Low Noise: 80 nV p-p (0.1 Hz to 10 Hz), 3 nV/
Low Drift: 0.2 V/C
High Speed: 2.8 V/s Slew Rate, 8 MHz Gain
Bandwidth
Low V
Excellent CMRR: 126 dB at V
: 10 V
OS
of ±11 V
CM
High Open-Loop Gain: 1.8 Million
Fits 725, OP07, 5534A Sockets
Available in Die Form
GENERAL DESCRIPTION
The OP27 precision operational amplifier combines the low
offset and drift of the OP07 with both high speed and low noise.
Offsets down to 25 µV and drift of 0.6 µV/°C maximum make
the OP27 ideal for precision instrumentation applications.
Exceptionally low noise, e
= 3.5 nV/√Hz, at 10 Hz, a low 1/f
n
noise corner frequency of 2.7 Hz, and high gain (1.8 million),
allow accurate high-gain amplification of low-level signals. A
gain-bandwidth product of 8 MHz and a 2.8 V/µsec slew rate
provides excellent dynamic accuracy in high-speed, dataacquisition systems.
A low input bias current of ±10 nA is achieved by use of a
bias-current-cancellation circuit. Over the military temperature
range, this circuit typically holds I
and IOS to ±20 nA and 15 nA,
B
respectively.
The output stage has good load driving capability. A guaranteed
swing of ±10 V into 600 Ω and low output distortion make the
OP27 an excellent choice for professional audio applications.
Hz
(Continued on page 7)
Operational Amplifier
OP27
PIN CONNECTIONS
TO-99
(J-Suffix)
BAL
BAL 1
–IN 2
+IN 3
OP27
4V– (CASE)
NC = NO CONNECT
8-Pin Hermetic DIP
(Z-Suffix)
Epoxy Mini-DIP
(P-Suffix)
8-Pin SO
(S-Suffix)
TRIM
OS
–IN
+IN
1
OP27
2
3
4
NC = NO CONNECT
V
V+
OUT
NC
8
V
TRIM
OS
7
V+
6
OUT
5
NCV–
NONINVERTING
INPUT (+)
INVERTING
INPUT (–)
R1 AND R2 ARE PERMANENTLY
*
ADJUSTED AT WAFER TEST FOR
MINIMUM OFFSET VOLTAGE.
Q6
Q3
R1*
R3
18
V
ADJ.
OS
Q2B
R4
R2*
Q2AQ1A Q1B
Q11 Q12
Figure 1. Simplified Schematic
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.
Input offset voltage measurements are performed ~ 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 versus. 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 µV. Refer to typical performance curve.
3
Sample tested.
4
See test circuit and frequency response curve for 0.1 Hz to 10 Hz tester.
5
See test circuit for current noise measurement.
6
Guaranteed by input bias current.
7
Guaranteed by design.
–2–
REV. A
Page 3
OP27
ELECTRICAL CHARACTERISTICS
(@ VS = ±15 V, –55C ≤ TA ≤ 125C, unless otherwise noted.)
OP27A OP27C
ParameterSymbolConditionsMinTypMaxMinTypMaxUnit
INPUT OFFSET
VOLTAGE
AVERAGE INPUT
OFFSET DRIFTTCV
1
V
OS
TCV
OS
OSn
306070300µV
2
3
0.20.641.8µV/°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 RATIO CMRRVCM = ±10 V10812294118dB
POWER SUPPLY
REJECTION RATIO PSRRVS = ±4.5 V to ±18 V216451µV/V
LARGE-SIGNAL
VOLTAGE GAINA
VO
RL ≥ 2 kΩ, VO = ±10 V 6001200300800V/mV
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 TCVOS performance is within the specifications unnulled or when nulled with RP = 8 kΩ to 20 kΩ. TCVOS is 100% tested for A/E grades, sample tested for
C/F/G grades.
3
Guaranteed by design.
