EP1325606A2

EP1325606A2 - Telephone for connection to a public telephone network

Info

Publication number: EP1325606A2
Application number: EP01986819A
Authority: EP
Inventors: Christian Kranz
Original assignee: Infineon Technologies AG
Current assignee: Infineon Technologies AG
Priority date: 2000-10-10
Filing date: 2001-10-02
Publication date: 2003-07-09
Also published as: JP2004511963A; WO2002032086A3; CN1264326C; CN1470123A; US6928159B2; WO2002032086A2; DE10050041A1; US20030179879A1

Abstract

The invention relates to a telephone in which telephone operational signals (ring signal, call charge signals and caller identifications) and audio signals are jointly processed by one integrated circuit (8). To this end, the signal levels of the individual signals have to be conditioned. Since the telephone signals are processed jointly by one chip, preferably by one digital signal processor (DSP), the amount of discrete components so far necessary can be reduced.

Description

description

Telephone device for connection to a telephone network

The invention relates to a telephone device which receives audio signals and telephone operating signals via a telephone network, and to a method for processing audio signals and telephone operating signals in a telephone device.

Various types of telephone operating signals are transmitted over the public telephone network, which have completely different signal levels. One of the telephone operating signals is the ringing signal, which has an amplitude of 120 V. The DC voltage component of this signal is 60 V. In addition, charge unit signals (meter pulse signals) whose signal amplitude is 12 V are transmitted via the telephone network. In addition, caller ID signals are transmitted over the network (CID: Caller Identification).

The very different signal levels of the individual telephone operating signals are historical. The bell signal was originally used to actuate mechanical bell devices electromagnetically. The short alternating voltage pulses of the meter pulse signal served as counting pulses for a mechanical charge meter.

Because of the very different voltage levels of the different signals, it is also necessary in modern telephone sets to decouple these signals in the reception path by means of discrete components and to process them separately. So far, separate, discretely constructed evaluation circuits for the different types of telephone operating signals have to be provided in each telephone set. In addition, different standards exist for the different telephone operating signals in the different states. On the one hand, the signal levels of the bell signal, the meter pulse signal, etc. differ in the various national telephone networks. On the other hand, the different telephone operating signals are also transmitted in different formats. While some national standards provide for the transmission of the caller ID in FSK (Frequency Shift Keying) format, other standards require the transmission of this ID in DTMF (Dual Tone Multi Frequency) format. In order to be able to evaluate these caller identifiers in accordance with the various national standards, additional, discretely constructed evaluation circuits are required. A telephone device that is to be produced in large numbers and is to be used in different countries must therefore be equipped with various discrete evaluation circuits. The advantage of higher quantities is offset by the disadvantage of increased component costs.

It is therefore an object of the invention to provide a telephone set and a method for processing telephone signals which can be implemented with less component expenditure and which enables adaptation to different telephone network standards.

This object is achieved according to the invention by a telephone set for connection to a telephone set according to claim 1 and a method for processing telephone operating signals and audio signals in a telephone set according to claim 21.

The telephone set according to the invention is suitable for connection to a telephone network and can be operated either in a waiting mode or in a talk mode. As a rule, the waiting mode corresponds to the operating mode with the handset on-hook. In the waiting mode the first telephone operating signals receive. These can be ring signals, for example. In call mode, audio signals, which are primarily voice signals, as well as second telephone operating signals, for example charge unit signals, are received.

According to the invention, the telephone set comprises means for signal conversion which, depending on the mode and / or the type of the received telephone operating signals, carry out a signal conversion of these signals. In addition, the telephony device comprises at least one integrated circuit that processes both the audio signals and the telephone operating signals. This measure completely eliminates the need for discrete circuits that were used to decouple the various telephone operating signals. This enables a cheaper and more compact structure of the telephone set.

The telephone signals are evaluated together by integrated circuits. These integrated circuits can be analog circuits or digital signal processors. As a result, the historically very different telephone signals can be subjected to a uniform signal evaluation. This makes it possible to process telephone operating signals such as the caller identifiers, which until now could only be evaluated in more expensive telephone sets, also in cheaper devices.

