7 Replies Latest reply on Mar 5, 2019 7:49 AM by jopa_1244706

    Possible to use PSoC 5 SAR ADC Ratiometrically?


      Considering a CY8C5888AXI-LP096.


      I need to measure the ratio of two input voltages at 1 MHz (so using the 12-bit SAR ADCs).  The larger voltage varies from 5V to ~100 mV over a period of perhaps a few ms, while the smaller voltage could be anywhere between 0-100% of the larger one.  I don't care about the values of each signal, just the ratio of the two.


      Trying to measure each signal directly against a fixed voltage reference and dividing in software would give poor resolution at the low end of the small signal.  Would it be possible to use the larger voltage as a reference into the SAR ADC so I can take the measurement ratiometrically? 


      I'm worried that the reference might be changing too quickly which would not be desirable for the SAR conversion, but I don't know what the limits might be and was wondering if there might be any information regarding the required stability of the SAR ADC reference on this PSOC?  Does this idea seem worth pursuing in general?



      Thanks in advance!