Alps Electric Co., Ltd.

Katsumi Tobita

Akiyuki Yoshisato

Tasuku Noji

Tamaki Yoshimoto

Masaki Kato

An automatic fine tuning (AFT) circuit for a CATV receiver system of a double conversion type having a first local oscillator and a second local oscillator and a first mixer and a second mixer respectively supplied with oscillation outputs from the first and second local oscillators is disclosed. A reception signal is sequentially subjected to frequency conversation by use of the first and second mixers so as to attain an intermediate frequency signal of a predetermined value. The AFT circuit includes a control voltage generator for outputting a control voltage which is a function of a frequency fluctuation of the intermediate frequency signal; a selector for selecting either the control voltage or a constant voltage and for supplying the selected voltage as an oscillation frequency control voltage controlling the oscillation frequency of the second local oscillator; an integration unit for integrating the oscillation frequency control voltage so as to produce an integrated control voltage; and a voltage comparator for comparing the integrated control voltage with a reference voltage so as to supply a result of the comparison to the selector. In response to the compare result from the voltage comparator, the selector supplies the control voltage to the second local oscillator when the integrated voltage is higher than the reference voltage and supplies the constant voltage to the second local oscillator when the integrated voltage is lower than the reference voltage.

AFT circuit for CATV receiver system

A subscription television system sends out a reference level signal together with a timing pulse on the transmitting side and, on the receiving side, extracts the reference level signal and suppresses the signal of a video signal interval, except for a synchronizing pulse interval, on the basis of the extracted reference level signal, whereby a descrambling process is performed.

Subscription television system

A demodulating system for the multivoice TV system, which is constituted so that a tuner is tuned to receive the sum signal and the difference signal of an aural signal and a pilot signal which are transmitted together with a video signal, the selected signal is given to an intercarrier demodulator and an aural signal band-pass filter, the intercarrier demodulator provides a beat signal corresponding to the difference between the video carrier and the sound subcarrier, the beat signal is demodulated to obtain the sum signal, and the sound subcarrier provided by the sound signal band-pass filter is demodulated to obtain the difference signal and the pilot signal. The demodulating system is intended to eliminate disturbing signals included in the composite signal and buzzing, and to obviate the malfunction of the MPX decoder due to the disturbing signal having the same frequency as that of the pilot signal.

Demodulating system for multivoice system

A CATV converter has a phase locked loop (PLL) circuit for controlling the sound carrier wave frequency of the audio signal component of the resulting TV signal. The PLL circuit receives as inputs a branched part of the video signal component and a part of the audio signal output of an audio modulator for providing an output control signal to the audio modulator representing a selected frequency difference to be maintained between the video carrier wave frequency of the video signal and the sound carrier wave frequency of the audio signal output of the audio modulator.

CATV converter having phase locked loop for sound carrier wave frequency

In a pay television channel selector, a reception contract selecting portion comprises parallel circuits which are disposed in correspondence with channels and whose impedances are made different between the contracted and uncontracted channels, and a control circuit device whose output level changes depending upon the impedances of the parallel circuits, so that the scrambled broadcast of the contracted channel is descrambled on the basis of the output control signal of the control circuit device. The tapping of the uncontracted channel ascribable to the imperfection of a double lock preventive mechanism of multi-throw switches used as channel selecting switches can be prevented.

Pay television channel selector

A CATV selection device adapted to convert the desired CATV signal into a vacant channel frequency of the TV set and to deliver the vacant channel frequency as an output to make it possible to watch the desired CATV broadcasting. The device has an input terminal adapted to receive both of the TV broadcasting signal and the CATV broadcasting signal, an output terminal for delivering the broadcasting signal to the input terminal of a TV set, a conversion circuit adapted to receive the CATV broadcasting signal corresponding to the selected channel into the vacant channel frequency of the TV set, and electronic switch circuit adapted to effect a switching between a first mode in which the broadcasting signal from said input terminal is bypassed to the output terminal and a second mode in which the same broadcasting signal is delivered to the conversion circuit, and a selection section having push buttons for selecting the desired CATV broadcasting channel and a bypass button for bypassing the broadcasting signal from the input terminal to the output terminal.

CATV selection device

A tuning system comprising a memory for storing therein local oscillation frequencies of a plurality of channels to be received and an intermediate frequency, a first control loop circuit for controlling an oscillation frequency of a controlled oscillator on the basis of one local oscillation signal stored in said memory, and a second control loop circuit for controlling a controlled oscillator in such a manner as to render the intermediate frequency of the tuner itself constant on the basis of the intermediate frequency stored in said memory after said first control loop circuit is locked.

Tuning system

A Colpitts type quartz crystal oscillator comprises a resonant circuit consisting of two capacitors connected in series across a quartz crystal, the latter serving as an inductive element. The resonant circuit is connected between the base and collector of a transistor, with the junction of the capacitors being connected to the emitter of the transistor to provide feedback. Means are provided to increase the gain of the transistor and thereby the driving excitation of the crystal above a normal value for a brief length of time after the oscillator is initially energized.

Growing community of inventors

Soma, Japan

Katsumi Tobita