GS2974B Datasheet, PDF (12/17 Pages) Gennum Corporation – HD-LINX III Adaptive Cable Equalizer

5. Application Information
5.1 High Gain Adaptive Cable Equalizers
The GS2974B is Gennum's latest multi-rate Adaptive Cable Equalizer. In order to
continue to extend the cable length that an equalizer will remain operational over, it is
necessary to increase the gain of the Equalizer.
A Video Cable Equalizer must provide wide band gain over a range of frequencies in
order to accommodate the range of data rates and signal patterns that are present in a
SMPTE compliant serial video stream.
The GS2974B has an increase in gain over the GS2974A at critical HD and 3Gbps
frequencies, and because of this the GS2974B will be sensitive to signals at the input that
the GS2974A will not be sensitive to.
Small levels of signal or noise present at the input pins of the Equalizer may cause
chatter at the output. In order to prevent this from happening, particular attention must
be paid to board layout.
Because the level and frequency of noise present in every system varies, please contact
Gennum at [e-mail] to get the most current recommendations.
5.2 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:
• PCB trace width for HD rate signals is closely matched to SMT component width to
minimize reflections due to change in trace impedance.
• The PCB ground plane is removed under the GS2974B input components to
minimize parasitic capacitance.
• The PCB ground plane is removed under the GS2974B output components to
minimize parasitic capacitance.
• High speed traces are curved to minimize impedance changes.
GS2974B GS2974B HD-LINX™ III Adaptive Cable
Equalizer
Data Sheet
45062 - 3
April 2009
12 of 17