Stratix® 10 Clocking and PLL User Guide

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

2.2.9. PLL Cascading

Stratix® 10 devices support PLL-to-PLL cascading. You can cascade a maximum of two PLLs. PLL cascading synthesizes more output clock frequencies than a single PLL.

If you cascade PLLs in your design, the source (upstream) PLL must have a low-bandwidth setting, and the destination (downstream) PLL must have a high-bandwidth setting for I/O PLL and medium-bandwidth setting for fPLL. During cascading, the output of the source PLL serves as the reference clock (input) of the destination PLL. The bandwidth settings of cascaded PLLs must be different. If the bandwidth settings of the cascaded PLLs are the same, the cascaded PLLs may amplify phase noise at certain frequencies.

Stratix® 10 devices support the following PLL-to-PLL cascading modes:

  • I/O-PLL-to-I/O-PLL cascading via dedicated cascade path—Upstream I/O PLL and downstream I/O PLL must be in the same I/O column.
  • I/O-PLL-to-I/O-PLL cascading via core clock fabric—No restriction on locations of upstream and downstream I/O PLL.

The permit_cal input of the downstream I/O PLL must be connected to the locked output of the upstream I/O PLL in both PLL cascading modes.

The following figures show the connectivity required between the upstream and downstream I/O PLL for both the PLL cascading modes.

Figure 16. I/O-PLL-to-I/O-PLL Cascading Via Dedicated Cascade Path
Figure 17. I/O-PLL-to-I/O-PLL Cascading Via Core Clock Fabric