Nec Corporation

Shigeru Kagawa

Kazuo Tokuda

In a gain-variable amplifier including a dual differential amplifier circuit for amplifying an input voltage to generate an output voltage with a gain in accordance with first and second control voltages, and a control voltage generating circuit, for generating the first and second control voltages in accordance with a gain control voltage, a polarity of a difference between the first and second control voltages is unchanged, when the gain control voltage is within a control range.

Gain-variable amplifier with wide control range

The invention provides a quadrature demodulator which removes unnecessary higher harmonic signals included in a demodulation output without giving rise to increase in number of externally connected parts and increase in current consumption. The quadrature demodulator includes a first double differential circuit to which a modulated signal and a first local signal are inputted, a first emitter follower circuit for effecting impedance conversion, a second double differential circuit to which the modulated signal and a second local signal having a phase shifted by 90-degrees from the first local signal are inputted, and a second emitter follower circuit connected to a pair of outputs of the second double differential circuit for effecting impedance conversion. The quadrature demodulator further includes a CR circuit including a resistor and a capacitor connected to each of the outputs of the first and second double differential circuits such that an active filter is formed from the CR circuit and a corresponding one of the first and second emitter follower circuits.

Quadrature demodulator having active filters formed with emitter

An amplifier circuit equipped with a negative feedback loop includes a differential amplifier circuit composed of a plurality of differential amplifier stages, first and second negative feedback circuits each including a low-pass filter and being provided between an associated one of an in-phase output and an opposite-phase output and an associated one of first and second inputs of the differential amplifier circuit. This amplifier circuit further includes a suppression circuit to suppress an a.c. component of a signal to be fed back by adding signals relative to the in-phase and opposite phase outputs.

Amplifier circuit having nagative feedback loop for self-bias

A stereo demodulation device includes an audio signal processing circuit, a muting circuit, a muting switch, and a variable resistor. At least a given signal processing function of the audio signal processing circuit is adjusted by supplying a control current from a control terminal thereof. The muting circuit outputs or blocks an audio signal processed by the audio signal processing circuit. A muting switch is commonly connected to a control terminal of the muting circuit and the control terminal for the given signal processing function of the audio signal processing circuit. The variable resistor adjusts the control current.

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Tokyo, Japan

Shigeru Kagawa