Patent ID: 8354630

Claim:
An A/D converter circuit comprising: a first capacitative element; a second capacitative element having an output end connected to an input end of the first capacitative element; a third capacitative element having an output end connected to an input end of the second capacitative element; a voltage comparator circuit having an input terminal connected to an output end of the first capacitative element, configured to compare a voltage value of the input terminal with a predetermined threshold voltage value; a first input circuit configured to input an externally inputted conversion object analog voltage signal to a first intermediate node provided between the first capacitative element and the second capacitative element; a second input circuit configured to input a first reference voltage to a second intermediate node provided between the second cap acitative element and the third capacitative element, the first reference voltage being used for a first conversion process to find a value of sequential bits containing the most significant bit, in digital data provided after the conversion object analog voltage signal has been converted; a third input circuit configured to input a second reference voltage to an input end of the third capacitative element, the second reference voltage being used for a second conversion process to find a value of unconverted bits in the digital data after the first conversion process; a control circuit configured to generate a control signal to hold a voltage value of the first reference voltage in the third capacitative element when an output of the voltage comparator circuit changes in the first conversion process; a first ramp voltage generator circuit configured to generate a first ramp voltage having a voltage value monotonously changing step-by-step, and output the first ramp voltage as the first reference voltage while at least the first conversion process is executed; a second ramp voltage generator circuit configured to generate a second ramp voltage having a voltage value monotonously changing step-by-step or sequentially, and output the second ramp voltage as the second reference voltage while at least the second conversion process is executed; a counter circuit configured to output a digital value counted in response to a change of the first ramp voltage and a change of the second ramp voltage; and a memory circuit configured to store the digital value when the output of the voltage comparator circuit changes.