Nippon Telegraph and Telephone Public Corporation

Nippon Telegraph and Telephone Corporation

Iwasaki Tsushinki Kabushiki Kaisha

Makoto Yoshitoshi

Hideo Kishimoto

Akihiro Kobayashi

Kunihiro Kato

Masaaki Terai

Yuuji Tsuruga

Keizo Sugita

Kazumi Kato

Tatsuhiro Naganawa

Isao Kawashima

Yutaka Nishino

A digital code decoding apparatus including a reference waveform storage section which prestores, as reference waveforms, at least m received waveforms corresponding to m possible values of m-value digital codes distorted during transmission, a waveform comparing section which compares at least m reference waveforms read out of the reference waveform storage section and the received waveform, respectively, and a decoded information output section which discriminates one of the reference waveforms which most resembles the received waveform, on the basis of the compared outputs from the waveform comparing section, and outputs, as decoded information, a digital code corresponding to the discriminated reference waveform.

Digital code decoding apparatus

A push-button dial circuit having a low DC resistance and a high output impedance. An oscillator for generating a multi-tone dial signal is connected through a buffer transistor to terminals for coupling the multi-tone dial signal to a subscriber's line. The terminals also supply a DC power source current to the dial circuit. A constant voltage circuit is connected to the oscillator to stabilize the DC current supplied to the oscillator, and a reactance transistor circuit is connected between the terminals and the oscillator for defining a DC supply path from the terminals through the reactance transistor circuit to the oscillator. The reactance transistor circuit includes a transistor having a capacitor and a resistor respectfully connected across the base-emitter path and across the base-collector path of the transistor.

Push-button dial circuit

A three-terminal power supply circuit for telephone set has an input terminal, an output terminal and a common terminal. The input terminal receives a DC voltage superposed with a sending or receiving signal transmitted to or from a telephone station through a subscriber line. The output terminal delivers DC power to a telephone circuit. Between the input and output terminals a constant current circuit and a discharge protection circuit are connected to each other in series. Between the output terminal and the common terminal a constant voltage circuit is connected. Between the input terminal and the common terminal an electronic switch is connected through the constant current circuit. The electronic switch is closed only when an instantaneous voltage applied between the input terminal and the common terminal is lowered to a predetermined value or a lower value. When it is closed, the electronic switch causes a short circuit in the constant voltage circuit through discharge protection circuit. This lowers the cutoff voltage applied on the input side of the power supply circuit, and both a sending signal and a receiving signal can be transmitted without being distorted.

Three-terminal power supply circuit for telephone set

There are provided a current detecting resistance element connected in series with a loop for supplying current to a telephone set, a switching circuit including a three terminal semiconductor switching element connected to be ON.OFF controlled by the voltage drop across the resistance element, and an impedance element controlled by the ON.OFF operation of the switching element to be connected across the loop for adding AC loss.

Automatic signal level adjusting circuits for use in telephone sets

Growing community of inventors

Musashino, Japan

Makoto Yoshitoshi