My lab has had good luck with the ADF4350 eval boards as clock generators. The snippet description on the analog devices website of them is incorrect though, they can accept a 10 MHz clock ref. The datasheet is definitely more accurate than the description.
-Ben On Mon, Dec 30, 2013 at 9:36 AM, Jim Lux <jim...@earthlink.net> wrote: > On 12/30/13 7:56 AM, Anders Wallin wrote: > >> I've tested the AD9912 evaluation board: >> http://www.anderswallin.net/wp-content/uploads/2013/12/ >> dds_test_2013-12-30.png >> >> I want to use it with a 10MHz external input clock, but it looks like the >> on-board PLL that generates a 1200MHz sample clock from my input isn't >> that >> great, since I get strong side-bands on the output that are only 18-20 dB >> down from the fundamental. >> >> So it looks like I need to supply a clean 800-1000MHz clock to the DDS to >> get a clean output. Any ideas/suggestions for generating this from a 10 >> MHz >> sine? >> Driving the DDS system clock from an expensive RF generator (e.g. HP >> 8648A) >> would be possible but I'd prefer a PLL from 10MHz if it's doable >> simply/cheaply. >> >> Most of the time, they're expecting you to filter the output of the DDS > to remove the spurs. > > Probably not a PLL, at least not one of the generic PLL chips, because > you'll get spurs and sidebands from the comparison frequency in the loop, > and they'll be fairly close in. > > You have two basic alternatives.. a PLL using a divider from your 1 GHz > and using the 10 MHz as the comparison frequency, and then good filtering > to get rid of the 10 MHz spurs. A bit challenging since that's a <1% > bandwidth filter. (maybe you could do that with the onchip reference > generator, and feed it back in) > > Or, You want a straight out multiplier chain with appropriate filtering in > between stages. Maybe a x7, followed by 70MHz BPF (which should be readily > available), then another x7 to 490 MHz, then a x2 or x3. Or end with a x5 > (to 350 MHz) and a x3 to 1050. > > A sort of hybrid approach might also work.. take your 10 and make > 100MHz(x5 x2) with it, then feed that into your DDS. That will put the > spurs 100 MHz away, which is a lot easier to filter than spurs that are 10 > MHz away. > > I'm pretty sure Wenzel has some application notes on this. > > When you say "clean", how clean do you need it? What sort of tuning range > are you going to run the DDS over? (maybe some of the spurs will wind up in > places you don't care about and can filter out) > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
