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Probability Density Function: PDF


PDF computes the power probability density function (PDF) a time domain signal.


Name Type Range
Block Diagram System Diagram N/A
Test Point System Meter N/A
Number of Bins Integer value >=2
Lower Threshold Real value <Upper Threshold
Upper Threshold Real value >Lower Threshold
Data Window in Samples Integer value >0
Sample Accumulation List of options N/A
Threshold Limit Handling List of options N/A
Y Axis Format List of options N/A
Power Display List of options N/A
*Start Offset Real value >= 0
*Signal Delay List of options N/A

* indicates a secondary parameter

NOTE: If the selected system diagram is configured for a swept simulation, the measurement will have additional parameters for specifying the plotting configuration for each swept parameter. These parameters are dynamic and change based upon which data source is selected. See Section 1.3.3 in the AWR VSS Modeling Guide for details.


This measurement returns real values.

Graph Type

This measurement can be displayed on a histogram graph, rectangular graph, or tabular grid.

Computational Details

The power probability density function (PDF) is computed by generating a a histogram of the measured signal. The number of samples histogramed is determined by the Data Window in Samples and Sample Accumulation parameters. If Sample Accumulation is:

  • Only Data Window Samples: The number of samples is Data Window in Samples.

  • Cumulative: All the samples up to the current measured time are used (the current measured time is determined by the slider bar).

The samples are sorted by instantaneous power into Number of Bins bins. The thresholds of the bins are calculated from:

Pbin,min = LT+bin·(UT-LT)/N   bin=0,1,...,N-1

where Pbin,min is the smallest power value allowed in the bin, bin is the bin number, LT is the Lower Threshold parameter, UT is the Upper Threshold parameter, and N is the Number of Bins parameter.

Samples that fall below the Lower Threshold value or are greater than or equal to the Upper Threshold value are included in bin 0 and bin N-1, respectively, if Threshold Limit Handling is set to "Include all samples". If Threshold Limit Handling is set to "Exclude samples beyond threshold limits" these samples are not counted.

The PDF is then calculated for each bin by dividing the number of samples in the bin by the total number of samples counted.

The x-axis can be set to display either the average power represented by each bin, or the average bin power relative to the average power of the histogramed samples (any samples discarded because they are outside the threshold range are not included in the average power calculation.) This is done through the Power Display parameter.

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