GS1508 Gennum Corporation, GS1508 Datasheet - Page 5

• Manufacturer Part Number: GS1508
• Description: Hd-linx(tm) HDTV Cable Driver
• Manufacturer: Gennum Corporation

OUTPUT RETURN LOSS MEASUREMENT
To perform a practical return loss measurement, it is
necessary to force the GS1508 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 GS1508 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 GS1508 can be adjusted by
changing the value of the R
and Table 1. For an 800mV
tolerance, a value of 53.6% is required. A ±1% SMT resistor
should be used.
The R
the GS1508. 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
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. 5 Static Protection Diodes
CC
H
H
SET
H
CC
-0.4V and V
-R
L
-R
= -18dB and R
for logic low, then the two values can
and V
L
L
GS1508
)/4
pin. In addition, PCB capacitance
)/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 6
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
TABLE 1: R
NOTE: For reliable operation of the GS1508 over the full
temperature range, do not use an R
1.000
0.800
0.600
0.400
0.200
0.000
R
500.0
150.0
75.0
53.6
43.2
SET
0.0000
Fig. 6 GS1508 Output Amplitude vs. 1/R
SET
R
vs V
OUT
0.0050
0.0100
0.0020
0.0067
0.0133
0.0187
0.0231
1/R
1 / R
SET
SET
(mho)
SET
0.0150
value below 49.9 .
OUTPUT SWING
0.0200
SET
0.095
0.298
0.575
0.785
0.937
522 - 02 - 04
0.0250