Differential charge pump based phase locked loop or delay locked loop

摘要

A phase locked loop includes a differential charge pump to cancel static phase error and reduce sensitivity to noise. The differential charge pump comprises two substantially identical single- ended charge pumps so that under locked condition, changes in voltage at the charge pumps' output terminals are substantially identical, thereby maintaining a substantially constant difference between the charge pumps' output voltage. A differential input voltage-controlled oscillator receives the output of the differential charge pump and generates a clock signal with a frequency proportional to the voltage difference output by the differential charge pump. A common mode bias circuit adjusts the common mode voltage output by the differential charge pump to optimize the voltage swing available at the differential charge pump's output terminals. The structure can be easily modified to implement a delay locked loop by replacing the differential input voltage-controlled oscillator with a differential input voltage-controlled delay circuit.