poor constellation after CIC filter

Started by fahim February 21, 2006
I am trying to simulate a rational sample rate conversion architetcure
using CIC filters (decimation) and farrow structure (interpolation). Input
data is QPSK modulated and upsampled by a large factor (325 to be exact). I
try to decimate the signal by 125 in three stages. each stage is in turn a
CIC (3-stage) decimation (by a factor of 5) filter. However the
constellation i get after CIC filter shows alot of points centered at
origin.I havent used any compensation filter...or may be i should increase
the oversampling ratio.

any suggestion(s) will be of valuable help.

best regards,