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Re: [Discuss-gnuradio] CIC stop band

From: Hans Glitsch
Subject: Re: [Discuss-gnuradio] CIC stop band
Date: Thu, 17 May 2007 08:06:22 -0700

Thank you for the graphs.  I wasn't aware that there was a HBF after the CIC.  Yes, I'd like to know the frequency response of the whole usrp from input to output when I decimate by 250.
Thank you to everyone for the help so far,
----- Original Message -----
Sent: Wednesday, May 16, 2007 11:19 PM
Subject: Re: [Discuss-gnuradio] CIC stop band

Dear Hans,

I think you meant the frequency response of CIC+ HBF  filters. However, the USRP CIC decimation filter has 4 stages. I did MATLAB analysis for 4 stages CIC filter with decimation rate of 250 (as you requested) without the HBF. The spectrum analysis result is attached. The first plot is for entire range [0 to Fs/2]. The second one is zoomed near the interested band. You will see a huge theoretical gain (more than 190 dB) because of CIC bit growth.


Eric Blossom <address@hidden> wrote:
On Wed, May 16, 2007 at 04:00:24PM -0700, Hans Glitsch wrote:
> Hello,
> What is the stop band of the FPGA CIC filter? How do I figure out the
> attenuation at a given frequency outside my bandwidth?
> I'm decimating by 250.
> Thanks,
> Hans

It's a fourth order CIC.
See http://users.snip.net/~donadio/cic.pdf for the transfer function.


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