I am using the ALTPLL IP block with a 30MHz reference clock and Quartus15.1.
From my understanding, the "locked" output of the ALTPLL megafunction will go low as soon as the phase frequency detector of the PLL detects a phase shift between the input reference clock and the feedback clock of the PLL.
There are given a number of reasons why this could happen in the MAX10 Clocking and PLL User Guide:
- Jitter on the reference clock
- Reference clock is not within the defined frequency
- Noise on the power supply
Now my questions are:
- Is it true, that the only reason for the "locked" output to go low is the detection of a phase shift between reference clock and PLL feedback (whatever the reason for that may be)?
- If so, then how big does that phase-shift need to be in order to force the "locked" output low?
I am using the MAX10: 10M25SCE144
Thank you for the response,
as I mentioned, I found the list of reasons which may cause the PLL to lose lock. What I do not know, and what I fail to find on the link you referenced, is: How are these "lock loss reasons" evaluated? My understanding so far is, that the only detection for any of the issues listed (Jitter, SSN, PLL reset) , is the detection of a phase difference between reference clock and PLL feedback loop. Is this assumption correct, or are there other means by which the PLL can detect a violation of the PLL specifications?
Thank you and kind regards