David Joseph Bonnici wrote:

> I made a mistake. I assummed that by convoluting the impluse response
> of the three cascaded filters would give the equivalent low pass
> filter appearing on the low frequency side. That is not correct.
> 
> Can someone suggest me how to do this please and I promise that if I
> understand I will not disturb anymore on this subject
> 
> David

What part of Andraka's message did you not follow?

If answering questions disturbed those who do, they wouldn't. Feel
welcome.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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I made a mistake. I assummed that by convoluting the impluse response
of the three cascaded filters would give the equivalent low pass
filter appearing on the low frequency side. That is not correct.

Can someone suggest me how to do this please and I promise that if I
understand I will not disturb anymore on this subject

David

Refer each filter to the highest sample rate in the system (the input
sample rate in a decimator), then you can add up the individual filters.
To refer the filter, insert r-1 zero's between each coeffcient where r is
the sample rate ratio.  The spectrum of the referred filter will be the
original filter replicated R times.

David Joseph Bonnici wrote:

> Please refer to
> www.intersil.com/data/fn/fn3651.pdf
> page 10 top and page 9 bottom.
>
> Please correct me if I assume something wrong.
>
> On figure 12 (pg 10) you see the aliasing profile of the CIC and how
> it does it translate to baseband. The filters performance can
> therefore be estimated. Quite understandable and easily programmable.
> (and it does apply to all multirate filters)
>
> Now the question is: How are you going to see the aliasing profile due
> to cascaded multirate stages so as to get the equivalent of Figure 11?
>
> I do not think that it makes sense to obtain the aliasing profile of
> each filter on its own and then sum up ?
>
> DJB

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930     Fax 401/884-7950
email ray@andraka.com
http://www.andraka.com

 "They that give up essential liberty to obtain a little
  temporary safety deserve neither liberty nor safety."
                                          -Benjamin Franklin, 1759

Please refer to 
www.intersil.com/data/fn/fn3651.pdf
page 10 top and page 9 bottom.

Please correct me if I assume something wrong.

On figure 12 (pg 10) you see the aliasing profile of the CIC and how
it does it translate to baseband. The filters performance can
therefore be estimated. Quite understandable and easily programmable.
(and it does apply to all multirate filters)

Now the question is: How are you going to see the aliasing profile due
to cascaded multirate stages so as to get the equivalent of Figure 11?

I do not think that it makes sense to obtain the aliasing profile of
each filter on its own and then sum up ?

DJB