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LMP7731

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LMP7731

0.1 PF

100 k:

10:

2 k:

4.7 PF

24.3 k:

100 k:

0.1 PF

4.3 k:

2.2 PF

22 PF

110 k:

SCOPE

x 1

VOLTAGE GAIN = 50,000

LMP7731

www.ti.com

SNOSAT6E – JULY 2007 – REVISED MARCH 2013

INPUT VOLTAGE NOISE MEASUREMENT

The LMP7731 has very low input voltage noise. The peak-to-peak input voltage noise of the LMP7731 can be

measured using the test circuit shown in Figure 45

Figure 45. 0.1 Hz to 10 Hz Noise Test Circuit

The frequency response of this noise test circuit at the 0.1 Hz corner is defined by only one zero. The test time

for the 0.1 Hz to 10 Hz noise measurement using this configuration should not exceed 10 seconds, as this time

limit acts as an additional zero to reduce or eliminate the noise contributions of noise from frequencies below 0.1

Hz.

Figure 46 shows typical peak-to-peak noise for the LMP7731 measured with the circuit in Figure 45 for the

LMP7731.

Figure 46. 0.1 Hz to 10 Hz Input Voltage Noise

Measuring the very low peak-to-peak noise performance of the LMP7731, requires special testing attention. In

order to achieve accurate results, the device should be warmed up for at least five minutes. This is so that the

input offset voltage of the op amp settles to a value. During this warm up period, the offset can typically change

by a few µV because the chip temperature increases by about 30°C. If the 10 seconds of the measurement is

selected to include this warm up time, some of this temperature change might show up as the measured noise.

Figure 47 shows the start-up drift of five typical LMP7731 units.

Copyright © 2007–2013, Texas Instruments Incorporated

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