GS1679 Cable Driver with HD/SD Capability

Data Sheet

54175 - 1

March 2011

10 of 16

4. Application Information

4.1 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 GS1679 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 GS1679 RSET pin and resistor to

minimize parasitic capacitance. The RSET resistor should be directly connected to

the VCC plane

• 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).

4.2 Typical Application Circuit

Figure 4-1: Typical Application Circuit

DDI

2

DDI

3

SDO1

12

SDO1

11

SDO2

10

SDO2

9

RSET

5

GS1679

VCC_Term

10n

GND

75R

4u7

4u7

4u7

4u7

75R

VCC_Term

VCC_Term

10n

75R

10n

GND

GND

4u7

4u7

75R

75R

75R

75R

75R

5n6*

5n6*

VCC

GND

VCC

10n

10n

GND

R*

* Typical value: varies with layout, and represents a trade-off

between good eye shape and output return loss.

5n6 is the optimum value for an 800mV output swing

and 3.3V operation.

4n7 is the optimum value for an 800mV output swing and

2.5V operation.

6n8 is the optimum value for an 1200mV output swing.

NOTE: All resistors in Ohms, capacitors in Farads,

and inductors in Henrys, unless otherwise stated.

*Customer to choose resistor value.

5n6*

5n6*