Another advantage of evaluating the signals together is that the way in which the signals are evaluated can be changed by reprogramming the integrated circuit. This makes it possible to adapt the telephone set to the telephone standards of different countries and in particular to the differently defined telephone operating signals. In particular, it is possible to manufacture a telephone device that can process all telephone standards used in Europe. According to an advantageous embodiment of the invention, the signal levels of the received signals are adapted as a function of the mode and / or the type of the received signal by the means for signal conversion. The signals received via the telephone network are characterized by very different signal levels. The bell signals have an amplitude of 120 V (with a DC voltage component of approximately 60 V), the maximum level values of the meter pulse signals are approximately 12 V, and the amplitude of the voice signals is approximately 3 V. an integrated circuit are processed together, they must first be transformed so that their signal levels correspond to each other after the transformation. This is the task of the means for signal conversion.

A further advantageous embodiment of the invention provides that the at least one integrated circuit is an integrated analog circuit. This has the advantage that an analog / digital conversion and a later digital / analog conversion of the audio signals can be omitted. The received signals can be processed analogue throughout; digital intermediate processing of the signals is no longer necessary.

Alternatively, it is advantageous if the at least one integrated circuit comprises an analog / digital converter unit and a digital signal processor unit arranged downstream. The analog / digital converter and the digital signal processor are preferably integrated on one chip, so that the entire signal processing is carried out

(at least) one integrated circuit can be made. In signal processing, there is currently a trend towards using digital signal processors. As soon as the received signal is in digitized form, it can be further processed by a digital signal processor unit in a freely definable manner. In the present case, an adjustment of the si Signal processing to the telephone network standards of different countries can be achieved. In this respect, digital signal processors enable a more flexible evaluation of the received signals.

Another advantage of using digital signal processors is that once a chip design has been created for an evaluation chip for telephone sets, it can also be used for future chip generations. With digital logic, it is generally possible to simply transfer the logic design to later generations of CMOS structures.

Digital processing also meets the increasing interest in comfortable telephone sets. For example, it is possible to save the caller ID or an oral message in a simple and flexible way.

The first telephone operating signals received during the waiting mode advantageously include ringing signals,

Charge unit signals and caller IDs. The reception of charge unit signals is necessary in the waiting mode insofar as these signals can still be transmitted even after a call has ended. Caller IDs are also transmitted from the exchange to the telephone in this mode.

The second telephone operating signals received during the conversation mode advantageously include charge unit signals and caller identifiers.

An advantageous embodiment of the invention provides that the at least one integrated circuit has separate inputs for the signals received in the waiting mode and the signals received in the talk mode. The signals received in waiting mode and in talk mode are routed along differently designed paths. One reason for this is that according to the Telecommunications authorities may not take any power from the telephone network in waiting mode, i.e. when the handset is on hook. In addition, the different paths prevent interference of the signals transmitted over the individual paths. The two paths, which are designed for the signals received in the waiting mode and the signals received in the talk mode, are fed to the integrated circuit via separate inputs. As a result, the signals can also be subjected to different (preprocessing) in the integrated circuit.

According to a preferred embodiment of the invention, the signals received in the waiting mode and the signals received in the talk mode are fed to the subsequent processing stages in multiplex mode. Due to this measure, the signals of both modes can be processed together. The multiplexer is preferably integrated on the at least one chip used for signal processing.

Another preferred embodiment of the invention is characterized in that the means for signal conversion comprise a voltage-dependent resistor that connects the connecting lines to the telephone network. A voltage-dependent resistor (varistor) is characterized by a non-linear characteristic and conducts better at high voltages than at low voltages. In the event of high voltage peaks from the telephone network, such as occur with electromagnetic interference (lightning strike), this component has a low resistance and thus functions as a first overvoltage protection element for the subsequently arranged modules. Voltage-dependent resistors are characterized by low manufacturing costs.

