A very simple nanovoltmeter with picovolt resolution. The high resolution is possible by using a chopper, auto correlation, a modified delta-sigma analog to digital converter, a 16 bit PWM with passive five pole RC filter configured in a self nulling loop.
All signal processing after the chopper is done in the AC domain with the circuit configured as a nulling amplifier. AC amplifier gain is 10,000,000 and the amplifier is fed into the Arduino ADC. This gives resolution of 100 pV per bit...