OP27A, OP27C, OP27E, OP27G

OP37A, OP37C, OP37E, OP37G

LOW-NOISE HIGH-SPEED PRECISION OPERATIONAL AMPLIFIERS

SLOS100B – FEBRUARY 1989 – REVISED AUGUST 1994

2–18

POST OFFICE BOX 655303

POST OFFICE BOX 1443

APPLICATION INFORMATION

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

Ω

Vno

100

Ω

500 k

Ω

500 k

Ω

[Vno2 – (130 nV)2]1/2

1 M

Ω × 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

as shown in Figure 36 does not degrade the temperature coefficient

creates an

The adjustment range with a 10-k

Ω 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 µV.

+

–

–15 V

Output

2

3

7

8

4

1

Input

6

15 V

10 k

Ω

–15 V

Output

2

3

7

8

4

1

Input

6

4.7 k

Ω

Figure 36. Standard Input Offset

Voltage Adjustment

Figure 37. Input Offset Voltage Adjustment With

Improved Sensitivity

15 V

1 k

Ω

4.7 k

Ω

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

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.