Teledyne LeCroy QPHY-ENET - Manual (Page 74)

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QPHY-ENET Operator’s Manual Rev G
Signal Path Calibration Procedure
Even the highest quality differential probes will be non-linear and have noise levels that may be unacceptable for
measuring 1000Base-T Ethernet signals. The noise and distortion in the probe will add to the signal being
measured and may result in mask or distortion failures. One way to eliminate probing effects is to connect the
signal under test directly to the oscilloscope inputs. By using the 50 Ω impedance of the oscilloscope channels
between each signal wire and ground, a 100 Ω differential impedance across the wire pair is achieved. This
configuration gives the ideal compliance load and eliminates the probe and its distortions.
This procedure measures the attenuation of the signal due to the fixture. The procedure is very important for
1000Base-T Mode 1 and 4 tests. Follow the procedure to set correct attenuation ratio of the fixture. The disturbing
signal adjustment, which is described in the next section, should be done, in order to set right amplitude at the
signal path. This procedure is using section D on the TF-ENET-B test fixture.
Figure 58. Ethernet test menu for Differential Data connection confirmation
Before proceeding with the calibration, please make sure that you have correct settings shown above. TF-ENET-
B uses 2 same length SMA cables connected to Channel 2 and Channel 3.
Differential Data on 2 Channels check box should be checked.
Source for + Data is C2.
Source for – Data is C3.
Note: When you check the Disturber Present box, the Fixture Calibration tab is shown.