CIC decimation filter increases aliasing and imaging in the

[boki]

Dear All,

I am trying [cicdecimate] toolbox, my signal is a 2nd order single-bit
sigma-delta modulator output, the sigma-delta modulator output
spectrum is correct, but the decimation filter output increase the
low-frequency noise, is this correct? I only use a CIC filter no other
low-pass filter connected.

CIC decimation filter increase aliasing and imaging in the signal
bandwidth?


BLOCK:

Voice band sinwave -> 2nd order SDM -> CIC decimation filter

SDM spectrum:
Good

CIC decimation filter spectrum:
Noise++ in signal band, quantization noise--


Thanks a lot.

Boki.

 

[Don Pearce]

On 1 Jun 2004 05:09:48 -0700, bokiteam@ms21.hinet.net (boki) wrote:

Dear All,

I am trying [cicdecimate] toolbox, my signal is a 2nd order single-bit
sigma-delta modulator output, the sigma-delta modulator output
spectrum is correct, but the decimation filter output increase the
low-frequency noise, is this correct? I only use a CIC filter no other
low-pass filter connected.

CIC decimation filter increase aliasing and imaging in the signal
bandwidth?


BLOCK:

Voice band sinwave -> 2nd order SDM -> CIC decimation filter

SDM spectrum:
Good

CIC decimation filter spectrum:
Noise++ in signal band, quantization noise--


Thanks a lot.

Boki.

You must implement a lowpass filter prior to decimation to make sure
that the new Nyquist rate does not introduce alias products into the
system.

d
Pearce Consulting
http://www.pearce.uk.com