Polyphase in Practice

On Sat, 2 Apr 2005 12:37:03 -0800, "Fred Marshall"
<fmarshallx@remove_the_x.acm.org> wrote:

>This generated some interesting posts - so it's been worth it so far.
>Yet, I didn't get an answer to the question I tried to pose.  Let me try 
>again:
>
>Given that a polyphase filter is just another FIR except for particular 
>observations about how the outputs are generated...
>And:
>Given that a polyphase filter can be implemented with clever software 
>design.... (this is the only example *I* know of)
>Then:
>Other than the *applications* (Addresses why would a polyphase filter be 
>encountered).  And, other than the clever software designs mentioned above, 
>are there other *implementations* of polyphase filters that are useful? 
>FPGA structures, etc?
>
>(I note that Rick's book shows a commutator which was the thing that got me 
>to understand polyphase filters in a new light!  In a real implementation, 
>the commutator implies delay elements doesn't it?).

I'm mostly familiar with hardware implementations of polyphase filters
that use feedback to lock to particular phase of the input signal.
The details of the architectures are generally proprietary, though.
Sorry...   ;)

I have, however, seen enough detailed block diagrams for hardware
implementations laying around the internet and/or various datasheets
that I wouldn't think it would be that tough to scare something up.

There are some very elegant ways to build them, and build them simply.
Personally, I don't know why they're not used more often for the
amount of flexibility one can get from them.


Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org

"Fred Marshall" <fmarshallx@remove_the_x.acm.org> wrote in message
news:yvednVQYdOXwn9LfRVn-jA@centurytel.net...
> This generated some interesting posts - so it's been worth it so far.
> Yet, I didn't get an answer to the question I tried to pose.  Let me try
> again:
>
> Given that a polyphase filter is just another FIR except for particular
> observations about how the outputs are generated...
> And:
> Given that a polyphase filter can be implemented with clever software
> design.... (this is the only example *I* know of)
> Then:
> Other than the *applications* (Addresses why would a polyphase filter be
> encountered).  And, other than the clever software designs mentioned
above,
> are there other *implementations* of polyphase filters that are useful?
> FPGA structures, etc?

I've seen other 'structures' described by fred harris in one of his classes.
I don't quite remember the exact details because they 'went over my head' at
that time. However, I'm fairly sure he discusses them in his new book - so
you can buy it if you are really interested.
The structure I faintly remember used a polyphase filter bank and a
transform block (I assume DFT) at the output of the polyphase to convert a
FDM input signal into a TDM signal. That's pretty much all I remember about
it and I'd be lying if I said I understand it.
You asked for other examples...here is one...but I refer you to the master's
book for more details.

Cheers
Bhaskar


> (I note that Rick's book shows a commutator which was the thing that got
me
> to understand polyphase filters in a new light!  In a real implementation,
> the commutator implies delay elements doesn't it?).
>
> Thanks,
>
> Fred
>
>