Fujitsu Corporation

Eiji Minamitani

Hiroshi Ishikawa

Mitsutoshi Ayano

Takuhito Kojima

Takashi Yokoto

Kiyoo Ozawa

A digital pad switch inserted in each highway of a time-division speech network in which there are disposed on the backward side of the speech network time switches, each time switch reading out speech information from a speech memory in the order of the memory cell address, assigning a memory cell address by the output from a channel counter. The digital pad switch is arranged so that it may send out, under the control of a common control unit, a selected converted input signal corresponding to an input signal from the input to the digital pad switch, the converted input signal respectively having been attenuated as compared the input signal by predetermined amounts and also sending out a converted input signal corresponding to a zero level signal regardless of the magnitude of the input signal. When cutting off a speech path set up in the time-division speech network, the digital pad switch is controlled by the common control unit so that the digital pad switch sends out the zero level signal as a signal of the speech path passing through the digital pad switch, and after writing the zero level signal in the speech memory of the time switch on the backward side, the speech path is cut off. A continuous tone signal passing through the time-division speech network is inputted into the digital pad switch. The digital pad switch is controlled by the common control unit to selectively send out the zero level signal for a desired period of time, thereby turning ON and OFF the tone signal. When sending out a howler tone, the amount of attenuation of the tone signal is decreased under the control of the common control unit in a stairstep manner. When testing a multi-frequency signal receiver, a multi-frequency signal transmitter and the multi-frequency signal receiver under test are connected to the backward and the forward side of the time-division speech network, respectively. A path is set up between them and then a signal on the path is attenuated variously by the digital pad switch in order to vary the level of the input signal to the multi-frequency signal receiver. Thus, the present invention permits efficient use of the digital pad switch.

Digital audio signal control system for a timedivision switching system

A time division electronic switching system including, as main structural elements, a central processing unit, a multi-frequency signal receiver unit, a signal processor and a time division switch including a speech path memory. Dial information from a subscriber or from another telephone office is detected in the multi-frequency signal receiver unit, the output of the multi-frequency signal receiver unit is written into the speech path memory, and an access circuit reads out the information written in the speech path memory and supplies it to the signal processor as read out information.

Time division electronic switching system

In the case where a two-wire circuit forming a trunk or a subscriber line of the two-wire system is converted by a hybrid circuit to a four-wire circuit of sending and receiving paths to form a transmission line between subscribers, if an impedance variation on the two-wire side is large, a leak from sending path to receiving path occurs and is amplified to cause singing. To eliminate the singing, a circuit for detecting the impedance fluctuation of the two-wire side is inserted in the two-wire circuit, and switching means inserted in the four-wire circuit is activated by an impedance detecting signal of the detecting circuit to electrically open the four-wire circuit, thereby preventing the singing phenomena. This method does not involve the use of an expensive attenuator which is troublesome to design for the prevention of singing.

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Yokohama, Japan

Eiji Minamitani