 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a handsfree communication
apparatus intended to be connected to a wireless telephone set, and more
particularly to a handsfree communication apparatus utilizing a plurality
of microphones to enable a plurality of persons to simultaneously
communicate with one another.
2. Description of the Related Art
A handsfree communication apparatus for a wireless telephone set
conveniently allows communication without requiring the use of both of a
user's hands, and mainly comprises a handsfree adapter, a microphone, and
a loudspeaker. In the case of loading into a vehicle, the handsfree
adapter is connected to the wireless telephone set lying within the
vehicle, while the microphone and the loudspeaker associated with the
handsfree adapter are firmly secured to predetermined points within the
vehicle. This configuration will ensure that a person (such as a driver)
within the vehicle is capable of transmitting speech by means of the
microphone of the handsfree communication apparatus instead of a
microphone of the wireless telephone set and receiving speech of the other
party by use of the speaker of the handsfree communication apparatus in
place of a loudspeaker of the wireless telephone set. In other words, this
will enable the user to communicate with the other party without actually
picking up the wireless telephone set.
Referring to FIG. 7, there is depicted, by way of example, a conventional
handsfree communication apparatus. The handsfree communication apparatus
generally designated at 100 is connected to a wireless telephone set 11.
The apparatus 100 comprises a handsfree adapter 10, a microphone 12, and a
loudspeaker 18. The handsfree adapter 10 includes an amplifier section 14
and a control section 16.
FIG. 8 depicts part of a circuit of the amplifier section 14 in which an
indispensable or central constituent element is an operational amplifier
18. A signal (an voice signal) fed to an input terminal 20 is supplied via
a resistor 22 to an inverting input terminal (-) of the operational
amplifier 18. A constant-voltage power supply 24 is coupled to a
non-inverting input terminal (+) of the operational amplifier 18. The thus
amplified signal is provided through an output terminal 26. Reference
numeral 28 denotes a feedback resistor.
In the configuration of FIG. 7, in the reception mode, a signal received by
the wireless telephone set 11 is output through a receiving terminal 11a,
subjected to a level regulation (a volume regulation) in the control
section 16, and amplified in the amplifier section 14, and then sent to
the loudspeaker 18 for speech conversion. In the transmission mode, an
voice signal from the microphone 12 is amplified in the amplifier section
14, subjected to processing such as level regulation in the control
section 16, and then fed to a transmitting terminal 11b. Then, a radio
transmission is executed by the wireless telephone set 11.
However, the above-described conventional handsfree communication apparatus
merely possesses a single microphone and a single loudspeaker, so that
when two or more persons wished to take part in a simultaneous
communication in the same vehicle, the plurality of persons had to speak
into the single microphone 12. In addition, if the persons were sitting
apart from each other, for example, in the front and back seats, the
simultaneous communication was difficult to carry out.
On the contrary, the microphone receives not only speech but also noise
(such as ambient noise, aliasing noise, and vehicular noise) having
substantially the same level as that of the speech, whereupon the noise
will be mixed into the voice signal, making the speech almost inaudible to
the other party.
Japanese Patent Laid-open Pub. No. 114245/1989 discloses a handsfree
communication apparatus equipped with a plurality of microphones, but is
silent on noise cancellation. Japanese Utility Model Laid-open Pub. No.
21997/1990 discloses a handsfree communication apparatus intended to be
mounted on a vehicle, in which a couple of microphones are accommodated in
the same case, preventing persons sitting separately, for example, in the
front and back seats, from taking part in simultaneous handsfree
communication.
SUMMARY OF THE INVENTION
The present invention was conceived to overcome the above problems involved
in the prior art. It is therefore an object of the present invention to
allow simultaneous communication by a plurality of persons positioned
apart from one another.
Another object of the present invention is to reduce the noise other than
speech.
A further object of the present invention is to provide a handsfree adapter
capable of reducing the vehicular noise other than speech so as to ensure
a pleasant communication by a plurality of persons within a vehicle.
In order to accomplish the above objects, a handsfree communication
apparatus of the present invention comprises a plurality of microphones
individually provided apart from one another; a plurality of amplifiers
for each amplifying output signals from the plurality of microphones; and
a speech extraction circuit for receiving output signals from the
plurality of amplifiers to cancel out common signal components and extract
different signal components among the output signals.
