I am trying to make ecg electrodes with capacitive coupling. Since my capacitor is only about 10 pF at max and I have to have as low cut-off frequncy as possible, I came up with a circuit like this.
My question is: Could it work?
Bias current of the op-amp is 5 pA.
simulate this circuit – Schematic created using CircuitLab
You can control the cutoff frequency of that high pass filter by using a resistor. I'd suggest removing the diodes since they're not really linear and would cause issues. Replace them with a resistor. When you do, you will have a first order HPF with a cutoff frequency of fc=1/(2*piRC). Calculate how much a resistor you would need based on that equation. Keep in kind that the higher the resistor value, the higher the thermal noise and the lower the value the higher the power consumption.
Also, in the case of EEG you would not want to decouple in the first stage amplifier since the signal is 10uv to start with. But in ECoG you can probably get away with it. Not suggested though.
I'm not at full speed for capacitive coupled trodes, but your positive terminal of your op amp can't source or sink current, so you'll need a resistive path to ground there.