O
RL ≥ 2 kΩ±11.5± 13.5±10.5±13.0V
REV. A
–3–
Page 4
OP27
(@ VS = ±15 V, –25C¯≤ TA ≤ 85C for OP27J, OP27Z, 0C ≤ TA ≤ 70C for OP27EP,
INPUT VOLTAGE
RANGEIVR±10.5±11.8±10.5 ±11.8±10.5 ±11.8V
COMMON-MODE
REJECTION RATIO CMRRVCM = ±10 V11012410212196118dB
POWER SUPPLY
REJECTION RATIO PSRRVS = ±4.5 V215216232µV/V
LARGE-SIGNAL
VOLTAGE GAINA
OUTPUT
VOLTAGE SWINGV
NOTES
1
The TCVOS performance is within the specifications unnulled or when nulled with RP = 8 kΩ to 20 kΩ. TCVOS is 100% tested for A/E grades, sample tested for
C/F/G grades.
2
Guaranteed by design.
OS
TCV
OS
B
VO
O
1
OS
2
OSn
to ±18 V
R
≥ 2 kΩ,
L
VO = ±10 V750150070013004501000V/mV
RL ≥ 2 kΩ±11.7±13.6±11.4 ±13.5± 11.0 ± 13.3V
OP27FP, and –40C ≤ TA ≤ 85C for OP27GP, OP27GS, unless otherwise noted.)
OP27E OP27F OP27G
20504014055220µV
0.20.60.31.30 41.8µV/°C
0.20.60.31.30 41.8µV/°C
1050148520135nA
±14±60±18±95±25± 150nA
–4–
REV. A
Page 5
DICE CHARACTERISTICS
DIE SIZE 0.109 0.055 INCH, 5995 SQ. MILS
(2.77 1.40mm, 3.88 SQ. mm)
1. NULL
2. (–) INPUT
3. (+) INPUT
4. V–
6. OUTPUT
7. V+
8. NULL
OP27
WAFER TEST LIMITS
(@ VS = ±15 V, TA = 25C unless otherwise noted.)
OP27NOP27GOP27GR
ParameterSymbolConditionsLimitLimitLimitUnit
INPUT OFFSET VOLTAGE*V
INPUT OFFSET CURRENTI
OS
OS
3560100µV Max
355075nA Max
INPUT BIAS CURRENTIB±40±55± 80nA Max
INPUT VOLTAGE RANGEIVR±11±11± 11V Min
COMMON-MODE REJECTION
RATIOCMRRV
= IVR114106100dB Min
CM
POWER SUPPLYPSRRVS = ±4 V to ±18 V101020µV/V Max
LARGE-SIGNAL VOLTAGE
GAINA
OUTPUT VOLTAGE SWINGV
POWER CONSUMPTIONP
NOTE
*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.
VO
A
VO
O
V
O
d
RL ≥ 2 kΩ, VO = ±10 V10001000700V/mV Min
RL ≥ 600 Ω, VO = ±10 V800800600V/mV Min
RL ≥ 2 kΩ±12.0± 12.0+11.5V Min
RL2600n±10.0±10.0± 10.0V Min
0.1 Hz to 10 Hz0.080.080.09µV p-p≥ 2 kΩ2.82.82.8V/µs
L
GAIN BANDWIDTH
PRODUCTGBW888MHz
NOTE
*Input offset voltage measurements are performed by automated test equipment approximately 0.5 seconds after application of power.
–6–
REV. A
Page 7
OP27
WARNING!
ESD SENSITIVE DEVICE
(Continued from page 1)
PSRR and CMRR exceed 120 dB. These characteristics, coupled
with long-term drift of 0.2 µV/month, allow the circuit designer
to achieve performance levels previously attained only by discrete designs.
Low-cost, high-volume production of OP27 is achieved by
using an on-chip Zener zap-trimming network. This reliable
and stable offset trimming scheme has proved its effectiveness
over many years of production history.
The OP27 provides excellent performance in low-noise, highaccuracy amplification of low-level signals. Applications include
stable integrators, precision summing amplifiers, precision voltagethreshold detectors, comparators, and professional audio circuits
such as tape-head and microphone preamplifiers.
The OP27 is a direct replacement for 725, OP06, OP07, and
OP45 amplifiers; 741 types may be directly replaced by removing the 741’s nulling potentiometer.
Package Type
3
JA
JC
Unit
TO 99 (J)15018°C/W
8-Lead Hermetic DlP (Z)14816°C/W
8-Lead Plastic DIP (P)10343°C/W
20-Contact LCC (RC)9838°C/W
8-Lead SO (S)15843°C/W
NOTES
1
For supply voltages less than ± 22 V, the absolute maximum input voltage is
equal to the supply voltage.
