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Design a precision ADC front end for measuring small signals with high common mode voltage at 1MHz frequency?

Hi, I want to build a electrical impedance measurement device using AD4003/AD4001, where a small current (around ~1mA, at 1MHz) is inject into the body and the difference voltage at two electrodes on the forehead is measured. The signal to be sampled is a small signal (Vpp<1V) with a relative large common mode voltage (from -10V to 10V). I draw a simplified schematic below.

I found some solution using AD629, however this opamp can not be used when the frequency (ac) is 1MHz. I also checked some instrumental amplifiers, however there is non with a relative large slew rate while maintain reasonable CMRR at 1MHz. So, how could I design a ADC front end for this specific application?


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