LMP2021/

LMP2022

IN

+

-

LMV771

-

+

OUT

IN

+

-

LMP2021, LMP2022

www.ti.com

SNOSAY9D – SEPTEMBER 2008 – REVISED JULY 2009

Figure 41. Noise Reducing Filter for Lower Gains

In order to achieve lower noise floors for even more noise stringent applications, a simple filter can be added to

the op amp’s output after the amplification stage. Figure 42 shows the schematic of a simple circuit which

achieves this objective. Low noise amplifiers such as the LMV771 can be used to create a single pole low pass

filter on the output of the LMP2021/LMP2022. The noise performance of the filtering amplifier, LMV771 in this

circuit, will not be dominant as the input signal on LMP2021/LMP2022 has already been significantly gained up

and as a result the effect of the input voltage noise of the LMV771 is effectively not noticeable.

Figure 42. Enhanced Filter to Further Reduce Noise at Higher Gains

Using the circuit in Figure 42 has the advantage of removing the non-linear filter bandwidth dependency which is

seen when the circuit in Figure 41 is used. The difference in noise performance of the circuits in Figure 41, 8

becomes apparent only at higher gains. At voltage gains of 10 V/V or less, there is no difference between the

noise performance of the two circuits.

Copyright © 2008–2009, Texas Instruments Incorporated

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