GS1528A
GS1528A / GS9068A Data Sheet
SDO
SDO
Figure 5-3: Static Protection Diodes
5.3 Output Return Loss Measurement
To perform a practical return loss measurement, it is necessary to force the
GS1528A/9068A 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 device 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:
RIH = 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.
30953 - 4 January 2006
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