GS2989 Datasheet, PDF (14/19 Pages) Gennum Corporation – Dual-Slew-Rate, Dual-Output Cable Driver with 3Gb/s Capability

5. Application Information
5.1 PCB Layout
Special attention must be paid to component layout when designing serial digital
interfaces for HDTV.
An FR-4 dielectric can be used, however, controlled impedance transmission lines are
required for PCB traces longer than approximately 1cm. Note the following PCB artwork
features used to optimize performance:
• The PCB trace width for HD rate signals is closely matched to SMT component
width to minimize reflections due to changes in trace impedance
• The PCB ground plane is removed under the GS2989 output components to
minimize parasitic capacitance (NOTE: care should be taken, as removing too much
of the plane will make the system susceptible to EMI)
• The PCB ground plane is removed under the GS2989 RSET pin and resistor to
minimize parasitic capacitance. The RSET resistor should be directly connected to
the VCC plane
• Input and output BNC connectors are surface mounted in-line to eliminate a
transmission line stub caused by a BNC mounting via high-speed traces
• High-speed traces are round-curved (rather than 45° or 90° angles) to minimize
impedance variations due to change of PCB trace width
NOTE: For more recommendations on Trace Lengths, ORL Inductor Values and other
PCB Layout Considerations, please refer to Gennum’s GS2989 Design Guide
(Doc ID 52070).
GS2989 Dual-Slew-Rate, Dual-Output Cable Driver
with 3Gb/s Capability
Data Sheet
52133 - 4
December 2010
14 of 19