Keysight Technologies N5511A, Руководство пользователя

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170 N5511A Phase Noise Test System User’s Guide
Residual and Additive Noise Measurement Fundamentals
What is Residual Noise?
Fundamental Measurement Technique
N5511A utilizes the quadrature technique to perform a residual measurement.
Establishing quadrature is used to cancel the noise not pertinent to the phase
noise of DUT. As shown in Figure 7-3 , quadrature is established when the two
inputs to the phase detector are 90° out of phase. This 90° phase shift can be
accomplished using line stretchers.
Figure 7-3 Quadrature Technique
When measuring a two-port device, 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 additive phase noise of the
DUT. Figure 7-4 shows this principle for a single channel configuration.
Figure 7-4 Single Channel Configuration
Using trigonometric identities, the additive noise of the DUT is the remaining
component at the output of the phase detector, assuming that
<0.2 rad.