The means for signal conversion advantageously comprise differential AC elements, by means of which the signal path for the signals received in waiting mode is decoupled from the telephone network. These differential AC elements are high-pass filters and only transmit the AC voltage component of the signals above a certain cut-off frequency. This AC voltage component contains all relevant information for the signals of the telephone network. The suppression of a DC voltage component prevents the power consumption from the telephone network.

Furthermore, it is advantageous that the means for signal conversion have high-resistance voltage dividers, which are arranged downstream of the differential AC elements in the signal path. These high-resistance voltage dividers serve on the one hand as a further protection against voltage peaks, on the other hand they ensure that the operating point of the signals received by the differential AC elements is in the range which is predetermined by the operating voltage of the telephone set. The high-resistance design of the resistors also results in low power consumption and high sensitivity.

A particularly preferred embodiment of the invention provides that the means for signal conversion comprise at least one controllable amplifier unit. In addition, it is advantageous if the means for signal conversion comprise at least one circuit for determining the maximum level values, the amplification being set as a function of the level values detected. It is particularly advantageous if the controllable amplifier unit and the circuit for determining the maximum level values are integrated on the at least one chip for signal processing.

The level of the incoming signals can be adjusted by means of the controllable amplifier unit in such a way that they fully utilize the permitted voltage range of the circuits arranged subsequently. The gain is preferably set as a function of the detected maximum level value of the signals. This ensures the highest possible sensitivity of the signal evaluation. Moreover very high incoming signal levels can be adapted by small amplification factors or even by amplification factors <0 dB for processing in the circuits arranged below.

According to a further advantageous embodiment of the invention, the at least one controllable amplifier unit is designed as a range selection circuit for the analog / digital converter. With analog / digital converters, the input range can be varied in powers of two. The analog / digital

The voltage range that can be read by the converter can be used in the best possible way in order to achieve the highest possible resolution of the digitized signals.

Another particularly preferred embodiment of the invention is characterized in that the means for signal conversion comprise at least one frequency-selective attenuator. A frequency selective attenuator is a simple measure to attenuate a telephone signal of a certain frequency. For example, the charge unit signals have a constant frequency of 12 kHz or 16 kHz and can be attenuated by such a frequency-selective attenuator.

It is also advantageous that the frequency-selective attenuator is arranged in the signal path for the signals received in the talk mode. Since all the signals received in the conversation mode are processed on the same path, this measure ensures that in particular the charge unit signals are not audible by the user of the telephone, but can still be processed in the circuits arranged below.

The frequency-selective attenuator advantageously comprises a parallel resonant circuit, the resonance frequency of which depends, for example, on the frequency of a certain type of received gene telephone operating signals is adapted. A parallel resonant circuit is characterized by an inductance connected in parallel with a capacitance and acts as a bandstop for incoming signals of a defined frequency. The resonance frequency is determined by the values of the capacitance and the inductance. For example, the frequency of the charge unit signals is 12 kHz or 16 kHz and can be damped by the parallel resonant circuit if the components are suitably designed.

It is also advantageous that a resistor is connected in parallel to the parallel resonant circuit. This measure has the advantage that the received signals, the frequencies of which are in the range of the resonance frequency of the parallel resonant circuit, are only attenuated to such an extent that they can still be processed by the subsequently arranged circuits. In particular, it is possible with such a circuit to adjust the level of the charge unit signals to the level of the audio signals.

According to a further preferred embodiment of the invention, the means for signal conversion include overvoltage protection elements for protecting the inputs of the at least one integrated circuit. For example, Zener diode circuits can be used for these overvoltage protection elements. Another advantage of these components is that signals with large signal amplitudes are clipped and that signal level adjustment takes place in this way. This applies in particular to the ringing signals which have high level values.

The method according to the invention for processing telephone operating signals and audio signals in a telephone set comprises the following steps: a) receiving first telephone operating signals in waiting mode or second telephone operating signals and audio signals in conversation mode; b) performing a level adjustment depending on the mode and / or the type of the received telephone operating signals; c) joint evaluation of both the audio signals and the telephone operating signals.

