3 Replies Latest reply on Feb 24, 2011 9:03 AM by user_156863

    ADC problems

    imran.khakoo

      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?

        • 1. Re: ADC problems
          imran.khakoo

          Ah. It seems the internal filter of the ADC is preventing me from subsampling.

             

          Is there any way to switch off the internal filters of the Delta Sigma ADC?

             

           

             

          (Time critical solution needed)

          • 2. Re: ADC problems
            udayan.umapathi

             Hi,

               

            Can you provide some more information about your input signal. You said its 1.5 Volts peak to peak? that means if you add a 1.5 Volts offset, the signal will vary between 0.75 Volts and 2.25 Volts. 

               

            Also how have configured the ADC, which mode. How are you reading the values from ADC.

               

            -Udayan

            • 3. Re: ADC problems
              user_156863

               Hi MechatronicsMan,

                 

              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.

                 

              Try the new Kit-050 for analog designs.

                 

              Kelly C.