A Versatile AD9832 DDS Synthesizer
For the "TV Tuner Spectrum Analyzer"
Project, which might be published here anytime, I needed a tunable oscillator
to replace the 4MHz crystal of a PLL to get smaller tuning steps. After different
attempts in pulling the crystal with varactor diodes I decided to use a DDS
And in my junkbox I found an AD9832, 25MHz DDS with SPI interface ;-) so here it is:
schematic ; click to enlarge!
The eagle files & C code snippet for dds control can be downloaded here.
This oscillator produces a great fine-adjustable
(sub-1-Hz) signal and was built really fast. The part values are missing in
the schematic but they were taken from the AD9832 datasheet.
For good signal purity you might add a low pass filter on the output as with every DDS-IC.
The sample code included in the RAR archive above shows my initialisation routine for the dds and the function which sets a frequency.
(c) Thomas Gulden, 03 / 2010