The signals received over the telephone network have very different signal levels. In order for them to be made available for joint evaluation, they must first be reshaped in such a way that after reshaping they are in a similar level range. The joint evaluation of all telephone operating signals and audio signals drastically reduces the number of electronic components required for signal processing. As a result, the method according to the invention can be operated more cost-effectively than previous methods.

The invention is described below with reference to several exemplary embodiments shown in the drawing. Show it:

Fig. 1 is an overview circuit diagram of the invention

Telephone apparatus in which the telephone signals are processed in digital form;

Fig. 2 shows a corresponding circuit of a telephone set for analog signal processing.

Both audio signals and telephone operating signals are transmitted over the telephone network. The connection to the respective telephone network is usually made via two connecting lines, which are designated in Fig. 1 with La and Lb. In addition, further connection lines can be provided. For example, in the German telephone network standard, an additional alarm line and an earth line are provided, so that a telephone connection comprises four telephone lines. There is a constant DC voltage of approx. 60 V between the connecting lines La and Lb. Both the audio signals and the other telephone operating signals are transmitted via the connecting lines La and Lb. One of these operating signals is the ringing signal or ringing signal, which signals incoming calls. The DC voltage of 60 V is superimposed on an AC voltage component with a frequency of 15 to 75 Hz. This superimposed AC voltage component also has an amplitude of approximately 60 V, so that the overall signal can have an amplitude of up to 120 V.

Charge unit signals, which are also referred to as meter pulse signals, are also transmitted via the connecting lines La and Lb. These are AC signals of a defined duration (100 msec), with each transmitted pulse indicating an accumulated charge unit. In the common European telephone network standards, frequencies of 12 kHz or 16 kHz are provided for the meter pulse signal. The amplitude of the meter pulse signal is 12 V, which is about four times the amplitude of the audio signal.

For incoming calls, a caller ID signal (also called Caller ID) is transmitted in order to be able to show the called party the telephone number of the caller. Two different standards are used in Europe to transmit this Caller ID, FSK (Frequency Shift Keying) and DTMF (Dual Tone Multi Frequency). In the FSK standard, the caller IDs are frequency modulated, while in the DTMF method a tone dialing sequence is used to transmit the number. The amplitude of the caller ID signal is of the order of 2 V, that is to say of the order of the audio signals.

In some telephone network standards, a polarity reversal signal (a so-called line reversal) is also provided for where the polarity of the connections La and Lb is exchanged. However, this polarity reversal signal is not provided for in all European standards.

The two connecting lines La and Lb are shown in Fig. 1 on the left side. These connecting lines are connected by a voltage-dependent resistor VDR, which is high-resistance (> 1 MΩ) in normal operation and draws little current. This voltage-dependent resistor VDR has a non-linear current-voltage characteristic; at high-lying

He is becoming increasingly tense. As a result, subsequent circuit parts can be effectively protected against potential voltage peaks (electromagnetic interference, lightning strikes, etc.), since the overvoltage that occurs is derived.

A telephone set is used in two operating modes, in a waiting mode with the handset on hook and in a talk mode. The regulations of the respective telecommunications authorities stipulate that no power may be drawn from the telephone network during the waiting mode. When the handset is on the hook, there must be a resistance of at least 1 MΩ (in some standards 10 MΩ) between the connection lines La and Lb.

Nevertheless, telephone operating signals must be able to be received and evaluated even during the waiting mode. In the circuit shown in FIG. 1, a separate transmission path is provided for these signals (ringing signal, caller ID, meter pulse signals), which includes the signal lines 1 and 2, the capacitances C1 and C2 and the resistors R1 to R6.

The path provided for the talk mode signals comprises the signal lines 2 and 3 and a bandstop which consists of the capacitance C0, the resistor R0 and the inductance L0. The Si connected to the output of the band stop Signal line 4 and signal line 2 are fed to the bridge rectifier 5. The line 6 for the conversation signal connects the output of the bridge rectifier 5 to the p-channel MOSFET T2.

