Multiplying with 11 using PIC

[richard]

the closest i get to 11 meg in mcc for a pwm module is 8meg next step down is 5.33 meg next up 16 meg

[HenrikOlsson]

Off list I tried to get Mike to put some sort of number on the needed frequency resolution and allowable jitter. I got neither. I tried to explain how the NCO works and he determined it wasn't up to the task. I did some experiments with the 18F57Q43 running at 64MHz and I'll post some images showing the output of the NCO.





Here we can see how the NCO generates an average frequency of 7.619MHz (as evident by the frequency counter in the top right corner). But when looking closely we can see that MOST of the time (as shown by the "warm" trace) the actual frequency is 7.936MHz and occationally (as shown by the "cold" trace) it's 6.309MHz. The NCO "dithers" between these two frequencies so that, over time, the average frequency is 7.619MHz.

I tried to squeeze 11MHz out of it but it won't do it, runt pulses and all sorts of weird looking stuff - some of which most likely comes from the setup and probing.

I still think something like an AD9850 with proper filtering on the output, and then turning that signal back to digital might work.