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 synthesizer chip.
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