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

Question asked by liubenyuan on Apr 8, 2017
Latest reply on Apr 14, 2017 by liubenyuan

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?