Folks
I am trying to use a complex fft (the green FFT block) for a spectrum analyzer
application.
I would like to use a 512 point FFT to compute on read time data. I need the
FFT to compute in less than 512 samples. I am using 4 taps in the input, and
running the FPGA at 128MHz. In this
hi tim,
the casper fft's are maximized to handle high bandwidths with
low resource utilization, but they are not optimized for low latency,
as astronomers use them in streaming applications where latency
is not important.
there are other FFT architectures - some 512 input FFT's can
convert from
I appreciate your response Dan.
Tim
From: dan.werthi...@gmail.com [dan.werthi...@gmail.com] on behalf of Dan
Werthimer [d...@ssl.berkeley.edu]
Sent: Friday, May 02, 2014 11:26 AM
To: Madden, Timothy J.
Cc: casper@lists.berkeley.edu
Subject: Re: [casper] FFT
tim,
one more thought:
the PFB FIR in front of the FFT dominates the latency of the PFB/FFT.
the PFB has latency of (Ntaps-1) x FFTlength / Nparallelinputs.
a four tap PFB has about three times the latency of the FFT,
so if you remove the PFB you will cut latency down by about a factor of
Dear Tim,
You are aware that the CASPER FFTs are streaming, right? By this, I mean
that they can accept data input at the full clock rate with no pausing
between FFT windows. Everything Dan says is correct about latency, but
historically there have been very few applications that have strict
Hi Tim,
Also, if we supply ONE and only ONE sync pulse, should the fft block compute
indefinately? My simulink seems to require a series of sync pulses to get
the FFt to work more than once.
That's right, one and only one sync pulse is sufficient to keep the
FFT operating indefinitely on
Aaron
I thought they were streaming until I tried using simulink.
If I give the FFTs ONE and only ONE pulse, they compute ONE FFT and stop. So I
have to give a series of pulses.
So then I must figure out what sync frequency is necessary. It seems to be true
that the FFTs need repeating sync
Jack
I have a problem then. Because in simulink, if I give ONE and only one sync
pulse, then the FFT stops after one compute. I am not sure what to do about
that, because the simulation seems to disagree with the documentation.
The reason I am trying to give ONE sync pulse in simulation is
Hi Tim,
On 2 May 2014 14:16, Madden, Timothy J. tmad...@aps.anl.gov wrote:
Aaron
I thought they were streaming until I tried using simulink.
If I give the FFTs ONE and only ONE pulse, they compute ONE FFT and stop. So
I have to give a series of pulses.
So then I must figure out what sync
Jack
I think this may be getting clearer in my murky mind. If I send one and only
one sync pulse into the PFB, conneced to FFT, I get one and only one sync out.
I am assuming that this means that the FFT runs once.
Should I assume that the FFT is still running forever? If this is the case I
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