| 摘要 |
<p>An subscriber's circuit for a four-wire-system local switch is provided with a tow-wire/four-wire hybrid circuit comprising: a two-wire/four-wire converter circuit; an incoming circuit device, connected between the converter circuit and a time-division switch section, for amplifying an incoming voice current, supplying a DC current to a subscriber's telephone set and generating a subscriber's line signal of large amplitude such as a bell and howler signal by repeating the polarity reversal of the DC current and also an alarm signal by stepwise changing the duration and the frequency of the repetitive polarity reversal in response to digital command signals supplied thereto from the time-division switch section; and an outgoing circuit device, connected between the converter circuit and the time-division switch section, for amplifying the output signal of the converter circuit, transmitting a signal representative of a subscriber's call or answer to the time-division switch section in response to the state of the DC current supplied to the subscriber's telephone set and stopping the operation thereof in response to the cut-off state of the DC current thereby to prevent singing.</p> |
