| 摘要 |
The invention relates to a circuit arrangement for a digital, transparent telephone station, where, for example, the feed voltage for the microphone amplifier is connected to the telephone station only by a code of the telephone system, and this code is triggered only by a preceding code from the telephone station to the telephone system (for example, signalling that the handset has gone off-hook). If the code is inadvertently or maliciously transmitted from the telephone system to the telephone station, this results in unauthorised activation of the microphone amplifier. This is intended to be prevented by the inventive idea. This is achieved in a simple fashion by inserting a contact in the microphone amplifier feed circuit which does not close until the handset actually goes off-hook.
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