DE3308984C2 - Circuit arrangement for a digital telephone station - Google Patents

Abstract

The invention relates to a circuit arrangement for a digital transparent telephone station, wherein, for example, the supply voltage for the microphone amplifier is only switched on by a code of the telephone system to the telephone station and that this code is only signaled by a preceding code from the telephone station to the telephone system (for example, signaling the pick-up of the handset ) is triggered. If the code is mistakenly or maliciously transmitted from the telephone system to the telephone station, the microphone amplifier is thereby switched on without permission. This is to be prevented by the idea of the invention. This is achieved simply by placing a contact in the supply circuit of the microphone amplifier which is only closed when the handset is actually picked up.

Description

The invention relates to a circuit arrangement for a digital telephone station, each by the Station subscriber or the remote subscriber performed action such. B. making the station ready for operation, Pressing the keyboard, etc. is assigned an individual code, this code to the telephone exchange is transmitted and there causes the return or forwarding of another code, which then brings about the implementation of the function desired by the action and continues to be ready for operation the telephone station the microphone amplifier the microphone in the handset to the internal or the remote supply voltage is switched on.

In modern digital and largely transparent telephone stations is proposed at a Connection establishment when picking up the handset at the station to a code to the telephone exchange send. The telephone exchange then puts this station in readiness for operation by means of a code it sends out, which, among other things, also switches on the microphone amplifier. (Participant stations in an integrated services digital communication network, NTZ Volume 32, 1979). Used by the aforementioned Station selected a remote subscriber station as the calling station, then this remote subscriber station becomes also put into operation after lifting the handset by a code of the telephone exchange. Under Commissioning is to be understood here, too, that initially all for the acceptance of the call and the production The units necessary for the speech connection can be connected to the internal or external supply. These units also include the microphone amplifier contained in the handset.

In such a circuit arrangement of a digital telephone station, it is possible that the code for Commissioning of the station mistakenly or maliciously z. E drawn from the telephone exchange can be. This activates the microphone amplifier and thus the microphone in the handset that is on top of it switched ready for operation and the noises and conversations arising in the immediate vicinity can be tapped will.

ίο For analog telephone stations it is known that To prevent eavesdropping on conversations in the vicinity of the station by suppressing the Alarm clock microphone switches a capacitor between the a / b wires, which is used when the handset is picked up disconnected from a wire of the subscriber line via at least one contact of the hook switch (DE-AS 12 59 392).

The object of the invention is therefore to be to prevent in a simple manner that unauthorized interception of Rau mes by transmitting the appropriate code on lead.

This object is achieved in that the supply voltage unit switched on by the corresponding code from the telephone exchange for the microphone amplifier is connected in a manner known per se to the supply input of the microphone amplifier via an additional contact which is closed only when the handset is lifted
This has the advantage that switching on the microphone feed and thus listening to the surrounding room is only possible when the handset has been picked up by the called subscriber.
The circuit arrangement according to the invention is explained with reference to a figure, only the units and parts essential to the invention being shown.

The figure consists of an indicated telephone exchange F, a subscriber line TL and a subscriber station TS with a microphone M, a microphone amplifier V, a supply voltage unit Sf and a contact k.

It is assumed that in a digital telephone system (F) a connection is to be established between two largely transparent telephone stations. Simply by picking up the handset at the calling station (z. B. TS) a first code is transmitted to the telephone exchange, which indicates the intention of the subscriber to start up this telephone station. This results in the return of a second code from the telephone exchange (F) to the calling subscriber station (TS), which puts it into operation. These include the connection of supply voltages to the individual for establishing a connection or for preparing messages to be sent out, e.g. B. to see necessary station units for text-enabled stations. These units also include the microphone amplifier V, which is provided for the microphone M provided in the handset and whose supply voltage input f is connected to the supply voltage unit SE . In the example according to the figure, an external supply is provided via the subscriber connection line TL , to which the supply voltage unit SE is connected in terms of DC voltage, while the microphone amplifier V is only connected to the subscriber power in terms of AC voltage.

In the above circuit, it is easily possible that the normally by lifting off the

Handset at the calling or called subscriber station by the telephone exchange for putting the subscriber station into operation is mistakenly or deliberately reproduced without permission. This switches on the microphone amplifier of the station and the corresponding surroundings can be heard. In order to prevent this, it is necessary to make the final commissioning of station units that enable eavesdropping at a subscriber station dependent on an action by the operator there. According to the invention, therefore, a contact k is arranged between the supply voltage input E of the microphone amplifier V and the supply voltage output A of the supply voltage unit SE, which contact only closes when the handset is lifted. This means that the power supply unit is already put into operation by the code from the telephone exchange. However, the microphone amplifier is only supplied with power after an operation at the corresponding station. The contact provided for this purpose can be a further fork switch contact or, for example, an electronic contact that is actuated by capacitive or also optical impulses.

From the above it can be seen that with the aid of the circuit arrangement according to the invention in In a simple way, it is possible to improperly switch on the microphone amplifier in digital telephone stations to prevent.

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Claims (3)

Patent claims: 1. Circuit arrangement for a digital telephone station, wherein each action carried out by the station subscriber or the remote subscriber, such as e.g. B. ready for operation of the station, pressing the keyboard, etc., an individual code is assigned, this code is transmitted to the central office and there causes the return or forwarding of another code, which then causes the implementation of the function desired by the action and continues When the telephone station is ready for operation, the microphone amplifier of the microphone in the handset is connected to the internal or remote supply voltage, characterized in that the supply voltage unit (SE) switched on by the corresponding code from the telephone exchange (F) for the microphone amplifier f V? is connected via an additional contact (k) , which is closed only when the handset is lifted, to the feed input (E) of the microphone amplifier f V ^ 2. Circuit arrangement according to claim 1, characterized in that the additional contact (k) is a contact of the hook switch 3. Circuit arrangement according to claim 1, characterized in that the additional contact a z. B. is controlled by a capacitive or optical sensor electronic contact