Abstract: A cathode ray tube comprises a series of quadrupolar lenses for focusing a beam of electrons, emitted from a cathode at one end of an evacuated envelope under the control of a control electrode, at a target screen at the other end of the envelope. After having been focused at the target by adjustment of electric potentials on the quadrupolar lenses, the electron beam will defocus upon change in a potential on the control electrode because then the crossover or initial focusing point of the electron beam will be displaced along the central axis of the envelope. With a view to ready refocusing of the beam at the target, a refocusing lens is provided between the crossover point and the quadrupolar lenses for providing a convering lens action of radial symmetry about the envelope axis. The beam can be refocused through adjustment of a single potential on the refocusing lens rather than through adjustment of several different potentials on the quadrupolar lenses.

Abstract: A key telephone system comprising a key service unit and key telephone sets is configured by the present invention so that system data are registered in an IC card and the system data so registered are fed to the key service unit by the insertion of the IC card in the key service unit.

Abstract: A noise removing circuit is disclosed for removing noise of a duration shorter than a predetermined period of time from an input signal. A monitor circuit is provided for monitoring the input signal to detect whether each time interval occuring between a change detected and a just succeeding change in the input signal is longer or shorter than the predetermined period of time. An output signal is delivered from a one-bit memory. A selector is provided for selectively applying the input signal or the output signal to the one-bit memory in dependent upon whether the time interval between the changes in the input signal is longer or shorter than the predetermined period of time, so that noise of the duration shorter than the predetermined period of time is not included in the output signal.

Abstract: A key telephone system provided with a power supply for supplying power to a specified key telephone set at all times and a controlled power supply capable of turning ON and OFF the power supply to controlled key telephone sets other than the specified key telephone set. The controlled power supply has provision for being automatically turned ON and OFF in accordance with a predetermined schedule or turned ON and OFF under control of the specified set. The power supply is turned ON upon receiving an incoming call or turned OFF upon ON - hooking of the key telephone set after a talking operation with a calling party or automatically turned ON and OFF in response to a specified dial signal incoming after automatically answering the incoming call. The key telephone system can have provision for individually controlling the power supply to each controlled key telephone set.

Abstract: A key telephone system comprising a key service unit and a plurality of key telephone sets is configured by this invention so as to permit use of IC cards which are adapted to admit user data for registration therein, to be inserted in any of the key telephone sets for the user data to be read out of the IC card, and to enable the user to utilize the key telephone set.

Abstract: CMI code has many features, but the interference on a transmission line resulted from radiant noise is an unavoidable problem. In the invention, WALSH 1 code is employed to solve the problem. Clock pulses having a frequency twice that of code on a transmission line in the WALSH 1 code are extracted. The extracted clock pulses consists of zero phase clock pulses and pi phase clock pulses, wherein the zero phase clock pulses are accurately extracted. An embodiment comprises an clock extraction circuit for extracting extracted clock pulses of 2f.sub.0 from a receive pulse train of frequency f.sub.

Abstract: A generally box-shaped electron lens system for use in an oscilloscopic or storage cathode-ray tube for the amplification of both vertical and horizontal deflections of the electron beam from the gun to the target of the CRT. The lens system comprises two electrodes at least partly displaced from each other along the CRT tube axis, with a gap therebetween for electrically insulating one from the other. A pair of tongues extend either from the gun-side electrode into the target-side electrode, or from the target-side electrode into the gun-side electrode, or two such pairs of tongues extend from both electrodes into interdigitating relation to each other. Upon application of prescribed potentials to the two electrodes, a quadrupolar lens field is created in the space between the pair or pairs of tongues for deflection amplification in both directions. On having been deflected vertically, the beam has its deflection amplified by having its traveling direction inverted with respect to the tube axis.

