I'm using the FirstTouch PSoC 3 kit. I have a 1.5V peak - to - peak 40kHz signal coming into my ADC, and i've offset this signal by 1.5V so that it lies between 0 and 3 V. I'm sampling this signal at 30kHz (subsampling). I've set up the ADC in 8 bit Single mode, running between Vssa and Vdda.
My problem is that the received ADC value should be varying between 0 and somewhere close to 255, but actually varies between 125 and 126 ( the centre line). What could the problem be?
I don't believe that you cannot use the Sigma-Delta converter to sub-sample. The principle of operation is to highly oversample the input and then use dynamic correction and digital filters to reduce to the final sample rate. For your application, you may be better off with the PSoC5. It has a SAR ADC, where the sub-sampling should work just fine. Alternatively, you can use the mixers.