an oversampling a / d converter with a few operational amplifiers is configured using a complex second - order integrator including first and second second - order integrators and first and second coupling circuits configured to couple these integrators together . each of the second - order integrators includes an operational amplifier , four resistance elements , and three capacitance elements . the first coupling circuit cross - couples one of two serially - connected capacitance elements inserted between the inverted input terminal and output terminal of the operational amplifier in the first second - order integrator to the counterpart in the second second - order integrator using two resistance elements . the second coupling circuit cross - couples the other capacitance element in the first second - order integrator to the counterpart in the second second - order integrator using two resistance elements .