JPS6021694A - Piezoelectric receiver - Google Patents

Abstract

PURPOSE:To obtain a flat sensitivity frequency characteristic and to attain sure operation by connecting a resistance element in series with a piezoelectric bimorph diaphram. CONSTITUTION:The volume of air chambers 2, 4 before and after the diaphragm 1 is constituted with a realizable dimension by connecting the resistance element 11 is series with the piezoelectric bimorph diaphragm 1 and the sensitivity frequency characteristic which is liable to be increased at high frequencies is made flat. Since the impedance of the receiver viewed from a reception amplifier is not zero at a high frequency, the stable operation of the amplifier is ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a piezoelectric receiver for use in telephones and the like.

[Prior art]

In general, piezoelectric handsets using a piezoelectric bimorph diaphragm are
It is constructed as shown in FIG. That is, the figure shows an example using a piezoelectric bimorph diaphragm 1 formed by fixing a piezoelectric plate 1b to a conductive substrate 1a, and 2 is a first front air chamber;
3 is an earpiece, 4 is a rear air chamber, 5 is a braking hole, and 6 and 7 are terminals, and the terminals 6.1 are electrodes attached to the surfaces of the substrate 1a and the piezoelectric plate 1b by lead wires 8 and 9, respectively. It is connected to the. When this receiver is placed against the ear, the inside of the ear acts as the second front air chamber 10.

So now, terminal 6. When an AC signal is applied to T,
The piezoelectric bimorph diaphragm 1 vibrates, and the second wave moves into the ear.
The front air chamber 10 operates as a telephone receiver by generating sound pressure.

Figure 2 shows the configuration of the acoustic vibration system of the receiver shown in Figure 1 replaced with an electrical equivalent circuit. In the figure, Vo is the equivalent volume of the diaphragm 1, and V-i is the first front air Volume of chamber 2, v+
1 indicates the volume of the rear air chamber 4, and vT2 indicates the volume of the second front air chamber 10.

As is clear from FIG. 2, this receiver constitutes an acoustic vibration system with three degrees of freedom (in FIG. 2, 1, 1...
three closed loops of 1 are formed). By configuring the acoustic vibration system f with multiple degrees of freedom in this way, it is possible to secure a reproduction bandwidth wider than the fundamental resonant frequency inherent to the diaphragm, and it is also advantageous for achieving high sensitivity. A piezoelectric type receiver using a piezoelectric bimorph diaphragm, which is generally employed in telephone receivers, can also be designed and realized based on such a concept, as shown in particular.

By the way, the equivalent volume of a piezoelectric bimorph diaphragm is generally smaller than that of a molded diaphragm. Therefore, in order to achieve flat sensitivity frequency characteristics, the air chambers before and after the diaphragm 1 need to have a small (narrow) volume commensurate with the equivalent volume of the diaphragm. However, as is clear from the figure, the rear air chamber 4 shown in FIG. It is impossible to set the volume below a certain level due to the presence of holes, etc., and it is therefore difficult to achieve the target flat sensitivity frequency characteristic.

Furthermore, it is clear that the electrical impedance of a piezoelectric handset decreases in proportion to frequency since it is capacitive. That is, when a receiving amplifier is used to drive the piezoelectric receiver, the output terminal of the amplifier is short-circuited in a high frequency region. This has the effect of damaging the output stage of the amplifier, making its operation unstable, increasing distortion, and other negative effects, which have been major drawbacks in the design and practical use of piezoelectric receivers.

[Object and structure of the invention]

The present invention has been made in view of the above circumstances, and an object thereof is to provide a piezoelectric receiver that can obtain flat force sensitivity frequency characteristics and ensure stable operation.

In order to achieve such an object, the present invention connects a resistance element in series to a piezoelectric bimorph diaphragm.

Hereinafter, the present invention will be explained in detail using Examples.

〔Example〕

FIG. 3 is a sectional view showing one embodiment of the present invention, and parts equivalent to those in FIG. 1 are indicated using the same symbols.

As is clear from FIG. 3, in this embodiment, in contrast to the configuration shown in FIG. 1, a resistance element 11 electrically connected between the lead wire 9 and the terminal T is installed inside the rear air chamber 4. It is characterized by the following points.

Next, the effects of the configuration of the present invention will be explained in comparison with the general configuration shown in FIG. 1.

(a) and (b) of FIG. 4 show that in the equivalent circuit shown in FIG.
This means that the clamp diameter of the diaphragm 1 is 2. g cm, the diameter of the piezoelectric plate 1b is 2.3 on, and the plate thickness is 0.1
The sound pressure generated in the second front air chamber 10 when a constant voltage is applied to the diaphragm 1, that is, the relative value of the sensitivity, is calculated by simulation.

In FIG. 4, the broken line (A) indicates the equivalent volume V of the diaphragm 1.
When the volumes of the first front air chamber 2 and the rear air chamber 4 are made equal to o, the solid line (b) shows the case where they are doubled, but as is clear from the figure, the volumes of the front and rear air chambers are It can be seen that by narrowing , a flat sensitivity frequency characteristic can be obtained.

However, as mentioned earlier, when actually constructing a handset, the volume V+1 of the front and rear air chambers, especially the rear air chamber 4, is half 0]
It is necessary to decide by taking into consideration the mounting dimensions, lead wire arrangement dimensions, terminal protrusion amount, etc. From now on, the diaphragm 1 and the terminals 6 and 7.
Assuming that a distance of 2 to 3 mm from the solder portion is ensured, the volume of the rear air chamber when the air chamber is formed with the above-mentioned diaphragm clamp dimensions will be 12 to 1.8 cc. This means that only the characteristics indicated by the solid line (A) in the upper right corner of FIG. 4 can be realized.

