Agilent Technologies E1420B, User Manual

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344 Agilent E5505A User’s Guide
15
Advanced Software Features
Max error
This is the measured error that still exists between the measured Loop
Suppression and the Adjusted Theoretical Loop Suppression. The four points
on the Loop Suppression graph marked with arrows (ranging from the peak
down to approximately ––8 dB) are the points over which the Maximum Error
is determined. An error of greater than 1 dB results in an accuracy
degradation.
Closed PLL bandwidth
This is the predicted Phase Lock Loop Bandwidth for the measurement. The
predicted PLL BW is based on the predicted PTR. The Closed PLL BW will not
be adjusted as a result of an accuracy degradation. If an accuracy degradation
is detected, the amount of error is determined from either the PLL Gain
Change or the Maximum Error, which ever is larger. The degradation itself is
1 dB less than the greater of these.
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.