0 Replies Latest reply on Oct 14, 2011 11:10 AM by jean.gonzalez

    PSOC3 filter fails the step test

    jean.gonzalez

      Hello

         

      The filter is a lowpass filter 64 taps (about 5% overshoot)

         

      on the picture we have :

         

      signal3 :  300kHz DMA clock (input and ouput of the filter are DMA)

         

      signal4 :  The duration of an ISR program that changes the input value of the filter from -100 to 120 and back, to perform a signed square signal

         

      signal5 : the sign bit of the filter output  (bit 7 of HOLDAH register)

         

      CH2 (red analogic curb) : the output of the filter  with an offset of 128 ==> 8 bits DAC

         

      We can see that at the end of the rising edge of CH2 (and before descent) the sign bit of the filter is swicthing to negative values generating  a bug in the response of the filter.

         

      Regards