Circuit and method for extending the usable frequency range of a phase locked loop (pll)

Abstract

An improved circuit and method is described herein for extending the usable frequency range of a high performance, narrow band phase locked loop (PLL) device. For example, the improved circuit and method may perform a calibration sequence for calibrating an LC-type voltage controlled oscillator (VCO) immediately before or during operation of the PLL device. Unlike previous methods, the calibration sequence described herein provides a fast and convenient method for extending the usable frequency range of a PLL by shifting the center frequency of the LC-type VCO to a desired frequency. For example, the VCO center frequency may be incrementally shifted (e.g., either high or low) to compensate for the actual environmental conditions in which the PLL is used (i.e., to compensate for specific process, voltage, and temperature conditions). Once the calibration bits are set to the desired frequency, the calibration sequence is disabled, and the appropriate calibration bit values are applied to the VCO during normal operation of the PLL.