GS1528
SDO
SDO
Figure 3-3:
Static
Protection Diodes
3.4 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
CC
or V
CC
-1.6V. Under normal operating conditions the
outputs of the GS1528 swing between V
CC
-0.4V and V
CC
-1.2V, so the measured value of
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
CC
-0.4V and V
CC
-1.2V based on the measurements at V
CC
and V
CC
-1.6V.
The two values of return loss (high and low) will typically differ by several decibels. If
the measured return loss is R
H
for logic high and R
L
for logic low, then the two values can
be interpolated as follows:
R
IH
= R
H
- (R
H
-R
L
)/4 and
R
IL
= R
L
+ (R
H
-R
L
)/4
Where R
IH
is the interpolated logic high value and R
IL
is the interpolated logic low value.
For example: if R
H
= -18dB and R
L
= -14dB, then the interpolated values are R
IH
= -17dB
and R
IL
= -15dB.
GS1528 HD-LINX II Multi-Rate SDI Dual Slew-Rate
Cable Driver
Data Sheet
16632 - 9
August 2010
9 of 13
GENNUM [ GENNUM CORPORATION ]
