2.1. Signal Integrity Analysis with Third-Party Tools
If the board trace is designed poorly or the route is too heavily loaded, noise in the signal can cause data corruption, while overshoot and undershoot can potentially damage input buffers over time.
As FPGA devices are used in high-speed applications, signal integrity and timing margin between the FPGA and other devices on the printed circuit board (PCB) are important aspects to consider to ensure proper system operation. To avoid time-consuming redesigns and expensive board respins, the topology and routing of critical signals must be simulated. The high-speed interfaces available on current FPGA devices must be modeled accurately and integrated into timing models and board-level signal integrity simulations. The tools used in the design of an FPGA and its integration into a PCB must be “board-aware”—able to take into account properties of the board routing and the connected devices on the board.
The Intel® Quartus® Prime software provides methodologies, resources, and tools to ensure good signal integrity and timing margin between Intel® FPGA devices and other components on the board. Three types of analysis are possible with the Intel® Quartus® Prime software:
- I/O timing with a default or user-specified capacitive load and no signal integrity analysis (default)
- The Intel® Quartus® Prime Enable Advanced I/O Timing option utilizing a user-defined board trace model to produce enhanced timing reports from accurate “board-aware” simulation models
- Full board routing simulation in third-party tools using Intel-provided or generated Input/Output Buffer Information Specification (IBIS) or HSPICE I/O models
I/O timing using a specified capacitive test load requires no special configuration other than setting the size of the load. I/O timing reports from the Intel® Quartus® Prime Timing Analyzer or the Intel® Quartus® Prime Classic Timing Analyzer are generated based only on point-to-point delays within the I/O buffer and assume the presence of the capacitive test load with no other details about the board specified. The default size of the load is based on the I/O standard selected for the pin. Timing is measured to the FPGA pin with no signal integrity analysis details.
The Enable Advanced I/O Timing option expands the details in I/O timing reports by taking board topology and termination components into account. A complete point-to-point board trace model is defined and accounted for in the timing analysis. This ability to define a board trace model is an example of how the Intel® Quartus® Prime software is “board-aware.”
In this case, timing and signal integrity metrics between the I/O buffer and the defined far end load are analyzed and reported in enhanced reports generated by the Intel® Quartus® Prime Timing Analyzer.
The information about signal integrity in this chapter refers to board-level signal integrity based on I/O buffer configuration and board parameters, not simultaneous switching noise (SSN), also known as ground bounce or VCC sag. SSN is a product of multiple output drivers switching at the same time, causing an overall drop in the voltage of the chip’s power supply. This can cause temporary glitches in the specified level of ground or VCC for the device.
This chapter is intended for FPGA and board designers and includes details about the concepts and steps involved in getting designs simulated and how to adjust designs to improve board-level timing and signal integrity. Also included is information about how to create accurate models from the Intel® Quartus® Prime software and how to use those models in simulation software.
The information in this chapter is meant for those who are familiar with the Intel® Quartus® Prime software and basic concepts of signal integrity and the design techniques and components in good PCB design. Finally, you should know how to set up simulations and use your selected third-party simulation tool.