GS1528-CKA Gennum Corp., GS1528-CKA Datasheet - Page 5

• Manufacturer Part Number: GS1528-CKA
• Description: HD-LINX II Multi-Rate SDI Dual Slew-Rate Cable Driver
• Manufacturer: Gennum Corp.

OUTPUT RETURN LOSS MEASUREMENT
To perform a practical return loss measurement, it is
necessary to force the GS1528 output to a DC high or low
condition. The actual measured return loss will be based on
the outputs being static at V
operating conditions the outputs of the GS1528 swing
between V
return loss will not represent the actual operating return
loss.
A simple method of calculating the values of actual
operating return loss is to interpolate the two return loss
measurements. In this way, the values of return loss are
estimated at V
measurements at V
The two values of return loss (high and low) will typically
differ by several decibels. If the measured return loss is R
for logic high and R
be interpolated as follows:
where R
interpolated logic low value.
For example, if R
interpolated values are R
OUTPUT AMPLITUDE ADJUSTMENT
The output amplitude of the GS1528 can be adjusted by
changing the value of the R
and Table 1. For an 800mV
tolerance, a value of 750Ω is required. A ±1% SMT resistor
should be used.
The R
the GS1528. The resistor should be placed as close as
possible to the R
should be minimized at this node by removing the PCB
groundplane beneath the R
GENNUM CORPORATION
SET
R
R
IH
IH
IL
resistor is part of the high speed output circuit of
= R
is the interpolated logic high value and R
CC
= R
-0.4V and V
L
H
+(R
- (R
Fig. 6 Static Protection Diodes
CC
SET
H
H
H
CC
-0.4V and V
-R
L
-R
pin. In addition, the PCB capacitance
= -18dB and R
for logic low, then the two values can
and V
L
L
GS1528
)/4
)/4 and
IH
CC
= -17dB and R
-1.2V, so the measured value of
SET
SET
CC
p-p
CC
-1.6V.
resistor and the R
resistor as shown in Figure 7
output with a nominal ±7%
or V
CC
-1.2V based on the
CC
L
-1.6V. Under normal
= -14dB, then the
IL
SDO
SDO
= -15dB.
SET
pin.
IL
is the
H
5
NOTE: For reliable operation of the GS1528 over the full
temperature range, do not use an R
APPLICATION INFORMATION
APPLICATION INFORMATION
APPLICATION INFORMATION
APPLICATION INFORMATION
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 groundplane is removed under the GS1528 output
components to minimize parasitic capacitance.
The PCB ground plane is removed under the GS1528 R
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 which are curved to minimize
impedance variations due to change of PCB trace width.
TABLE 1: R
1100
1000
900
800
700
600
500
R
SET
SET
995
824
750
600
573
Fig. 7 Output Amplitude Adjustment
vs V
R (Ω)
OD
600
R
SET
700
R (Ω)
SET
800
OUTPUT SWING
value below 573Ω.
1040
608
734
800
884
900
16632 - 0
1000
SET
pin