using IIR in DDC

[Sasa Bremec]

Hello!

My question is what are the benefits of using IIR filters instead of CIC and
FIR filter in digital down converter implemented in FPGA. My collogue has
got this idea, and I am not 100% convinced in its theory. I have made some
research on the net and I didn't find any piece of information regarding
IIR filters used in DDC, has any of you any kind of experience dealing with
IIR in FPGA?


Thanks, Sasa

some info about the design:

Device: V2P
Fclk = Fs = 108MHz
Finput = 27Mhz
Decimation = 128

 

[Ray Andraka]

If the downconverter is used for digital data, then you'll want a linear phase
characteristic. That is much easier to achieve with an FIR filter. The
feedback required for an IIR filter can make the design challenging (you have
one sample time between the input and the output which has to be available at
the input during the next sample time) because it cannot be pipelined. Finally,
IIR filters are considerably more sensitive to quantization, so you'll likely
need more precision than you would need for an FIR filter. FIR filters also
offer a possibility of using polyphase techniques to reduce the processing
load. About the only advantage an IIR filter has is that it generally takes
fewer coefficients to obtain a given response, but to get that you give up phase
linearity.

Sasa Bremec wrote:

Hello!

My question is what are the benefits of using IIR filters instead of CIC and
FIR filter in digital down converter implemented in FPGA. My collogue has
got this idea, and I am not 100% convinced in its theory. I have made some
research on the net and I didn't find any piece of information regarding
IIR filters used in DDC, has any of you any kind of experience dealing with
IIR in FPGA?

Thanks, Sasa

some info about the design:

Device: V2P
Fclk = Fs = 108MHz
Finput = 27Mhz
Decimation = 128

--
--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

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