On 11/26/2012 01:30 AM, Hal Murray wrote:
Suppose I have an A/D running at 1 MHz. The standard simple minded approach is that it will work for any input signal with a bandwidth up to 1/2 MHz. We usually think of that in the baseband, but it also works for, say 1.25 to 1.5 MHz. The input signal gets aliased down into the baseband. (and if you are unlucky, which is easy, some of the aliasing reflects back and overlaps so you can't tell X-y from X+y) There is similar math for D/A, the reverse direction. I think this applies for a DDS making higher frequencies than simple arithmetic would allow it to generate. Does anybody have a good web page for how that works? My simple expectations are that it would have to generate lots of harmonics and then go through a filter to get rid of all the wrong stuff. I'm missing the step where all the harmonics come from. Are they just really tiny and I have to do a lot of good filtering and amplification? Do I need something other than a traditional DDS for this sort of stuff?
I think you would enjoy digging up the Analog Devices DDS material, which goes into this and many other things.
http://www.analog.com/static/imported-files/tutorials/450968421DDS_Tutorial_rev12-2-99.pdf See section 10. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
