# PAM VEC

The Vertical Eye Closure (VEC) PAM measurement is based on an Eye Height measurement at a probability of 1E-5 and level measurements (used to determine AV). Eye Height is measured with the same algorithm as is used for the PAM Eye Heights measurement. This measurement can also be used for NRZ coded signals. VEC is measured for each of the PAM eyes. The higher the result (decibels) the more the eye is closed.

## (Vertical Eye Closure) Select Measurement Settings dialog

When the measurement button is first clicked, the (Vertical Eye Closure) Select Measurement Settings dialog is shown. Use this dialog to select the measurement's Eye Opening Definition.

The VEC measurement is referenced to the eye opening, where the ideal opening is the spacing between the measured levels surrounding the eye. The levels are measured using the same algorithm as is used in the PAM Levels measurement.

### Eye Opening Definition

Settings Dialog for Zero Hits

The Eye Opening Definition can be set to Zero Hits, shown in the above picture, or At Probability, shown in this picture. When At Probability is selected the dialog is expanded to give access to the Eye Opening Probability setting. The default Eye Opening Probability is 10–6.

Settings Dialog for At Probability

The IEEE method of measuring VEC would be to select the Reference to Eye Opening and the Eye Opening Definition to At Probability with a probability of 1.0E–5.

## To measure

1. Click Auto Scale in the menu toolbar.
2. Click the measurement toolbar's PAM tab.
3. On the toolbar, locate and click the Vertical Eye Closure button.

## SCPI Command

`:MEASure:EYE:PAM:VECLosure`