27 for A1; R1-R2-C1-C2 form a very accurate RIAA net-
with standard component values. The popular method to
work
accomplish
RIAA phono equalization is to employ frequencydependent feedback around a high-quality gain block. Properly
chosen, an RC network can provide the three necessary time
constants of
3180 ms, 318 ms, and 75 ms.
1
For initial equalization accuracy and stability, precision metalfilm resistors and film capacitors of polystyrene or polypropylene
are recommended since they have low voltage coefficients,
dissipation factors, and dielectric absorption.4 (High-K ceramic
capacitors should be avoided here, though low-K ceramics—
such as NPO types, which have excellent dissipation factors,
and somewhat lower dielectric absorption—can be considered
for small values or where space is at a premium.)
The OP37 brings a 3.2 nV/÷Hzvoltage noise and 0.45 pA/÷Hz
current noise to this circuit. To minimize noise from other sources,
R3 is set to a value of 100 W, which generates a voltage noise of
While the tape-equalization requirement has a flat high frequency
gain above 3 kHz (t2 = 50 ms), the amplifier need not be stabilized
for unity gain. The decompensated OP37 provides a greater
bandwidth and slew rate. For many applications, the idealized
time constants shown may require trimming of Ra and R2 to
optimize frequency response for non ideal tape head performance and other factors.
The network values of the configuration yield a 50 dB gain at 1 kHz,
and the dc gain is greater than 70 dB. Thus, the worst-case
put
can
The tape head can be coupled directly to the amplifier input,
since the worst-case bias current of 85 nA with a 400 mH, 100 min.
head (such as the PRB2H7K) will not be troublesome.
One potential tape-head problem is presented by amplifier biascurrent transients which can magnetize a head. The OP27 and
1.3 nV/÷Hz. The noise increases the 3.2 nV/÷Hzof the amplifier
G
=+
Ê
0 101 1
.
Á
Ë
ˆ
R
1
˜
R
¯
3
it will produce less than 0.03% total harmonic distortion
TAPE
HEAD
–
OP37
Ca
Ra
+
R2
5k
100k
R1
33k
0.01F
0.47F
T1 = 3180s
T2 = 50s
15k
Figure 9. Tape-Head Preamplifier
5
out-
offset is just over 500 mV. A single 0.47 mF output capacitor
block this level without affecting the dynamic range.
REV. B
–13–
Page 14
OP37
OP37 are free of bias-current transients upon power up or power
down. However, it is always advantageous to control the speed
of power supply rise and fall, to eliminate transients.
In addition, the dc resistance of the head should be carefully
controlled, and preferably below 1 kW. For this configuration,
the bias-current induced offset voltage can be greater than the
Gain may be trimmed to other levels, if desired, by adjusting R2
or R1. Because of the low offset voltage of the OP27, the output
offset of this circuit will be very low, 1.7 mV or less, for a 40 dB
gain. The typical output blocking capacitor can be eliminated in
such cases, but is desirable for higher gains to eliminate switching
transients.
170 pV maximum offset if the head resistance is not sufficiently
controlled.
A simple, but effective, fixed-gain transformerless microphone
preamp (Figure 10) amplifies differential signals from low impedance microphones by 50 dB, and has an input impedance of 2 kW.
Because of the high working gain of the circuit, an OP37 helps
to preserve bandwidth, which will be 110 kHz. As the OP37 is a
decompensated device (minimum stable gain of 5), a dummy
resistor, R
, may be necessary, if the microphone is to be
P
unplugged. Otherwise the 100% feedback from the open input
may cause the amplifier to oscillate.
C1
5F
R6
100
R7
10k
OUTPUT
Capacitor C2 and resistor R2 form a 2 ms time constant in this
circuit, as recommended for optimum transient response by
the
unity-gain
stant is not necessary, C2 can be deleted, allowing the faster
OP37 to be employed.
LOW IMPEDANCE
MICROPHONE INPUT
(Z = 50 TO 200)
R3
R4
=
R1
R2
R1
1k
R2
1k
Rp
30k
R3
316k
–
OP37
+
R4
316k
Some comment on noise is appropriate to understand the
Figure 10. Fixed Gain Transformerless Microphone
Preamp
Common-mode input-noise rejection will depend upon the match
of the bridge-resistor ratios. Either close-tolerance (0.1%) types
should be used, or R4 should be trimmed for best CMRR. All
resistors should be metal-film types for best stability and low noise.