According to the above configuration, the microphones are individually
arranged apart from one another so as to allow simultaneous communication
by a plurality of persons. Output signals from the microphones are
amplified in the amplifiers and then subjected to a differential operation
between the respective signals in the speech extracting circuit. In this
instance, between the output signals from the respective microphones,
speech components of respective persons are not coincident with one
another due to their difference in speech level, whereas noise components
are coincident with one another as long as the noise sources are
identical. Consequently, it is possible, through the differential
amplification to extract only the speech signals and to cancel out the
noise. In other words, the differential ential amplification can be
utilized to perform speech extraction and noise cancellation. The ambient
noise generated from the entire body of a vehicle, in particular, will
simultaneously enter the plurality of microphones, whereupon the noise
components can be effectively canceled out or reduced by the differential
amplification.
In the preferred embodiments of the present invention, the amplifiers are
comprised of operational amplifiers each executing a signal amplification.
On the other hand, the differential amplifier is comprised of an
operational amplifier for executing differential amplification between
output signals from the respective amplifier circuits.
It will be appreciated that the differential amplifier circuit consists of
one or a plurality of operational amplifiers depending on the number "n"
of microphones. More specifically, the number of differential type
operational amplifiers is equal to n-1. In the case of using, for example,
two microphones, respective output signals are fed to two input terminals
of a single differential type operational amplifier. For the use of three
or more microphones, a plurality of operational amplifiers may be
connected with one another in a staged manner (in a tournament
arrangement) to constitute a differential amplifier circuit.
Also, a switch section may be provided to individually change over the
actions of the respective microphones, thereby reducing unwanted sounds to
heighten the articulation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing a configuration of a first embodiment of the
present invention.
FIG. 2 is a circuit diagram an amplifier section (or noise canceller
serving as a speech extracting section) of the first embodiment.
FIG. 3 is a diagram showing a configuration of a second embodiment of the
present invention.
FIG. 4 is a circuit diagram of another amplifier section (or noise
canceller serving as a speech extracting section).
FIG. 5 is a diagram showing a configuration of a third embodiment of the
present invention.
FIG. 6 illustrates a principal part of a switch section.
FIG. 7 depicts a conventional handsfree communication apparatus.
FIG. 8 is a partial circuit diagram of a conventional amplifier section.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is depicted an overall configuration of a
handsfree communication apparatus in accordance with a first embodiment of
the present invention. In this embodiment, the apparatus is designed to be
loaded into a vehicle to allow simultaneous communication by a plurality
of persons.
In FIG. 1, the handsfree communication apparatus generally designated at
200 comprises a handsfree adapter 30, two microphones 12a and 12b, and one
or a plurality of loudspeakers (not shown). In this embodiment, the two
microphones 12a and 12b independently provided apart from each other are
connected via cables to the handsfree adapter 30. The handsfree adapter 30
includes an amplifier section (a noise canceller or a speech extracting
section) 32, and a control section 16 for regulating the volume (speech
level).
It is to be appreciated that a receive signal from a wireless telephone set
11, in the same manner as the prior art, is subjected to level regulation
in the control section 16, and amplified in the amplifier section 32, and
then reproduced as speech through the loudspeaker(s) not shown.
A concrete configuration of the amplifier section 32 is shown in FIG. 2.
The amplifier section 32 includes an amplifier circuit 34 consisting of
two operational amplifiers 38 and 40, and a differential amplifier circuit
36 consisting of an operational amplifier 42. Output signals of the
microphones 12a and 12b are respectively delivered via input terminals 32a
and 32b to inverting input terminals (-) of the operational amplifiers 38
and 40 and are amplified therein in the conventional manner.
In this embodiment, output signals of the operational amplifiers 38 and 40
are provided to two input terminals (an inverting input terminal (-), and
a non-inverting input terminal (+)) of the operational amplifier 42, and
are subjected to differential amplification. This differential
amplification serves to cancel out signal components of the same level.
More specifically, the differential amplification will ensure that aural
components, of signals from the respective microphones are combined since
they are not fundamentally coincident in level with each other, to emerge
at an output terminal 32c for transmission to the wireless telephone set
11. On the contrary, components of the vehicular noise and the like are
mutually canceled out and reduced due to their coincidence in phase. As a
result, the voice signal will be heard clearly by the other party. It is
to be noted that the amplification factor of the amplifier circuit 34 can
be regulated depending on the magnitudes of resistors 38a, 38b, and
resistors 40a and 40b.
In the first embodiment, as described above, two microphones are arranged
separate from each other so as to allow simultaneous communication by a
plurality of persons in the same vehicles and to utilize the separate
arrangement for canceling the noise components while maintaining the
speech components by virtue of the differential amplification. For
example, one of the two microphones may be disposed on the driver's seat,
and the other on the passenger seat. Preferably, one is disposed on the
front seat and the other on the back seat.
