Reference Levels VI

Owning Palette: Level VIs

Requires: Jitter Analysis Toolkit

Computes reference levels based on an input waveform or on state levels computed before this VI runs. LabVIEW uses the reference levels to define the boundaries of edges in waveforms. Wire data to the state levels settings input and the waveform input to determine the polymorphic instance to use or manually select the instance.

Details  Examples

Reference Levels (waveform in, DBL)

Use this polymorphic instance to calculate the reference levels of a waveform when you do not know its high and low state levels.

This instance operates on the waveform data type when the Y data values are double-precision, floating-point numeric values. Use the I8 instance of this VI with integer data to reduce the size of the data and the memory usage.

	waveform is the waveform to measure. t0 specifies the start time of the waveform. dt specifies the time interval in seconds between data points in the waveform. Y specifies the data values of the waveform.
	state levels settings sets the method this VI uses to determine the high and low state levels of a waveform. Note  With any method you use to calculate state levels, very irregular waveforms might result in inaccurate state level measurements. In this case, manually specify state levels that are appropriate for the specific waveform. method specifies how LabVIEW computes the high and low state levels of the waveform. 0 histogram (default)—Returns the levels of the histogram bins with the maximum number of hits in the upper and lower regions of the waveform. The upper and lower regions of the waveform include the upper and lower 40%, respectively, of the peak-to-peak range of the waveform. 1 peak—Searches the entire waveform for its maximum and minimum levels. 2 auto select—Determines whether the histogram bins that correspond to the high and low state levels each have over 5% of the total hits. If so, LabVIEW returns those results. Otherwise, LabVIEW uses the peak method. This ensures a reasonable answer for either a square wave (ignoring the overshoot and undershoot) or a triangle wave (where a histogram fails). 3 auto select independent—Determines whether the histogram bins that correspond to the high and low state levels each have over 5% of the hits within their respective regions. If so, LabVIEW returns those results. Otherwise, LabVIEW uses the peak method. This ensures a reasonable answer when positive pulses in the waveform are much longer than negative pulses, and vice versa, such as when the waveform contains duty cycle distortion. histogram size specifies the number of bins in the histogram LabVIEW uses to determine the high and low state levels of the waveform. If you select the peak method, LabVIEW ignores this input. histogram method specifies how LabVIEW computes the high and low state levels of the waveform. Currently, mode is the only available histogram method. 0 mode search width/total bins specifies the percent level of the waveform at which to set the upper boundary of the region that corresponds to the low state of the waveform and the lower boundary of the region that corresponds to the high state. LabVIEW uses the lesser of this value and 0.5. The default is 0.45. If you select the peak method, LabVIEW ignores this input.
	reference levels settings defines how this VI measures the reference levels of the waveform. high ref level specifies the high reference level of the waveform as a percentage (default) or in absolute units. The default is 90.00. mid ref level specifies the middle reference level as a percentage (default) or in absolute units. The default is 50.00. low ref level specifies the low reference level as a percentage (default) or in absolute units. The default is 10.00. ref units specifies how this VI uses the high ref level, mid ref level, and low ref level inputs to compute the actual reference levels of the waveform. 0 absolute—Specifies to return the input reference level values unchanged in the reference levels output. 1 percent (default)—Specifies to calculate the reference levels using the input reference level settings as percentages of the amplitude of the high and low state levels. For more information about how this VI calculates reference levels, refer to the Details section of this topic.
	error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
	waveform dup returns waveform unchanged.
	state levels returns the state level information from the waveform. amplitude is the difference between high state level and low state level. high state level returns the level at which a pulse or transition waveform is defined to be in its highest state. low state level returns the level at which a pulse or transition waveform is defined to be in its lowest state
	reference levels contains the high, middle, and low reference levels of a waveform in absolute units. high ref level returns the high reference level. mid ref level returns the middle reference level. low ref level returns the low reference level.
	error out contains error information. This output provides standard error out functionality.

Reference Levels (waveform in, I8)

Use this polymorphic instance to calculate the reference levels of a waveform when you do not know its high and low state levels.

This instance operates on the waveform data type when the Y data values are 8-bit signed integers.

