Abstract: A click tone removing system for a time division switching system which performs switching of speech channels by a highway switch inserted in a highway. When a hook information detector and a dial information detector detect hook information and a dial information, respectively, delivery of a PCM speech sending signal to the highway is prevented by a blocking function for a fixed period of time, so that the highway is controlled to switch the speech channel, thereby removing a click tone generated by dialing.

Abstract: A transmission system for a key telephone system, in which speech signals and control signals are transmitted through two pairs of transmission conductors between a key service unit and each of a plurality of key telephone sets, and in which DC electric power is supplied from the key service unit to each of a plurality of telephone sets. In accordance with the present invention, the speech signal and the control signal are transmitted through a first transmission line of high frequency band provided by one pair of the transmission conductors from the key telephone set to the key service unit, and the speech signal and the control signal are transmitted through a second transmission line of high frequency band provided by the other pair of the transmission conductors from the key service unit to the key telephone set.

Abstract: A facsimile connection system, which is provided with a plurality of facsimile terminal equipments having no CO line interface circuit, at least one facsimile signal processor having a CO line interface circuit, and an exchange for interconnecting the plurality of facsimile terminal equipments and the facsimile signal processor, so that the facsimile terminal equipments can use the facsimile signal processor in common to them. An additional information generator may be further provided in common to the facsimile terminal equipments so as to be connected to the exchange.

Abstract: A control signal transmission system for a key telephone system, in which control signal information is transmitted in a parallel signal configuration between a plurality of key telephone sets and a key service unit by the use of transmission lines one-to-one corresponding to the individual key telephone sets, and in which the information between the key telephone sets is transmitted using a serial signal format of a frame configuration so that time slots of respective frames are synchronized with respect to all of the transmission lines.

Abstract: A time interval measuring system, which is proposed for measuring in a digital memory, etc. a time interval between two time points meeting with measurement conditions indicative of two kinds of optionally presettable threshold levels, polarities and the numbers of slopes in a digital value train converted from an analog signal.

Abstract: A key telephone system having a plurality of key telephone sets and a key service unit. Intercom lines connect the key service unit and the key telephone sets. A synchronizing system in each key telephone set is provided for synchronizing signal transmissions from the corresponding individual key telephone sets of the key service unit with the transmissions from the key service unit. The individual synchronizing systems receive a multiplex transmission from the key service unit and the transmission has a multiplexed frequency signal as a control signal and also has a voice signal. The control signal includes control transmission data to the synchronizing system and includes a start bit following a fixed number of signals having a binary state opposite to a binary state of the start bit. Circuitry is provided including a high pass filter which removes the voice signal and for converting the frequency shift signal free of the voice signal to the transmission data control signal with control transmission data.

Abstract: A subscriber circuit in a time-division telephone switching system having a supervisory circuit connected to a subscriber telephone set for supervision of incoming calls, call-answering, line-busy and on-hook supervision on the telephone set. A common control circuit receives signals from the supervisory circuit through a scan circuit and when it receives a signal indicating that the handset has not been properly replaced. A howler tone source of a howler tone transmission circuit generates a low-level howler tone signal which is modulated by a modulator in the howler tone transmission circuit. This modulated tone signal is applied to a demodulator in the subscriber circuit through a speech connecting network for the transmission of speech to and from the telephone set without further need of connecting link such as a trunk line or the like. The telephone set converts the demodulated tone signal to a continuous howler tone audible signal.

Abstract: A reception system for a key telephone system, in which a voice signal and a control signal having the form of a frequency shift signal are multiplexed in an intercom line for transmission. In accordance with the present invention, there is provided means for extending by a predetermined period of time the period of a first clock pulse at the time of a key service unit transfering from the transmitting state to the receiving state, so that the center of data transmitted may coincide with the readout timing for reception.The means for extending is arranged so that it may apply a reset pulse to a reset terminal of a frequency divider of an oscillator for generating the lock pulses.

Abstract: A power source circuit having a reference voltage generating circuit for generating a DC reference voltage a current output circuit provides across output lines a current proportional to an input voltage, and an error voltage integration circuit is provided for integrating a voltage proportional to a difference between the DC reference voltage and the voltage across the output lines at a required integration time constant to apply the integrated output as the input voltage to a current output circuit. The integration time constant is set so that an output terminal connected to the output lines may have a low output impedance in terms of direct current to maintain a predetermined constant DC output voltage and have a high output impedance with respect to an AC signal applied to the output lines.

Abstract: A signal transmission system which perform two-way signal transmission between a first transmitter-receiver and a second transmitter-receiver via a pair of signal lines and supplies a DC current from the first transmitter-receiver to the second transmitter-receiver. In each of the first transmitter-receiver and the second transmitter-receiver, there are provided a current varying circuit for varying a signal line current by a transmission pulse signal so that the signal line current may assume a value in a predetermined current region lower than a minimum level of a load current to the other transmitter-receiver during sending out a signal pulse, a current detector for detecting a current or voltage variation in the signal line current, and a gate circuit for blocking the detected output from the current detector while the transmission pulse is sending out to the current varying circuit.

