Teledyne LeCroy QPHY-ENET - Manual (Page 44)

44
QPHY-ENET Operator’s Manual Rev G
100Base-TX Amplitude, Symmetry, and Overshoot
The peak differential voltage of the MLT-3 signal should be +/-1 V, and the overshoot of transitions must be
limited to 5 %. Additionally, the symmetry between the positive and negative pulses must be within 2 % of each
other.
The overshoot value is measured by capturing the peak voltage at a transition from 0 V to 1 V (or 0 V to -1 V) and
comparing this level to the mean voltage of the signal when no transitions are occurring. The waveform for this
test must consist of a transition followed by 14 bit times during which the signal has no transitions.
The signal amplitude symmetry (SAS) is determined from the positive and negative peak voltage values using the
following equation:
02 . 1
| |
| |
98 . 0 ≤
−
+
≤
out
out
V
V
1. Apply power to the Device Under Test. An MLT3 signal trace should be displayed on the oscilloscope
screen at this point.
2. Set the Device Under Test to transmit the appropriate waveform, containing transitions between 0 V and
alternately +1 V and -1 V, with each state followed by 14 bit times during which no transition takes place.
3. Select 100Base-TX in the “Select Standard” field.
4. Select Amplitude Measurements in the “Select Test” field.
5. Check Differential Data on 2 Channels.
6. Enter C2 in the Source for + Data field and C3 in the Source for - Data field.
7. Touch the Set Up and Start Test button to begin testing.
8. Parameter P1 indicates the differential output voltage (DOV), P2 indicates the signal amplitude symmetry
(SAS), P3 indicates the overshoot for positive-going pulses, and P4 indicates the overshoot for negative-
going pulses.
9. The Average Result checkbox, when checked, averages measurements over the number of sweeps
(acquisitions) specified in the Avg Weight field.
PLEASE NOTE THE FOLLOWING:
• Maximizing the signal on the oscilloscope screen gives the best measurement results. Failure to adjust the signal to its highest level
may result in false failures being reported for the test.
• If you use a Random Pattern instead of the DCD (01010 NRZ bit) pattern, you may have a different test result.