	waveform is the waveform to measure. t0 specifies the start time of the waveform. dt specifies the time interval in seconds between data points in the waveform. Y specifies the data values of the waveform.
	state levels settings sets the method this VI uses to determine the high and low state levels of a waveform. Note  With any method you use to calculate state levels, very irregular waveforms might result in inaccurate state level measurements. In this case, manually specify state levels that are appropriate for the specific waveform. method specifies how LabVIEW computes the high and low state levels of the waveform. 0 histogram (default)—Returns the levels of the histogram bins with the maximum number of hits in the upper and lower regions of the waveform. The upper and lower regions of the waveform include the upper and lower 40%, respectively, of the peak-to-peak range of the waveform. 1 peak—Searches the entire waveform for its maximum and minimum levels. 2 auto select—Determines whether the histogram bins that correspond to the high and low state levels each have over 5% of the total hits. If so, LabVIEW returns those results. Otherwise, LabVIEW uses the peak method. This ensures a reasonable answer for either a square wave (ignoring the overshoot and undershoot) or a triangle wave (where a histogram fails). 3 auto select independent—Determines whether the histogram bins that correspond to the high and low state levels each have over 5% of the hits within their respective regions. If so, LabVIEW returns those results. Otherwise, LabVIEW uses the peak method. This ensures a reasonable answer when positive pulses in the waveform are much longer than negative pulses, and vice versa, such as when the waveform contains duty cycle distortion. histogram size specifies the number of bins in the histogram LabVIEW uses to determine the high and low state levels of the waveform. If you select the peak method, LabVIEW ignores this input. histogram method specifies how LabVIEW computes the high and low state levels of the waveform. Currently, mode is the only available histogram method. 0 mode search width/total bins specifies the percent level of the waveform at which to set the upper boundary of the region that corresponds to the low state of the waveform and the lower boundary of the region that corresponds to the high state. LabVIEW uses the lesser of this value and 0.5. The default is 0.45. If you select the peak method, LabVIEW ignores this input.
	reference levels settings defines how this VI measures the reference levels of the waveform. high ref level specifies the high reference level of the waveform as a percentage (default) or in absolute units. The default is 90.00. mid ref level specifies the middle reference level as a percentage (default) or in absolute units. The default is 50.00. low ref level specifies the low reference level as a percentage (default) or in absolute units. The default is 10.00. ref units specifies how this VI uses the high ref level, mid ref level, and low ref level inputs to compute the actual reference levels of the waveform. 0 absolute—Specifies to return the input reference level values unchanged in the reference levels output. 1 percent (default)—Specifies to calculate the reference levels using the input reference level settings as percentages of the amplitude of the high and low state levels. For more information about how this VI calculates reference levels, refer to the Details section of this topic.
	error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
	waveform dup returns waveform unchanged.
	state levels returns the state level information from the waveform. amplitude is the difference between high state level and low state level. high state level returns the level at which a pulse or transition waveform is defined to be in its highest state. low state level returns the level at which a pulse or transition waveform is defined to be in its lowest state
	reference levels contains the high, middle, and low reference levels of a waveform in absolute units. high ref level returns the high reference level. mid ref level returns the middle reference level. low ref level returns the low reference level.
	error out contains error information. This output provides standard error out functionality.

Reference Levels (states in)

Use this polymorphic instance to calculate the reference levels of a waveform from high and low state levels computed before this VI runs.

	state levels specifies the high and low state values in the waveform and the corresponding amplitude. You can use the State Levels VI to generate this cluster. amplitude is the difference between high state level and low state level. high state level specifies the level at which a pulse or transition waveform is defined to be in its highest state. low state level specifies the level at which a pulse or transition waveform is defined to be in its lowest state
	reference levels settings defines how this VI measures the reference levels of the waveform. high ref level specifies the high reference level of the waveform as a percentage (default) or in absolute units. The default is 90.00. mid ref level specifies the middle reference level as a percentage (default) or in absolute units. The default is 50.00. low ref level specifies the low reference level as a percentage (default) or in absolute units. The default is 10.00. ref units specifies how this VI uses the high ref level, mid ref level, and low ref level inputs to compute the actual reference levels of the waveform. 0 absolute—Specifies to return the input reference level values unchanged in the reference levels output. 1 percent (default)—Specifies to calculate the reference levels using the input reference level settings as percentages of the amplitude of the high and low state levels. For more information about how this VI calculates reference levels, refer to the Details section of this topic.
	error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
	state levels dup returns the state levels unchanged. amplitude is the difference between high state level and low state level. high state level returns the level at which a pulse or transition waveform is defined to be in its highest state. low state level returns the level at which a pulse or transition waveform is defined to be in its lowest state
	reference levels contains the high, middle, and low reference levels of a waveform in absolute units. high ref level returns the high reference level. mid ref level returns the middle reference level. low ref level returns the low reference level.
	error out contains error information. This output provides standard error out functionality.

Reference Levels Details

When ref units is percent, this VI uses the following equation to compute the reference levels:

where    y_x% is the value of a particular reference level

level(s₁) is the low state level

A is the difference of the high and low state levels, or amplitude

x represents the percentage for that reference level that you specify in reference levels settings.

Examples

Refer to the following VIs for examples of using the Reference Levels VI:

• Basic Eye Diagram VI: labview\examples\Jitter Analysis\Eye Diagram Measurements
• Simulated Signal with Jitter VI: labview\examples\Jitter Analysis\Jitter Measurements
• Overshoot Demo VI: labview\examples\Jitter Analysis\Level Measurements