Stratix® V Device Handbook: Volume 1: Device Interfaces and Integration

ID 683665
Date 10/18/2023
Public
Document Table of Contents

4.2.5. PLL Cascading

Stratix® V devices support two types of PLL cascading.

PLL-to-PLL Cascading

This cascading mode synthesizes a more precise output frequency than a single PLL in integer mode. Cascading two PLLs in integer mode expands the effective range of the pre-scale counter, N and the multiply counter, M.

Stratix® V devices use two types of input clock sources.

  • The adjpllin input clock source is used for inter-cascading between fracturable fractional PLLs.
  • The cclk input clock source is used for intra-cascading within fracturable fractional PLLs.

Altera recommends using a low bandwidth setting for the source (upstream) PLL and a high bandwidth setting for destination (downstream) PLL.

Counter-Output-to-Counter-Output Cascading

This cascading mode synthesizes a lower frequency output than a single post-scale counter, C. Cascading two C counters expands the effective range of C counters.