Scope Bilevel Measurements Panel

Bilevel Measurements

Note

The Bilevel Measurements panel requires a DSP System Toolbox™ or Simscape™ license.

Display information about signal transitions, overshoots, undershoots, and cycles. To open the Bilevel Measurements panel:

  • From the menu, select Tools > Measurements > Bilevel Measurements.

  • On the toolbar, click the Bilevel Measurements button.

Settings

The Settings pane enables you to modify the properties used to calculate various measurements involving transitions, overshoots, undershoots, and cycles. You can modify the high-state level, low-state level, state-level tolerance, upper-reference level, mid-reference level, and lower-reference level.

  • Auto State Level — When this check box is selected, the Bilevel measurements panel detects the high- and low- state levels of a bilevel waveform. When this check box is cleared, you can enter in values for the high- and low- state levels manually.

    • High — Used to specify manually the value that denotes a positive polarity, or high-state level.

    • Low — Used to specify manually the value that denotes a negative polarity, or low-state level.

  • State Level Tolerance — Tolerance within which the initial and final levels of each transition must be within their respective state levels. This value is expressed as a percentage of the difference between the high- and low-state levels.

  • Upper Ref Level — Used to compute the end of the rise-time measurement or the start of the fall time measurement. This value is expressed as a percentage of the difference between the high- and low-state levels.

  • Mid Ref Level — Used to determine when a transition occurs. This value is expressed as a percentage of the difference between the high- and low- state levels. In the following figure, the mid-reference level is shown as the horizontal line, and its corresponding mid-reference level instant is shown as the vertical line.

  • Lower Ref Level — Used to compute the end of the fall-time measurement or the start of the rise-time measurement. This value is expressed as a percentage of the difference between the high- and low-state levels.

  • Settle Seek — The duration after the mid-reference level instant when each transition occurs used for computing a valid settling time. This value is equivalent to the input parameter, D, which you can set when you run the settlingtime function. The settling time is displayed in the Overshoots/Undershoots pane.

Transitions Pane

Display calculated measurements associated with the input signal changing between its two possible state level values, high and low.

A positive-going transition, or rising edge, in a bilevel waveform is a transition from the low-state level to the high-state level. A positive-going transition has a slope value greater than zero. The following figure shows a positive-going transition.

When here is a plus sign (+) next to a text label, the measurement is a rising edge, a transition from a low-state level to a high-state level.

A negative-going transition, or falling edge, in a bilevel waveform is a transition from the high-state level to the low-state level. A negative-going transition has a slope value less than zero. The following figure shows a negative-going transition.

When there is a minus sign (–) next to a text label, the measurement is a falling edge, a transition from a high-state level to a low-state level.

The Transition measurements assume that the amplitude of the input signal is in units of volts. For the transition measurements to be valid, you must convert all input signals to volts.

  • High — The high-amplitude state level of the input signal over the duration of the Time Span parameter. You can set Time Span in the Main pane of the Visuals—Time Domain Properties dialog box.

  • Low — The low-amplitude state level of the input signal over the duration of the Time Span parameter. You can set Time Span in the Main pane of the Visuals—Time Domain Properties dialog box.

  • Amplitude — Difference in amplitude between the high-state level and the low-state level.

  • + Edges — Total number of positive-polarity, or rising, edges counted within the displayed portion of the input signal.

  • + Rise Time — Average amount of time required for each rising edge to cross from the lower-reference level to the upper-reference level.

  • + Slew Rate — Average slope of each rising-edge transition line within the upper- and lower-percent reference levels in the displayed portion of the input signal. The region in which the slew rate is calculated appears in gray in the following figure.

  • – Edges — Total number of negative-polarity or falling edges counted within the displayed portion of the input signal.

  • – Fall Time — Average amount of time required for each falling edge to cross from the upper-reference level to the lower-reference level.

  • – Slew Rate — Average slope of each falling edge transition line within the upper- and lower-percent reference levels in the displayed portion of the input signal.

Overshoots / Undershoots Pane

The Overshoots/Undershoots pane displays calculated measurements involving the distortion and damping of the input signal. Overshoot and undershoot refer to the amount that a signal respectively exceeds and falls below its final steady-state value. Preshoot refers to the amount before a transition that a signal varies from its initial steady-state value.

This figure shows preshoot, overshoot, and undershoot for a rising-edge transition.

The next figure shows preshoot, overshoot, and undershoot for a falling-edge transition.

  • + Preshoot — Average lowest aberration in the region immediately preceding each rising transition.

  • + Overshoot — Average highest aberration in the region immediately following each rising transition.

  • + Undershoot — Average lowest aberration in the region immediately following each rising transition.

  • + Settling Time — Average time required for each rising edge to enter and remain within the tolerance of the high-state level for the remainder of the settle-seek duration. The settling time is the time after the mid-reference level instant when the signal crosses into and remains in the tolerance region around the high-state level. This crossing is illustrated in the following figure.

    You can modify the settle-seek duration parameter in the Settings pane.

  • – Preshoot — Average highest aberration in the region immediately preceding each falling transition.

  • – Overshoot — Average highest aberration in the region immediately following each falling transition.

  • – Undershoot — Average lowest aberration in the region immediately following each falling transition.

  • – Settling Time — Average time required for each falling edge to enter and remain within the tolerance of the low-state level for the remainder of the settle-seek duration. The settling time is the time after the mid-reference level instant when the signal crosses into and remains in the tolerance region around the low-state level. You can modify the settle-seek duration parameter in the Settings pane.

Cycles Pane

The Cycles pane displays calculated measurements pertaining to repetitions or trends in the displayed portion of the input signal.

Properties to set:

  • Period — Average duration between adjacent edges of identical polarity within the displayed portion of the input signal. The Bilevel measurements panel calculates period as follows. It takes the difference between the mid-reference level instants of the initial transition of each positive-polarity pulse and the next positive-going transition. These mid-reference level instants appear as red dots in the following figure.

  • Frequency — Reciprocal of the average period. Whereas period is typically measured in some metric form of seconds, or seconds per cycle, frequency is typically measured in hertz or cycles per second.

  • + Pulses — Number of positive-polarity pulses counted.

  • + Width — Average duration between rising and falling edges of each positive-polarity pulse within the displayed portion of the input signal.

  • + Duty Cycle — Average ratio of pulse width to pulse period for each positive-polarity pulse within the displayed portion of the input signal.

  • – Pulses — Number of negative-polarity pulses counted.

  • – Width — Average duration between rising and falling edges of each negative-polarity pulse within the displayed portion of the input signal.

  • – Duty Cycle — Average ratio of pulse width to pulse period for each negative-polarity pulse within the displayed portion of the input signal.

When you use the zoom options in the Scope, the bilevel measurements automatically adjust to the time range shown in the display. In the Scope toolbar, click the Zoom In or Zoom X button to constrict the x-axis range of the display, and the statistics shown reflect this time range. For example, you can zoom in on one rising edge to make the Bilevel Measurements panel display information about only that particular rising edge. However, this feature does not apply to the High and Low measurements.

See Also

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