Michael Anthony Marra

Modeling of a phase-locked loop servo controller with encoder feedback

This paper presents a model of a phase-locked loop servo control mechanism using describing function analysis. A closed-loop control system is obtained by replacing the voltage-controlled oscillator of the phase-locked loop with a servo system with encoder feedback. In this way, the velocity of the servo is controlled via the phase-locked loop. A model of the system is obtained using describing function methodology. Control analysis of the resulting nonlinear system is also discussed.

Modified phase-frequency detector for improved response of PLL servo controller

Presents a modification of a well known phase-frequency detector to improve closed-loop damping in a phase-locked loop DC servo control mechanism. In a closed-loop servo system that contains non-linearities, disturbances in the steady-state response are expected. These disturbances may cause the system to break phase-lock. If this occurs there will be more disturbances created by the PLL as phase-lock is achieved again. A modified PFD is discussed that allows for a small amount of steady-state disturbances without losing phase-lock.