2
The OP27’s 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
is specified for worst-case mounting conditions, i.e., JA is specified for
JA
device in socket for TO, CERDIP, and P-DIP packages; JA is specified for
device soldered to printed circuit board for SO package.
4
Absolute Maximum Ratings apply to both DICE and packaged parts, unless
otherwise noted.
Burn-in is available on commercial and industrial temperature range parts in CERDIP, plastic
DIP, and TO-can packages.
2
For devices processed in total compliance to MIL-STD-883, add /883 after part number.
Consult factory for 883 data sheet.
3
Not for new design; obsolete April 2002.
4
For availability and burn-in information on SO and PLCC packages, contact your local
sales office.
2
3
3
4
MIL
IND/COM
MIL
XIND
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 OP27 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.
REV. A
–7–
Page 8
OP27
–Typical Performance Characteristics
100
90
80
70
60
GAIN – dB
50
TEST TIME OF 10sec FURTHER
LIMITS LOW FREQUENCY
40
(<0.1Hz) GAIN
30
0.01
TPC 1. 0.1 Hz to 10 Hz
0.1110100
FREQUENCY – Hz
Noise Tester
p-p
Frequency Response
10
TA = 25C
= 15V
V
S
1
0.1
RMS VOLTAGE NOISE – V
0.01
1001k10k
BANDWIDTH – Hz
TPC 4. Input Wideband Voltage
Noise vs. Bandwidth (0.1 Hz to
Frequency Indicated)
100k
10
9
8
7
6
5
4
3
I/F CORNER = 2.7Hz
2
VOLTAGE NOISE – nV/ Hz
1
1
101001k
FREQUENCY – Hz
TA = 25C
= 15V
V
S
TPC 2. Voltage Noise Density vs.
Frequency
100
10
TOTAL NOISE – nV/ Hz
1
TA = 25C
= 15V
V
S
AT 10Hz
AT 1kHz
RESISTOR NOISE ONLY
SOURCE RESISTANCE –
R
R1
R2
S
– 2R1
TPC 5. Total Noise vs. Sourced
Resistance
100
741
10
VOLTAGE NOISE – nV/ Hz
1
1
I/F CORNER =
2.7Hz
INSTRUMENTATION
I/F CORNER
LOW NOISE
OP27
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
VOLTAGE NOISE – nV/ Hz
1
10k1001k
–50 –250255075 100 125
AT 10Hz
AT 1kHz
TEMPERATURE – C
VS = 15V
TPC 6. Voltage Noise Density vs.
Temperature
5
T
= 25C
A
4
3
2
VOLTAGE NOISE – nV/ Hz
1
01040
TOTAL SUPPLY VOLTAGE (V+ – V–) – V
AT 10Hz
AT 1kHz
2030
TPC 7. Voltage Noise Density vs.
Supply Voltage
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
–8–
5.0
4.0
TA = +125C
3.0
TA = –55C
2.0
SUPPLY CURRENT – mA
1.0
TA = +25C
15253545
5
TOTAL SUPPLY VOLTAGE – V
TPC 9. Supply Current vs. Supply
Voltage
REV. A
Page 9
OP27
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
–75
–50 –25 0 25 50 75 100 125 150 175
TEMPERATURE – C
OP27C
OP27A
OP27A
OP27A
OP27C
TPC 10. Offset Voltage Drift of
Five Representative Units vs.
Temperature
OPEN-LOOP GAIN – dB
30
25
TA =
25C
20
15
10
5
0
–20
= 70C
T
A
THERMAL
SHOCK
RESPONSE
BAND
DEVICE IMMERSED
IN 70C OIL BATH
02040
TIME – Sec
VS = 15V
6080
100
TPC 13. Offset Voltage Change Due
to Thermal Shock
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
INPUT BIAS CURRENT – nA
50
40
30
20
10
0
–50
–25 025 50 75 100 125 150
OP27C
OP27A
TEMPERATURE – C
VS = 15V
TPC 14. Input Bias Current vs.