The call path is deactivated during the waiting mode. This is done by the HOOK signal, which is present via the resistor R12 at the base of the npn transistor Tl. In the waiting mode, that is to say with the receiver on-hook, the HOOK signal blocks the transistor T1. As a result, the signal line 7 connected to the gate of the p-channel MOSFET T2 is pulled to a positive potential via the resistor R1, and the p-channel MOSFET T2 blocks. Therefore, no conversation current I _s flows during the waiting mode. This meets the requirement not to draw any power from the telephone network during the waiting mode.

The signals received in the waiting mode, i.e. the ringing signal, the meter pulse signal and the caller IDs, are fed via the signal lines 1 and 2 to the capacitances C1 and C2, which act together with the resistors arranged below as AC elements and only transmit the AC voltage component of the signals present at La and Lb.

The resistor R1 is followed by a high-resistance voltage divider, which includes the resistors R2 and R5. Accordingly, the output of resistor R4 feeds the voltage divider made up of R3 and R6. These high-resistance, discrete voltage dividers serve as protection against

Telephone lines always encountering high voltages. They are also used to determine the signal offset, which is located between VSS and VDD and is defined by the ratio of R2 to R5 (or from R3 to R6). The AC voltage component of the received signals relies on these signal

Offsets on and is fed to the inputs for wait mode signals DLP and DLN of the integrated circuit 8. The A- gears DLP and DLN are designed as differential signal inputs so that interference that affects both signal lines equally can be eliminated.

The further signal processing is carried out by the integrated circuit 8, on which all units serving for further signal processing are integrated. The inputs DLP and DLN of the integrated circuit 8 for the wait mode signals are each protected by one of the two overvoltage protection elements D1 and D2. These overvoltage protection elements are made up of Zener diodes, with one diode in the flow direction and the other in the reverse direction, regardless of the polarity of the incoming signal. These elements are intended to protect the subsequent components of the integrated circuit against high incoming voltage peaks. In addition, the signal amplitudes of the bell signals are clipped.

The inputs DLP and DLN of the integrated circuit 8 are connected to the analog multiplexer MUX. The AIN input for the talk mode signals is also connected to the MUX analog multiplexer. The call mode signals are designed as single-ended signals and are implemented by the analog multiplexer MUX together with the ground AIP. The analog multiplexer MUX forwards the signals present at its inputs to the analog amplification stage 11 on two signal lines.

Furthermore, the inputs DLP and DLN of the integrated circuit 8 are connected to the signal peak detector 9. This determines the maximum voltage values of the wait mode signals present at these inputs and forwards this information to the gain control 10. The task of the gain control 10 is to set the gain factors of the analog gain stage 11 for the wait mode signals in such a way that the full permitted voltage range of the subsequent components is used as far as possible. There are the gain factors 0 dB, 6 dB, 12 dB and 18 dB are available. In the normal case, the gain control 10 selects the highest sensitivity; the gain factor is reduced accordingly only at high signal levels. In contrast, the gain factor for the talk mode signals always has a constant value.

The signals amplified by the analog amplification stage 11 are passed on to the analog / digital converter A / D. This converts the analog signals into digital signals so that they can be processed further by the subsequent digital signal processor DSP. The digital signal processor DSP enables analysis and separation of the various signals. In this way, caller IDs or charge unit signals can be displayed on a digital display of the telephone set. The audio signals can then be converted back into analog signals by a digital / analog converter so that they can be heard in the receiver or loudspeaker.

If the telephone set is to be switched from the waiting mode to the talk mode, a voltage is applied to the HOOK input such that the npn transistor Tl conducts. As a result, the gate of the p-channel MOSFET T2 is at ground and a conversation current I _s can flow through the component as a drain current. This current flows primarily through the transmission transistor T3, the resistor R8 and the line impedance ZL through the common ground. The conversation flow I _s is modulated by the received speech signals and is present via the coupling capacitor C4 at the input AIN for conversation mode signals.

