EP2AGX95EF29C6N Datasheet, PDF (271/380 Pages) Altera Corporation – Device Interfaces and Integration

Chapter 8: High-Speed Differential I/O Interfaces and DPA in Arria II Devices
Source-Synchronous Timing Budget
8–25
Transmitter Channel-to-Channel Skew
Transmitter channel-to-channel skew (TCCS) is an important parameter based on the
Arria II transmitter in a source synchronous differential interface. This parameter is
used in receiver skew margin calculation.
TCCS is the difference between the fastest and slowest data output transitions,
including the TCO variation and clock skew. For LVDS transmitters, the TimeQuest
Timing Analyzer provides a TCCS report, which shows TCCS values for serial output
ports.
f You can get the TCCS value from the TCCS report (report_TCCS) in the Quartus II
compilation report under the TimeQuest analyzer or from the Arria II Device Data
Sheet chapter.
Receiver Skew Margin for Non-DPA Mode
Changes in system environment, such as temperature, media (cable, connector, or
PCB), and loading, effect the receiver’s setup and hold times; internal skew affects the
sampling ability of the receiver.
Different modes of LVDS receivers use different specifications, which can help in
deciding the ability to sample the received serial data correctly. In DPA mode, use
DPA jitter tolerance instead of receiver skew margin (RSKM).
In non-DPA mode, use RSKM, TCCS, and sampling window (SW) specifications for
high-speed source-synchronous differential signals in the receiver datapath. The
relationship between RSKM, TCCS, and SW is expressed by the RSKM equation
shown in Equation 8–1:
Equation 8–1.
RSKM
=
-^T---^U-----^I---–-----^S---^W--------–----^T----^C----^C----^S--
2
Where:
■ TUI—the time period of the serial data.
■ RSKM—the timing margin between the receiver’s clock input and the data input
SW.
■ SW—the period of time that the input data must be stable to ensure that the data is
successfully sampled by the LVDS receiver. The sampling window is the device
property and varies with the device speed grade.
■ TCCS—the difference between the fastest and slowest data output transitions,
including the t_CO variation and clock skew.
You must calculate the RSKM value to decide whether or not the data can be sampled
properly by the LVDS receiver with the given data rate and device. A positive RSKM
value indicates the LVDS receiver can sample the data properly; a negative RSKM
indicates the receiver cannot sample the data properly.
July 2012 Altera Corporation
Arria II Device Handbook Volume 1: Device Interfaces and Integration