Chris38ParticipantChris38 June 15, 2017 at 12:55 am
VSG25 documentation indicates that two-tone third order intercept is typically around +25 dBm, I need 10dB more for testing my system (80dB of IM3 with an RF power of -8dBm per carrier).
Is it possible to evaluate improvement we can expect by introducing predistorsion in a a custom arbitrary waveform generator file.
Please could you describe how to create and optimise such file? Tools ?
Thank a lot for your help
Justin CrooksModeratorJustin Crooks June 15, 2017 at 9:47 am
That sounds like an ambitious project. Off the top of my head, it sounds doable. You’d have to generate a CSV file with your two tones, measure the amplitude and phase of the 3rd order responses (in a highly linear measurement system), and then subtract the 3rd order responses from your CSV file (or something similar). I would expect that you could drop your 3rd order intermod products by 20 dB at least, but you’d have to try it to know. And it would vary with temperature and frequency, so you would probably want to do it right before using it or after a 30 minute warmup. Assuming you want tones spaced 2 MHz (+/- 1 MHz) you’d want to choose a DAC clock that is a multiple of 6 * tone spacing. Something like 96 MHz would probably work nicely.
If you can’t get phase info, you could use the amplitude of the IM products and hunt for the right phase that exactly cancels the undesired IM products.
You must be logged in to reply to this topic.