Download Broad-Bandwidth FPGA-Based Digital Polyphase

NASA USRP - Internship Final Report
(semi-near future): Add RLOCs to constrain each butterfly into its own box. I have a pretty well
thought out plan for how this will happen, including the exact values the constraints should take.
I won't be starting this until everyone's perfectly happy with the unconstrained block though.
^^^ doing this will change a lot of things. Many of the parameters that are presently settable will
no longer need to be, as many delays are only there because bits of the butterflies are placed far
from each other. I imagine we can save massively on fabric by doing this, and then use BRAMs
for most of the delays and coefficients (since they're going to be well placed) to save even more
on fabric.
(distant future): fully auto-placing biplex blocks, given that the block is either:
a. attached directly to one of the ADCs, or
b. attached directly to a PFB (which is attached directly to one of the ADCs)
FFT_Direct
Parameter
Format
Bounds
FFT Size
Integer
1 <= x <= <larger_fft_size>
Larger FFT Size
Integer
<fft_size><= x
Input Bit Width
Integer
1 <= x <= 24 (recommended max 18)
# Coefficient Bits
Integer Array(FFTSize-2) 1<= x <=18
Inter-Stage Bit Widths
Integer Array (FFTSize-1) 1 <= x <= 24 (recommended max 18)
Output Bit Width
Integer
x >0
Delay Input
Boolean
x >= 0; Recommend 1
Inter-stage Delays
Integer Array (FFTSize-1) x >= 0; Recommend 1
Delay Output
Boolean
x >= 0; Recommend 1
Add Sync Tree to Input?
Boolean
<0 or 1>
Register Coefficients?
Boolean
<0 or 1>
Coefficient Grouping Array
<read below>
<read below>
Coefficient Step Size
Integer Array (FFTSize)
x >= 0; see below
Shift after n-th stage?
BooleanArray (FFTSize)
<0 or 1>
Comments:
I actually haven't tested the new direct FFT for anything other than FFTSize=3. Worth
considering.
Bit Growth FFT: Like the biplex FFT, this also supports bit growth. Coefficients too (but again,
I recommend 9 or 18 bit coefficients.
Again, I'm not quite sure if carrying 24 data bits has any benefit over using only 22 or 23. I'll
test this later
As in the biplex FFT, options to change the down-converts at each stage to use rounding or
saturation have been removed.
27
Summer 2011 Session