Abstract text

An operational amplifier includes, between an input and an output of an operational amplifier (an operational amplification stage) 10, a feedback capacitor 34 connected in negative feedback, a phase control circuit 100 having a resistor element (a resistor unit) 30 connected in series to the feedback capacitor 34. Load capacitors (load units) 32 are connected on the output side of the operational amplifier 10 and driven by an output signal from the operational amplifier 10. In a case that the capacitance values of the load capacitor 32 and 33 are increased and the phase margin of the operational amplifier becomes excessive in comparison with the optimum value, a resistance value R_O of the resistor element 30 is increased to control the phase margin of the operational amplifier so as to fall within the optimum range, and thus accelerated settling properties are realized. This invention thus provides a phase control circuit applicable even to a single-stage operational amplifier, and by enhancing the properties of the operational amplifier itself and enabling the phase margin to be controlled, realizes accelerated settling properties even in a case that a transient response is deteriorated.