User`s guide

Locktime Tool
Applications
• Measure Locktime or PLL settling time.
• View the synchronous jitter.
• Locktime Tool enables the user to view information about the measured function of the signal on the
measurement channel with respect to some arming point. The user can view any synchronous jitter
pattern that may exist. View the frequency or period settling time of a PLL after a change, such as a
lock signal or input frequency change.
Overview
The Locktime tool is actually an automated histogram process. The tool gathers time measurements to
create many histograms. Statistical information from these histograms is then plotted.
The Locktime tool can be used for making synchronous time measurements with an external arm signal
used as a point of reference. This allows the user to view locktime, or settling time.
This tool uses the Arm (see Arming) for synchronization to a signal such as a frequency lock or power-
up signal. In the following discussion, Period measurements are used, though rise-time, fall-time,
positive pulse width, negative pulse width and frequency can be chosen.
A histogram of time measurements is created of the period following the arm. The period being
measured is then incremented to the 2nd period following the arm and a histogram is created. Then the
3rd period is measured to create a histogram and this process repeats until the Span (edges) value has
been reached. The number of time measurements in each histogram is chosen by Hits per Measure.
Statistical information from these histograms is then plotted relative to the corresponding period. So in
View, if Time is chosen, the mean (y-axis) is plotted relative to the period after the arm (x-axis).
Similarly, other Views will plot the Pk-Pk or 1-sigma values.
The Arm must be periodic in order for the measurement process to work. A single power up or a single
frequency lock will not allow this process to occur. Using a signal from a pulse generator works well as
the Arm and lock signal.
© WAVECREST Corporation 2005 Section 4 - GigaView
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