Spartan-3A LVDS
Demonstration
A Reference Design for Spartan™-3A Starter kit
Rev 1: June 2007
Page 2
LVDS Demonstration
This demo shows how the Spartan-3A starter kit uses the ChipScope™ debugger to help
check the high speed LVDS performance using low cost connectors (J2, J15).
While the design does NOT show the maximum achievable performance, the designer will
get a very good idea of the performance and can see how to better understand the DCM
operation and debugging without using extensive oscilloscope setups.
Highlighted features
– XAPP485 – LVDS Receiver that deserializes LVDS for FPD applications
– XAPP486 – LVDS Transmitter that serializes LVDS for FPD applications
– DCM
• Clock synchronization is always critical in any high speed design. Even at the 600 Mbps data rates
used by displays, balancing the routing delays within the device becomes an important factor. For the
LVDS design the DCM is used to both synchronize incoming data as well as create the multiplied
clock rates required for displays.
• Additional features of the DCM are used to better understand the skew and approximate data eye
size.
– ChipScope – Debugging high speed data
– VIO – Used to control demo using ChipScope
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LVDS Design Block Diagram
One of five different data patterns are
generated by the Pattern Generator block.
The data is then serialized using the 7-to-1
LVDS Tx block (XAPP486) and sent over a
low cost twisted pair cable (not included).
The data is received and de-serialized
using the LVDS deserializer (XAPP485).
An equivalent pattern generator is then
synchronized to the incoming data to
check to ensure the data has been
received correctly.
The number of pattern errors are tracked
by flags within the design so that the
design can determine which channel is
failing. To see what data is transmitted and
received the designer can use the supplied
ChipScope project.
The parallel 100 ohm termination
resistors that are required for LVDS
receivers use the on-chip termination,
DIFF_TERM.
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LVDS For Displays
• The design is set up to match commonly found
display devices using LVDS. Further
modifications may be easily made in the design
files as discussed in XAPP485/486.