In the present invention, a resistance element 11 is provided in order to correct the sensitivity frequency characteristic of the upper right corner to a flat characteristic, and FIG. 5 shows a temperature-wise configuration in this case.

In FIG. 5, C indicates the capacitance of the piezoelectric plate 1, to which a resistor R corresponding to the resistive element 11 is connected in series. TI and T2 indicate electrical terminals, and an alternating current signal is applied between these terminals for use.

As is clear from FIG. 5, since this is an RC series circuit, a constant voltage with respect to the frequency is applied to the electrical terminal T 1 +
When applied between T 2 , the voltage applied across the piezoelectric plate 10 decreases with a slope of 6 d BAc t at frequencies above the cutoff frequency fc=”/2πCR.

In FIG. 4, the dashed line (c) indicates the frequency characteristic of the terminal voltage of the piezoelectric plate 1 when fc=IKH2. Therefore, by adding the sensitivity characteristic shown in the figure (extension) to this voltage characteristic, a nearly flat sensitivity frequency characteristic can be obtained as a result. If you want to obtain a frequency characteristic other than this, change the value of the series resistor R to obtain the cutoff frequency f. You just need to set it to an appropriate value, but in the case of a telephone handset,
Since it is sufficient to consider the playback bandwidth in the range of approximately 0.2 to 4 KHz, in that sense, the above cutoff frequency is 0.2.
Resistor element 1 is set so that it is set within the range of ~4 KHz.
It is sufficient to select a resistance value of 1.

In the embodiment shown in FIG. 3, the resistance element 11 was connected between the lead wire 9 and the terminal 7, but as is clear from FIG. , for example, may be connected between the lead wire 8 and the terminal 6. Similarly, the embodiment shown in FIG. 3 is an example in which the resistance element 11 is installed inside the rear air chamber 4, that is, inside the housing of the receiver unit.
It may be connected between one end of the telephone and terminal J, in which case both terminals 8 and 12 are the electrical terminals serving as the handset.

FIGS. 7 and 8 show examples of characteristics of a piezoelectric handset constructed according to the present invention. In other words, Figure 7 shows the relative value of sensitivity. In the figure, the broken line (A) indicates when there is no series resistance,
The solid line (b) shows the sensitivity frequency characteristic when measured with the resistance element 11 connected in series to the piezoelectric plate 1 so that the cut 17 frequency is I KHz.

Moreover, FIG. 8 shows the frequency characteristics of impedance, and in the figure, the broken line (A) is the impedance frequency characteristic when there is no series resistance, and the solid line (B) is the impedance frequency characteristic when measured with a series resistance connected.

As is clear from the actual measurement example in FIG. 7, it has been confirmed that a flat sensitivity frequency characteristic can be achieved by adding a series resistor.
Even at high frequencies, the impedance of the handset does not become smaller than the above series resistance value.

Furthermore, another advantage of adding a series resistor is that the higher-order resonance level of the diaphragm is suppressed. In other words, when driving a piezoelectric Pimo/I/7 diaphragm, the frequency is generally about 4 times, 9 times, etc. of the fundamental resonance frequency.
A sharp rise in level due to high-order resonance is observed at the frequency of , but this unnecessary level can also be reduced by the effect of a low-pass filter consisting of an RC series circuit.

Although the above example uses a piezoelectric bimorph diaphragm formed by fixing a piezoelectric plate on a conductive substrate, the present invention is not limited to this, and other
For example, it goes without saying that the present invention can be similarly applied to the case where a piezoelectric bimorph'yi motion plate made by IfG is used, which is made by bonding two piezoelectric plates together.

〔Effect of the invention〕

As explained above, according to the present invention, by connecting a resistance element in series to the piezoelectric bimorn diaphragm, the air chamber volume before and after the diaphragm can be configured to a size that can be realized, and the upper right diaphragm can be It is possible to flatten the sensitivity frequency characteristic.

Further, since the impedance of the receiver connected to the amplifier does not become zero even at high frequencies, there is an advantage that stable operation of the amplifier is ensured. Furthermore, it is also effective in reducing the level of high-order resonance such as secondary and tertiary of the flat diaphragm, which is one of the important advantages.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a conventional piezoelectric telephone receiver, FIG. 2 is a diagram showing its acoustic vibration system as an electrical equivalent circuit, FIG. 3 is a cross-sectional view showing an embodiment of the present invention, and FIG. The figure is a diagram showing relative values of sensitivity and voltage frequency characteristics based on simulation, and Figure 5 is an electric circuit diagram of a piezoelectric type receiver according to the present invention.
FIG. 6 is a sectional view showing another embodiment of the present invention, FIG. 7 is a diagram showing an actual measurement example of the sensitivity frequency characteristic of the piezoelectric receiver according to the invention, and FIG. 8 is an actual measurement example of the impedance frequency characteristic. FIG. 111@...Piezoelectric bimorph diaphragm, 1a...Substrate, 1b...Piezoelectric plate, 2...Φ.First front air chamber, 4.
... Rear air chamber, 11... Resistance element. 1 drawing 2 drawings + I 1t

Claims (1)

[Claims] Air chambers and acoustic elements are arranged before and after the piezoelectric bimorph diaphragm to provide multiple degrees of freedom for the acoustic vibration system.In the FT piezoelectric receiver, a resistance element is provided that is electrically connected in series to the piezoelectric bimorph diaphragm. A piezoelectric receiver characterized by: