Clock/Data Alignment

When an Explicit clock recovery method is selected, the Clock/Data Alignment control lets you specify whether clock edges are:

• Center Aligned with data.

  Normally, the clock is referenced to the center of the data eye. When the clock edge occurs, data is sampled to determine its logical value. This is called Center Aligned and is the default setting.

• Edge Aligned with data.

  In some unusual cases, the clock edges and data edges may occur in phase. The clock edges occur about the same time as the data edges. This is called Edge Aligned.

The Clock/Data Alignment selection has implications for things like symbol recovery and Time Interval Error (TIE) measurements:

• For symbol recovery:

  • When Center Aligned, the data waveform is sampled at the clock location to extract the symbols.

  • When Edge Aligned, the data waveform is sampled at the midpoint between two clocks to extract the symbols.

• TIE is a measure of where the data edges occur relative to where they should occur according to the recovered clock:

  • When Center Aligned, TIE is calculated by measuring the data edge times to the midpoint between two clocks.

  • When Edge Aligned, TIE is calculated by measuring the data edge relative to the corresponding clock edge.