Configure Measurements (Top-Base Definition tab)

Meas. mode:

Use the Top-Base Definition tab of the Configure Measurements dialog box to define the top and base levels which are used to locate the lower, middle, and upper threshold levels.

You can select either Auto or Custom Top-Base Definitions.

Measurements Affected by Top-Base Definitions
Instrument Mode
Oscilloscope Eye TDR/TDT
Average Eye Amplitude Average
Duty Cycle Eye Height Fall Time
Fall Time Eye Width Rise Time
Rise Time One Level Δ Time
Frequency Zero Level Time at Edge
Preshoot Fall Time Time at Amplitude
Oversoot Rise Time
Period Crossing Time
+ Pulse Width Δ Time
— Pulse Width Crossing %
Δ Time Duty Cycle Distortion
Time at Edge Signal to Noise Ratio
Time at Amplitude Jitter
RMS Extinction Ratio
Amplitude at Upper OMA at Crossing
Amplitude at Middle VECP
Amplitude at Lower Bit Rate

Auto Top-Base Definitions

The Auto (default) setting computes the top (100%) and base (0%) levels, which are relative or proportional to the signal amplitude.

Top-Base definition values also affect Mask Test Alignment.

Custom Top-Base Definitions

The Custom setting allows you to enter absolute values for the top-base levels. Setting custom thresholds causes the measurement results table to display the text "user defined." The following table shows the amplitude units for the various waveform content windows.

Units Used for Displayed Content Window Graphs
Name of Content Window Graphs Amplitude Units Example Source
Waveform Selections
Oscilloscope, Eye, and TDR/TDT Modes
Window Volts and Watts Channel 2B
Differential 1A
Port 1+ (1A)
TDR/TDT T-Domain Parameters
Time-Ohms Ohms T11 Ohms
Time-Volts Volts TCC21 Volts
Time-% Percent T21 Percent
TDR/TDT S-Parameters and FFT Math Operator Waveforms
Freq-Mag Decibels FFT[2A] (F1)
S21 Magnitude
Phase Degrees FFT[2A] (F2)
S12 Phase
GrpDelay Seconds FFT[2A] (F3)
SCD11 Delay

The Custom option is not recommended when measuring eye diagrams.