Question

If you were to choose an op-amp to implement an amplifier circuit for picking up ECG (electrocardiographic) pulses from adhesive electrodes, which type of op-amps, instrumentation (INA121, AD620 etc), FET-input (AD547, OPA128 etc) or BJT-input (uA741, OP27 etc), should you choose? Perform an internet search on the data-sheet of these op-amps. Compare their performance characteristics. Provide THREE justifications to support your decision.

Answer 1

Characteristics	INA121(FET)	AD547(BJT)	uA71 Opamp
CMRR	91 dB	76 to 80 dB	90 dB
Slew Rate	0.7 V/uS	3 V/uS	0.5 V/uS
Input offset Voltage	200 uV(0.2 mV)	2 mV	1 mv

Higer CMRR higher noise rejction capability. ECG signals are very small so higher CMRR component required.

ECG signal is having a maximum frequency of 20 Hz so it is very less any of these are capable to work. Higher Slew Rate supports higher frequency signal without clipping.

The input offset voltage should be minimum for removing the error

SO bu comparing the Best choice is INA121 for ECG signal amplifier.