Stratix® 10 Clocking and PLL User Guide

ID 683195
Date 7/11/2024
Public
Document Table of Contents

2.2.5.6. External Feedback Mode

In external feedback (EFB) mode, the output of the M counter (fbout) feeds back to the PLL fbin input (using a trace on the board) and becomes part of the feedback loop.

One of the dual-purpose external clock outputs becomes the fbin input pin in this mode. The external feedback input pin, fbin is phase-aligned with the clock input pin. Aligning these clocks allows you to remove clock delay and skew between devices.

In EFB mode, you must use the same I/O standard on the input clock, feedback input, and clock outputs.

Figure 15. Example of Phase Relationship Between the PLL Clocks in EFB Mode