Phase-locked loop and automatic frequency calibration circuit thereof and phase-locked loop self-tuning locking method

Abstract

The invention discloses a phase-locked loop and an automatic frequency calibration circuit thereof. The phase-locked loop comprises a phase/frequency detector, a charge pump, a filter, a voltage-controlled oscillator (VCO) and a first frequency divider which are connected in sequence, wherein the phase-locked loop further comprises the automatic frequency calibration circuit; the automatic frequency calibration circuit reduces the oscillation frequency CKV of the VCO when the oscillation frequency CKV of the VCO after undergoing frequency division by the first frequency divider is higher than the reference frequency CKR, and increases the oscillation frequency CKV of the VCO when the oscillation frequency CKV of the VCO is lower than the reference frequency CKR; and a precharging circuit A0 is connected at the input end of the filter and carries out precharging when AFC carries out searching. The phase-locked loop has the rapid self-tuning locking function and ensures the VCO to carry out coarse tuning automatically to approach the final tuning coil, thus reducing the locking time of the phase-locked loop.

Description

technical field [0001] The invention belongs to the technical field of integrated circuit design, and relates to a phase-locked loop, in particular to an automatic frequency calibration circuit of the phase-locked loop; meanwhile, the invention also relates to a self-tuning and locking method of the phase-locked loop. Background technique [0002] In the field of wireless communication, where more and more channels are carried in a limited high-frequency range, phase-locked loops are widely used to generate stable frequencies for transceivers. The closed-loop phase-locked loop circuit is composed of a frequency and phase detector, a charge pump, a loop filter, a voltage-controlled oscillator VCO and a frequency divider. [0003] The varactor in the VCO resonates with the inductor to obtain the oscillation frequency. Once a certain inductor is selected, the oscillation frequency is usually controlled by the varactor. In one published patent, coarse tuning and fine tuning are...

AI Technical Summary

Problems solved by technology

[0006] First of all, the initial tuning voltage of the VCO is an arbitrary value, so after the coarse tuning is completed, the tuning voltage after the fine tuning is locked may be far from the initial voltage, thereby increasing the locking time of the PLL;

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