| 摘要 |
The invention relates to a telephone extension circuit, of analogue type, which is equipped with an input device (1) intended to be linked to a telephone line, with a circuit (2) for controlling a ringer (3), with a dialling circuit (10) for serving a keypad (11), with a device (12) for opening/closing the loop for decimal dialling through which other devices of the extension are fed with energy, of at least one earpiece amplifier (7) and/or a microphone amplifier (8). The extension circuit includes a common device (6) for interfacing between devices and extension circuits, organised around a main transistor, and being substituted for the usual transmission circuit of the other extensions, in order to fulfil the functions of two wire/ four wire conversion, of electronic choke and of matching. <IMAGE>
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