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BACKGROUND OF THE INVENTION
The present invention relates to an audio current pick-up device and,
particularly, to such a device for picking-up audio information from an
electric current flowing through an electric wire.
In order to pick-up audio information from a minute electric current
flowing through an electric wire such as a telephone cord, it is usual to
use a receiver including an amplifier having a high amplification factor.
Since, in such a scheme, there is a tendency to generate howling in the
receiver, it is difficult to increase the sound output to a level high
enough to be heard. This is particularly true when the receiver is a
hearing-aid.
As to a conventional receiver for picking-up an audio information from a
minute electric current flowing an electric wire, FIG. 7 shows a
hearing-aid 2 in intimate contact with a telephone receiver 1. The
hearing-aid 2 includes an induction coil therein which picks up magnetic
flux leakage from the receiver 1 and provides an electric signal
corresponding to a variation thereof. The signal is amplified by an
amplifier of the hearing-aid 2 having an amplification function and a
frequency characteristics correction function to a level suitable for the
user so that he can hear it through an earphone (not shown) connected to a
cord 3.
A further conventional scheme is shown in FIG. 8 in which a telephone coil
4 is mounted on a receiver 1. Magnetic flux leakage from the receiver is
picked up by the coil 4 an electric output signal of which is supplied
through a wire 5 to a user's hearing-aid 2.
In the scheme shown in FIG. 7 or 8, it is impossible to pick up a sound
current of practically sufficient S/N ratio when the magnetic flux leakage
from the telephone receiver 1 is small.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a receiver for use with an
electric wire carrying information in the form of electric current, which
is capable of providing an audio output at a level with a practically
acceptable S/N ratio, which is high enough to make it possible to obtain
the information clearly even if the magnetic flux leakage from the wire is
very small.
The above object can be achieved, according to the present invention, by
providing a receiver which comprises a pair of substantially identical
magnetic induction coil means disposed in parallel to each other with a
certain axial deviation and orthogonal to an electric wire such as a
telephone cord carrying sound current. Each coil means includes a magnetic
core in the form of a rod and at least one coil wound thereon.
According to a first aspect of the present invention, the coils wound on
the parallel magnetic induction coil means are deviated axially by a
predetermined distance L/2, where L is about a half length of the rod
core. A sound output signal is derived as a combination of output signals
of these coils.
According to a second aspect of the present invention, each magnetic
induction coil means includes a pair of induction coils wound in opposite
directions on respective halves of its core rod. The induction coils are
connected in parallel to each other.
According to a third aspect of the present invention, an output of the
induction coil of one of the magnetic induction coil means is
phase-shifted by a preset amount and composited with an output of the
other magnetic induction coil means to form a sound pick-up signal from
which a sound output signal is derived.
With the arrangement of the magnetic induction coil means with the axial
positional deviation, a magnetic flux leakage from the telephone cord
disposed in between these induction coil means and orthogonally thereto
can be picked up by the induction coils thereon efficiently. Further, with
the oppositely wound, parallel connected induction coils on each induction
coil means, it is possible to reduce the effect of external noise on the
output sound signal.
Further, the composition of an output signal of the induction coil of one
of the magnetic induction coil means and that of the other induction coil
means shifted in phase by the predetermined amount assures that it is
possible to obtain a sufficient sound output signal regardless of a
twisting angle of the telephone cord with respect to the induction coil
means.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block circuit diagram of an embodiment of the present
invention;
FIG. 2 is a partial cross section of an induction coil portion of the
embodiment in FIG. 1;
FIG. 3 is a basic circuit diagram of the magnetic induction coil means
shown in FIG. 2;
FIG. 4 shows plots of measured composite output level of the magnetic
induction coil means with respect to a relative position of the telephone
cord to the induction coil means;
FIG. 6 shows plots of measured output level of the induction coil means
with respect to a twisting angle of the telephone cord positioned at a
certain position in between the induction coil means;
FIG. 6 illustrates another embodiment of the induction coil portion of the
present invention;
FIG. 7 is a perspective view of a conventional hearing-aid means; and
FIG. 8 is a perspective view of another conventional hearing-aid means.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 which is a block circuit diagram of an embodiment of the present
invention, a receiver 11 is composed of a signal processing circuit
portion 12, a microphone 13, an ear-phone 20 and an induction coil portion
25. The signal processing portion 12 includes a hearing-aid circuit 12A
and a sound signal detection circuit 12B. The microphone and the
hearing-aid circuit 12A may have conventional constructions, respectively,
except that the hearing-aid circuit 12A further includes a switch circuit
15. In this embodiment, the hearing-aid circuit 12A includes an amplifier
14 for amplifying a sound signal S1 from the microphone 13, the switch
circuit 15, a tone control circuit 16, a volume control circuit 17,
another amplifier 18 and an output limiter circuit 19 whose output S2 is
connected to the conventional earphone 20. This circuit construction and
its operation are well known and therefore details thereof are omitted in
this specification.
The sound signal detection circuit 12B is composed of a first signal
processing portion 12B1 and a second signal processing portion 12B2. The
first signal processing portion 12B1 includes a frequency characteristics
compensator 61 having an input connected through two of four lines of an
electric conductor 51 to an output of the induction coil portion 25, an
amplifier 62 for amplifying an output of the frequency characteristics
compensator 61, a phase shifter 63 for shifting the phase of an output of
the amplifier 62, and an amplifier 64 connected to an output of the phase
shifter 63. The second signal processing portion 12B2 includes a frequency
characteristics compensator 65 having an input connected to the induction
coil portion 25 through the remaining two lines of the conductor 51 and an
amplifier 66 for amplifying an output of the compensator 65. Outputs of
the amplifiers 64 and 66 are connected together to another input of the
switch circuit 15 of the hearing-aid portion 12A.
FIG. 2 is a partial cross section of an embodiment of the induction coil
portion 25 shown in FIG. 1. In FIG. 2, the magnetic induction coil portion
25 comprises a first magnetic induction coil portion 26 and a second
induction coil portion 27 each of which includes a magnetic core in the
form of rod and a pair of induction coils wound, in opposite directions,
on respective halves thereof. The magnetic induction coil portions 26 and
27 are supported substantially in parallel to each other and symmetrically
of a center line Lc with an axial deviation of a predetermined amount by a
housing 28.
FIG. 3 is a circuit diagram of the induction coil portion 25 shown in FIG.
2. In FIG. 3, the magnetic induction coil portion 26 includes the magnetic
core 30 on halves of which the coils 32A and 32B are wound in opposite
directions. The coils 32A and 32B are connected in parallel to each other
and connected to internal connection terminals 36 and 37 through lead
wires 33 and 34, respectively.
The magnetic induction coil potion 27 has the same construction as that of
the magnetic coil portion 26 and includes the magnetic core 38 and coils
39A and 39B wound thereon which are connected in parallel to each other
and to internal connection terminals 42 and 43 through lead wires 40 and
41, respectively.
The housing 28 takes in the form of a general U-shape with leg portions in
which the magnetic induction coil portions 26 and 27 are housed,
respectively, being different in length due to the axial deviation
thereof. A valley 44 of the U-shaped housing 28 is bottomed with a stop
wall 45 adapted to receive a telephone cord 6 so that the telephone cord 6
can be received thereby perpendicularly to the magnetic coils on the
magnetic induction coil portions 26 and 27.
The axial mutual deviation of the magnetic induction coil portions 26 and
27 is set to a value L/2 where L is an axial length of one of the coils on
each magnetic core, which may close to a half length of the magnetic core
rod.
The internal connection terminals 36, 37, 42 and 43 are supported by a
connector 35. An output signal S21 on the internal connection terminals 36
and 37 connected to the magnetic induction coil portion 26 is supplied to
external terminals 53 and 54 which are connected to the first processing
circuit portion 12B1 of the sound signal detection circuit 12B through the
conductor 51.
