Intel® Quartus® Prime Standard Edition User Guide: Design Recommendations

ID 683323
Date 9/24/2018
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1.2.1.3. Avoid Delay Chains in Clock Paths

Delays in PLD designs can change with each placement and routing cycle. Effects such as rise and fall time differences and on-chip variation mean that delay chains, especially those placed on clock paths, can cause significant problems in your design. Avoid using delay chains to prevent these kinds of problems.

You require delay chains when you use two or more consecutive nodes with a single fan-in and a single fan-out to cause delay. Inverters are often chained together to add delay. Delay chains are sometimes used to resolve race conditions created by other asynchronous design practices.

In some ASIC designs, delays are used for buffering signals as they are routed around the device. This functionality is not required in FPGA devices because the routing structure provides buffers throughout the device.