Intel® MAX® 10 Clocking and PLL User Guide

ID 683047
Date 12/26/2023
Public
Document Table of Contents

3.3.3. Guideline: Self-Reset

The lock time of a PLL is the amount of time required by the PLL to attain the target frequency and phase relationship after device power-up, after a change in the PLL output frequency, or after resetting the PLL.

A PLL might lose lock for a number of reasons, such as the following causes:

  • Excessive jitter on the input clock.
  • Excessive switching noise on the clock inputs of the PLL.
  • Excessive noise from the power supply, causing high output jitter and possible loss of lock.
  • A glitch or stopping of the input clock to the PLL.
  • Resetting the PLL by asserting the areset port of the PLL.
  • An attempt to reconfigure the PLL might cause the M counter, N counter, or phase shift to change, causing the PLL to lose lock. However, changes to the post-scale counters do not affect the PLL locked signal.
  • PLL input clock frequency drifts outside the lock range specification.
  • The PFD is disabled using the pfdena port. When this happens, the PLL output phase and frequency tend to drift outside of the lock window.

The Avalon ALTPLL Intel® FPGA IP allows you to monitor the PLL locking process using a lock signal named locked and also allows you to set the PLL to self-reset on loss of lock.