:MEASure:EYE:PAM:LINearity

Eye Linearity Commands

Command Syntax

:MEASure:EYE:PAM:LINearity

Query Syntax

:MEASure:EYE:PAM:LINearity?

Description

Starts the PAM Linearity measurement, which measures the linearity RLM (Ratio Level Mismatch) between all amplitude levels of a PAM eye diagram. To specify the RLM algorithm used, use the :MEASure:EYE:PAM:LINearity:DEFinition child command. Linearity is a measure of the variance in amplitude separation (distribution) between the different PAM levels.

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

PAM linearity is measured as:

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:

which is equal to 0.715.

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.

Related Commands

:MEASure:PAM:EYE:ESTiming Receiver Sample Timing Configures the timing for sampling the signal data for all PAM measurements.
:MEASure:PAM:EYE:ELMethod Eye Center Location Selects the basis for determining the location of an eye's center on the waveform: at maximum eye width or maximum eye height.
:MEASure:PAM:EYE:PPERcent Eye Level Width Defines the timespan (in percentage of symbol width) over which an eye's amplitude level is measured.
:MEASure:PAM:EYE:TIME:LTDefinition Time of Level Specifies the method used to locate the time at which to measure an eye's level.

This measurement can be applied to both NRZ eye and PAM eye diagrams.

The linearity measurement will not yield the same value as the linearity measurement for PAM waveforms. This is due to the waveform measurement being made at the center of individual symbols, while eye diagram measurements are made on the center of all acquired symbols at once.

Example Command Sequence

:CHANnel1:SIGNal:TYPE PAM4  //  Specify signal type, if needed.
:SYSTem:AUToscale
:MEASure:EYE:PAM:LINearity:SOURce ECHannel1
:MEASure:EYE:PAM:LINearity:DEFinition RLMA120
:MEASure:EYE:PAM:LINearity  //  Measure and return value.
:MEASure:EYE:PAM:LINearity?