An output signal S22 from the magnetic induction coil portion 27 and
appearing on the internal connection terminals 42 and 43 of the connector
35 is sent through the external connection terminals 55 and 56 of the
connector 35 and the conductor 51 to the second processing circuit portion
12B2 of the sound signal detection circuit portion 12B.
Returning to FIG. 1, the output signal S21 of the magnetic induction coil
portion 26 supplied to the frequency characteristics correction circuit 61
is corrected in frequency and, after being amplified by the amplifier 62,
is shifted in phase by the phase shifter 63.
The frequency characteristics correction circuit 61 functions to change the
frequency characteristics of the sound output, signal S21 from the
magnetic induction coil portion 26 correspondingly to a magnetic flux
leakage from the telephone cord 6, which, otherwise, tends to result in
uncomfortable metallic sound.
The phase shifter 63 functions to shift the phase of the signal S21 by a
predetermined amount, for example, advance it by 90.degree., and a
resultant phase-shifted output signal S21X is amplified by the amplifier
64.
The output signal S22 from the induction coil portion 27 is supplied to the
frequency characteristics correction circuit 65 of the second processing
circuit portion 12B2 and, after correction of frequency characteristics
thereof, is amplified by the amplifier 66.
The phase-shifted output signal S21X from the first processing circuit
portion 12B1 and the output signal from the second processing circuit
portion 12B2 are combined at a point 67 and supplied to the switch circuit
15 as a sound pick-up signal S3.
In this embodiment, the switch circuit 15 is switchable between three
states. In a first switch state, the switch circuit 15 selects the signal
S1 and sends it to the tone control circuit 16 as a switch output signal
S4. In a second switch state, it combines the signal S1 and the pick-up
signal S3 and sends a resultant signal as the switch output signal S4. In
a third switch state, it selects the pick-up signal S3 and sends the
latter as the switch output signal S4.
Since the magnetic induction coil portions 26 and 27 are axially deviated
by L/2, it is possible to form the sound pick-up signal S3 stably with a
practically sufficiently high level from the output signals S21 and S22 of
the portions 26 and 27 regardless of the position of the telephone cord 6
received in the valley 44 and regardless of the twist angle of the core
lines 6A and 6B of the cord 6, which is represented by an angle of a
line Lh connecting the centers of the core lines 6A and 6B with respect to
a line Ln normal to the center line Lc.
That is, as shown in FIG. 4 which shows plots of the output level of the
induction coil portions with respect to the position of the telephone cord
in between the induction coils, it has been found that a signal level of
the output signal S21 decreases through null at an intermediate position
P0 between the coils 32A and 32B when the telephone cord 6 is moved in
parallel to the magnetic induction coil portion 26 toward a position -P1
along the center line Lc while keeping the line LH coincident on the line
Ln, i.e., .theta.=0, the null output being due to the fact that magnetic
flux leakage from the telephone cord 6 couples to the coils 32A and 32B
substantially equally, which are wound in opposite directions.
It has been also found that, when the telephone cord 6 moves in an opposite
direction from the position P0 which may be a center position of the coils
32A, 32B toward a position P1 by a distance corresponding to L/2, the
coupling of flux leakage to the induction coil portion 26 increases and
thus the output signal level of the signal S21 increases correspondingly.
At the position P1, the signal level of the signal S21 became maximum.
When the telephone cord 6 was further moved toward a top position P2 of the
coil 32A, the magnetic coupling of the coil 32A decreased gradually and
therefore the level of the output signal S21 also decreased. At the
position P2, the output signal level became null.
When the telephone cord 6 was moved from the intermediate position P0
through an intermediate position -P1 to a top position -P2 of the coil 32B
the direction of which is opposite to that of the coil 32A, the level of
the output signal S21 decreased from null to the negative peak and then
increased to null as shown by the solid line in FIG. 4.
