FPGA progress of sorts

Terry Fox tfox at knology.net
Fri Jul 31 18:43:21 CDT 2009

Last weekend, I created an FPGA project for the Nexys2 board that uses the
DDS Intellectual Property (IP) in the Xilinx IP core.  The output of the DDS
was fed to a small D/A board (PMOD DA2) that is available from Digilent,
that has two 12-bit D/A chips on it.  It worked great, after some debugging.
The reason for doing this was to learn how to use the Xilinx IP cores.
After I got the basic DDS going with one D/A chip, I rebuilt the DDS IP to
have both sine and cosine outputs, then fed those to the two D/A chips.  The
result was as predicted, two sine waves 90 degrees apart, albeit at only


Today, I built up a small board that plugs into two PMOD jacks on the
Digilent Nexys2 FPGA board, which has one AD9744 14-bit 200+Ms/s D/A
converter chip.  This is the same D/A used on the HPSDR Penelope and the
Ahlstrom digital transmitter board, and has a significantly higher clock
frequency (up to 210 Ms/s).


The gods were smiling on me.  Not only did I wire up the board correctly the
first time, but my first attempt at FPGA code to drive this D/A chip worked
right out of the gate!!!  No errors, but a few warnings.  Right now, the
AD9744 D/A output is also only 25kHz, but I plan to build a completely new
FPGA project that will have the chip make RF from a DDS.  Then, I will
change to a digital up-converter (DUC), which uses a Cordic, CIC, and FIR
filters.  All these pieces are also available as free-to-use-on-Xilinx FPGA
IP along with the basic Xilinx software. There is also a fast FFT, and other
stuff.  In addition, there is a lot of IP that does cost money to use, but I
don't think we need to use any of it.  I'm using Verilog now, and have found
a couple of books that may be of interest to fellow beginners.


Both the HPSDR and QS-1R projects also have SDR FPGA Verilog code that is
generally useable by hams.


This FPGA stuff is becoming very interesting!


(I'm hoping to prod more AMRADer's into SDR interest here..)





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