Keysight Technologies N5511A, User Manual

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60 N5511A Phase Noise Test System User’s Guide
Absolute Measurement Fundamentals
The Phase-Lock Loop Circuit
The Phase-Lock Loop Circuit
The Capture and Drift tracking ranges
Like other PLL circuits, the phase lock loop created for the measurement has a
Capture Range and a drift tracking range. The Capture Range is equal to 5% of
the system's peak tuning range, and the drift tracking range is equal to 24% of
the system's peak tuning range.
The system's peak tuning range is derived from the tuning characteristics of
the VCO source used for the measurement. Figure 5-5 illustrates the
relationship that typically exists between the VCO's peak-to-peak tuning range
and the tuning range of the system. The system's drift tracking range is limited
to a small portion of the peak tuning range to minimize the possibility of
measurement accuracy degradation caused by non-linearity across the VCO's
tuning range.
Peak tune range (PTR)
The peak tuning range is determined using two parameters:
— VCO tuning sensitivity (Hz/Volt)
— Total voltage tuning range (Volts)
PTR = (VCO Tuning Sensitivity) X (Total Voltage Tuning Range)
PTR = (100 Hz/V) X (10 V) = 1000 Hz
Figure 5-5 Capture and Drift-Tracking Range with Tuning Range of VCO
As an example:
A Peak Tuning Range of 1000 Hz provides the following ranges:
Capture Range = 0.05 X 1000 Hz = 50 Hz
Drift Tracking Range = 0.24 X 1000 Hz = 240 Hz