Abstract: A key telephone system in which a key service unit is provided for selectively connecting a plurality of key telephone sets to at least a pair of CO lines through at least one control line provided in correspondence to the CO lines and a common line.

Abstract: A waveform searching system for a sampling oscilloscope, in which the instantaneous level of a high-speed sawtooth signal generated by a trigger signal synchronized with an input analog signal and the instantaneous level of a properly attenuated or amplified X-axis sweep wave are compared with each other to generate a pulse in a case of coincidence therebetween, thereby to generate sampling pulses sequentially delayed after the trigger signal by a constant time; the input analog signal is sampled by the sampling pulses to produce sampled pulses; and the sampled pulses are displayed by the X-axis sweep signal on a CRT.

Abstract: A hybrid circuit, in which the differential output of an amplifier of the four-wire receive port having the differential output of low output impedance is connected to a series-connected circuit composed of a variable impedance circuit and the primary winding of a transformer connected to the two-wire port of the hybrid circuit, and in which the input of an amplifier of the four-wire transmit port of the hybrid circuit having a high input impedance is connected to the node connection of the variable impedance circuit and the primary winding of the transformer. In the case where the impedances of the variable impedance circuit and the transformer are in a state of mutual equilibrium, the neutral point potential of the amplifier of the four-wire receive port is applied as an input to the amplifier of the four-wire transmit port.

Abstract: 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.

Abstract: A channel switching network, in which each cross-point of a switch matrix is constituted as a channel switch of balanced type using two PNPN semiconductor elements. Each of the two PNPN semiconductor elements is arranged in a forward direction with respect to a direct current flowing from the channel switching network to a corresponding terminal equipment. A column of cross-points and a line of cross-points in the switch matrix are designated to select a simultaneously designated cross-point in response to a pair of selection signals. A control circuit is provided for each pair of the incoming lines and the outgoing lines of the switch matrix so that the terminal voltage of a power source for flowing the direct current in the PNPN elements is controlled to temporarily rise to turn ON the PNPN elements at the selected cross-point and thereafter to drop to such a value as only to maintain the PNPN elements in the ON states.

Abstract: A synchronization system for a key telephone system, in which key information or the like information signal between a key service unit and each key telephone set is transmitted in the form of a time-division pulse signal under the control of a counter provided in the key service unit. The information signal has a format which is divided into a first signal from the key service unit to each key telephone set and a second signal from each key telephone set to the key service unit so as to make distinction between the first and second signals in terms of time. The first signal is disposed in a time slot preceding the second signal to provide a pair of signal groups. A one-pulse start signal is disposed in the foremost time slot of the signal groups and a one-pulse answer signal is disposed in a time slot between the first signal and the second signal.

Abstract: A light signal observation device, which is provided in combination with light receiving means for detecting a light signal, light intermitting means for intercepting or passing therethrough the light signal incident to the light receiving means, amplifying means for amplifying the output from the light receiving means; time base signal generating means for generating a sawtooth wave in synchronism with the light signal and also while the light signal is intercepted and for generating a luminance modulation signal in the period of generation of the sawtooth wave, and display means for displaying an optical signal waveform including a 0 level on the basis of the output signal from the amplifying means and the sawtooth signal and the luminance modulation signal from the time base signal generating means. The light signal observation device of this invention may be constructed as a synchroscope or a sampling oscilloscope.

Abstract: A key telephone system adapted to selectively connect a plurality of key telephone sets to a plurality of CO lines through a key service unit and pluralities of talking lines and control lines and provided with a calling device in at least one of the key telephone sets, in which automatic holding of the CO line is enabled upon depression of a calling key. In case of transferring the incoming call from a receiving key telephone set to a called one of the other key telephone set, depression of the individual calling switch automatically starts calling of the called key telephone set and enables the called party to recognize the incoming call by means of lamp indication and answer the calling CO line. The number of cable conductors interconnecting the key service unit and the key telephone sets is effectively reduced.

Abstract: A key telephone system, in which a key service unit is provided for selectively connecting a plurality of key telephone sets to a CO line by two control lines and a talking line. The key service unit is comprised of a DC power source having two terminals of a positive output voltage and a negative output voltage, a first detector connected to one of two control lines for detecting a state where one of the two output voltages is applied across the two control lines to flow a current of predetermined value therethrough, a first switch for connecting the other output voltage across the control lines in response to the output of the first detector, a second detector connected to the other of the two control lines for detecting a state where the other of the output voltages is applied across the two control lines to flow a current larger than a certain value therethrough, and a second switch for connecting the talking line to the CO line in response to the output of the second detector.

Abstract: A key telephone system, in which a plurality of key telephone sets are selectively connected to a plurality of CO lines by the use of a plurality of talking lines under control of a key service unit and a plurality of control lines. In order to seize a CO line, a CO line seizure signal from one of key telephone sets is time-divisionally transmitted at a low speed and received by a speed change memory of the key service unit. A high-speed output from the speed change memory is added with dial or hook information and then space-divided for seizing a desired one of the CO lines. A talking operation, a holding operation, a privacy operation and a synchronizing operation in this system are performed on the base of the above operation principle.