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

This paper 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 will be discussed that allows for a small amount of steady-state disturbance without losing phase-lock.