Patent ID: 7639169

Claim:
An A/D converter circuit for converting an analog voltage signal input to an input signal line into a binary digital data and outputting the same to an output data line, the A/D converter circuit comprising: a first pulse circulating circuit in which a plurality of inverting circuits are coupled together in a ring form, the plurality of inverting circuits using the analog voltage signal input from the input signal line as a power supply voltage, and of which an inverting operation time for inverting and outputting an input signal varying depending upon the power supply voltage, one of the plurality of inverting circuits being formed as a start-up inverting circuit of which the inverting operation is controlled from an outer side, and a pulse signal circulating accompanying the start of operation of the start-up inverting circuit; a first counter for counting the number of times of circulation of the pulse signal circulating in the first pulse circulating circuit, and for outputting a counted value; converted data output control means for outputting the counted value output from the first counter as the binary digital data onto the output data line at a predetermined time point; a second pulse circulating circuit in which inverting circuits that use a predetermined reference voltage as a power supply voltage and of which an inverting operation time for outputting an input signal in an inverted manner varies depending upon the power supply voltage, are connected in the same number and in the same manner as the inverting circuits that form the first pulse circulating circuit, a start-up inverting circuit which is one of the plurality of inverting circuits starting the operation simultaneously with a start of operation of the start-up inverting circuit in the first pulse circulating circuit, and the inverting circuits and the start-up inverting circuit of the second pulse circulating circuit being formed to be thermally coupled to the first pulse circulating circuit; a second counter for counting the number of times of circulation of the pulse signal circulating in the second pulse circulating circuit, and for outputting a counted value; time point notifying means which, when the counted value output from the second counter reaches a predetermined value, notifies a predetermined time point to the converted data output control means; and reference data output means for outputting the predetermined value as a digital data of the predetermined reference voltage.