I am using AD80066 as a 4 channel ADC to fetch the signal from the front amplifier. I have been play with this part for a while,but I still can not make it work properly. I connected everything as the suggested circuit in the datasheet. And I send the command from SPI to configure the mux and configuration register as full speed/full range/SHA/2 byte/internal voltage reference on/4 channel mode. But the weird thing is, I tried to bias the signal to sit on the middle of 1.8V and the ADC cannot pick it up. Instead, I found I need to put an negative offset like -1V and it starts to giving out data. I don't know what is wrong. Is there anyone has ever encountered this before?