In talk mode, additional signals go into the circuit via the HOP input. These are the speech signals from the user of the telephone set. They are first transformed by a voltage divider made up of the impedances ZI and Z2. Then only your AC voltage happens share the capacity C3. The voltage divider consisting of the resistors R9 and RIO passes on a fraction of this signal via the gate line 12 to the gate of the transmission transistor T3. The transmission transistor T3 is modulated with the frequency of the speech signal HOP. As a result, the conversation current I _{s is} modulated with the AC voltage component of the speech signal HOP, so that the other, distant subscriber receives a current I _s modulated in accordance with the speech signal.

The Wheatstone bridge consisting of the line impedances ZL and ZL ', the resistors R7 and R8, the transmission transistor T3 and the additional impedance Z3 has the effect that the signal present at the node 13 is only modulated according to the speech signals of the distant call partner. This

Speech signals are fed to the integrated circuit 8 via the coupling capacitor C4 and the input AIN. The Wheatstone bridge means that the subscriber's own speech signals, which are coupled in via HOP, are not present at node 13 and are therefore also inaudible. The purpose of the Wheatstone bridge is therefore to suppress the speech signals HOP transmitted by the user of the telephone set in the reception path for the conversation mode signals so that the user's own speech is not perceived by the user in the receiver.

In Fig. 2 the integrated circuit 8 of a telephone set is shown, in which the signals are processed completely analog. The wait mode signals are again present at the inputs DLP and DLN of the integrated circuit 8. The following components are protected from high voltage peaks by the surge protective elements Dl and D2. The waiting mode signals are converted into two signal lines by the analog multiplexer MUX together with the call mode signals present at the input AIN. For this purpose, the maximum voltages of the wait mode signals are determined by the signal peak detector 9, so that the gain control 10 can set the amplification factor of the analog amplification stage 11 for the wait mode signals. The gain factors 0 dB, 6 dB, 12 dB and 18 dB are also available for this. The talk mode signals are amplified by the analog amplification stage 11 with a constant amplification factor. The signals are then forwarded to the analog signal processing 14. All signals are separated and analyzed there by analog filter circuits.

Claims

Patent claims

1. Telephone device for connection to a telephone network, which is operated either in a waiting mode or in a conversation mode, with first telephone operating signals being received in the waiting mode, and with audio signals and second telephone operating signals being received in the conversation mode, marked by - Means for signal conversion, which carry out a signal conversion of these signals depending on the mode and / or the type of telephone operating signals received; - At least one integrated circuit (8) which processes both the signal-converted audio signals and the signal-converted telephone operating signals.

2. Telephone device according to claim 1, so that the means for signal conversion adapt the signal level of the received signals depending on the mode and / or the type of the received signal.

3. Telephone device according to one of the preceding claims, so that the at least one integrated circuit is an integrated analog circuit.

4. Telephone device according to claim 1 or claim 2, so that the at least one integrated circuit comprises an analog / digital converter unit (A / D) and a subsequently arranged digital signal processor unit (DSP).

5. Telephone device according to one of the preceding claims, characterized in that the first telephone operating signals received during the waiting mode include ringing signals, charge unit signals and caller IDs.

6. Telephone device according to one of the preceding claims, so that the second telephone operating signals received during the conversation mode include charge unit signals and caller IDs.

7. Telephone device according to one of claims 1 to 6, characterized in that the at least one integrated circuit (8) has separate inputs (DLP, DLN and AIN) for the signals received in the waiting mode and the signals received in the conversation mode.

8. Telephone device according to claim 7, so that the signals received in the waiting mode and the signals received in the conversation mode are fed to the subsequent processing stage in multiplex operation.

9. Telephone device according to one of the preceding claims, so that the means for signal conversion include a voltage-dependent resistor (VDR) which connects the connecting lines (La, Lb) to the telephone network.

10. Telephone device according to one of the preceding claims, so that the means for signal conversion comprise differential AC elements (Cl, C2), through which the signal path for the signals received in waiting mode is decoupled from the telephone network.