Temperature
TA = 25C
= 15V
V
S
10
OP27 C/G
OP27 F
5
CHANGE IN INPUT OFFSET VOLTAGE – V
1
014
TIME AFTER POWER ON – Min
23
OP27 A/E
TPC 12. Warm-Up Offset Voltage
Drift
50
40
30
20
OP27C
10
INPUT OFFSET CURRENT – nA
0
–75
–50 –25 025 50 75 100 125
OP27A
TEMPERATURE – C
VS = 15V
TPC 15. Input Offset Current vs.
Temperature
5
130
110
90
70
50
VOLTAGE GAIN – dB
30
10
–10
1
10 100 1k 10k 100k 1M 10M 100M
FREQUENCY – Hz
TPC 16. Open-Loop Gain vs.
Frequency
REV. A
70
60
50
PHASE MARGIN – Degrees
4
3
2
SLEW RATE – V/s
–75
M
GBW
SLEW
–50
–25 025 50 75 100 125
TEMPERATURE – C
VS = 15V
10
9
8
7
6
TPC 17. Slew Rate, Gain-Bandwidth
Product, Phase Margin vs.
Temperature
–9–
25
GAIN
PHASE
MARGIN
= 70
FREQUENCY – Hz
GAIN BANDWIDTH PRODUCT – MHz
20
15
10
5
GAIN – dB
0
–5
–10
1M10M100M
TPC 18. Gain, Phase Shift vs.
Frequency
TA = 25C
= 15V
V
S
80
100
120
140
160
180
200
220
PHASE SHIFT – Degrees
Page 10
OP27
2.5
TA = 25C
2.0
RL = 2k
1.5
RL = 1k
1.0
OPEN-LOOP GAIN – V/V
0.5
0
01040
2030
TOTAL SUPPLY VOLTAGE – V
50
TPC 19. Open-Loop Voltage Gain vs.
Supply Voltage
100
% OVERSHOOT
80
60
40
20
V
S
V
IN
A
V
= 15V
= +1
= 100mV
28
24
20
16
12
8
PEAK-TO-PEAK AMPLITUDE – V
4
0
1k10k100k1M
FREQUENCY – Hz
T
= 25C
A
= 15V
V
S
10M
TPC 20. Maximum Output Swing vs.
Frequency
20mV
50mV
0V
500ns
A
VCL
= 15pF
C
L
= 15V
V
S
= 25C
T
A
= +1
–50mV
18
16
POSITIVE
14
12
10
8
6
4
MAXIMUM OUTPUT – V
2
0
–2
100
SWING
NEGATIVE
SWING
LOAD RESISTANCE –
1k10k
TA = 25C
= 15V
V
S
TPC 21. Maximum Output Voltage
vs. Load Resistance
2V
+5V
0V
–5V
2s
A
VCL
= 15V
V
S
= 25C
T
A
= +1
0
05002000
10001500
CAPACITIVE LOAD – pF
2500
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 – Min
TPC 25. Short-Circuit Current vs.
Time
TPC 23. Small-Signal Transient
Response
140
120
100
CMRR – dB
80
60
1k
FREQUENCY – Hz
VS = 15V
T
A
V
CM
10k100k1M100
TPC 26. CMRR vs. Frequency
= 25C
= 10V
TPC 24. Large-Signal Transient
Response
16
12
8
4
0
–4
–8
COMMON-MODE RANGE – V
–12
–16
05
TA = +25C
TA = –55C
TA = +125C
TA = –55C
TA = +25C
TA = +125C
101520
SUPPLY VOLTAGE – V
TPC 27. Common-Mode Input Range
vs. Supply Voltage
–10–
REV. A
Page 11
OP27
0.1F
100k
OP27
10
D.U.T.
VO LTAG E
GAIN
= 50,000
4.7F
2k
OP12
100k
24.3k
0.1F
4.3k
2.2F
22F
SCOPE 1
RIN = 1M
110k
TPC 28. Voltage Noise Test Circuit
(0.1 Hz to 10 Hz)
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 29. Open-Loop Voltage Gain vs.
