GS1528 Data Sheet
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.
16632 - 5
June 2005
9 of 13
GENNUM [ GENNUM CORPORATION ]
