Megachips Corporation

Hidetoshi Tsubota

Hideyuki Sato

In the frequency calibration circuit, the digital phase-locked-loop circuit repeats a calibration operation involving outputting the digital control signal corresponding to a time difference between the first clock signal which is input from the first oscillator and has a first frequency accuracy, and the second clock signal which is input from the second oscillator and has a second frequency accuracy lower than the first frequency accuracy, changing the capacitance of the discrete type capacitor bank in accordance with the digital control signal using the second oscillator as a digital control oscillator, and changing an oscillation frequency of the second clock signal in accordance with the capacitance of the discrete type capacitor bank, thereby calibrating a phase of the second clock signal to a phase of the first clock signal.

Frequency calibration circuit and frequency calibration method

A clock generator comprises a voltage controlled oscillator including a ring oscillator which has a plurality of differential inverter circuits connected in a ring shape, and a phase controller to control an output of a differential inverter circuit which belongs to a second group, in a first state or a second state, for a predetermined time period. The differential inverter circuit which belongs to the second group is distinct from a differential inverter circuit which belongs to a first group. The differential inverter circuit which belongs to the second group, in the first state, outputs a first logic signal from a first differential output terminal and outputs a second logic signal from a second differential output terminal. Further, the differential inverter circuit which belongs to the second group, in the second state, outputs the second logic signal from the first differential output terminal and outputs the first logic signal from the second differential output terminal.

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Chiba, Japan

Hidetoshi Tsubota