Preshoot

Preshoot is a distortion that precedes a waveform edge transition. This measurement may be compatible with PAM signals, depending on the PAM waveform. Preshoot occurs before the edge crosses through the waveform threshold levels and can occur on either the rising or falling edge. Annotation labels are placed on the waveform showing the top (100%) and base (0%) levels. These levels are calculated over the display, waveform, or region. Therefore, the top and base labels are displayed on both ends of the graticule or region. An additional annotation label is placed on the peak amplitude of the preshoot (local Vmax or Vmin). Perform preshoot on single-valued waveforms only.

If the waveform edge is falling, the preshoot is computed as follows:

When computing preshoot, a local minimum and maximum (also referred to as preshoot intervals) is located. The local minimum or maximum occurs in the first 50 percent of the time defined along the threshold. The local maximum (preshoot interval) is found half way from the 90% threshold level on the rising edge to the next 90% threshold level at the falling edge.

If the waveform edge is rising (upward slope), the preshoot is computed as follows:

The local minimum is found half way from the 10% threshold level of the falling edge to the next 10% threshold level at the next rising edge. The default setting for the threshold levels are the 10% to 90% points on the transition.

PAM Compatibility. Because this measurement is based on waveform top and base levels and the passing of the waveform's edge through lower, middle, and upper thresholds, the measurement is not designed for PAM signals. However, the measurement may be able to be made on PAM signals if the waveform top and base definitions are manually set. This can be attempted using the Thresholds tab of the Configure Measurements dialog box.

This measurement may be compatible with PAM signals, depending on the PAM waveform.

Configurable Measurement Parameters

This measurement is affected by the following settings (choose Measure > Thresholds...):

To measure

  1. Click the toolbar's Amplitude tab.
  2. Click the toolbar's More buttons to locate the Preshoot button.
  3. Click the button.
  4. Select the signal on which to make the measurement.
  5. Select the Region in which to make the measurement:
    • Displayed Waveform — is what you see in the waveform window (which can be a zoomed-in view of the complete waveform).
    • Entire Waveform — specifies the complete waveform.
    • Region N — If regions are enabled for the selected signal, you can select one of those regions.
  6. Select the number of Occurrences to measure per acquisition:
    • Measure One — makes one measurement per acquisition using edges closest to the timebase reference.
    • Measure All — makes as many measurements per acquisition as possible using all edges in the acquisition. In this case, the measurement closest to the timebase reference is the "current" measurement (and is the one with annotations).

  7. Select the Edge Direction: Rising or Falling to specify the edges to be measured.

SCPI Command

:MEASure:VERTical:PREShoot