Fixed-phase loop (FPL)

There exist a number of applications in which oscillations must be produced at a certain phase shift with respect to a reference signal. Phase-lock loop (PLL) is widely used for this purpose. PLL uses a closed-loop control principle for tracking the required phase shift. Another solution, which uses an open-loop control principle for the phase angle, can be realized on the TRC considered in this book. This solution is named here a fixed-phase loop (FPL). FPL is an oscillator consisting of a TRC and a low-pass (LP) filter that generates a periodic voltage signal of the frequency corresponding to a certain specified phase lag of the LP filter. Regardless of the LP filter connected in a loop with the TRC, oscillations are always produced at the same phase lag value. Two different circuits are considered: without and with an additional integrator. The purpose of the considered self-oscillating circuit is to produce a periodic reference signal at the output of the filter with desired frequency and amplitude. Sufficient conditions for orbital asymptotic stability of the closed-loop system is verified through the Poincaré map. The two FPL circuits are illustrated by simulations and experiments.