TYPICAL APPLICATION CIRCUIT
V
CC
75
C
L
COMP
100n
COMP
75
75
PECL INPUT
4µ7
+
1
2
3
4
8
7
6
5
SDI
SDI
SDO
SDO
GND
OUT
OUT
75
GS1508
+
V
L
EE
COMP
Z
Z
0
0
V
CC
4µ7
C
R
V
COMP
SET
CC
1n
All resistors in ohms,
all capacitors in farads,
unless otherwise shown.
53.6
0µ1
TABLE 2: Typical Application Circuit Component Values
COMPONENT
RSET
VALUE
53.6
COMMENT
For 800mV Output
For 50Ω PCB trace impedance
Z0
50Ω
LCOMP
12nH
0.5pF
Typical value. Component value will vary depending on PCB layout.
Typical value. Component value will vary depending on PCB layout.
CCOMP
APPLICATION INFORMATION
PCB LAYOUT
Special attention must be paid to component layout when
designing serial digital interfaces for HDTV. Figures 8
through 11 show the artwork for a four layer printed circuit
evaluation board for the GS1508. The schematic is shown in
Figure 7. 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 GS1508
output components to minimize parasitic capacitance.
The PCB ground plane is removed under the GS1508 RSET
pin and resistor to minimize parasitic capacitance
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 are curved to minimize
impedance changes due to change of PCB trace width.
6
522 - 02 - 03
GENNUM [ GENNUM CORPORATION ]
