Differential ring oscillator and method for calibrating the differential ring oscillator

A differential ring oscillator, comprising:

• a plurality of delay stages, connected in a ring, wherein at least one of the delay stages comprises:
• a current source, arranged to generate a bias current according to a coarse tuning signal;
• a latching circuit, coupled to the current source and arranged to generate a differential output signal to a next delay stage according to a differential input signal from a previous delay stage;
• a capacitive array, coupled to the latching circuit and arranged to provide a first capacitance according to a fine tuning signal;
• and
• a varactor device, coupled to the capacitive array and arranged to provide a second capacitance according to a controllable signal such that an oscillating frequency of the differential ring oscillator is locked to a target frequency;
• wherein the coarse tuning signal is arranged for adjusting the oscillating frequency of the differential ring oscillator to reach a predetermined frequency range including the target frequency, and the fine tuning signal is arranged for adjusting the oscillating frequency of the differential ring oscillator to approach the target frequency in the predetermined frequency range.