Noise performance of this circuit is limited more by the input
resistors R1 and R2 than by the op amp, as R1 and R2 each
generate a 4 nV/÷Hznoise, while the op amp generates a 3.2 nV/
÷Hz
noise. The rms sum of these predominant noise sources will
be about 6 nV/÷Hz, equivalent to 0.9 mV in a 20 kHz noise band-
or nearly 61 dB below a l mV input signal. Measurements
width,
confirm
this predicted performance.
For applications demanding appreciably lower noise, a high quality
capability of this circuit. A 150 W resistor and R1 and R2 gain
resistors connected to a noiseless amplifier will generate 220 nV
of noise in a 20 kHz bandwidth, or 73 dB below a 1 mV reference
level. Any practical amplifier can only approach this noise level;
it can never exceed it. With the OP27 and T1 specified,
additional noise degradation will be close to 3.6 dB (or –69.5
referenced to 1 mV).
2. Jung, W.G., IC Op Amp Cookbook, 2nd Ed., H.W. Sams and Company,
3. Jung, W.G., Audio /C Op Amp Applications, 2nd Ed., H.W. Sams and Com-
4. Jung, W.G., and Marsh, R.M., “Picking Capacitors.” Audio, February &
5. Otala, M., “Feedback-Generated Phase Nonlinearity in Audio Amplifiers,”
microphone-transformer-coupled preamp (Figure 11) incorporates
the internally compensated. T1 is a JE-115K-E 150 W/15 kW
6. Stout, D.F., and Kaufman, M., Handbook of Operational Amplifier Circuit
transformer which provides an optimum source resistance for
the OP27 device. The circuit has an overall gain of 40 dB, the
product of the transformer’s voltage setup and the op amp’s
voltage gain.
C2
1800pF
150
SOURCE
T1*
R1
121
R3
100
R2
1100
A1
OP27
*
T1 – JENSEN JE – 115K – E
JENSEN TRANSFORMERS
10735 BURBANK BLVD.
N. HOLLYWOOD, CA 91601
OUTPUT
Figure 11. Microphone Transformer Coupled Preamp
transformer manufacturer. With C2 in use, A1 must have
stability. For situations where the 2 ms time con-
the
p. 458-4S1.
1980.
pany, 1978.
March, 1980.
London AES Convention, March 1980, preprint 197B.
Design, New York, McGraw Hill, 1976.
–14–
REV. B
Page 15
OUTLINE DIMENSIONS
8-Lead Ceramic DIP – Glass Hermetic Seal [CERDIP]
(Q-8)
Dimensions shown in inches and (millimeters)
OP37
0.005 (0.13)
MIN
85
PIN 1
0.200 (5.08)
0.200 (5.08)
0.125 (3.18)
0.023 (0.58)
0.014 (0.36)
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
1
0.100 (2.54) BSC
0.405 (10.29) MAX
MAX
8-Lead Plastic Dual-in-Line Package [PDIP]
(N-8)
Dimensions shown in inches and (millimeters)
0.375 (9.53)
0.365 (9.27)
0.355 (9.02)
8
1
0.100 (2.54)
0.180
(4.57)
MAX
0.150 (3.81)
0.130 (3.30)
0.110 (2.79)
0.022 (0.56)
0.018 (0.46)
0.014 (0.36)
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
COMPLIANT TO JEDEC STANDARDS MO-095AA
BSC
5
4
0.295 (7.49)
0.285 (7.24)
0.275 (6.98)
0.015
(0.38)
MIN
SEATING
PLANE
0.060 (1.52)
0.050 (1.27)
0.045 (1.14)
0.325 (8.26)
0.310 (7.87)
0.300 (7.62)
0.150 (3.81)
0.135 (3.43)
0.120 (3.05)
0.015 (0.38)
0.010 (0.25)
0.008 (0.20)
0.055 (1.40)
MAX
4
0.070 (1.78)
0.030 (0.76)
0.310 (7.87)
0.220 (5.59)
0.060 (1.52)
0.015 (0.38)
0.150 (3.81)
MIN
SEATING
PLANE
0.320 (8.13)
0.290 (7.37)
15
0
0.015 (0.38)
0.008 (0.20)
8-Lead Standard Small Outline Package [SOIC]
Narrow Body
(RN-8)
Dimensions shown in millimeters and (inches)
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
0.25 (0.0098)
0.10 (0.0040)
COPLANARITY
0.10
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN