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JPH0375000

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DESCRIPTION JPH0375000
[0001]
(1) Field of the Invention The present invention relates to a piezoelectric receiver circuit to which
a magnetic field generating coil is connected. (2) Prior Art and Problems Thereof FIG. 1 is a
circuit diagram in which a magnetic field generating coil is connected in series to a piezoelectric
receiver and driven by an amplifier. Here, 1 is a magnetic field generating coil, 2 is a piezoelectric
receiver, and includes, for example, a ceramic piezoelectric body, a polymer piezoelectric body,
and a composite piezoelectric body. 3 is an audio signal amplifier. Usually, since the impedance
of the magnetic field generating coil 1 is smaller than the impedance of the piezoelectric receiver
2 and the impedance of the piezoelectric receiver 2 is capacitive, as shown in FIG. 2, the magnetic
field generating coil 1 and the piezoelectric receiver 2 The total impedance decreases in
proportion to the frequency. Therefore, when the output voltages of the output terminals R and
Rz of the audio signal amplifier 3 are constant with respect to the frequency, the audio signal
current flowing through the magnetic field generating coil 1 increases in proportion to the
frequency as shown in FIG. Since the strength of the magnetic field generated from the magnetic
field generating coil 1 is proportional to the current flowing through the magnetic field
generating coil 1, the magnetic field strength increases in proportion to the frequency as shown
in FIG. Since the frequency characteristic of the magnetic field strength is required to be flat, in
this case the frequency characteristic of the magnetic field strength rises in the high frequency
band and the requirement is not satisfied. (3) Object of the Invention The present invention
provides a piezoelectric receiver circuit in which the frequency characteristic of the magnetic
field intensity is flattened by solving the defect due to the capacitive impedance inherent to the
piezoelectric receiver. (4) Configuration and Operation of the Invention In order to achieve the
object, the piezoelectric receiver circuit of the present invention is configured to connect a
capacitor in parallel with the magnetic field generating coil or connect a resistor in parallel or in
series with the piezoelectric receiver. have. Hereinafter, the present invention will be described in
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detail. (Embodiment 1) FIG. 4 shows an embodiment of the present invention, in which 4 is a
capacitor connected in parallel to the magnetic field generating coil 1. The audio signal current i
is a current i to the magnetic field generating coil 1. Then, the current m3a is shunted to the
capacitor 4 and the impedance of the capacitor 4 becomes smaller at a high frequency, so the
current il flowing through the magnetic field generating coil 1 as shown in FIG. It is less than the
curve 4a when not connected. By appropriately selecting the impedance of the capacitor 4 with
respect to the impedance of the magnetic field generating coil 1 and the impedance of the
piezoelectric receiver 2, the current 11 flowing through the magnetic field generating coil l can
be made substantially constant in the audio frequency band The frequency characteristics of the
magnetic field intensity proportional to the current il can be made flat.
-As an example, when the impedance (DC resistance) of the magnetic field generating coil 1 is
100Ω, the capacity of the piezoelectric receiver 2 is 0.055 μF, and the capacity of the parallel
capacitor 4 is 4.7 μF, as shown in FIG. The current flowing to 1 becomes as shown by curve 4b.
(Embodiment 2) FIG. 6 shows a second embodiment of the present invention, in which 5 is a
resistor connected in parallel to the piezoelectric receiver 2. The voice signal current i is divided
into the piezoelectric receiver 2 by the current it and by the resistor 5 by the current il, and the
impedance of the piezoelectric receiver 2 is increased and the current 12 is reduced at a low
frequency, but the impedance of the resistor 5 is The current il flows constantly because it is
constant regardless of it. In this case, as indicated by the curve 5a in FIG. 7, the current 11
flowing through the magnetic field generating coil 1 is lower in the case where the resistor 5 is
not connected when the resistor 5 is connected (the same curve 5b). growing. By appropriately
selecting the impedance of the resistor 5 with respect to the impedance of the magnetic field
generating coil 1 and the impedance of the piezoelectric receiver 2, the current il flowing
through the magnetic field generating coil 1 can be made substantially constant in the audio
frequency band. It is possible to flatten the frequency characteristic of the magnetic field
intensity proportional to. As an example, when the impedance (DC resistance) of the magnetic
field generating coil 1 is 100 Ω, the capacity of the piezoelectric receiver 2 is 0.055 μF, and the
resistance of the parallel resistor 5 is 1 Ω, as shown in FIG. i flowing to l. Becomes like curve 5a.
