US Patent 7242224 Continuous, wide-range frequency synthesis and phase tracking methods and apparatus

Circuitry and methods are provided for continuously adjustable frequency synthesis. The synthesis covers a wide range of possible frequencies and can be performed to a high degree of precision. In an embodiment of the invention, an analog phase-locked loop (“PLL”) performs relatively coarse wide-range frequency synthesis, while a digital PLL performs relatively fine narrow-range frequency synthesis and phase alignment. The analog PLL is capable of varying frequency in a stepwise linear fashion. The digital PLL communicates with the analog PLL to ensure that the output of the analog PLL is within the digital PLL's specified pull-in range.