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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.)
for the measurement.
Untuned
source
source
Figure 71 Simplified block diagram of the phase lock loop configuration
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.
106
Figure 71
shows a simplified diagram of the PLL configuration used
Phase
detector
inputs
VCO
Phase
Low-pass
detector
filter
Phase lock
loop control
Phase
Low-noise
detector
amplifier
output
Tune voltage
E5505a_phase_lock_loop
output
25 Feb 04 rev 1
Agilent E5505A User's Guide
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