CHARGE PUMP PHASE LOCKED LOOP WITH IMPROVED POWER SUPPLY REJECTION

摘要

A phase lock loop circuit ( 60 ) has a phase frequency detector ( 62 ), a charge pump ( 64 ), an active filter ( 87 ) and a voltage-controlled oscillator ( 100 ). The phase detector generates signals responsive to reference signal F_R and VCO output signal F_V. A charge pump generates a voltage at the input of a first transmission gate ( 76 ) according to the values of the phase detector signals. A predetermined voltage is generated at the input of a second transmission gate ( 112 ). When the transmission gates ( 76, 110 ) are closed (low impedance) the charge pump may sink or source current to the inverting input of the operational amplifier ( 86 ) of the active filter 86 and the predetermined voltage is applied to the non-inverting input. When the transmission gates are open (high impedance state) the inverting input is electrically isolated from the node and the non-inverting output is isolated from the power supply.