I've made a AC voltage measurement board, the structure is simply:
input -> gain -> block capacitor - ADC.
Now I want to calibrate it. Because the input may be sub mVs, so I'm considering calibrate it by using a DC input (sure, I need bypass the block capacitors). And I've heard someone said it's convenient to calibrate AC channel using DC input, because a DC can be measured more precisely. Is it true? How the commercial DMM's AC measurement channels are calibrated, particularly at small signal input?