Procedures

Commands

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The Quartus^® II Timing Analyzer allows you to analyze the timing performance of designs that use the LVDS I/O standard. When you run a timing analysis on a design that uses an LVDS receiver megafunction, the Timing Analyzer reports the receiver input skew margin (RSKM) available before the LVDS receiver megafunction fails to operate. When you run a timing analysis on a design that uses the LVDS transmitter megafunction, the Timing Analyzer reports the transmitter channel-to-channel skew (TCCS).

The Timing Analyzer calculates LVDS timing by deriving RSKM from the data and clock signal delays in each LVDS circuit. RSKM is defined as the total time margin that remains after subtracting the sampling window (SW) size and the transmitter channel-to-channel skew (TCCS) from the time unit interval (TUI), as shown in the following formula:

RSKM = (TUI - SW - TCCS) /2

The time unit interval is the LVDS clock period (1/f_MAX). The sampling window is the period of time that the input data must be stable to ensure that the data is successfully sampled by the LVDS receiver megafunction. The sampling window size varies by device speed grade. TCCS is the difference between the fastest and slowest data output transitions, including the t_CO variation and clock skew. In order to obtain an accurate analysis of an LVDS circuit, you should specify any appropriate project-wide external input delay or individual external input delay to the LVDS receiver megafunction. This external delay should equal the transmitter channel-to-channel skew (TCCS) plus any board skew. The following illustration shows the relationship between the LVDS timing parameters.

The Timing Analyzer reports the RSKM timing analysis results for each LVDS receiver megafunction in the design in the RSKM section of the Compilation Report. The Timing Analyzer reports the TCCS timing analysis results for each LVDS transmitter megafunction in the design in the TCCS section of the Compilation Report. After timing analysis is complete, you can list the timing paths in the RSKM and TCCS calculations.

	More information is available on Timing Analysis on the Altera® web site.

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