EMRFD Message Archive 3183

Message	Date	From	Subject
3183	2009-06-11 22:09:10	n2toh	Dealing with a dirty output from an Analog Devices AD8954 DDS chip
I met with an old friend the other day and finally got to play with my AD8954 eval board, not only did I discover that the output drive from the chip is very low it was also surprisingly dirty. My question is would it be worth the trouble to build bandpass filters for each band to block the unwanted crap from getting to the mixers? -Justin n2toh
3185	2009-06-12 12:10:41	Gary Johnson	Re: Dealing with a dirty output from an Analog Devices AD8954 DDS ch
Justin, I assume you're testing a genuine AD9854 eval board, as opposed to a homebrew one. There should be no issues regarding output quality with that board, assuming it's set up correctly. You should get nearly 0 dBm from each output. Spurs will meet the datasheet specs--mostly 60 dB down or greater. Since the outputs are single-ended, even-order harmonics will be a bit high, but otherwise expect a very clean output, especially if you operate well below Fclock/2. Those of using the IQPro (based
3186	2009-06-12 13:14:11	n2toh	Re: Dealing with a dirty output from an Analog Devices AD8954 DDS ch
Yes it is a legit eval board from Analog Devices not a homemade board. Well I was using a single supply to power the board that may be a factor. and I was sampling the unfiltered output J5, but that board only has a lowpass filter and most of the junk I was seeing was below the passband of the filter. the low output may have been due to incorrect termination, I had connected the output pin of J5 via a 2000pF cap to block any DC from reaching the analyzer. -Justin n2toh