Investigation of non-linear operation of PLL FM demodulators

The non-linear behavior of PLL FM demodulators were investigated theoretically and experimentally. A test circuit with a complete receiver, a PLL FM demodulator, and measurement system was devised in order to excite an second order type II PLL with arbitrary FM waveforms. Phase error and/or VCO tuning voltage variation were recorded in order to generate a range of parameters using Matlab, Poincaré sections, phase-plane portraits, VCO spectra and bifurcation diagrams. An optimum waveform was derived, which was capable of causing a non-linear response with minimum peak deviation.