Abstract: The disclosure relates to a digital to analog converter capable of suppressing "glitches" or transient spikes in the analog output signal. The digital to analog converter includes a plurality of current switches corresponding to the number of digital input bit signals and a resistive ladder of the conventional R-2R configuration. The R-2R ladder network has a plurality of input ports each connected to the output of a corresponding current switch. Logic inputs to the current switches determine which of the current switches are to be turned on to supply reference currents to corresponding input ports of the ladder network which in turn decrements the received reference currents by a factor of 2 as they pass through each stage to provide an analog output signal at the output terminal of the converter.

Abstract: A start bit detecting circuit is disclosed, which employs a waveform reshaper, a detection and start circuit and a decision circuit. The waveform reshaper has threshold values T+ and T-. The detection and start circuit starts the start bit detecting circuit upon detection of a predetermined pulse width. The decision circuit judges, for a plurality of decision points, coincidence between the input signal and a specific pattern having a start-signal element, which comprises a plurality of bits.

Abstract: A subscriber's line closing circuit, in which at least one first photo coupler and at least one second photo coupler connected in parallel but in reverse polarities are inserted in a closing loop so as to detect an incoming call, to form a DC Loop and to sense the direction of a direct current flowing through the closing loop.

Abstract: A shield case consists of a case member for housing an electronic circuit. The case member consists of a single printed wiring board having first and second copper films formed on two major surfaces thereof. The first copper film serves as an outer surface coating of the case and is connected to a frame ground terminal. The second copper film serves as an inner surface coating of the case and is connected to a signal ground terminal.

Abstract: A current supply circuit for supplying a speech current via subscriber's lines to a telephone set, in which a pair of constant-current circuits, each so constituted as to hold the potential between the base and the emitter of a control transistor therein to be consant, is connected across the subscriber's lines so that the control transistors are connected in series to a DC power source. A constant-voltage circuit is connected across the bases of the control transistors for making the voltage of the base-emitter paths of each of the control transistors to be constant. At least one of the constant-current circuits may be connected across the subscriber's lines via a light emitting diode of a photo coupler.

Abstract: A time domain reflectometer includes a combined a pulse generator for generating a pulse which is fed to an object under test such as a optical fiber and a sampler for sampling a reflection signal such as a back scattering signal. The pulse generator is controlled by analog delay means and the sampler is controlled by digital delay means. It, therefore, is possible to sample the small back scattering signal and to measure a very long fiber without influences of undesirable signals.

Abstract: A bias circuit accurately compensates temperature coefficient of an optical multiplication in an avalanche photodiode with low power consumption. Temperature coefficient voltage for compensating temperature coefficient of the multiplication of the photodiode is delivered from an emitter follower added a constant voltage to an input of an operational amplifier. The output of the operational amplifier is added, via a voltage regulating diode, to a base of a transistor of which emitter and collector are respectively connected to a terminal of the photodiode and a negative power source. Emitter voltage of the transistor is dividedly connected to another input terminal of the operational amplifier, wherein this connection is negative feedback. The temperature coefficient voltage generated at the emitter follower is amplified inversely proportional to the divided ratio of the emitter voltage of the transistor in order to compensate the temperature coefficient of the multiplication of the photodiode.

Abstract: A conference system is disclosed which is capable of freely setting the sound volume level by making the sound volume levels of the input and output of the conference circuit variable for each participant, by pluralities of input and output ROM converters so that the levels of voices of participants of large and small line losses are made as close to each other as possible and that the participant of a large line loss is supplied with a voice of low attenuation.

Abstract: A time division multiplex telecommunications system is disclosed as adapted for a key telephone system providing for intercommunication between any two of a series of key telephone sets in cascade connection to a switching control circuit, possibly with facilities for association with the nationwide telephone network. The control circuit receives from the tandem connection of telephones an outgoing data signal of time division multiplex frame format having a succession of frames each comprising a frame sync signal and channels of outgoing data from the respective telephones. Rearranging the channels of data in the received outgoing data signal, the control circuits delivers back to the successive telephones an incoming data signal of similar frame format. Each telephone is equipped for rearrangement of the frame sync signal and data channels of the incoming and outgoing data signals, with the result that all the telephones can be of the same circuit configuration.