Load Resistance
POWER SUPPLY REJECTION RATIO – dB
160
140
120
100
80
60
40
20
0
1
10 100 1k 10k 100k 1M 10M 100M
NEGATIVE
SWING
POSITIVE
SWING
FREQUENCY – Hz
TA = 25C
TPC 31. PSRR vs. Frequency
1 SEC/DIV
80
40
0
0.1Hz to 10Hz p-p NOISE
VOLTAGE NOISE – nV
120
–40
–90
–120
TPC 30. Low-Frequency Noise
APPLICATION INFORMATION
OP27 series units may be inserted directly into 725 and OP07
sockets with or without removal of external compensation or
nulling components. Additionally, the OP27 may be fitted to
unnulled 741-type sockets; however, if conventional 741 nulling
circuitry is in use, it should be modified or removed to ensure
correct OP27 operation. OP27 offset voltage may be nulled to
zero (or another desired setting) using a potentiometer (see
Offset Nulling Circuit).
The OP27 provides stable operation with load capacitances of
up to 2000 pF and ±10 V swings; larger capacitances should be
decoupled with a 50 Ω resistor inside the feedback loop. The
OP27 is unity-gain stable.
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.
OFFSET VOLTAGE ADJUSTMENT
The input offset voltage of the OP27 is trimmed at wafer level.
However, if further adjustment of V
potentiometer can be used. TCV
is necessary, a 10 kΩ trim
OS
is not degraded (see Offset
OS
Nulling Circuit). Other potentiometer values from 1 kΩ to 1 MΩ
can be used with a slight degradation (0.1 µV/°C to 0.2 µV/°C)
of TCV
. Trimming to a value other than zero creates a drift of
OS
approximately (V
TCV
will be 0.33 µV/°C if VOS is adjusted to 100 µV. The
OS
/300) µV/°C. For example, the change in
OS
offset voltage adjustment range with a 10 kΩ potentiometer is
±4 mV. If smaller adjustment range is required, the nulling
sensitivity can be reduced by using a smaller pot in conjuction
with fixed resistors. For example, the network below will have a
±280 µV adjustment range.
1
V+
84.7k4.7k1k POT
Figure 2.
NOISE MEASUREMENTS
To measure the 80 nV peak-to-peak noise specification of the
OP27 in the 0.1 Hz to 10 Hz range, the following precautions
must be observed:
1. 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 µV due to increasing chip temperature
after power-up. In the 10-second measurement interval,
these temperature-induced effects can exceed tens-ofnanovolts.
2. For similar reasons, the device has to be well-shielded from
air currents. Shielding minimizes thermocouple effects.
REV. A
–11–
Page 12
OP27
3. Sudden motion in the vicinity of the device can also
“feedthrough” to increase the observed noise.
4. 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. The test time of 10 seconds acts as an additional zero
to eliminate noise contributions from the frequency band
below 0.1 Hz.
5. 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.
UNITY-GAIN BUFFER APPLICATIONS
When Rf ≤ 100 Ω and the input is driven with a fast, large signal
pulse (>1 V), the output waveform will look as shown in the
pulsed operation diagram (Figure 3).
During the fast feedthrough-like portion of the output, the input
protection diodes effectively short the output to the input and a
current, limited only by the output short-circuit protection, will
be drawn by the signal generator. With R
capable of handling the current requirements (I
the amplifier will stay in its active mode and a smooth transition
will occur.
When R
> 2 kΩ, a pole will be created with Rf and the amplifier’s
f
input capacitance (8 pF) that creates additional phase shift and
reduces phase margin. A small capacitor (20 pF to 50 pF) in
parallel with R
will eliminate this problem.
f
R
f
–
OP27
+
Figure 3. Pulsed Operation
COMMENTS ON NOISE
The OP27 is a very low-noise monolithic op amp. The outstanding
input voltage noise characteristics of the OP27 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 OP27A/E has I
and IOS of only ±40 nA and 35 nA at 25°C
B
respectively. 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
of 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 OP27’s noise advantage disappears when high
source-resistors are used. Figures 4, 5, and 6 compare OP27’s
observed total noise with the noise performance of other devices
in different circuit applications.
≥ 500 Ω, the output is
f
≤ 20 mA at 10 V);
L
2.8V/s
, VOS, and TCV
B
OS
12
/
2
+
S
Total Noise
Voltage Noise
()
Current Noise R
=
()
sistor Noise
Re
()
2
+
×
2
Figure 4 shows noise versus source-resistance at 1000 Hz. The
same plot applies to wideband noise. To use this plot, multiply
the vertical scale by the square root of the bandwidth.
