Patent ID: 7391353

Claim:
An analog-to-digital converter for converting an input voltage that is an analog signal into a digital signal, comprising: a first VCO (Voltage Controlled Oscillator) for outputting a first pulse signal oscillating at a first period; a second VCO for outputting a second pulse signal oscillating at a second period; and a digital value calculating unit, wherein: a ratio of said first period and said second period is A:B (A≠B); said first and second periods are controlled by said input voltage while said ratio is maintained; said first VCO starts oscillation of said first pulse signal by free running; said second VCO starts oscillation of said second pulse signal in response to activation of a sampling signal indicating a sampling period for said digital signal; and said digital value calculating unit calculates: a high order bit of said digital signal according to the number of pulses in said first pulse signal contained in said sampling period; and a low order bit of said digital signal according to the number of pulses in said first or second pulse signal contained from an activation time point of said sampling signal to a time point at which phases of said first and second pulses match.