Linearity Results

Meas. mode:
Jitter
Waveform type:
PAM4
PAM Level Table

Do you know?

From FlexDCA, you can create non-linear PAM4 waveforms by adjusting waveform levels 1 and 2 on:

Click Linearity on Jitter Mode's Measurement (Meas) toolbar to activate one of three types of Linearity measurements. Linearity is a measure of the variance in amplitude separation (distribution) between the different PAM4 levels. The linearity ratio is always equal to or less than 1.0. The value 1.0 indicates that the separations between all levels are equal. For non-compliant measurements, you can use a PRBS signal. For compliant measurements, you will need to use compliance linearity pattern that is called out in the relevant standard.

After selecting Linearity, the Linearity Select Measurement Setting dialog opens where you select the type of linearity measurement:

  • RLM (Ratio Level Mismatch) (IEEE 802.3 Annex 120D). Shown in Level table as RLM (A_120D).
  • RLM (Ratio Level Mismatch) (IEEE 802.3 Clause 94). Shown in Level table as RLM (CL_94).
  • Eye Linearity (CEI 4.0). Shown in Level table as Eye Linearity.

The measurement algoritms used for the linearity measurements in Oscilloscope mode, Eye mode, and Jitter mode are identical. However, between these modes the measurement results yield small differences as the waveform data is represended differently within each instrument mode. For example, in oscilloscope mode measurement are made at the center of individual UIs while eye mode measurements are made on the center of all acquired UIs at once.

Examples of PAM Signal Linearity
Good Linearity Poor Linearity
V3-2 = V2-1 = V1-0 V3-2 ≠ V2-1 ≠ V1-0

RML IEEE 802.3 Annex 120D Measurement

Optimize this Algorithm

  1. Open the Amplitude Measurements tab of the Jitter Mode Measurement Setup dialog.
  2. In the Symbol Level Defintions field, select Average.

The linearity is defined as a function of the mean signal level transmitted for each PAM4 symbol level. The following picture identifies the voltage levels used in the following equations. In the following equations, the term ES stands for the Effective Symbol Level.

RML IEEE 802.3 Clause 94 Measurement

Optimize this Algorithm

  1. open the Amplitude Measurements tab of the Jitter Mode Measurement Setup dialog.
  2. In the Symbol Level Defintions field, select Consecutive Identical Digits and enter the longest number of identical digits possible with your waveform. The higher the number, the more accurate the results will be.

If the four levels measurements are the following values:

  • L3 = 14.6 mV
  • L2 = 7.5 mV
  • L1 = –8.0 mV
  • L0 = –15.2 mV

then, the linearity will be 0.715 as given by:

Eye Linearity (CEI 4.0) Measurement

Optimize this Algorithm

  1. Open the Thresholds tab of the Jitter Mode Measurement Setup dialog.
  2. Select Amplitude Level Width based on Percent and enter a Percent of UI of 5%. The level data is averaged over the center 5% of the UI.

Eye linearity is the ratio of minimum eye amplitudes (in Volts) to maximum eye amplitudes (in Volts).

SCPI Command

:MEASure:PLEVel:LINearity