GB2209906A - Telephone instrument - Google Patents

Abstract

A telephone instrument, having a handset incorporating a microphone 1 and a receiver 2, is adapted and arranged whereby a transmitting circuit connected to the microphone is only activated by speech from a user's mouth in very close proximity to the microphone, and a receiving circuit connected to the receiver is deactivated while the transmitting circuit is activated. A noise discrimination circuit may be provided to prevent activation of the microphone circuit by background noise. <IMAGE>

Description

TITLE: TELEPHONE INSTRUMENT This invention relates to telephone instruments of the type having a handset incorporating a microphone and a receiver. When such instruments are used in a noisy environment, eg in factories or busy offices, difficulties are encountered in that background noise is picked up by the microphone in the handset and transmitted by the receiver in the handset to the user's ear, via the sidetone circuit of the instrument. In addition, the background noise is transmitted by the microphone along the telephone line to the user of another telephone instrument. The pick up and transmission of such background noise by telephone instruments can seriously hamper conversation between users.

A further problem encountered with telephone handsets is that during a telephone conversation it is sometimes required for one party to be able to break off to consult with someone nearby in the same room, but without the party at the other end of the telephone line hearing what is being said. This is difficult, unless the instrument is provided with a manually-operated 'hold' switch arrangement to temporarily disconnect the other party, such an arrangement being inconvenient. Modern telephone instruments tend to pick up and transmit even if a hand is used to cover that end of the handset at which the microphone is located and this previously popular method of achieving a degree of secrecy can no longer be relied upon.

It is an object of the present invention to overcome or minimise the aforementioned problems.

The present invention provides a telephone instrument having a handset incorporating a microphone and a receiver, said instrument being adapted and arranged whereby a transmitting circuit connected to said microphone is only activated by speech from a user's mouth in very close proximity to the microphone, a receiving circuit connected to said receiver being deactivated while said transmitting circuit is activated.

Means are suitably provided to sense signal levels from the microphone and levels of signals received by the instrument over a line from a remote source, and, according to which of the two levels is the higher, to activate the said transmitting circuit or the said receiving circuit. Triggering means is suitably provided such that the transmitting circuit is only activated when the signal levels from the microphone exceed a predetermined threshold level which is only attained by a user of the instrument speaking very close to the microphone.

The triggering means is suitably adapted and arranged to compare signal levels from the microphone with a pre-set level and to activate the transmitting circuit when said pre-set level is reached or exceeded. The said pre-set level is preferably adjustable by a user of the instrument and suitably corresponds to a signal level expected from the microphone as a result of speech from a user's mouth in very close proximity thereto.

Noise discriminating means are preferably also provided, operating to prevent the transmitting circuit from being activated by background noise.

Means may be provided for adjustment of the volume level of signals received at the receiver, whereby a desired volume level may be obtained appropriate to background noise levels in the environment of the handset.

A first attenuator means may be provided for signals transmitted from the microphone and a second attenuator means may be provided for incoming signals received by the instrument, attenuator control means being provided such that said first attenuator means is arranged to be in a low impedance state when said second attenuator means is in a high impedance state and vice versa and whereby incoming signals received by the instrument are prevented from reaching the receiver while signals from the microphone are being transmitted, and vice versa.

The microphone may be of any well-known form, eg condenser, electret or rocking armature form. The receiver may also be of any well-known form, eg rocking armature or moving coil form.

A technique of voice activation has previously been employed in telephone instruments of the hands-free or loud speaking types. Such instruments operate without the use of a handset. Reception of incoming calls takes place by way of a loudspeaker in the instrument and change over from receiving to transmitting mode occurs automatically when a user speaks and his voice is picked up by a microphone in the instrument. The user is remote from the instrument, and hence from the microphone, and consequently background noise, including the voices of other people in the same room will be picked up by the microphone in addition to the user's voice.

In the present invention, although use is made of voice activation techniques, they are employed in a telephone instrument which operates with a handset. It is arranged that the transmitting circuit connected to the microphone in the handset will only be activated when a user speaks with his or her lips close to the part of the handset where the microphone is accommodated. The effects of background noise will therefore be minimised. Furthermore, while the transmitting circuit is activated, the receiving circuit connected to the receiver in the handset is deactivated and therefore sounds picked up by the microphone are not transmitted to the ear of the person speaking into the microphone.By simply moving the handset away from his or her mouth, the user may converse with someone else in the same room, during the course of a telephone call, without the person at the other end of the line being able to overhear the conversation.

The invention is now described by way of example with reference to the accompanying drawing which is a schematic representation of the essential elements of an embodiment of telephone instrument according to the invention.

