A single-lead ECG front-end needs a low-pass filter ahead of its digitiser

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 Active filters, oscillators and timers

Problem

A single-lead ECG front-end needs a low-pass filter ahead of its digitiser, corner at 150 Hz150\,\mathrm{Hz}, Q=0.707Q=0.707. The nearest E12 values are R=100 kΩR = 100\,\mathrm{k}\Omega for both frequency-setting resistors and C=10 nFC = 10\,\mathrm{nF} for both frequency-setting capacitors, with passband gain K=1.586K=1.586. The op-amp's input voltage-noise density is en=15 nV/Hze_n = 15\,\mathrm{nV}/\sqrt{\mathrm{Hz}}, and the filter's noise-equivalent bandwidth is 1.11f01.11 f_0. Room temperature is 290 K290\,\mathrm{K}. ((a)) Find the realised corner frequency f0f_0. ((b)) Find the rms output noise voltage, from the two 100 kΩ100\,\mathrm{k}\Omega resistors in series and the amplifier only, referred through KK. ((c)) Mains hum at ten times the corner frequency must be rejected by at least 40 dB40\,\mathrm{dB}. Find the minimum filter order nn.

Browse the problem library