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Tuning Requirements
Often the reference source you select will also serve as the
VCO source for the PLL measurement. (The VCO source can
be either the device-under-test (DUT) or the reference
source.) To configure a PLL measurement, you will need to
know the following tuning information about the VCO
source you are using:
• Tuning Constant (Hz/V) (within a factor of 2)
• Tuning Voltage Range (V)
• Center Voltage of Tuning Range (V)
• Input Resistance of Tuning Port (ohms)
The primary consideration when evaluating a potential VCO
source for your measurement is whether it will provide the
system with sufficient Capture and Drift Tracking Ranges to
maintain lock throughout the measurement. To make this
determination, you must estimate what the drift range of the
sources you are using will be over the measurement period
(thirty minutes maximum). (Details on the relationship
between the Capture and Drift Tracking Ranges and the
tuning range of the VCO source are provided in Chapter 2.
This information will help you evaluate your VCO source
based on the estimated drift of your sources.)
Table 3-27 lists the tuning parameters for several VCO
options.
Signal Source Applications
3-145
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