Analysis of a PLL System as Analog Processor in CW Doppler Flowmeters

In this paper a phase-locked loop (PLL) system is analyzed in order to evaluate its performance for estimating the average frequency of an input spectrum made up by N discrete components allocated in a frequency interval B. The system was studied first in the simplified case that the phase comparator has a linear characteristic. Next, a computer-aided simulation of the PLL system was performed taking into account the nonlinear characteristic of the phase comparator, assuming that the input spectral components have mutual random phase in (-?, +?) interval and amplitudes with a distribution either uniform or obtained from a particular parabolic velocity profiles. The obtained results show that the estimate given by a PLL system differs from the true average frequency value for a negligible percent error. It is also shown that the PLL estimate is generally better than the zero-crossing detector estimate.