Hi!
I'd like to make a simple ECG circuit where I'd like drive the right leg with the inverted common mode voltage based on this design. In this design, they inject the CMV interference back into the patient's body with a gain of 91 (the OP97 inverting opamp does this).
So I created a simple simulation where I placed a 4 mV CMV above an 100 mV differential voltage and amplified with INA129 with a gain of ~10. Yes, I know it is not realistic. The simulation screenshot is attached. What I don't understand is the CMV value. It is rather high and if it would go into an inverting amplifier stage (right leg driver) of gain 91 then it will clearly saturate the inverting opamp, right? With only 4mV of CMV. As far as I know, CM interference is always greater than 4mV.
What's wrong with this calculation?
I'd like to make a simple ECG circuit where I'd like drive the right leg with the inverted common mode voltage based on this design. In this design, they inject the CMV interference back into the patient's body with a gain of 91 (the OP97 inverting opamp does this).
So I created a simple simulation where I placed a 4 mV CMV above an 100 mV differential voltage and amplified with INA129 with a gain of ~10. Yes, I know it is not realistic. The simulation screenshot is attached. What I don't understand is the CMV value. It is rather high and if it would go into an inverting amplifier stage (right leg driver) of gain 91 then it will clearly saturate the inverting opamp, right? With only 4mV of CMV. As far as I know, CM interference is always greater than 4mV.
What's wrong with this calculation?