I wish to design an 8 channel biopotential amplifier to measure EMG signals. In the figure, the signals from electrodes (E1 to E8) are fed to InAmps (IN1, IN2... IN8) and Band Pass Filters (not shown) before DAQ. The OpAmps (OP1, OP2) are part of the feedback loop for Common Mode Cancellation which feed the Reference Electrode (E_Ref). For a single InAmp circuit, the CM1 signal is fed to the +ve input of the OP1.
How do I combine multiple Common Mode signals (CM1 to CM8) to the same feedback circuit?
Is the answer as simple as a summing amplifier? If I do that, how will it impact the InAmp stage? A descriptive answer would be extremely helpful.
I understand there are many companies which sell such products but due to budget constraints, I have to design the circuit myself. Please help. Thank you.
Ok, this may sound redundant , why not take CM1 to CM8 to a comparator !!
OR , if you want individual common mode signal then why not use a sigma-delta modulator for differentiating them ...
The comparator sounds like a great idea. Thank you.
I did not understand your 2nd suggestion: to use a Sigma-Delta Modulator to differentiate? Could you please elaborate?
Thank you.
Sigma-delta is a ADC so you need to digitize them and then use digital logic to decode and drive the DAC .
Yes, summing amplifier is one of the right answers, An inverting summing amplifier should be implemented to develop the common body reference circuit. Then the inverting summing amplifier provides an average output results with the right ratio of resistors values. I've designed 4 channels EMG circuit and I've used summing amplifier for averaging the Body references
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