Hello!
I have a circuit with a PCM1803A setup to take a 0-5V input signal. I've scoped both signals going into VINL and VINR and looked at the recorded values.
I have verified that the input is in the proper range (no negative voltage)
I have verified my 5V and 3.3V supplies
I have verified my connections of VREF1 and VREF2 to ground with the recommended cap values.
Both channels seem to have a pretty big dead zone up to like 1V where no input is detected. Other ADC using the same input topology show full range no problem.
VINL at like 0.5V or so shows a reading coming out. It's a VERY narrow range that this happens, but it's a blip I can see as I rotate a voltage coming in.
Driving into ADC is a R2R opamp -> 100R -> VIN, with a 10nF cap to ground.
This is DC measurements.
With largest oversampling, there is just a blip
With smallest oversampling, as it goes to zero, it rises up.
Vref2 shows 5V
Vref1 shows 1V
I notice that I have the wrong caps for the larger cap on vref (non-electrolytic) could this cause the problem?