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7
Residual Measurement Fundamentals
Assumptions about Residual Phase Noise Measurements
The following are some basic assumptions regarding Residual Phase Noise
measurements. If these assumptions are not valid they will affect the
measured results.
• The source noise in each of the two phase detector paths is correlated at the
• Source AM noise is comparatively small. A typical mixer-type phase
• The DUT does not exhibit a bandpass filter function. A bandpass filter type
Given these assumptions, when the DUT is connected to either of the two
inputs of the phase detector, all of the source noise cancels and only the
residual noise of the DUT is measured. See
Source
E5505a_typ_res_phase_noise
27 Feb 04 rev 1
Figure 146 Setup for typical residual phase noise measurement
204
phase detector for the frequency offset range of interest. When the source
noise is correlated at the phase detector, the source phase noise cancels,
leaving only the residual phase noise of the DUT.
detector only has about 20 to 30 dB of AM noise rejection. If the AM
component of the signal is greater than 20 to 30 dB above the residual
phase noise, it will contribute to the residual phase noise measurement and
show the residual phase noise as being greater than it really is.
response will cause the source noise to be decorrelated at the edge of the
filter. This decorrelation of the noise causes the system to measure the
source noise level directly at offsets beyond the filter bandwidth.
Power
splitter
Figure
Device
under
test
Phase
detector
146.
Base band
analysis
Agilent E5505A User's Guide
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