100
50
1
OP08/108
OP07
10
5
5534
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 RS MATCHED
= 10k, RS1 = RS2 = 5k
e.g. R
S
R
S1
R
S2
2
Figure 4. Noise vs. Source Resistance (Including Resistor
Noise) at 1000 Hz
At RS <1 kΩ, the OP27’s low voltage noise is maintained. With
R
<1 kΩ, total noise increases, but is dominated by the resis-
S
tor noise rather than current or voltage noise. lt is only beyond
of 20 kΩ that current noise starts to dominate. The argument
R
S
can be made that current noise is not important for applications with low to moderate source resistances. The crossover
between the OP27, OP07, and OP08 noise occurs in the 15 kΩ to
40 kΩ region.
Figure 5 shows the 0.1 Hz to 10 Hz peak-to-peak noise. Here
the picture is less favorable; resistor noise is negligible and current
noise becomes important because it is inversely proportional to
the square root of frequency. The crossover with the OP07
occurs in the 3 kΩ to 5 kΩ range depending on whether balanced or unbalanced source resistors are used (at 3 kΩ the I
B
and IOS error also can be three times the VOS spec.).
1k
OP08/108
500
5534
OP07
100
OP27/37
p-p NOISE – nV
50
REGISTER
10
5010k
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
Figure 5. Peak-to-Peak Noise (0.1 Hz to 10 Hz) as Source
Resistance (Includes Resistor Noise)
–12–
REV. A
Page 13
OP27
Therefore, for low-frequency applications, the OP07 is better
than the OP27/OP37 when R
> 3 kΩ. The only exception is
S
when gain error is important. Figure 6 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.
Table I.
Source
DeviceImpedanceComments
Strain Gauge<500 ΩTypically used in low-
frequency applications.
Magnetic<1500 ΩLow is very important to
Tapeheadreduce self-magnetization
problems when direct coupling
is used. OP27 I
can be
B
neglected.
Magnetic<1500 ΩSimilar need for low I
in
B
Phonographdirect coupled applications.
CartridgesOP27 will not introduce any
self-magnetization problem.
Linear Variable<1500 ΩUsed in rugged servo-feedback
Differentialapplications. Bandwidth of
Transformerinterest is 400 Hz to 5 kHz.
Open-Loop Gain
Frequency atOP07OP27OP37
3 Hz100 dB124 dB125 dB
10 Hz100 dB120 dB125 dB
30 Hz90 dB110 dB124 dB
For further information regarding noise calculations, see “Minimization of Noise
in Op Amp Applications,” Application Note AN-15.
100
50
OP08/108
1
2
Figure 7 is an example of a phono pre-amplifier circuit using the
OP27 for A1; R1-R2-C1-C2 form a very accurate RIAA network with standard component values. The popular method to
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, 318, and 75 µs.
1
For initial equalization accuracy and stability, precision metal
film 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.)
MOVING MAGNET
CARTRIDGE INPUT
Ra
47.5k
Ca
150pF
A1
OP27
C4 (2)
220F
++
LF ROLLOFF
C3
0.47F
R1
97.6k
R2
7.87k
R3
100
G = 1kHz GAIN
C1
0.03F
C2
0.01F
R1
1 +
= 0.101 ( )
= 98.677 (39.9dB) AS SHOWN
R3
OUT IN
R4
75k
R5
100k
OUTPUT
Figure 7.
The OP27 brings a 3.2 nV/√Hz voltage 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 Ω, which generates a voltage
noise of 1.3 nV/√Hz. The noise increases the 3.2 nV/√Hz of the
amplifier by only 0.7 dB. With a 1 kΩ 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:
The following applications information has been abstracted
from a PMI article in the 12/20/80 issue of Electronic Design magazine and updated.
REV. A
–13–
R
G
=+
0 101 1
.
1
R
3
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, it will produce less than 0.03% total harmonic distortion
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 switchselected 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
Page 14
OP27
against the RlAA-amplified low-frequency noise components and
pickup-produced low-frequency disturbances.
A preamplifier for NAB tape playback is similar to an RIAA
phono preamp, though more gain is typically demanded, along
with equalization requiring a heavy low-frequency boost. The
circuit in Figure 7 can be readily modified for tape use, as shown
by Figure 8.
