Forum Discussion

roeekalinsky's avatar
roeekalinsky
Icon for Contributor rankContributor
4 years ago

Optimal frequency selection for IOPLL's VCO: minimize or maximize?

Is best IOPLL performance obtained by minimizing the VCO frequency, or maximizing it? The IOPLL IP generator GUI appears to be confused on this issue, at least for Stratix 10. It describes one thin...
roeekalinsky's avatar
roeekalinsky
Icon for Contributor rankContributor
4 years ago

Hi @Ash_R_Intel, thanks for the response.

A simple example case is as the IOPLL IP generator GUI comes up by default: refclk 100 MHz, outclk0 100 MHz.

For reference, both Arria 10 and Stratix 10 in -1 speed grade have IOPLL VCO frequency operating ranges of 600 MHz min to 1600 MHz max.

So, based on the description given in the IOPLL IP generator GUI, we'd expect it to set the VCO frequency to 600 MHz (N=1, M=6, C0=6). And this is exactly what it does for an Arria 10 target, but not for a Stratix 10 target. For a Stratix 10 (-1 speed grade), it sets the VCO frequency to 1600 MHz (N=1, M=16, C0=16), which is opposite of what we'd expect.

Thanks,
-Roee