DE3426815A1 - Level adjustment for a telephone station with a hands-free facility - Google Patents

Abstract

The invention relates to a telephone station with a hands-free facility, the object being to create a high-performance, reliably operating, low-cost product based on a novel level adjustment. To achieve this, an automatic reception volume adjustment controlled by incoming signals and prevalent ambient noise is provided, a receiving device differentiating between voice network signals and ambient noise is provided, in the event of sudden significant changes in the ambient level the control range is set in such a way that no part of the call is lost and the range setting of the level control of a call in progress is the initial setting for a following call. The defined object can thereby be achieved. The invention relates to all telephone stations with a hands-free facility.

Description

Level regulation for a telephone station with

Hands-free.

The invention relates to a level regulator for a telephone station with speakerphone.

The object of the invention is to provide a new telephone station with hands-free calling, which is based on a new principle of level regulation is a very powerful, safe and inexpensive product.

This is achieved in that the circuit arrangement is automatic Receiving volume control contains (EV, LK, K).

Both the incoming line level and the room noise level recorded by the microphone is also used (volume increase with increased room noise).

The object is also achieved in that a receiving device (LK, LE, K) is provided, which can be transmitted via the microphone (FM or HAM) input voice network signals and input via the microphone (FM or HAM) Differentiates ambient noise.

As a result, both the control sensitivity and the detection of interfering noises in the transmission channel as well as the transmission level decreased, the effect the fact that people speak louder in noise-filled surroundings are exploited. Simultaneously the receiving volume is increased accordingly, reducing the signal-to-noise ratio is improved. Using the volume control is practically superfluous, once the subjectively comfortable volume is set.

The object is also achieved in that with self-interruption the level control through spatial sudden changes in the interference level when transmitting and Receiving the control stroke is automatically increased or decreased until the undesired Effect is eliminated.

This prevents parts of the conversation from being canceled or an undesired change of call direction takes place.

The object is also achieved in that at the beginning of a new Conversation at the telephone station, the hub settings with regard to the interference level useful signal setting and transmit / receive level from the setting by a previous conversation.

This eliminates the need for constant stroke adjustment with each new one Avoided conversation.

The function of the telephone station is explained with the aid of a figure.

The figure contains the parts listed in the list of reference symbols and functional units.

Functional description of the telephone station.

The (thick) speech signal paths for the send and receive directions have the following course: Dependent whether with the handset or hands-free speaking (pressing the handsfree key F), the hook switch switches (GU) one of the two microphones (microphone in the HAM handset, hands-free microphone FM) to the input of the microphone amplifier MV. The GU also causes a switchover its amplification to adapt to the different acoustic sensitivity both microphones. The attenuator DGGE reduces noise-filled in hands-free operation Surrounds the transmission level so far that the incoming subscriber through the background noise is not "pushed away", i.e. the control does not erroneously switch to sending. In the digital attenuator send (DDGS) the microphone signal is used when the handset is in operation not influenced, with handsfree talking dependent on the direction of speech and the control stroke more or less attenuated. This attenuator is (just like the one on the receiving side DDGE) consisting of a resistor network and digitally controllable switches (C-MOS) built up. Each attenuation from 0 to 31.5 dB can be set in steps of 0.5 dB will. The subsequent adaptive hybrid circuit (AG) separates the speech direction of outgoing and incoming voice signals. Instead of the previously common differential transformer a bridge circuit (Wheatstone bridge) is used. According to the relationship R1 ~ Z line R2 = Z simulation is used to reduce the required transmission power the simulation is designed to have a higher resistance by a factor of 10 than the line impedance. The transmission signal is generated in one of the bridge diagonals by means of a controlled current sink coupled, in the other through a differential amplifier the received signal decoupled. Via the contacts of the hook switch or the handsfree button the transmission signal on the line.

The received signal is after handset operation (handset HA) the hybrid circuit (possibly via a low-pass filter) of the earpiece. With handsfree the signal is received by the digital attenuator (DDGE) more or less attenuated, to the same extent, but in opposite directions as the transmitted signal through the identically constructed transmission-side attenuator DDGS.

The power amplifier EV amplifies the incoming speech signals on the necessary speaker level.

