GS1528 Datasheet, PDF (9/13 Pages) Gennum Corporation – GS1528 HD-LINX-TM II Multi-Rate SDI Dual Slew-Rate Cable Driver

GS1528
SDO
GS1528 Data Sheet
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
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