Monitoring the S
DI Physical Layer
To Manually Mea
sure Risetime
Using Variable Gain
1. Pe rform the initial setup for Eye
measurements. (See page 61, Ta k i n g
Eye M easurements.)
2. Press the VAR button to turn on variable
gain.
3. Use the General knob to resiz e the
waveform to 10 major divisions. Position
the top and bottom of the waveform on
graticule lines.
4. Press the CURSOR button to display the
measurement cursors.
5. Po sition the first timing cursor at the
crossing of the rising edge of the Eye
waveform and the graticule line two
divisions above the bottom of the
waveform.
6. Position the second time cursor at the
crossing of the rising edge of the Eye
waveform and the graticule line two
divisions below the top of the waveform.
7. Notice the 20 – 80% rise time
measurement displayed in the Delta time
readout.
Automatic Eye Measurements
The following procedure describes how to take automatic m easurements of the Eye waveform. (Available with Option
PHY onl
y.)
NOTE. If you use the measurement cursors to manually measure the eye waveform, you m ay get a different result than that
shown in the automatic eye m easurements readout. This i s because the automatic amplitude measurement uses histograms
in ord
er to be minimally affected by overshoot, ringing, and noise on the signal. Similarly, the automatic risetime and falltime
measurements use histograms to find the centers of the d istributions of 20% and 80% crossings. The difference between
manual and automatic measurements is usually insigni ficant for clean, symmetrical signals.
64 Waveform Rasterizers Quick Start User Manual
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