PLL with stable phase discriminator.

摘要

A PLL comprises a charge pump (14) with a current source (32) and a current sink (34) to control a VCO (12), and a phase discriminator (18) to compare a VCO's signal to a stable reference signal for controlling the charge pump. The phase discriminator includes a resettable D-flipflop (52) to provide the current source control signal and a resettable D-flipflop (54) to provide the current sink control signal. The reset signal keeps both sink and source temporarily alive to avoid a dead zone region. The reset signal is produced by a logical gate (56) under combined control of the sink and source control signals and, in addition, of the reference signal to enhance stability.