Digital would definitely work but then the question is what level of accuracy is desired?
Going from your response, I assume the signal is just positive i.e. monopolar? Bipolar would require a precision rectifier and transmitting the sign separately or biasing at DC which would need some zero trimming.
How about transmitting the AC and low frequency/DC signals separately? 20kHz to 20kHz can be sent across an isolation transformer and all information below 20kHz could be sent digitally at a high resolution using an audio ADC.
I wish to build four voltage measurement channels.
One is to measure the dc-link input voltage to a 3-phase inverter (the voltage is 0~50VDC, unipolar).
Another three are to measure the phase voltages of a 3-phase induction machine (bipolar).
I think 12-bit resolution is enough for my application.
Do you mean "20kHz to 20kHz" or "20kHz to 200kHz" can be sent across an isolation transformer. By the way, what is the maximum frequency that an isolation transformer can take without distortion?
Cheers.