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