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Absolute Measurement Fundamentals
The Phase Lock Loop Technique
Figure 6-2 Typical Relationship of Capture Range and Drift Tracking Range to Tuning Range of
VCO
As an Example:
A Peak Tuning Range of 1000 Hz will provide the following ranges:
Capture Range = 0.05 X 1000 Hz = 50 Hz
Drift Tracking Range = 0.24 X 1000 Hz = 240 Hz
Tuning Requirements
The peak tuning range required for your measurement will depend on the
frequency stability of the two sources you are using. The signals from the
two sources are mixed in the system's phase detector to create a beatnote. In
order for the loop to acquire lock, the center frequencies of the sources must
be close enough together to create a beatnote that is within the system's
Capture Range. Once the loop is locked, the frequency of the beatnote must
remain within the drift tracking range for the duration of the measurement.
In
Figure 6-3 on page
6-5, the ranges calculated in the previous example are
marked to show their relationship to the beatnote frequency.
6-4 Agilent Technologies E5500 Phase Noise Measurement System
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