Q
Here is a query from our customer who need a sine signal and the output
frequency is 500~600MHz and the phase is controllable. I think the 2nd harmonic
of the output of AD9910 can solve his question but not so sure. Since the phase
of fundamental is adjustable by configuring the POW register, whether the 2nd
harmonic and image can also be controlled by the register? In addition, the
phase response of band pass filter to extract the 2nd harmonic is not ideal.
Could you please give me some advice.
A
The fundamental and image frequencies will have the same frequency
resolution via changing FTW register value. However, the phase offset
resolution will be different between the fundamental and image. The phase
offset resolution on the image will decrease proportional to the fundamental
but will still phase offset the image. Note, the 2nd harmonic of the
fundamental is probably too low in magnitude to work for this application, so
use the image instead. I have attached application note AN-939 and our next
generation DDS, the AD9914. The AD9914 fundamental is valid up to 1.4Ghz.
You might try different band pass filter types, and/or operate away from the
roll off response as possible for both sides of the band pass filter for best
phase response. Sorry I’m not a filter expert.
