OP27A, OP27C

LOW-NOISE HIGH-SPEED PRECISION OPERATIONAL-AMPLIFIER

SLOS100E − FEBRUARY 1989 − REVISED FEBRUARY 2010

15

POST OFFICE BOX 655303

APPLICATION INFORMATION

noise testing (continued)

1.

The device should be warmed up for at least five minutes. As the operational amplifier warms up, the

offset voltage typically changes 4

μV due to the chip temperature increasing from 10°C to 20°C starting

from the moment the power supplies are turned on. In the 10-s measurement interval, these

temperature-induced effects can easily exceed tens of nanovolts.

2.

For similar reasons, the device should be well shielded from air currents to eliminate the possibility of

thermoelectric effects in excess of a few nanovolts, which would invalidate the measurements.

3.

Sudden motion in the vicinity of the device should be avoided, as it produces a feedthrough effect that

increases observed noise.

4.3 k

Ω

110 k

Ω

2.2

μF

Oscilloscope

22

μF

100 k

Ω

0.1

μF

LT1001

4.7

μF

2 k

Ω

100 k

Ω

10

Ω

0.1

μF

Voltage

Gain = 50,000

+

−

OP27

Device

Under

Test

24.3 k

Ω

0.01

0.1

1

10

100

100

90

80

70

60

50

40

30

f − Frequency − Hz

+

−

NOTE: All capacitor values are for nonpolarized capacitors only.

Figure 26. 0.1-Hz to 10-Hz Peak-to-Peak Noise Test Circuit and Frequency Response