Zero-order quadrature-based phase-locked loop in aerospace applications

A method of minimizing dynamics and reducing phase error towards zero for arbitrary input frequency/phase profile while maintaining stability in a quadrature-based phase-locked loop is presented. Theoretically, the system transfer function becomes of zero order and the error is zero. Practically, the steady-state phase error approaches zero and the system is of minimum dynamics/order. The method is in synthesizing a feedforward control that is added to the quadrature-based phase-locked loop. The feedforward comprises a frequency-to-voltage converter based on a phase/frequency estimation while implementing an inverse feedforward control principle relative to the part of the feedback loop seen after the summing junction.