A transimpedance amplifier's output passes through a first-order low-pass filter with and

PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Feedback, operational amplifiers and analogue signal processing · Feedback, operational amplifiers and analogue signal processing

Electronics for Measurement, Ch Noise and the signal-to-noise ratio

Problem

A transimpedance amplifier's output passes through a first-order

RC

low-pass filter with

R = 15\,\mathrm{k\Omega}

and

C = 10\,\mathrm{nF}

, giving a

-3\,\mathrm{dB}

corner at

f_c

. Ahead of the filter, the amplifier's output-noise density is white at

e_n = 15\,\mathrm{nV}/\sqrt{\mathrm{Hz}}

, flat well beyond

f_c

. Wanting a quick estimate of the rms output noise, someone argues: "The filter cuts everything above

f_c

, so I can treat it as an ideal brick-wall filter of bandwidth

f_c

. The rms noise is then

e_n\sqrt{f_c}

." ((a)) Calculate

f_c

. ((b)) Calculate the noise-equivalent bandwidth

\Delta f

of the filter. ((c)) Calculate the rms output noise correctly, and state by what percentage the argument above underestimates it.

Browse the problem library