Patent ID: 8749414

Claim:
An apparatus that calibrates a time constant of an integrator using a resistor and a capacitor in a low pass delta sigma modulation apparatus, the apparatus comprising: a reference current generator that generates a reference current; a reference resistor that is connected between the reference current generator and a ground terminal; a comparison circuit that compares a first reference voltage that is generated by the reference resistor and the reference current and a plurality of second reference voltages, and that converts the first reference voltage to a digital signal; and a digital processor that generates a digital control signal that varies a value of at least one of the resistor and the capacitor from the digital signal and that outputs the digital control signal to the integrator, wherein the resistor includes: a plurality of unit resistors that are coupled in series between an input terminal of the low pass delta sigma modulation apparatus and an operational transconductance amplifier of the integrator, and a plurality of first switches that are each connected to both ends of some unit resistors of the plurality of unit resistors, wherein on/off of the plurality of first switches is determined according to the digital control signal.