1000BASE-T/100BASE-TX/10BASE-T Physical Layer Compliance Tests Manual
Intel Confidential
33
100BASE-TX Differential Output Voltage (UTP)
4. Select the horizontal cursors. Move one cursor to +V
OUT
and the other to the zero crossing of
the waveform.
can be used as a reference. The differential output voltage is the
difference between the two cursors. V
OUT
is defined as the intersection of the straight line best
fit for amplitude with the vertical line indicating the start of the transition from 0 V to V
OUT
.
This does not include overshoot.
5. Record actual values.
6. Repeat steps 4 through 5 on the negative going waveform. Configure the oscilloscope using
7. CV
OUT
and -V
OUT
fall within specification.
Note:
+V
OUT
should be between 950 mV and 1050 mV. Although it is not specifically mentioned in
specification 9.1.2.2, -V
OUT
should also be between -950 mV and -1050 mV.
Record Length
Large enough to enable viewing of one complete MLT-3 (3-level)
waveform by scrolling horizontally
Display Type
Average
Table 8-2. Setting for Negative Differential Output Voltage (UTP)
Scope Parameter
Setting
Pulse Width Triggering
Triggering information is provided to give a good starting point for measurement. The
following guidelines will help the tester achieve the most stable display.
1. Set the trigger level to approximately 500 mV.
2. Select pulse width triggering.
3. Set the upper bound parameter to approximately 200 ns and the lower bound
parameter to approximately 116 ns.
4. Set the trigger mode to normal.
5. Increase the lower bound parameter gradually until the triggering is lost.
6. Decrease the lower bound parameter slowly in 5 ns increments until triggering
resumes.
7. Decrease the upper bound parameter until it is 5 ns to 15 ns above the lower trigger
bound parameter.
Measuring Peak Voltages
When measuring positive and negative peak voltages, do not use the absolute values on the
screen. Often it will appear as thought the start and finish of the MLT-3 waveform do not go
through zero. This is caused by the oscilloscope or probes adding in a small DC offset. To
record the correct peak values, run one horizontal cursor through the middle of the “zero” of
the waveform as shown in
and
, and use the other cursor to measure
the peak by running it though the average final value of the waveform. Record the average
value between the two cursors.