INTERFACE UNIT FOR COUPLING SEVERAL MICROPHONE/LOUDSPEAKER DEVICES TO A TELEPHONE TERMINAL

Abstract: A telephone interface unit for coupling a handset (1) and an all-in-the-ear type device (2) to a telephone terminal (10) having access to a single telephone channel. The interface unit has a comparator (5) for comparing signals generated by the microphones of the handset and the all-in-the-ear device and for generating a control signal (8) identifying which is the largest. This control signal (8) provides switching input to a switch means (4) which selectively couples that one of the handset and the all-in-the-ear device generating the largest microphone signal to the telephone terminal (10).

Description: INTERFACE UNIT FOR COUPLING SEVERAL MICROPHONE/LOUDSPEAKER DEVICES TO A TELEPHONE TERMINAL. The present invention relates to telephone switching interface and in particular, though not necessarily, to telephone switching interfaces for connecting several microphone/loudspeaker devices to a telephone terminal. Conventional telephones have a terminal unit with a numeric dialling keypad. A telephone handset is held by a cradle in the terminal. By picking up the handset a user takes the telephone "off-hook" and is connected to the telephone line, whereupon he can dial the required number. It is increasingly common to have telephones with several audio devices, having both a microphone and a loudspeaker, connected to only a single terminal. Sometimes these audio devices are not of the conventional handset type and may be in the form of headsets (with one or two earphones mounted on a head support and a boom microphone) or all-in-the-ear type devices (where both the microphone and the loudspeaker are contained in a single ear piece) . A significant problem with this approach, particularly where headsets and all-in- the-ear devices are used, is that it is difficult to provide mechanically operable means to place all of the devices which are not in use on-hook and to place only that device which is in use off-hook. It is an object of the present invention to provide an interface for coupling a plurality of microphone/loudspeaker devices to a telephone terminal and which is arranged to determine which one of the devices is in use and to couple only that device to the telephone terminal. According to a first aspect of the present invention there is provided an interface unit for coupling a plurality of microphone/loudspeaker devices to a telephone terminal having a single telephone channel to enable bidirectional transmission between the devices and the telephone terminal, determining which of the device microphones is generating the largest signal and switch means, coupled to the comparator means, for coupling the device generating the largest signal to the telephone terminal. Thus the present invention provides a unit for interfacing between a telephone terminal and multiple audio input/output devices, where the unit is able automatically to route transmission between the terminal and only that audio input/output device which is in use. The problem of having several devices simultaneously connected to the terminal when not required is therefore eliminated. The audio inpu /output devices may be telephone handsets or headsets, which latter may be all-in-the-ear type devices. Where at least one of the microphone/loudspeaker devices is an all-in-the-ear type device, the unit preferably includes signal gain control and optionally signal conditioning means for adjusting the signal(s) generated by the microphones of the all-in-the-ear type device(s) prior to transmission of the signal(s) to the comparator means in order to compensate for any significant difference in sensitivity of the microphones in the various audio input/output devices. Thus with an all-in-the-ear type device signal attenuation can reduce the possibility of ambient noise causing the interface unit to switch erroneously to an all-in-the ear device which is not actually in use, a problem to which all- in-the-ear type devices are particularly suspectible, due to their normally higher sensitivity. Of course if there is used a handset with a higher sensitivity microphone then the unit can be provided with signal attenuation means for reducing the gain on the signal from that microphone and/or signal amplification means for increasing the signal from the headset microphone. In general the comparator means is arranged to compare each of the signals generated by the device microphones against.,a threshold level when the telephone terminal provides an indication that the telephone has been taken off-hook. If none of the signals exceeds the threshold level because the user is simply listening - then all the devices remain coupled. Once a user begins to speak into one of the devices so that the microphone signal from that device exceeds the threshold level, then that device i.e. generating the largest signal, is coupled to the terminal. In order to prevent the interface from switching between audio devices during a call, the telephone terminal may include means for disabling the comparator means following the initial section of a device. An embodiment of the present invention comprises a circuit which has multiple inputs, one for each earphone or handset which is to be used, where each one of said inputs goes to switch or multiplexing means and comparator means. The switch or multiplexing means has one output, where said output goes to the telephone terminal. The comparator means compares the signals present on the inputs of the multiplexing means and generates an output that controls the multiplexing means. The control output from the comparator means ensures that the microphone with the strongest input signal (after any gain control and/or conditioning adjustment) is connected via the multiplexing means to the telephone terminal, the other handsets and/or headsets being disabled. According to a second aspect of the present invention there is provided a telephone system comprising a telephone terminal for coupling to a telephone line, a plurality of microphone/loudspeaker devices, and an interface unit according to the above first aspect of the invention for coupling the microphone/loudspeaker devices to the telephone terminal. The telephone interface unit may be incorporated into the telephone terminal or may be in the form of a plug-in module which can be used with a conventional or modified telephone terminal. According to a third aspect of the present invention there is provided a method of enabling bidirectional transmission between a plurality of microphone/loudspeaker devices and a telephone terminal, the method comprising comparing the amplitudes of the signals generated by the device microphones to determine which of these signals is the largest and coupling only that device for which the microphone signal is largest to the telephone terminal. For a better understanding of the present invention and in order to show how the same may be carried into effect reference will now be made by way of example to the accompanying drawing which shows in schematic form an automatic telephone interface unit. The interface unit 3 is arranged to couple a conventional telephone handset 1 and an all-in-the-ear type device (or earpiece) 2 to a substantially conventional telephone terminal or base 10, where the telephone terminal is connected in a normal manner to a telephone line 11 such that telephone calls can be transmitted and received over the telephone line. The terminal 10 operates to convert signals received from the handset or earpiece 1,2 , via connecting input/output lines 9a, 9b from the interface 3 into a form suitable for transmission along the telephone line 11 and vice versa. The handset and the earpiece 1,2 are connected to the interface 3 by respective microphone and loudspeaker lines 14a, 14b, 15a, 15b. The interface unit 3 operates to ensure that only one of the handset 1 and earpiece 2 is connected to the lines 9a, 9b at any one time. This operation is achieved by way of a comparator 5 and a switch means or multiplexer 4. When the telephone terminal 10 is taken off-hook, e.g. by lifting the handset 1 or by pressing a button, a dialling . tone is present on the line 9a carrying signals from the terminal 10 to the interface 3. This dialling tone is supplied to a detector 12 which in turn provides an enable signal via a line 13 to the comparator 5. The signal received from the microphone of the earpiece 2 via line 15b is attenuated by an attenuator 6, which may be a potential divider resistor arrangement. This attenuation compensates the earpiece signal for ambient noise which may increase the signal relative to the signal produced by the handset microphone (earpiece devices are more susceptible to ambient noise than handset devices because they are necessarily less directional) . The attenuated earpiece microphone signal, together with the signal from the handset microphone received via line 14b, are then input to the comparator 5 which enabled by the detector 12. The comparator 5 continuously compares the two received signals to determine which has the largest amplitude. The comparator 5 has a control output 8 which may be a single line or a set of lines and which is set according to which one of the audio input/output devices is generating the largest input signal. The control output 8 of the comparator 5 provides a selection input for the switch means 4. The switch means receives both the microphone and loudspeaker lines from the handset 1 and the earpiece 2 and also receives the input and output terminal lines 9a, 9b from the telephone terminal 10. If the signal generated by the handset microphone is greater than that generated by the earpiece microphone, the selection input is such that the switch means 4 couples the handset lines 14a, 14b to the terminal lines 9a, 9b. Similarly, if the signal generated by the earpiece is the greatest, the earpiece lines 15a, 15b are connected to the terminal lines 9a, 9b. When the line selection has been made, the detector 12 „ _,,„ PCT/GB95/00809 - 6 - disables the comparator 5 in order that the selection made is maintained for duration of the call, i.e. until the telephone terminal 10 is places on-hook. Whilst the above embodiment describes the use of only two audio devices it will be clear that more than two or several devices can be used with a signal interface unit in accordance with the present invention. The embodiment described above may be implemented either using digital components or analogue components or a combination of both. In particular, the switch means 4 may be a relay or a set of relays and the comparator 5 may be a digital comparator. It will be appreciated by the skilled person that further modifications may be made to the above described embodiment without departing from the scope of the present invention. In those cases where it is desirable to allow more than one audio input/output device simultaneously e.g. to allow two people to listen to a caller at the same time, then additional user - operable switch means could be provided to couple a second device to the terminal in addition to the automatically coupled one.