(Embodiment 3) FIG. 8 shows a third embodiment of the present invention, in which 6 is a
resistor connected in series to the magnetic field generating coil 1 and the piezoelectric receiver
2. The audio signal current i flows as the resistance current lht of the resistor 6 and the magnetic
field generating coil current fl + the piezoelectric receiver 12. In this case, as shown by the curve
6a in FIG. 9, since the impedance of the resistor 6 is constant regardless of the frequency, the
impedance of the piezoelectric receiver 2 decreases and the voice signal current i increases at a
high frequency. The audio signal current i does not increase as shown by the curve 6b. Current i
flowing through the magnetic field generating coil 1. Is smaller at high frequencies than when
the resistors 6 are not connected in series. By appropriately selecting the impedance of the
resistor 6 with respect to the impedance of the magnetic field generating coil 1 and the
impedance of the piezoelectric receiver 2, the current il flowing through the magnetic field
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generating coil can be made substantially constant in the voice frequency band. The frequency
characteristics of the proportional magnetic field strength can be made flat.
As an example, when the impedance (DC resistance) of the magnetic field generating coil 1 is
100 Ω, the capacity of the piezoelectric receiver 2 is 0.055 μF, and the resistance of the series
resistor 6 is IOK Ω, as shown in FIG. The flowing current iI is as shown by the curve 6b. When
the present invention is configured, for example, as a piezoelectric receiver circuit for a
telephone, the following combinations are possible as a form for mounting on a telephone main
body or a handset. (2) A mode in which the voice signal amplifier 3 is mounted on the telephone
body, and the magnetic field generating coil 1 and the piezoelectric receiver 2 are mounted in the
handset to constitute a piezoelectric receiver circuit. (2) A mode in which the voice signal
amplifier 3 and the magnetic field generating coil 1 are mounted on the telephone body, and the
piezoelectric receiver 2 is mounted in the handset to constitute a piezoelectric receiver circuit. (2)
A type in which the voice signal amplifier 3, the magnetic field generating coil 1, and the
piezoelectric receiver 2 are integrally mounted in a handset to constitute a piezoelectric receiver
circuit. (2) A mode in which the voice signal amplifier 3 is mounted on the telephone main body,
and the piezoelectric receiver 2 is integrated with the magnetic field generating coil 1 so as to be
housed in the handset to constitute a piezoelectric receiver circuit. (1) In the type in which the
voice signal amplifier 3 and the magnetic field generating coil 1 are integrally incorporated in the
piezoelectric receiver 2 and this is accommodated in a handset to constitute a piezoelectric
receiver circuit. It goes without saying that any of these mounting forms is included in the
present invention. Further, the present invention is not limited to the use for telephones, and can
be used in various fields as an acoustic transducer. (5) As described in detail in the invention,
according to the present invention, the frequency characteristic of the magnetic field strength
generated from the magnetic field generating coil can be flattened, and the requirement for the
piezoelectric receiver circuit can be satisfied.
[0002]
Brief description of the drawings
[0003]
1 is a circuit diagram in which a magnetic field generating coil and a piezoelectric receiver are
connected in series and connected to an audio signal amplifier, FIG. 2 is a frequency
characteristic diagram of the combined impedance of the magnetic field generating coil and the
piezoelectric receiver, FIG. Fig. 4 shows the frequency characteristics of the current flowing
through the magnetic field generating coil and the magnetic field intensity generated from the
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magnetic field generating coil. Fig. 4 shows an embodiment of the present invention in which a
capacitor is connected in parallel to the magnetic field generating coil. FIG. 5 is a circuit diagram
showing an example, FIG. 5 is a frequency characteristic diagram of current flowing in a
magnetic field generating coil with and without a capacitor in FIG. 4, and FIG. 6 is a circuit
diagram showing a second embodiment of the present invention. 7 is a frequency characteristic
diagram of the current flowing through the magnetic field generating coil with and without the
resistance connected in FIG. 6, and FIG. 8 is added to FIG. 1 in series with the magnetic field
generating coil and the piezoelectric receiver. Connect resistance Circuit diagram showing a third
embodiment of the present invention, FIG. 9 is a frequency characteristic diagram of the current
flowing through the field generating coil with and without connecting the resistors in Figure 8.
1 · · · magnetic field generating coil, 2 · · · Piezoelectric handset, 3 · · · voice signal amplifier, · · · · · ·
· · · voice signal current that flows through the whole, i + · · · · · · current flowing in the magnetic
field generating coil, Current flowing to the piezoelectric receiver, i4: current flowing to the
capacitor 4, 4: capacitor connected in parallel to the magnetic field generating coil 1, 5 resistance
connected in parallel to the piezoelectric receiver 2, i: a current flowing through the resistor 6: a
resistor connected in series to the magnetic field generating coil 1 and the piezoelectric receiver
2 a current flowing through the resistor 6 Figure 1 Figure 2
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