Rohm Co., Ltd.

Isoshi Takeda

Shigeyoshi Hayashi

Yoshikazu Shimada

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.

Oscillation circuit

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.

FM signal processor

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.

Phase shifting circuit

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. The control volage generating circuit may include a first generator for generating a first control voltage which controls the operating current of the first amplifier and a second generator for generating a second control voltage which controls the operating current of the second amplifier.

Integrated circuit having self-contained voltage control oscillation

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., and a positive feedback loop for feeding back the output signal of the third amplifier to the input of the first amplifier and operating currents of the first and second amplifiers are controlled by the control voltage such that the first oscillation signal is derived from the output of one of the first amplifier and second amplifiers, and the second oscillation signal is derived from one of the input and output of one of the first and second amplifiers.

Stereo signal demodulator circuit and stereo signal demodulator using

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. The control current generating circuit comprises: a voltage-to-current conversion circuit for converting the control voltage into a first control current; and a current value regulating circuit including a resistor circuit constituted by a plurality of resistors for generating a regulating current corresponding to a resistance value of the resistor circuit; and means for generating a second control current by adding the regulating current to the first control current.

Voltage control oscillation circuit

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.

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Kyoto, Japan

Isoshi Takeda