Plls covering wide operating frequency ranges

Abstract

The present invention provides a method and mechanism for adapting a single phase-locked loop (PLL) for a wider range of frequencies than has been possible with prior art solutions. An analog comparator circuit that senses the output of a charge pump and provides a signal to a digital control circuit to choose a suitable load circuit for the PLL voltage controlled oscillator (VCO). The analog comparator with the digital control circuit changes the VCO loads to select the best VCO range to achieve the incoming signal frequency lock. A single PLL with the VCO load selection method disclosed, with use of built-in hysteresis, in addition to the phase and frequency feedback of the prior art, allows multiple overlapping frequency ranges to be covered in a stable fashion. This enables frequency locking of the PLL over a wide range of frequencies with a small die size and low power consumption.