Self-calibrating, fast-locking frequency synthesizer

Abstract

A frequency synthesizer for dual-band high frequency RF application. The frequency synthesizer first uses a frequency-locked loop circuit ('FLL') to achieve self-calibration and frequency-locking, and then uses a phase-locked loop circuit ('PLL') to achieve phase-locking. During the FLL, the PLL is de-activated by control signals from the digital control and state machine of the FLL. The varactor of the VCO is initially connected to a fixed voltage, thus isolating the varactor from the PLL. The FLL adjusts the VCO's capacitor array by varying the five binary control bits from the state machine and digital control, until frequency-locking and self-calibration is achieved. Then, those five binary weighting control bits are also fixed for the VCO. The PLL is then activated to perform a fine-tuning and phase-locking loop, where the varactor of the VCO is controlled by the signal from the charge pump and the low-pass filter.