3 Replies Latest reply on Mar 20, 2013 5:13 AM by ramanathan.av

    Comparator not responding; offset in PGA generated reference!


      Hi All,


      Yet another PSoC beginner. I've approximated an SC block as an op-amp to use it as a differentiator. (My Input after external Capacitor goes to P2.3; the o/p port P0.3 is shorted to P2.3 via a feedback resistor).  A very simple application.




      I'm giving a reference voltage of 1.25V thru a PGA (Vinp=AGND; Gain=0.5) to the SC block's ACMux. My input is fed to BMux after going through external capacitor.  My differentiator's (SCblock's) o/p has to start at 1.25V.




      I face the following problems,




      1. The differentiator's o/p starts at 1.6V rather than 1.25V. Reason for this offset ? Also, I measured the PGAs o/p before it was routed to SC block and it gave 1.25V.




      2. The differentiator's o/p is routed to another SC block approximated as op-amp which I use as a comparator. This one has a reference from another PGA (1.72V). I observe on the CRO that my differentiator's o/p crosses 1.72V comfortably but still the comparator doesnt switch to 5V. Why  ?




      Please clarify,