GS2994 Datasheet, PDF (15/20 Pages) Semtech Corporation – GS2994 Adaptive Cable Equalizer

(0V), OP_CTL is forced LOW (0V). The input level at which the part is muted can be set
by the SQ_ADJ pin through suitable voltage variances as described in Section 4.4.
NOTE: when SQ_ADJ functionality is used and/or in Auto_mute, the SLEEP pin should
be left open.
5. Application Information
5.1 High Gain Adaptive Cable Equalizers
The GS2994 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 have high gain in 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 GS2994 has an increase in gain over the GS2974A at critical HD and 3Gb/s
frequencies, and because of this, the GS2994 may 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.
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 3Gb/s 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 GS2994 input components to minimize
parasitic capacitance
• The PCB ground plane is removed under the GS2994 output components to
minimize parasitic capacitance
• High-speed traces are curved to minimize impedance changes
GS2994 GS2994 Adaptive Cable Equalizer
Data Sheet
53967 - 4
August 2012
15 of 20