Re: Do you think NI can fix my PLL? -- Details

Tim Wescott wrote:
CC wrote:
Can you say anything from experience about the implications of "slight nonlinearities" such as let's say a -25%/+50% variation in DC transfer gain, coupled with a 10-20% variation in transient response on the rising edge vs. the falling? Does it seem that such nonlinearities would make it impossible to get a decent loop going?

Those should be quite easy, if that's all that's going on. You'd have to make somewhat conservative loop tuning, but you wouldn't have to back it off that much. The real question is how jitter do you get running open loop compared to what you get in closed loop. If you're not getting any significant jitter at all then you should be able to make a really slow loop and be done with it.

If you _are_ getting open loop jitter you need to deal with it. Then you need to ask what the frequency content of the jitter is, what the achievable bandwidth of the loop is, and what (if anything) you can do to reduce the amplitude of the jitter.


Well it will be easy enough to take another look at the open loop jitter. But it leads me to wonder, how does one know if the jitter is electrical or mechanical in nature? There is jitter introduced by bearings, etc.

I'll check this out next week!


--
_____________________
Christopher R. Carlen
crobc@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
SuSE 9.1 Linux 2.6.5
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