![](http://datasheet.mmic.net.cn/180000/OP-37AJG_datasheet_11339767/OP-37AJG_18.png)
OP27A, OP27C, OP27E, OP27G
OP37A, OP37C, OP37E, OP37G
LOW-NOISE HIGH-SPEED PRECISION OPERATIONAL-AMPLIFIER
SLOS100C – FEBRUARY 1989 – REVISED SEPTEMBER 2000
18
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
noise testing (continued)
When measuring noise on a large number of units, a noise-voltage density test is recommended. A 10-Hz
noise-voltage density measurement correlates 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.
Figure 35 shows a circuit measuring current noise and the formula for calculating current noise.
+
–
10k
Vno
100
500 k
500 k
[Vno2 – (130 nV)2]1/2
1 M
× 100
In =
Figure 35. Current Noise Test Circuit and Formula
offset voltage adjustment
The input offset voltage and temperature coefficient of the OP27 and OP37 are permanently trimmed to a low
level at wafer testing. However, if further adjustment of VIO is necessary, using a 10-k nulling potentiometer
as shown in Figure 36 does not degrade the temperature coefficient
αVIO. Trimming to a value other than zero
creates an
αVIO of VIO/300 V/°C. For example, if VIO is adjusted to 300 V, the change in αVIO is 1 V/°C.
The adjustment range with a 10-k
potentiometer is approximately ±2.5 mV. If a smaller adjustment range is
needed, the sensitivity and resolution of the nulling can be improved by using a smaller potentiometer in
conjunction with fixed resistors. The example in Figure 37 has an approximate null range of
±200 V.
+
–
–15 V
Output
2
3
7
8
4
1
Input
6
15 V
10 k
–15 V
Output
2
3
7
8
4
1
Input
6
4.7 k
Figure 36. Standard Input Offset
Voltage Adjustment
Figure 37. Input Offset Voltage Adjustment With
Improved Sensitivity
15 V
1 k
4.7 k
offset voltage and drift
Unless proper care is exercised, thermoelectric effects caused by temperature gradients across dissimilar
metals at the contacts to the input terminals can exceed the inherent temperature coefficient
∝VIO of the
amplifier. Air currents should be minimized, package leads should be short, and the two input leads should be
close together and at the same temperature.