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106 Agilent E5505A User’s Guide
5
Absolute Measurement Fundamentals
The Phase-Lock-Loop Technique
The phase lock loop measurement technique requires two signal sources; the
source-under-test and a reference source. This measurement type requires that
one of the two sources is a voltage-controlled-oscillator (VCO).
You will most likely use the phase lock loop technique since it is the
measurement type most commonly used for measuring signal source devices.
This chapter focuses on this measurement type for signal source
measurements.
Understanding the Phase-Lock-Loop Technique
This measurement technique requires two signal sources set up in a phase
locked loop (PLL) configuration. One of the sources is the DUT. The second
source serves as the reference against which the DUT is measured. (One of the
two sources must be a VCO source capable of being frequency tuned by the
System.)
Figure 71 shows a simplified diagram of the PLL configuration used
for the measurement.
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.
Figure 71 Simplified block diagram of the phase lock loop configuration
Phase
detector
inputs
Phase
detector
output Phase
detector
Low-pass
filter
Low-noise
amplifier
Tune voltage
output
Untuned
source
VCO
source
Phase lock
loop control
E5505a_phase_lock_loop
25 Feb 04 rev 1