A second embodiment of the present invention will now be described with
reference to FIG. 3.
Depicted in FIG. 3 is a handsfree communication apparatus generally
designated at 300. Although two microphones are connected to the handsfree
adapter in the first embodiment, three microphones 12a, 12b, and 12c are
connected to an amplifier section 46 within a handsfree adapter 44 in the
second embodiment. Similarly to the amplifier section 32 of the first
embodiment, the amplifier section 46 includes a plurality of operational
amplifiers for amplifying signals from the microphones, and a plurality of
operational amplifiers for executing differential amplification between
output signals from the plurality of amplifiers. The amplifier section 46
performs speech extraction as well as noise cancellation. A control
section 16 has substantially the same function as that of the control
section 16 of FIG. 1.
Referring next to FIG. 4, there is illustrated a circuit configuration of
an amplifier section 48 to which four microphones are connected. The
amplifier section 48 includes an amplifier circuit 50 consisting of
operational amplifiers 54, 56, 58, and 60 equal in number to microphones
connectable thereto, and a differential amplifier circuit 52 for executing
differential amplification between output signals from the amplifier
circuit 50.
Input terminals 48a, 48b, 48c and 48d receive output signals from
corresponding microphones. The signals from the input terminals 48a, 48b,
48c and 48d are amplified, in the same manner as above, by the operational
amplifiers 54, 56, 58 and 60 and are sent to the differential amplifier
circuit 52. The differential amplifier circuit 52 consists of three
operational amplifiers 62, 64 and 66. The operational amplifiers 62 and 64
of the first stage each execute differential amplification for signals
from the respective two microphones associated therewith. The operational
amplifier 66 of the second stage executes differential amplification for
output signals from the two operational amplifiers 62 and 64.
According to such a circuit configuration, the combination of four
different signals will contribute to a cancellation and reduction of noise
which has been simultaneously input through the plurality of microphones,
allowing the speech components to be extracted from an output terminal
48e.
It will be appreciated that the amplification degrees for respective
signals can be controlled by regulating the values of resistors 54a and
54b, resistors 56a and 56b, resistors 58aand 58b, and resistors 60a and
60b.
As described hereinabove, the number of operational amplifiers has only to
be increased to cope with three or more microphones. As shown in FIG. 4,
the differential amplifier circuit can be comprised of a plurality of
differential amplification type operational amplifiers connected in the
tournament arrangement. In this case, the number of differential
amplification type operational amplifiers is equal to (the number of
microphones -1). It is to be noted that both the amplifier circuit 50 and
the differential amplifier circuit 52 can be constituted of the same type
of operational amplifiers and that the use of the same type of operational
amplifiers would contribute to a reduction in the production cost.
Description will now be given of a third embodiment of the present
invention.
Referring to FIG. 5, there is illustrated a configuration of the third
embodiment, in which a handsfree communication apparatus generally
designated at 400 includes a handsfree adapter 67 having a switch section
68 interposed between handsfree adapter 67 having a switch section 68
interposed between microphones 12a and 12b and an amplifier section 32.
The switch section 68 acts to switch individually the microphones on or
off, and is automatically or manually operated. A control section 16 and
the amplifier section 32 have the same configurations as those of the
control section 16 and the amplifier section 32, respectively, of FIG. 1.
A configuration of a principal part of the switch section 68 is shown in
FIG. 6. A switch 70 is provided for each of the microphones. By
controllably changing over the switch 70, the user is capable of
individually switching the actions of the respective microphones. In FIG.
6, a signal from the microphone is fed to an input terminal 70a, and if
the switch 70 is at the ON position, it emerges intact at an output
terminal 70b.
Thus, according to the third embodiment, the action of the microphone not
required to pickup sound can be switched off to reduce unwanted sounds and
therefore to improve the articulation of target speech.
In this manner, according to the embodiments described hereinabove, there
is implemented a handsfree communication apparatus allowing simultaneous
communication by a plurality of persons positioned apart from one another
and enabling noise cancellation. Also, the differential amplifier may be
of a simple configuration. Further, the action of the microphone not
required to pick-up sound can be switched off.
If the handsfree communication apparatus of the embodiments is installed in
a vehicle, in particular, the microphones for the exclusive use of
respective persons can be utilized to realize simultaneous communication
while reducing the vehicular noise except speech. Within the vehicle, a
first microphone may be disposed in front of the driver, and a second
microphone may be disposed in front of the passenger seat. Further, the
back seat may be provided with a plurality of microphones confronting
passengers. The microphones may be of good directivity to improve the
articulation of speech.
* * * * *
|
|
 |
|
 |
Description |
|
