AN4451

Noise reduction

DocID025985 Rev 1

11/15

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Noise reduction

The Cf capacitor added in parallel with the Rf resistor helps to stabilize the transimpedance

of the application. It also lowers the bandwidth of the system. The cut off frequency is given

by formula (14).

If we consider a feedback capacitance of Cf = 10 pF, the bandwidth is limited to 1.9 kHz

and noise is also reduced on the output. A simple RC filter may also be added on the

output of the OA1MPA to obtain an overall second filter Rn, Cn as shown in Figure1 and as

described in formula (15).

If the bandwidth is a critical requirement, choose an op-amp with a higher

bandwidth like the TSV731 (GBP = 900 kHz). In addition, try to reduce the

transimpedance gain (Rf) and add a second stage of voltage gain. The drawback

is higher noise on the output.

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