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Re: [Discuss-gnuradio] CIC + halfband filter compensation


From: Andy Walls
Subject: Re: [Discuss-gnuradio] CIC + halfband filter compensation
Date: Thu, 26 Apr 2018 14:45:11 -0400

> From:         Geoffrey Mainland
> Date:         Wed, 25 Apr 2018 16:39:11 -0400
> 
> I hope you will forgive a few naive signal processing questions :)
> 
> 1) What is the frequency response of the CIC and halfband filters in
> the
> USRP? This was addressed long ago on the mailing list
> (https://lists.gnu.org/archive/html/discuss-gnuradio/2007-05/msg00191
> .html),
> but the associated MATLAB script is no longer available now that the
> nabble archive is gone.

Attached are images generated from an Octave script, showing the
performance of the X310's CIC filter and 3 half-band filters,
filtering, decimating, and folding-in from the radio's 200 Msps down to
6.25 Msps.

The CIC filter is in blue.  It's droop hardly worth mentioning.

The Octave script is also attached.  It is far from generic.  It will
need significant modification if you have a different situation.


> 2) How do I design a filter to compensate appropriately?
>
> I know there are other methods for avoiding CIC droop, like
> oversampling, but I'd like to understand how to compensate with a
> filter
> as well.

As far as CIC compensation filters go:

http://lmgtfy.com/?q=cic+compensation+filter

:)

Seriously, there is plenty of reading material out there.

Regards,
Andy

> Thanks!
> Geoff

Attachment: Folding_CIC_droop.png
Description: PNG image

Attachment: Folding_CIC_droop_zoomed.png
Description: PNG image

Attachment: hbx310.m
Description: Text Data


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