External Memory Interface Handbook Volume 2: Design Guidelines

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ID 683385
Date 5/08/2017
Public
Document Table of Contents

1.6. PLL Cascading

Arria II GZ PLLs, Stratix III PLLs, Stratix IV PLLs, Stratix V and Arria V GZ fractional PLLs (fPLLs), and the two middle PLLs in Arria II GX EP2AGX95, EP2AGX125, EP2AGX190, and EP2AGX260 devices can be cascaded using either the global or regional clock trees, or the cascade path between two adjacent PLLs.
Note: Use cascading PLLs at your own risk. You should use faster memory devices to maximize timing margins.

The UniPHY IP supports PLL cascading using the cascade path without any additional timing derating when the bandwidth and compensation rules are followed. The timing constraints and analysis assume that there is no additional jitter due to PLL cascading when the upstream PLL uses no compensation and low bandwidth, and the downstream PLL uses no compensation and high bandwidth.

The UniPHY IP does not support PLL cascading using the global and regional clock networks. You can implement PLL cascading at your own risk without any additional guidance and specifications from Intel® . The Quartus Prime software does issue a critical warning suggesting use of the cascade path to minimize jitter, but does not explicitly state that Intel® does not support cascading using global and regional clock networks.

Some Arria II GX devices (EP2AGX95, EP2AGX125, EP2AGX190, and EP2AGX260) have direct cascade path for two middle right PLLs. Arria II GX PLLs have the same bandwidth options as Stratix IV GX left and right PLLs.

The Arria 10 External Memory Interface IP does not support PLL cascading.

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