TA P E
HEAD
–
OP27
Ca
Ra
+
R2
5k
100k
R1
33k
0.01F
0.47F
T1 = 3180s
T2 = 50s
15k
Figure 8.
While the tape-equalization requirement has a flat high-frequency
gain above 3 kHz (T
= 50 µs), the amplifier need not be stabilized
2
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 R1 and R2 to
optimize frequency response for nonideal tapehead performance
and other factors.
5
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
output offset is just over 500 mV. A single 0.47 µF output capaci-
tor can block this level without affecting the dynamic range.
The tapehead can be coupled directly to the amplifier input,
since the worst-case bias current of 80 nA with a 400 mH, 100
µ inch head (such as the PRB2H7K) will not be troublesome.
One potential tapehead problem is presented by amplifier biascurrent transients which can magnetize a head. The OP27 and
OP37 are free of bias-current transients upon power-up or powerdown. 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 kS2. For this configuration,
the bias-current-induced offset voltage can be greater than the
100pV maximum offset if the head resistance is not sufficiently
controlled.
A simple, but effective, fixed-gain transformerless microphone
preamp ( Figure 9) amplifies differential signals from low impedance microphones by 50 dB, and has an input impedance of 2 kΩ.
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, Rp, may be necessary, if the microphone is to be
unplugged. Otherwise the 100% feedback from the open input
may cause the amplifier to oscillate.
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/√Hz noise, while the op amp generates a 3.2 nV/√Hz
–14–
noise. The rms sum of these predominant noise sources will be
about 6 nV/√Hz, equivalent to 0.9 µV in a 20 kHz noise band-
width, or nearly 61 dB below a 1 mV input signal. Measurements
confirm this predicted performance.
C1
5F
R6
100
R7
10k
OUTPUT
LOW IMPEDANCE
MICROPHONE INPUT
(Z = 50 TO 200 )
R3
R4
=
R1
R2
R1
1k
R2
1k
Rp
30k
R3
316k
–
OP27/
OP37
+
R4
316k
Figure 9.
For applications demanding appreciably lower noise, a high
quality microphone transformer-coupled preamp (Figure 10)
incorporates the internally compensated OP27. T1 is a JE-115K-E
150 Ω/15 kΩ 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 10.
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.
+18V
OP27
–18V
Figure 11. Burn-In Circuit
Capacitor C2 and resistor R2 form a 2 µs time constant in this
circuit, as recommended for optimum transient response by the
transformer manufacturer. With C2 in use, A1 must have unitygain stability. For situations where the 2 µs time constant is not
necessary, C2 can be deleted, allowing the faster OP37 to be
employed.
REV. A
Page 15
OP27
0.0098 (0.25)
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
8
0
0.0196 (0.50)
0.0099 (0.25)
45
85
41
0.1968 (5.00)
0.1890 (4.80)
0.2440 (6.20)
0.2284 (5.80)
PIN 1
0.1574 (4.00)
0.1497 (3.80)
0.0500 (1.27)
BSC
0.0688 (1.75)
0.0532 (1.35)
SEATING
PLANE
0.0098 (0.25)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
Some comment on noise is appropriate to understand the
capability of this circuit. A 150 Ω 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, the
additional noise degradation will be close to 3.6 dB (or –69.5 referenced to 1 mV).
R
P
INPUT
10k
OP27
V–
V+
OUTPUT
Figure 12. Offset Nulling Circuit
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead PDIP Package (P-Suffix)
(N-8)
References
1. Lipshitz, S.R, “On RIAA Equalization Networks,” JAES,
Vol. 27, June 1979, p. 458–481.
2. Jung, W.G., IC Op Amp Cookbook, 2nd. Ed., H.W. Sams and
Company, 1980.
3. Jung, W.G., Audio IC Op Amp Applications, 2nd. Ed., H.W.
Sams and Company, 1978.
4. Jung, W.G., and Marsh, R.M., “Picking Capacitors,” Audio,
February and March, 1980.
5. Otala, M., “Feedback-Generated Phase Nonlinearity in
Audio Amplifiers,” London AES Convention, March 1980,
preprint 1976.
6. Stout, D.F., and Kautman, M., Handbook of OperationalAmplifier Circuit Design, New York, McGraw-Hill, 1976.