4 Replies Latest reply on Jul 25, 2017 11:10 AM by jim_reich_1873026

    Problem with the SAR ADC on PSOC4 -- limited to VDD/2?

    jim_reich_1873026

      Hello. I am having trouble with the SAR ADC. It doesn't seem to be able to measure voltages above VDD/2. I'm using it in single ended, signed input mode with internal 1.024v bypassed (with the appropriate cap in place). I've verified that Vref is about 1.024v. The ADC configurator says my range should be 0-2.048v. 

         

      But at 3.0v VDD, a 2v triangle wave starts at about 0.3v (it shows a sharp corner on the triangle, not saturation) and then shows a decreased gain at 1.4v and stops completely at 1.6v. At 2.6v VDD, the max drops to 1.4v and the offset shrinks, while at 3.6v VDD, the max goes up to 1.8v and the offset grows to 0.4v.

         

      Has anyone else seen this behavior before? Should I configure my SAR differently somehow? I can't seem to find any of these limitations mentioned in the documentation...