The level of the output signal S22 of the coils 39A and 39B of the
induction coil portion 27 with a movement of the telephone cord 6 from an
intermediate position P10 through the center position P11 to the position
P12 of the coil 39A increased through a positive peak and then returned to
null. With an opposite movement through the position -P11 to the -P12 in
the direction of the coil portion 39B, the level changed through the
negative peak to null.
Since the induction coil portions 26 and 27 are deviated in position by
L/2, points at which the signal S21 becomes 0 level, a point at which it
becomes positive peak and a point at which it becomes negative peak, i.e.,
P2, P1, P0, -P1 and -P2, are deviated by L/2 from corresponding points for
the ouput signal S22, i.e., P12, P11, P10, -P11 and -P12, respectively.
It has been found that the plots in FIG. 4 show the output level variations
of the signals S21 and S22 which may be approximated by sinusoidal
waveforms, respectively, with a phase difference of about 90.degree..
In this embodiment, the depth of valley 44 is determined such that the
telephone cord 6 can move within a range ARA (FIG. 4) corresponding to a
distance and position between positions P0 and P1 of the induction coil
portion 26 which correspond to positions P11 and P12 of the induction coil
portion 27, respectively.
FIG. 5 shows a relation between the output signals S21 and S22 and the
twist angle .theta. of the line Lh connecting the centers of the conductor
cores 6A and 6B of the telephone cord 6 with respect to the line Ln which
is orthogonal to the center line Lc, within the range ARA. It has been
found that the output levels of the signals S21 and S22 from the induction
coil portions 26 and 27 change substantially sinusoidally with a change of
the twisting angle .theta. from 0.degree. to 360.degree.. That is, when
the twisting angle .theta. is changed from 0.degree. to 360.degree. while
the telephone cord 6 is positioned at the position P0 in FIG. 4, the
output signal S21 from the induction coil portion 26 may be approximated
by the following equation:
S21=M sin.alpha. sin .theta. (1)
where sin .alpha. represents a signal component of a sound current. As is
clear from the above equation, an amplitude component M sin .theta. of the
output signal changes sinusoidally from 0 level at the position P0 in FIG.
4 with .theta.=0.degree..
Similarly, the signal S22 from the induction coil portion 27 may be
approximated by the following equation:
S22=M sin .alpha. cos.theta. (2)
Thus, it is clear that an amplitude component M cos .theta. of the signal
S22 changes sinusoidally from maximum at the position P11 in FIG. 4 with
.theta.=0.degree., with a phase difference of 90.degree. with respect to
the signal S21.
The output signal S22 represented by the equation (2) is phase-shifted by
the phase shifter 63 of the first processing circuit portion 12B1 by
90.degree. as mentioned previously. Therefore, a resultant signal S21X can
be represented by the following equation:
S21X=M cos .alpha. cos .theta. (3)
Thus, the sound current component is converted from sin .alpha. into cos
.alpha.. As a result, the sound pick-up signal S3 obtained at the point 67
in FIG. 1 can be represented as a sum of the output signal S21 represented
by the equation (1) and the phase-shifted output signal S21X represented
by the equation (3), which can be represented by the following equation:
##EQU1##
Thus, it is possible to convert the signal S3 into a sinusoidal signal cos
(.alpha.-.theta.) having an amplitude M which is constant regardless of
the twist angle of the telephone cord 6.
In operation, the magnetic induction coil means 25 is adapted to be coupled
to a telephone receiver set after a hook switch thereof is turned on, in
such a way that the telephone cord 6 thereof is received in the valley 44
of the magnetic induction coil means 25. The output signals S21 and S22
produced by the magnetic coupling of the induction coil portions 26 and 27
to sound current flowing through the core conductors 6A and 6B of the
telephone cord 6 through magnetic flux leakage therefrom are supplied to
the frequency characteristics correction circuits 61 and 65 of the first
and the second processing circuit portions 12B1 and 12B2 of the sound
signal detection circuit 12B and amplified by the amplifiers 62 and 66
thereof, respectively.