The selector (WO) and are in the usual arrangement on the hook switch the electronic alarm clock (EW) (piezo transducer PW) is connected. An incoming call is saved briefly (SP) and electrically isolated after switching on the telephone (PT) queried by the microprocessor (P). It depends on incoming calls started with a relatively high, for outgoing calls with a lower control stroke. In the first case, quiet signals can also be heard, while in the second case the usually quite loud dial tone not to unsightly control oscillations of the automatic Volume control can result. The power supply (S) couples the necessary operating direct current for the entire amplifier from the line without increasing the AC impedance change.

This is done by an electronic throttle circuit. For quick readiness to speak and operating voltage stabilization, the stabilization ST is necessary. She separates the relatively large charging capacitor for the push-pull B output stage during the switch-on phase of the loudspeaker (LS) from the rest of the circuit.

The direction of speech is recognized as with previous telephone amplifiers by comparing (K) the two rectified speech signals (rectifier send GSI and rectifier receiving GE). The comparator output will connected to the microprocessor. The rest position is achieved by means of the rectifier GS 2 (neither of the two interlocutors speaks) recognized and also the processor reported. The microprocessor adjusts according to the state of its inputs special program the two attenuators. These attenuators have one special, independently controllable OFF state, if necessary (e.g. DTMF dial frequency display, Click suppression in the loudspeaker) to block the respective channel completely.

The desired volume is set with the potentiometer for the volume setpoint Volume specified by the user. The processed by the rectifier-regulator (GR) Loudspeaker voltage is compared with the nominal voltage in the volume comparator (LK) and the result is fed to the microprocessor. Via the analog-to-digital converter (D / A) this carries out a comparison of the rule loop and controls accordingly the stroke of the digital attenuators.

This means that the volume remains different within certain limits Incoming calls keep the loudspeaker volume constant at the desired level.

This means that there is background noise in the room of the free-speaking participant (Air conditioning, aircraft etc.) the voice control is not blocked in the 'Send' position, the microphone level is reduced by means of the noise detection element (DGGE) below the Switching threshold lowered. This attenuator is controlled by the microprocessor, which is its information on the distinction between speech and background noise received from the gap detector LE. At the same time, the processor can reduce the damping Stability gain achieved in the transmission channel to increase the volume in the reception channel, use adapted to the background noise.

In order to minimize the mutual flow of conversations debilitating Get along control stroke, the undesired coupling of the transmission channel with the Reception channel can be kept small via the hybrid circuit. This is done by that the line simulation has the same impedance as the respective line. For this purpose, the processor controls C-MOS switches, which active and reactive resistances connect to the fork bridge circuit. The rear ear recognition RE in connection with the D / A converter provides the feedback about the respective back loss to the Processor. After the calibration process has been carried out for the slightest listening, the corresponding the control stroke is reduced and the gain on the receiving side is increased. When falling below a certain residual stroke, this optimization process is ended so that the then there is little attenuated connection of the hall impression due to the spatial The hands-free situation on the other side does not become too strong.

The indicated in the figure low-pass filter TP in the line to the telephone of the handset HA is used to remove background noises lying outside the voice band fade out.

4 claims 1 figure List of REFERENCE SYMBOLS AG Adaptive Hybrid D / A digital to analog converter DDGE digital attenuator reception DDGS digital attenuator sending EV power amplifier EW electronic ¢ ~ her alarm clock FM hands-free microphone GE rectifier receive GS 1 rectifier transmit 1 GS 2 rectifier send 2 GR rectifier regulator GU, F hook switch, handsfree button HA handset K comparator La, Lb telephone line LE gap detection LK volume comparator LS loudspeaker MV microphone amplifier PW piezo transducer RE rear ear recognition S power supply (electronic throttle) ST voltage stabilization P microprocessor WO selector TP low pass SP charge storage PT potential separation

Claims (4)

Claims 1. Level regulation for a telephone station, thereby characterized in that the circuit arrangement has an automatic reception volume control contains (EV, LK, K). 2. Level regulation for a telephone station, d u r c h g e it is not indicated that a receiving device (LK, LE, K) is provided, the user voice signals entered between the transmitter via the microphone (FM or HAM) and distinguishes ambient noise input via the microphone (FM or HAM). 3. Level regulation for a telephone station, d u r c h g e no indication that the level is controlled by self-interruption Sudden spatial change in the interference level when sending and receiving the control stroke is automatically increased or decreased until the undesired effect is eliminated is. 4. Level regulation for a telephone station, d u r c h g e it does not indicate that at the beginning of a new conversation at the telephone station the deviation settings with regard to the interference level useful signal setting and the transmit / receive level from the setting from a previous conversation.