Table of Contents
Advertisement
8
Residual Measurement Fundamentals
Basic Assumptions Regarding Residual Phase Noise Measurements
Basic Assumptions Regarding Residual Phase Noise Measurements
Frequency
Translation Devices
8-4
E5500 Phase Noise Measurement System Version A.02.00
The following are some basic assumptions regarding Residual Phase
Noise measurements. If these assumptions are not valid they will
affect the measured results.
G
The source noise in each of the two phase detector paths is
correlated at the 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 UUT.
G
Source AM noise is comparatively small. A typical mixer-type
phase 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.
G
The UUT does not exhibit a bandpass filter function. A bandpass
filter type 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.
Given these assumptions, when the unit-under-test (UUT) is
connected to either of the two inputs of the Phase Detector, all of the
source noise will cancel and only the residual noise of the UUT will
be measured. See
Figure
Figure 8-3 Setup for Typical Residual Phase Noise Measurement
If the UUT is a frequency translating device (such as a divider,
multiplier, or mixer), then one UUT must be put in each path. The
result will be the sum of the noise from each UUT. In other words,
each UUT is at least as quiet as the measured result.
8-3.
Document Part No. E5500-90024 Ed. 1.0
Advertisement
Table of Contents
