Number of TAP nyquist filter

[Patrick]

hello,

I'm working about a DQPSK modem 4 Mbits/s.

My problem is to implant the 4 nyquist filter (on (I and Q) *2
(transmitter and receiver).

I use a Stratix - FPGA.

When I developp the filter with ONLY 12 taps the four filters utilizes
76 DSP block and I have only 80 DSP blocks.

After Matlab simulation, I must have 48 taps for a correct impulse
response.

The sampling frequency is 80 MHz and the filter bandpass is 2 MHz.

Is it possible to implant 4 filters with 48 taps in a single Stratix
FPGA.

thanks for response

 

[Symon]

Patrick,
I would suggest you read up about decimation. You can reduce your
computation requirement considerably, especially as you have a minimum
theoretical sampling requirement of only 4Msps, i.e. double the bandwidth of
interest.
You might also consider using distributed arithmetic. In basic terms, this
squeezes extra computation out of the FPGA by running it at higher speeds.
As ever, Google is your mate!
Cheers, Syms.

 

[Ray Andraka]

Yes, but not with the approach you are currently using. You have 80 DSP
blocks. The multipliers in those are capable of quite a bit more than 80
MHz. One possibility is to time multiplex the data into the same filter,
running it at 4x the clock rate. Now 320 MHz is not an easy target,
especially for a new user. If you are also mixing to baseband, you could
use a polyphase decimator architecture to reduce the sample rate seen at
each multiplier. Another option, is to use distributed arithmetic, which
is a technique whereby the multiplications are rearranged at the bit level
to take advantage of the small luts in the FPGA fabric. It won't use the
DSP blocks in that case. As with many things, there is more than one way
to approach the problem.

hello,

I'm working about a DQPSK modem 4 Mbits/s.

My problem is to implant the 4 nyquist filter (on (I and Q) *2
(transmitter and receiver).

I use a Stratix - FPGA.

When I developp the filter with ONLY 12 taps the four filters utilizes
76 DSP block and I have only 80 DSP blocks.

After Matlab simulation, I must have 48 taps for a correct impulse
response.

The sampling frequency is 80 MHz and the filter bandpass is 2 MHz.

Is it possible to implant 4 filters with 48 taps in a single Stratix
FPGA.

thanks for response

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email (e-mail address removed)
http://www.andraka.com

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