Since the signal levels of these signals S21 and S22 are determined
according to the position of the telephone cord 6 in the valley 44 as
mentioned previously with reference to FIG. 4, it is not always possible
to obtain the maximum signal levels. However, by regulating the twist
angle .theta. of the telephone cord 6 within the valley 44 according to
the relation mentioned with reference to FIG. 5, it is possible to obtain
the maximum signal levels. The regulation of the twist angle may be
performed by changing an applying direction of the magnetic induction coil
means 25 onto the telephone cord 6.
The output of the amplifier 62 of the first processing circuit portion 12B1
is phase-shifted by 90.degree. by the phase shifter 63 to provide the
signal S21X which, after being amplified by the amplifier 64, is added to
the output of the amplifier 66 at the point 67 to provide the composite
pickup signal S3 whose signal level is automatically kept substantially
constant practically regardless of change in the twist angle .theta. of
the telephone cord 6 with respect to the magnetic induction coil means 25.
The construction of the oppositely wound induction coils of each of the
magnetic induction coil portions 26 and 27 is effective in blocking
external noise in the form of magnetic flux. That is, magnetic flux such
as shown by .PHI..sub.n1 and .PHI..sub.n2 in FIG. 3 may constitute
external noise. In the present invention, however, these fluxes pass
through the opposite coils 32A and 32B and the opposite coils 39A and 39B,
respectively. Therefore, voltages induced in each coil pair are opposite
in polarlity and cancel out each other. Thus, they have no effect on the
output signals therefrom.
On the other hand, magnetic flux .PHI..sub.s1 and .PHI..sub.s2 produced by
currents flowing through the core conductors 6A and 6B of the telephone
cord 6 couple to only portions of the induction coil portions 26 and 27,
in FIG. 3, portions of the coils 32A and 39A, respectively. Therefore,
they are not cancelled out each other and can be derived as the output
signals S21 and S22.
Although the present invention has been described mainly as being applied
to the hearing-aid, the present invention is not limited thereto. It
should be noted that the present invention can be applied to any audio
receiver.
Further, it is possible to apply this invention to other electric wires
than the telephone cord so long as they carry sound current.
It should be noted further that the amount of phase shift to be introduced
in the output signal S21 by the phase-shifter 63 of the first processing
circuit portion 12B1 in FIG. 1 is not limited to 90.degree. and may be
changed within a range, for example, 90.degree..+-.45.degree., so long as
the amplitude of the signal S3 can be maintained practically constant.
Further, the amount of relative axial deviation of the magnetic induction
coil portions is not limited to L/2. In FIG. 4, for example, it may be
changed to values corresponding to .+-.45.degree. in phase difference
between the signals S21 and S22.
It may be possible to support the magnetic induction coil portions 26 and
27 rotatably about a position around the stop wall 45 of the valley 44,
respectively. When it is desired to put the electric wire 6 in the valley
44, the portions 26 and 27 are rotated outwardly to open the valley 44
and, after the wire 6 is put therein, the portions 26 and 27 are rotated
inwardly to pinch the wire therebeteween.
It should be noted that, although the induction coil portions 26 and 27 are
identical and arranged with a relative positional deviation, they may be
not always identical so long as the regions thereof on which the induction
coils are wound are relatively deviated in position by a predetermined
amount substantially.
Further, it should be noted that the output signal which is subjected to
phase-shift can be either of the output signals obtained from the
induction coil portions.
The output signal S2 in FIG. 1 can be applied to any other audio device
than the earphone.
In addition, the telephone cord 6 may be associated with the induction coil
portions 26 and 27 in such a way as shown in FIG. 6. In FIG. 6, a
telephone cord 6 is arranged outside a housing of the magnetic induction
coil means orthogonally of the induction coil portions 26 and 27.
As described hereinbefore, according to the present invention, it becomes
possible to pick up sound effectively from sound current flowing through
the electric wire without external noise, regardless of twisting of the
wire.
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