RJ PJ Separation VI

Owning Palette: Jitter VIs

Requires: Jitter Analysis Toolkit

Separates the random and periodic components of jitter in a jitter sequence and returns their RMS and peak-to-peak values.

Refer to the Details section of this topic for more information about random and periodic jitter.

Details  Examples

nTone

After this instance resamples the jitter sequence, as described in the Details section, it computes periodic jitter by modeling spectrum peaks as sinusoids and returning the sum of the identified sinusoids. This instance searches for peaks above a threshold within the amplitude spectrum of the jitter sequence.

	mode specifies how this VI identifies periodic jitter. 0 search for fit (default)—Searches for the minimum number of periodic components that are above the threshold and that yield the best fit of the data. This mode is useful because it provides an effective method that typically avoids over-fitting the data. 1 manual—Uses all tones whose amplitude is greater than the threshold to fit the data, up to a maximum number of tones you specify in the periodic fit settings input.
	jitter sequence is an array of jitter measurements.
	jitter timestamps describes the waveform and the times at which measurements in the corresponding sequence occur. t0 specifies the time at which the first sample occurs in the original waveform. dt specifies the time interval in seconds between the individual samples in the original waveform. indexes contains the index numbers of the samples in the waveform with values that fall at the crossing level.
	periodic fit settings contains the following elements that determine how this VI identifies periodic jitter. threshold specifies the minimum amplitude that peaks in the input sequence must exceed to be measured as periodic jitter. Setting a threshold allows you to ignore peaks that result from noise rather than periodic jitter mechanisms. max num tones specifies the maximum number of tones that this VI extracts. If you set max num tones to –1, this VI extracts all tones whose amplitude exceeds threshold.
	error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
	periodic search info returns the following elements that describe the periodic jitter in the jitter sequence. actual num tones returns the number of tones whose amplitude exceeds the threshold value that defines periodic jitter. min amplitude returns the amplitude of the smallest tone that exceeds the threshold.
	periodic jitter (s p-p) returns the periodic jitter measured as a peak-to-peak value.
	periodic jitter (s rms) returns the standard deviation of the periodic jitter in the jitter sequence.
	random jitter (s rms) returns the RMS value of the original jitter sequence minus the periodic jitter.
	error out contains error information. This output provides standard error out functionality.
	jitter spectrum is a graph that displays the spectrum of the original jitter sequence and the periodic jitter in the signal.

Spectral Trend

After this instance resamples the jitter sequence, as described in the Details section, it removes the DC level and then computes the power spectrum. This instance approximates and removes the spectrum trend and peaks, leaving the random portion of the spectrum.

	jitter sequence is an array of jitter measurements.
	jitter timestamps describes the waveform and the times at which measurements in the corresponding sequence occur. t0 specifies the time at which the first sample occurs in the original waveform. dt specifies the time interval in seconds between the individual samples in the original waveform. indexes contains the index numbers of the samples in the waveform with values that fall at the crossing level.
	error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
	periodic jitter (s p-p) returns the periodic jitter measured as a peak-to-peak value.
	periodic jitter (s rms) returns the standard deviation of the periodic jitter in the jitter sequence.
	random jitter (s rms) returns the RMS value of the original jitter sequence minus the periodic jitter.
	error out contains error information. This output provides standard error out functionality.
	jitter spectrum is a graph that displays the spectrum of the original jitter sequence and the periodic jitter in the signal.

RJ PJ Separation Details

If you wire waveform data to the jitter timestamps input, this VI resamples the input jitter sequence so it is evenly sampled. Otherwise, this VI assumes the measurements in the jitter sequence are already evenly sampled. Jitter sequences are not evenly sampled in time because the jitter is measured when the last value required to measure the jitter occurs. For example, time interval error values have corresponding timestamps at the level crossing of the data signal, while period jitter values have corresponding timestamps at the time of the second level crossing of the data signal. Thus, the resampling allows the jitter sequence to be evenly spaced for the FFT.

Random Jitter vs. Periodic Jitter

Random jitter is unbounded and does not achieve a maximum or minimum phase deviation within any time interval. By contrast, deterministic jitter is bounded and reaches maximum and minimum phase deviation values within an identifiable time interval. Periodic jitter is a type of systematic deterministic jitter that is not data dependent, or correlated with a specific sequence of bits in a waveform.

Examples

Refer to the following VIs for examples of using the RJ PJ Separation VI:

• Rj Dj Separation VI: labview\examples\Jitter Analysis\Jitter Measurements
• Rj Dj Delta Delta Separation VI: labview\examples\Jitter Analysis\Jitter Measurements