Abstract: An electrical quantity sensor includes, an oscillation circuit for producing a clock signal of predetermined frequency, a light-emitting element which blinks at a predetermined frequency in accordance with the clock signal output from the oscillation circuit, a switching element which is optically coupled to the light-emitting element and is brought into conduction when the light-emitting element illuminates, a transformer whose primary winding is connected, by way of the switching element, to input terminals which receive a d.c. electrical signal and a synchronization detecting circuit which synchronously detects an a.c. electric signal developing in a secondary winding of the transformer while the clock signal is taken as a reference, thereby producing a d.c. voltage signal corresponding to the amplitude of the d.c. electric signal.

Abstract: An electrical quantity sensor includes, an oscillation circuit for producing a clock signal of predetermined frequency, a light-emitting element which blinks at a predetermined frequency in accordance with the clock signal output from the oscillation circuit, a switching element which is optically coupled to the light-emitting element and is brought into conduction when the light-emitting element illuminates, a transformer whose primary winding is connected, by way of the switching element, to input terminals which receive a d.c. electrical signal and a synchronization detecting circuit which synchronously detects an a.c. electric signal developing in a secondary winding of the transformer while the clock signal is taken as a reference, thereby producing a d.c. voltage signal corresponding to the amplitude of the d.c. electric signal.

Abstract: An oscillation circuit is provided which is easily adjusted with a high degree of accuracy. The oscillation circuit including a filter having a time constant and an inverting amplifier which feeds back the output of the filter to the input side of the filter so that an oscillation condition is fulfilled. The filter includes a gm amplifier formed of a differential amplifier, and a capacitor. The constant current source of the differential amplifier is connected to a free running oscillation frequency adjusting circuit. The adjusting circuit includes a microcomputer, a decoder which decodes the output data of the microcomputer and a switching circuit driven by the output of the decoder and varying the current value according to the output of the decoder. A current in accordance with a current value depending on the setting of the switch flows through the constant current source.

Abstract: An FM signal phase-shifted by 90.degree. and an FM signal not phase-shifted are supplied to a multiplier to demodulate a stereo composite signal. A 90.degree. phase shifting circuit has a first oscillation circuit whose phase shift amount varies according to a timing at which the amount of a current flowing through a charging and discharging capacitor is changed. A multiplexer is provided to process the stereo composite signal to output left and right channel signals. The multiplexer has a second oscillation circuit for generating a signal multiplied by the stereo composite signal to extract the left and right channel signals from the composite signal. The first and second oscillation circuits each have a differential amplifier. The constant current of the constant current source of each differential amplifier is set by trimming-regulate it by a regulating circuit.

Abstract: A phase shifting circuit has an oscillation circuit. The oscillation circuit is provided with a charging and discharging capacitor at which the oscillation signal is generated. The oscillation signal has a constant level period and a saw tooth wave period. A valve of current flowing through the capacitor is changed in the middle of the saw tooth wave period by an input signal. An output of the phase shifting circuit is phase-shifted by 90.degree. with respect to the input signal.

Abstract: An integrated circuit has a self-contained voltage control oscillation circuit wherein the oscillating frequency is controlled according to a control voltage; The circuit includes a first oscillation circuit which forms a first oscillation loop including a first amplifier for generating a first output signal with an oscillating frequency which is controlled according to an operating current of the first amplifier and a second oscillation circuit which forms a second oscillation loop including a second amplifer for generating a second output signal with an oscillating frequency which is controlled according to an operating current of the second amplifer; A circuit for generating a control voltage controls the operating currents of the first and second amplifers and a current regulating circuit for generating an operating current regulating signal regulates the operating currents of the first and second amplifers.

Abstract: A stereo signal demodulator circuit demodulates a stereo signal by using a PLL circuit including a voltage-controlled oscillator (VCO) for generating a first oscillation signal and a second oscillation signal having a phase different from that of the first oscillation signal by 90.degree.. The voltage-controlled oscillator circuit includes a first amplifier for outputting a signal whose phase is different from that of an input signal by 90.degree., a second amplifier for outputting a signal whose phase is different from that of an input signal by 90.degree., and a third amplifier for outputting a signal whose phase is different from that of an input signal by 180.degree.. The first, second and third amplifiers are connected in series so that an output signal of the third amplifier is different, in phase, from the input signal of the first amplifier by 360.degree.

Abstract: A voltage control oscillation circuit comprises an oscillation loop and a control current generating circuit. The oscillation loop comprises: a first charge-discharge circuit including a first transistor circuit for converting a reverse voltage signal as a first input voltage into a first charge-discharge current according to a first conversion ratio, and a first capacitor which is charged and discharged by the first charge-discharge current for generating a first charge-discharge voltage signal; a second charge-discharge circuit including a second transistor circuit for converting the first charge-discharge voltage signal as a second input voltage into a second charge-discharge current according to a second conversion ratio, and a second capacitor which is charged and discharged by the second charge-discharge current for generating a second charge-discharge voltage signal; and a reverse circuit for reversing the second charge-discharge voltage signal into the reverse voltage signal.

Abstract: The emitter of a first pnp transistor is connected to a power supply voltage via a first resistor. The base and collector of the first transistor are not only connected to each other but connected to a ground terminal via a current source. The emitter of a second pnp transistor is connected to the power supply voltage via a second resistor. The bases of the first and second transistors are connected to each other. An input terminal of this current mirror circuit is connected to the emitter of the first transistor, and an output terminal is connected to the collector of the second transistor.