11. Telephone device according to claim 10, characterized in that the means for signal conversion include high-resistance voltage dividers (R2, R5 and R3, R6), which are arranged downstream of the differential AC elements (Cl, C2) in the signal path.

12. Telephone device according to one of the preceding claims, characterized in that the means for signal conversion comprise at least one controllable amplifier unit (11).

13. Telephone device according to one of the preceding claims, characterized in that the means for signal conversion comprise at least one circuit (9) for determining the maximum level values, the gain being adjusted depending on the detected level values.

1 . Telephone device according to claim 12, characterized in that the at least one controllable amplifier unit (11) is implemented as a range selection circuit for the analog/digital converter (A/D).

15. Telephone device according to one of the preceding claims, so that the means for signal conversion include at least one frequency-selective attenuator.

16. Telephone device according to claim 15, characterized in that the frequency-selective attenuator is arranged in the signal path for the signals received in conversation mode.

17. Telephone device according to claim 15 or claim 16, characterized in that the frequency-selective attenuator comprises a parallel resonant circuit (C0, L0).

18. Telephone device according to claim 17, characterized in that the resonance frequency of the parallel resonant circuit (C0, L0) is adapted to the frequency of a specific type of received telephone operating signals.

19. Telephone device according to claim 17, so that a resistor (R0) is connected in parallel to the parallel resonant circuit.

20. Telephone device according to one of the preceding claims, so that the means for signal conversion include overvoltage protection elements (Dl, D2) for protecting the inputs (DLP, DLN, AIN) of the at least one integrated circuit (8).

21. Method for processing telephone operating signals and audio signals in a telephone device, characterized by the following steps: a) receiving first telephone operating signals in the waiting mode or of second telephone operating signals and audio signals in the conversation mode; b) performing level adjustment depending on the mode and/or type of telephone operating signals received; c) joint evaluation of both the audio signals and the telephone operating signals.

22. The method according to claim 21, characterized in that the joint evaluation of both the audio signals and the telephone operating signals is carried out by at least one integrated analog circuit.

23. The method according to claim 21, characterized in that the joint evaluation of both the audio signals and the telephone operating signals is carried out by means of at least one integrated circuit, which comprises an analog/digital converter unit (A/D) and a subsequently arranged digital signal processor unit (DSP).

24. The method according to one of claims 21 to 23, characterized in that the first telephone operating signals received during the waiting mode include ringing signals, charge unit signals and caller IDs.

25. The method according to one of claims 21 to 24, characterized in that the second telephone operating signals received during the conversation mode include charge unit signals and caller IDs.

26. The method according to one of claims 21 to 25, so that the level adjustment takes place by means of a voltage-dependent resistor (VDR) which connects the connecting lines (La, Lb) to the telephone network.

27. The method according to one of claims 21 to 26, so that the level adjustment is carried out by means of differential AC elements (Cl, C2), which decouple the signal path for the signals received in waiting mode from the telephone network.

28. The method according to claim 27, so that high-resistance voltage dividers (R2, R5 and R3, R6) are used for signal level adjustment, which are arranged downstream of the differential AC elements (Cl, C2) in the signal path.

29. Method according to one of claims 21 to 28, characterized in that the level adjustment is carried out by controlling the gain.

30. The method according to claim 29, so that in order to adjust the level of the received signals, the signal peak of the received signals is first detected and the gain is then regulated depending on the detected signal peak.

31. The method according to claim 30, characterized in that the gain control is implemented by selecting the range of the analog/digital converter (A/D).

32. Method according to one of claims 21 to 31, characterized in that a frequency-selective attenuator is used for level adjustment.

33. The method according to one of claims 21 to 32, so that a parallel resonant circuit is used for level adjustment, the resonance frequency of which is adapted to the frequency of a specific type of received telephone operating signals.

34. The method according to one of claims 21 to 33, so that the signal level adjustment is carried out with the help of overvoltage protection elements (Dl, D2).

35. The method according to one of claims 21 to 34, so that the signals received in the waiting mode and the signals received in the conversation mode are processed in multiplex operation.