Claims: CLAIMS 1. An interface unit for coupling a plurality of microphone/loudspeaker devices (1,2) to a telephone terminal (10) having a single telephone channel to enable bidirectional transmission between the devices and the telephone terminal, the interface unit (3) comprising comparator means (5) for determining which of the device microphones is generating the largest signal and switch means (4) , coupled to the comparator means (5) , for selectively coupling the device (1,2) generating the largest signal to the telephone terminal (10) . 2. An interface unit according to claim 1, wherein the microphone/loudspeaker devices (1,2) are selected from telephone handset, headset, and all-in-the-ear type devices. 3. An interface unit according to claim 2, wherein when at least one of the microphone/loudspeaker devices (1,2) is an all-in-the-ear type device, the interface unit includes signal gain control means (6) for adjusting the signal(s) generated by the microphone(s) of the all-in-the-ear type device(s) prior to transmission of the signal(s) therefrom to the comparator means (5) . 4. An interface unit according to any one of the preceding claims, wherein the comparator means (5) is formed and arranged to compare each of the signals generated by the device microphones against a threshold level, and all the devices (1,2) are kept coupled to the terminal (10) unit until one of the signals from one of the devices (1,2) exceeds the threshold level,whereupon the other devices (1,2) are selectively uncoupled. 5. A telephone system comprising a telephone terminal (10) for coupling to a telephone line, a plurality of microphone/loudspeaker devices (1,2), and an interface unit (3) according to any one of the preceding claims for selectively coupling the microphone/loudspeaker devices (1,2) to the telephone terminal (10). 6. A method of enabling bidirectional transmission between a plurality of microphone/loudspeaker devices (1,2) and a telephone terminal (10) , the method comprising comparing the amplitudes of the signals generated by the device microphones to determine which of these signals is the largest and coupling only that device (1,2) for which the microphone signal is largest to the telephone terminal (10) .

Inventors: DEAS ALEXANDER ROGER, DEAS, ALEXANDER, ROGER
Applicants: DEAS ALEXANDER ROGER, JABRA CORP, DEAS, ALEXANDER, ROGER, JABRA CORPORATION
Application year: 1995
Main classification: H04M1
IPC codes: H04M1