I am making a small board for EMG measurement placed on the face skin. To achieve this I use the AD8422 as an instrumentation amplifier. There will be 2 board and therefore 2 EMG channels that will then be processed by ADC on the motherboard. The electrodes will be stainless steel electrodes with a diameter of 1 cm separated by 1 cm. After realization of the prototype, I notice several problems:
• The appearance of an offset on the output of the amplifier AD8422, I tried to make filters pass high on each input, to add a capacitor in series with the resistance RG but it does not work. I also tried to create a RLD circuit for the reference electrode but without success (the RLD circuit does not seem suitable for a multi-channel system). I don’t know if the problem is an impedance mismatch of the electrodes, so I added serial resistors to the amplifier inputs but without success.
• My reference electrode is currently connected to the ground of the system, but it doesn’t seem to work to cancel out the common voltage of the skin.
I see several circuits on the potentially functional internet, but despite my tests I can’t find the one that would be functional with the AD8422.
Thank you for your help