FPGA progress of sorts

[Terry Fox]

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
25kHz.

 

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..)

 

Terry

WB4JFI

 

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