Abstract: A level detector having good linearity and a high detection efficiency is arranged so as to be small in size and inexpensive to produce, thereby being well suited for use in a semiconductor integrated circuit. The detector employs a common emitter amplifier having two transistors connected in parallel so that odd order harmonic distortion components are mutually eliminated while DC and even order harmonic components appear at the collector thereof. The detector further includes a high impedance load for the two parallel connected transistors. The load is composed of a transistor normally biased in its active region so as to thereby raise the detection efficiency.

Abstract: An electronically controlled variable semiconductor resistor having a three layer construction of either an NPN-type or a PNP-type which is similar to that of a bipolar transistor and basically using the base region and collector region of the transistor as a variable resistor having its resistance value controlled by varying its emitter current. The conductivity of the base region adjoining the emitter region and that of the collector region opposite the emitter region across the base region are modulated largely by minority carriers injected into the base region from the emitter. The carrier density at each emitter, base or collector region is reasonably controlled so as to thereby make it possible to obtain a variable resistor whose resistance value changes about in an inverse proportion to the emitter current and the electrode of proper construction is designed to allow the control signal component for controlling the emitter current not to appear at both ends of the resistor electrode at the resistor.

Abstract: An AM stereo broadcasting system for transmitting stereo signals in the AM broadcasting band. The system is based on amplitude modulation by two carriers having the same frequency and a 90.degree. phase difference from each other, and is capable of increasing the modulation depth of pilot signals (used for stereo signal identification) irrespective of the stereo signals, so that the pilot signals can be easily detected. By modulating both the sum and difference signals by the pilot signal, the receiver portion of the present system can derive the pilot signal irrespective of the stereo signals, thereby obviating many of the previous AM stereo broadcasting system problems.

Abstract: A multiplexed signal receiver is arranged such that two independent signals are multiplexed on a single carrier by amplitude and frequency modulation or amplitude and or phase modulation. The multiplexed signal receiver includes a balanced type amplitude limiter and two double balanced type product detectors for amplitude and frequency or amplitude and phase demodulation. The receiver uses the direct coupling between said amplitude limiter and the two product detectors to facilitate the circuit integration thereof on a monolithic semiconductor chip.

Abstract: A superheterodyne type multiplex signal receiver for multiplex signal transmission systems for receiving two independent signals transmitted by amplitude modulation and angle modulation of single carriers, and for detecting an intermediate frequency by an intermediate frequency detector when changing the local oscillating frequency by a dial operation to select the received signal. The receiver has a switching circuit so composed that it operates a demodulation circuit which demodulates, from the modulated carrier, the two independent signals, which are then transmitted to two independent audio amplifiers provided at a later stage of an intermediate frequency amplifier for driving two speakers for reception of the multiplex signal, when the intermediate frequency is extremely close to a normally determined frequency.

Abstract: The present invention is an integrated front end circuit for a VHF receiver including a high frequency grounded base amplifier, a mixer having a differential type amplifier, a constant current type oscillator, and a bias circuit. In the mixer, a resistor is inserted between common emitters of the transistors of a differential amplifier and the collector of a constat current transistor driving the differential amplifier. In order to keep the oscillation frequency constant during a change in source voltage, there is provided a certain relation between the change in source voltage and the driving current of the oscillator by means of a bias circuit. The collectors and bases of the transistors used for the high frequency amplifier, the differential amplifier and the oscillator use the same D.C. potential.

Abstract: A magnetic tape reproducing system for providing a still picture of a slow motion picture. A magnetic tape is provided on which video signals are recorded in successive fields of a unit length in the longitudinal direction of the tape and a plurality of rotary magnetic reproducing heads are placed on the periphery of a rotating disc at equal angular intervals from each other so as to reproduce one complete field of the video signals. The magnetic reproducing heads are arranged so that the distance between the two gaps of two adjacent heads is equal to an integral multiple of the distance along the tape corresponding to a period of horizontal synchronizing signals contained in the video signals.