Alias Frequencies

Document created by analog-archivist Employee on Feb 23, 2016
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I'd like a sine wave of 2.375 GHz, so the plan is to generate 375 MHz but as
the sample rate is 1 Gsps, the aliases will appear at 625 MHz, 1.375 GHz, 1.625
GHz, 2.375 GHz 2.625 GHz and so on.

Can the DACs available achieve these high frequency components, or does
something about the devices (output filter, slew rate limited output?) mean
that this approach rules out certain parts?

 

The main additional roll-off you will encounter is the R-C time constant of the
DAC’s output transistors (big CMOS devices = C) and the load resistance of your
system (likely 50 ohms). With the AD9734, it would be tough to get 9 GHz. If
you used the AD9129, you could directly synthesize your 2.375 GHz signal using
mix-mode and a high clock rate of 2.8 GHz. You’d likely be able to see your 9
GHz signals if you loaded the AD9129 output with 25 ohms or even 12.5 ohms and
then transformed it back up to 50 ohms with a 2:1 or 4:1 balun. Check the
recently released article on the AD9129 for improved matching and what it did
for the output response.

http://edn.com/design/analog/4429553/2/Understanding-and-designing-wideband-outp
ut-networks-for-high-speed-D-A-converters-

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