Soft dB SPM PLL User Guide - Manual (Page 10)

SPM - PLL User’s Manual 10
Resonator Sweep Interface
The resonator sweep interface automatically sets the time constant of the phase detector at 1ms to
obtain a precise measurement of both the phase and amplitude. The original time constant for the
phase detector is replaced after the sweep measurement.
Before starting the measurement, the start and stop frequencies must be adjusted along with the
frequency resolution and the excitation amplitude. The Measurement Pause control specifies the
waiting period between a change in excitation frequency and the corresponding measurement. When
the resonator Q factor is large, the stabilization time after the excitation change can be long. For
instance, for a Q factor of 25k and a resolution of 0.05Hz, a stabilization time of 300ms is necessary. At
the end of the measurement, the resonance frequency, the gain at the resonance, the phase at the
resonance frequency and the Q factor are computed and presented by the interface. Two methods are
used to compute the Q factor: 1) phase derivative at the maximum gain and 2) half maximum method.
Use the Quit button to quit the measurement interface. The interface will ask for an update of the
frequency reference and the phase reference. If the user clicks yes, the phase and the frequency
references will be updated with the new phase at the resonance and the new resonance frequency.
Note: The Q factor and the gain at the resonance are important information for the auto-adjustment
function of the amplitude controller.