Differential lc-vco, charge pump, and loop filter architecture for improved noise-immunity in integrated phase-locked loops

Abstract

A differential LC-based voltage-controlled oscillator (LC-VCO), charge pump and loop filter architecture for providing improved noise immunity in integrated phase-locked loops (PLLs). A pair of voltage control signals are provided from a differential charge pump and loop filter architecture to respective voltage control inputs in the LC-VCO to differentially control the LC-VCO. The voltage control inputs are connected to respective terminals on opposite ends of a varactor tuning circuit. The differential voltage applied across the varactor tuning circuit determines the LC characteristics of the varactor tuning circuit which, in turn, determines the operating frequency of the VCO. One of the voltage control inputs is passed through an operational amplifier buffering stage before being transmitted to its respective terminal in the varactor tuning circuit. The LC-VCO utilizes a PMOS transistor core to provide good substrate isolation and low flicker (1/f) noise. The PMOS core further eliminates parasitic diode problems while maintaining the whole supply range for tuning. The differentially-controlled LC-VCO is integrated into a PLL using a differential charge pump having a simple common mode correction circuit which does not require a clean reference signal. The differential LC-VCO and charge pump architecture of the present invention reduces the sensitivity of the components to supply, ground, and substrate noise without a significant increase in power consumption and without sacrificing the tuning range of the LC-VCO.