Patent ID: 8872684

Claim:
A delta-sigma A/D converter comprising: a loop filter including a resonant filter and configured to receive a first input signal; a quantizer configured to convert an output of the loop filter into a digital signal; and a feedback D/A converter configured to convert an output of the quantizer into an analog signal and feed back the analog signal to the loop filter, wherein the resonant filter includes a resonator including a resistor and a capacitor and configured to receive a second input signal, and a feedback path configured to connect an output of the resonator to an input of the resonator, in a positive feedback fashion, through a first switch configured to be switched on and off based on a first external signal and a feedback resistor configured to allow a resistance value thereof to be controlled based on a second external signal, the resonant filter operates as an oscillator when the first switch is controlled to be on and therefore the output of the resonator is positively fed back to the input of the resonator through the feedback path, and as a filter when the first switch is controlled to be off and therefore the feedback path is open, and at least one of the resistor and the capacitor of the resonator is configured to allow a resistance value or a capacitance value thereof to be adjusted based on a third external signal.