Abstract: The disclosed serial control type voltage regulator can prevent current from flowing from a backup capacitor (C1) to the side of the voltage regulator, when the control transistor (Q1) stops operating, reducing the power consumption of the backup voltage supply. In the serial control type voltage regulator having a control transistor (Q1) connected in series between an input terminal (1) and where an output terminal (2), an output voltage detector (6) and an error amplifier (4) are used for comparing an output voltage detected by the output voltage detector with a reference voltage (E3) to control the control transistor, there are provided a first switching element (Q3) for cutting off the output voltage detector (4) when the control transistor (Q1) stops operating and a second switching element (Q4) for cutting off the error amplifier (4) also when the control transistor (Q1) stops operating.

Abstract: A leapfrog filter comprising a first and a second integrator each consisting of an operational amplifier and integrating capacitor. The leapfrog filter includes differential amplifier which is arranged to differentially supply current to the first and second integrators through a first and a second current source circuit respectively; and a third current source circuit for adjusting the sum of currents supplied to the first and second current source circuits, wherein characteristics such as the center frequency f.sub.o and quality factor Q of the leapfrog filter are controlled by adjusting the respective current values.