A telephone instrument is constructed having a handset of well-known form incorporating a microphone 1, eg of condenser, electret or rocking armature form, and a receiver 2, eg of rocking armature or moving coil form. Sounds detected by the microphone 1 are amplified by an amplifier 3 and the resulting amplified signal is compared, by means of a comparator 4, with a threshold setpoint generated by a threshold amplifier 5. The threshold setpoint is adjustable, by a user, to a required level by means of a control 12 on the instrument, in order to suit the environment in which the instrument is being used. This threshold setpoint level suitably corresponds to a signal level expected from the microphone as a result of speech from a user's mouth in very close proximity thereto.The comparator 4 has an output from which a transmitted signal, resulting from sounds above a pre-set level detected by the microphone 1, is fed simultaneously to a transmitted signal attenuator 7, a noise discriminating circuit 6 and a comparator 9 for transmitted and received signals. The noise discriminating circuit 6 produces an output to an attenuator control 8 such that the latter causes the transmitted signal attenuator 7 to be high impedance to the transmitted signal, in the case of background noise being detected by the microphone 1, and low impedance to the transmitted signal in the case of speech from a user's mouth in very close proximity to the microphone 1. An attenuator 11 is provided for incoming signals received by the instrument over a telephone network 16.The attenuator control 8 has a pair of outputs which are arranged to be complementary such that the transmitted signal attenuator 7 is high impedance, and the received signal attenuator 11 is low impedance, or vice versa. This ensures that when a signal is being transmitted from the microphone in the handset, no signal will be received at the receiver in the handset. The attenuator control 8 has, as one of its inputs, an output from the comparator 9 which compares the relative levels of a transmitted signal from the output of the comparator 4 and a signal received over the network 16 and amplified by an amplifier 14. The output from the comparator 9 accordingly determines the state of operation of the attenuator control 8.

When the transmitted signal attenuator 7 is in its low impedance state, signals resulting from a person speaking close to the microphone 1 are transmitted from the instrument over the network 16. When the received signal attenuator 11 is in its low impedance state, signals received over the network 16 pass through the attenuator 11 and are amplified by an amplifier 10 to an appropriate level to suit the receiver 2 in the handset. Volume control means may be provided whereby a user may set the volume of the received signals to a desired level.

A 2-wire to 4-wire converter 13 is provided for interfacing the signals transmitted by the microphone, and also the received signals, with the signal processing circuits. Converter 13 may be of well-known hybrid form, involving a multi-winding transformer, or may comprise other known forms of integrated transmission circuits. Appropriate interfacing circuitry 15 may also be provided for connecting the telephone instrument to the network 16.

Although the attenuator control 8 may provide two-way transmission by means of a simplex path, in which the instrument may either receive or transmit, but not both simultaneously, it may also be arranged to provide transmission by means of a duplex or semi-duplex path, in which the instrument is capable of transmitting and receiving simultaneously, either in full or at reduced level.

Claims (9)

1. A telephone instrument having a handset incorporating a microphone and a receiver, said instrument being adapted and arranged whereby a transmitting circuit connected to said microphone is only activated by speech from a user's mouth in very close proximity to the microphone, a receiving circuit connected to said receiver being deactivated while said transmitting circuit is activated.

2. A telephone instrument according to Claim 1 in which means are provided to sense signal levels from the microphone and levels of signals received by the instrument over a line from a remote source, and, according to which of the two levels is the higher, to activate the said transmitting circuit or the said receiving circuit.

3. A telephone instrument according to Claim 2 in which triggering means is provided such that the transmitting circuit is only activated when the signal levels from the microphone exceed a predetermined threshold level which is only attained by a user of the instrument speaking very close to the microphone.

4. A telephone instrument according to Claim 3 in which the triggering means is adapted and arranged to compare signal levels from the microphone with a pre-set level and to activate the transmitting circuit when said pre-set level is reached or exceeded.

5. A telephone instrument according to Claim 4 in which the said pre-set level is adjustable by a user of the instrument and corresponds to a signal level expected from the microphone as a result of speech from a user's mouth in very close proximity thereto.

6. A telephone instrument according to any preceding Claim in which noise discriminating means are also provided, operating to prevent the transmitting circuit from being activated by background noise.

7. A telephone instrument according to any preceding Claim in which means are provided for adjustment of the volume level of signals received at the receiver, whereby a desired volume level is obtained appropriate to background noise levels in the environment of the handset.

8. A telephone instrument according to any preceding Claim in which a first attenuator means is provided for signals transmitted from the microphone and a second attenuator means is provided for incoming signals received by the instrument, attenuator control means being provided such that said first attenuator means is arranged to be in a low impedance state when said second attenuator means is in a high impedance state and vice versa and whereby incoming signals received by the instrument are prevented from reaching the receiver while signals from the microphone are being transmitted, and vice versa.

9. A telephone instrument constructed and arranged substantially as hereinbefore described with reference to the accompanying drawing.