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PSOC3 filter fails the step test | Cypress Semiconductor

PSOC3 filter fails the step test

Summary: 0 Replies, Latest post by gz on 14 Oct 2011 11:10 AM PDT
Verified Answers: 0
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gz
gz's picture
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16 posts

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

 

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