N5511A Phase Noise Test System User’s Guide 311
Advanced Software Features
Phase-Lock-Loop Suppression
Peak tune range
This is the Peak Tuning Range (PTR) for the measurement determined from the
VCO Tune Constant and the Tune Range of VCO. This is the key parameter in
determining the PLL properties, the Drift Tracking Range, and the ability to
phase lock sources with high close in noise.
The PTR displayed should be approximately equal to the product of the VCO
Tune Constant times the Tune Range of VCO. This is not the case when a
significant accuracy degradation is detected (4 dB) by the Loop Suppression
Verification. In this case, the PTR and Assumed Pole are adjusted when fitting
the Theoretical Loop Suppression to the smoothed measured Loop
Suppression, and the test system will display the adjusted PTR. If the PTR must
be adjusted by more than 1 dB, as indicated by an accuracy degradation of
greater than 0 dB, the Phase Detector Constant or the VCO Tune Constant is in
error at frequency offsets near the PLL BW, or the PLL BW is being affected by
some other problem such as injection locking.
Assumed pole
This is the frequency of the Assumed Pole required to adjust the Theoretical
Loop suppression to match the smoothed measured Loop suppression. The
Assumed Pole frequency is normally much greater than the Closed PLL BW. An
Assumed Pole frequency of less than 10 X PLL BW is an indication of peaking
on the PLL Suppression curve. For PLL BWs less than 20 kHz, an Assumed Pole
of less than 10 X PLL BW indicates a delay or phase shift in the VCO Tune Port.
For PLL BWs greater than 20 kHz, the Assumed Pole may be adjusted to less
than 10 X PLL BW to account for phase shifts in the test set.
Detector constant
This is the phase Detector Constant (sensitivity of the phase detector) used for
the measurement. The accuracy of the Phase Detector Constant is verified if
the PLL suppression is verified. The accuracy of the phase Detector Constant
determines the accuracy of the noise measurement.
The phase Detector Constant value, along with the LNA In/Out parameter,
determines the Keysight N5511A system noise floor, exclusive of the reference
source. “VCO CONSTANT” is the VCO Tune Constant used for the
measurement. The accuracy of the VCO Tune Constant determines the
accuracy of the PLL noise measurement for offset frequencies in segments
where the entire plotted frequency range is less than the PLL BW / 4. The
accuracy of the VCO Tune Constant is verified if the PLL Suppression is verified.
The VCO Tune Constant times the Tune Range of VCO determines the Peak
Tune Range (PTR) value for the measurement. The PTR sets the drift tracking
and close-in noise suppression capabilities of the test system.
Summary of Contents for N5511A
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