Continuously auto-tuned and self-ranged dual-path PLL design with hybrid AFC

Abstract

This paper describes a dual-path phase locked loop (PLL) design which automatically tunes to capture the desired frequency as well as the input control voltage range of the dual-path LC voltage-controlled oscillator (VCO). A hybrid automatic frequency calibration (AFC) circuit provides digital frequency calibration and mixed-mode continuous frequency tuning. Since the hybrid AFC circuit independently controls the coarse-tuning control voltage of VCO in this structure, the VCO input control voltage range can be preset before the PLL is locked. Therefore, an optimum loop filter voltage range can be chosen to have good charge pump matching or VCO gain linearity. Simulation results verify that the self-ranged control can be achieved by adjusting the output range of the limiting amplitude amplifier (LAA) during the PLL transient mode.