OP27
0.1 F
100k
OPEN-LOOP VOLTAGE GAIN – V/ V
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
100
0.1Hz to 10Hz p-p NOISE
VOLTAGE NOISE – nV
T
A
= 25 C
V
S
= 15V
1 SEC/DIV
120
80
40
0
–40
–90
–120
10
OP27
D.U.T.
VOLTAGE
GAIN
= 50,000
4.7 F
2k
4.3k
OP12
100k
0.1 F 2.2 F
24.3k
SCOPE 1
R
IN
= 1M
110k
22 F
1k
10k
LOAD RESISTANCE –
100k
TPC 28. Voltage Noise Test Circuit
(0.1 Hz to 10 Hz)
TPC 29. Open-Loop Voltage Gain vs.
Load Resistance
TPC 30. Low-Frequency Noise
160
POWER SUPPLY REJECTION RATIO – dB
140
120
100
80
60
40
20
0
POSITIVE
SWING
NEGATIVE
SWING
T
A
= 25 C
1
10
100
1k 10k 100k 1M 10M 100M
FREQUENCY – Hz
TPC 31. PSRR vs. Frequency
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 main-
tained at the same temperature.
OFFSET VOLTAGE ADJUSTMENT
approximately (V
OS
/300)
µV/°C.
For example, the change in
TCV
OS
will be 0.33
µV/°C
if V
OS
is adjusted to 100
µV.
The
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
4.7k
1k
POT
4.7k
8
V+
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-of-
nanovolts.
2. For similar reasons, the device has to be well-shielded from
air currents. Shielding minimizes thermocouple effects.
–11–
The input offset voltage of the OP27 is trimmed at wafer level.
However, if further adjustment of V
OS
is necessary, a 10 kΩ trim
potentiometer can be used. TCV
OS
is not degraded (see Offset
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
OS
. Trimming to a value other than zero creates a drift of
REV. A
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