Phase detector characteristic


A phase detector characteristic is a function of phase difference describing the output of the phase detector.
For the analysis of Phase detector it is usually considered the models
of PD in signal domain and phase-frequency domain.
In this case for constructing of an adequate nonlinear mathematical model of PD in phase-frequency domain it is necessary to find the characteristic of phase detector.
The inputs of PD are high-frequency signals and the output contains a low-frequency error correction signal, corresponding to a phase difference of input signals. For the suppression of high-frequency component of the output of PD a low-pass filter is applied. The
characteristic of PD is the dependence of the signal at the
output of PD on the difference of phases
at the input of PD.
This characteristic of PD depends on the realization of PD and the types of waveforms of signals. Consideration of PD characteristic allows to apply averaging methods for high frequency oscillations and to pass from analysis and simulation of non autonomous models of phase synchronization systems in time domain to analysis and simulation of autonomous dynamical models in phase-frequency domain

Analog multiplier phase detector characteristic

Consider a classical phase detector implemented with analog multiplier and low-pass filter.
Here and denote high-frequency signals, piecewise differentiable functions, represent waveforms of input signals, denote phases, and denotes the output of the filter.
If and satisfy the high frequency conditions then phase detector characteristic is calculated in such a way that time-domain model filter output
and filter output for phase-frequency domain model
are almost equal:

Sine waveforms case

Consider a simple case of harmonic waveforms and integration filter.
Standard engineering assumption is that the filter removes
the upper sideband from
the input but leaves the lower sideband
without change.
Consequently, the PD characteristic in the case of sinusoidal waveforms is

Square waveforms case

Consider high-frequency square-wave signals and.
For this signals it was found that similar thing takes place.
The characteristic for the case of square waveforms is

General waveforms case

Consider general case of piecewise-differentiable waveforms,.
This class of functions can be expanded in Fourier series.
Denote by
the Fourier coefficients of and.
Then the phase detector characteristic is
Obviously, the PD characteristic is periodic, continuous, and bounded on.
Modeling method based on this result is described in

Examples