JPS6239880B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electret capacitor type transducer, and more particularly to one that improves its sensitivity and distortion characteristics.

In general, capacitor type transducers used in microphones and headphone for audio equipment use changes in capacitance between a movable pole (vibrating membrane) and a fixed pole to convert mechanical electricity (acoustic electricity). It is a business.

Recently, in such a capacitor type transducer, either the movable pole or the fixed pole is equipped with an electret that has the property of being charged in advance under predetermined conditions and maintained semi-permanently. A so-called electret capacitor type transducer has been developed for this purpose. In other words, by using electrets, a bias power supply can be eliminated, and the size can be reduced accordingly.
This is advantageous for lowering prices.

As such electrets, corona electrets, thermal electrets, etc. have been realized depending on the manufacturing method.

However, regardless of the manufacturing method used for electrets, it is difficult to arbitrarily form the electret charge distribution on the surface. Not only is it not easy to achieve this, but it also tends to cause the fatal problem of the movable pole being attracted to the fixed pole and the transducer no longer being able to operate normally. It was hot.

FIG. 1 shows the basic configuration when the above-described electret capacitor type transducer is applied to a microphone. In other words, this is a case of the so-called back electret method in which an electret is used on the fixed pole 11 side, and the electret surface charge (voltage) of the fixed pole 11 is
As shown in FIG. 2, the distribution is uneven from the ends E ₁ and E ₂ to the center M, but has a substantially flat characteristic.

On the fixed electret pole 11, a movable pole 14, which is stretched on a support ring 13 with a predetermined gap formed by a spacer 12, is disposed oppositely, and when the movable pole 14 receives external sound pressure, The vibration changes the gap between the fixed pole 11 and the capacitance between the two poles. Then, this change in capacitance is immediately extracted from the output terminal OUT as an electrical signal corresponding to the sound pressure via an impedance conversion circuit including a field effect transistor FET ₁₁ and the like.

However, in this case, even in a static state where there is no external sound pressure, the movable pole 14 is drawn toward the electret fixed pole 11 by the attractive force due to Coulomb's law, as shown by the broken line in the figure. Disadvantages peculiar to so-called single-type transducers are that the electrical signal extracted from the output terminal OUT is always distorted on the shore side, and high sensitivity cannot be achieved due to the problem of adsorption, which limits the effective capacity. cannot escape from it.

In other words, this is because the surface charge distribution of the fixed electret pole 11 is uniform and from the viewpoint of the support structure of the movable pole 14, the central part of the movable pole 14 is largely bent toward the fixed electret pole 11. This is because the so-called static balance cannot be maintained correctly.

Therefore, this invention was made in view of the above points, and by making the surface charge of the electret used for either the fixed pole or the movable pole such that the central part is weaker than the peripheral part,
It is an object of the present invention to provide an extremely good electric capacitor type transducer which has been improved so that the static balance can be maintained as accurately as possible, and the distortion characteristics and sensitivity can be improved.

An embodiment of the present invention will be described in detail below with reference to the drawings.

That is, FIG. 3 shows a case where the microphone is applied to a back electret type microphone, in which a movable pole 24 is stretched over a support ring 23 with a predetermined gap formed by a spacer 22 on the electret fixed pole 21. Oppositely installed, electret fixed pole 2
1 is connected to the output terminal OUT via an impedance conversion circuit including a field effect transistor FET ₂₁ and the like.

Here _, the electret fixed pole 21 has an electret surface charge distribution such that, as shown in _FIG . As shown in the figure, it is assumed that it is formed with radial or lattice-like unevenness (where the coarse portions have a small charge and the dense portions have a large charge).

The electret capacitor type transducer constructed as described above is formed such that the surface charge distribution of the fixed electret pole 21 is such that the charge at the center is smaller than the charge at both ends. In a static state where there is no sound pressure from
It is in a state where it is possible to maintain correct static balance without being sucked to the side.

Therefore, even when external sound pressure is applied, the electrical signal extracted to the output terminal OUT will not be distorted on either half-skin side, and will have a low distortion rate and high fidelity.

In addition, this makes it possible to eliminate as much as possible the problem of the movable pole 24 being attracted to the electret fixed pole 21, so the effective capacity can be made as large as possible without being subject to any restrictions. , which can also contribute to improvement in sensitivity.

It goes without saying that the present invention is not limited to the embodiments described above and illustrated, and that various modifications and applications can be made without departing from the gist of the invention.

Therefore, as detailed above, according to the present invention, the static balance is achieved by making the surface charge of the electret used for either the fixed pole or the movable pole such that the central part is weaker than the peripheral part. be as accurate as possible,
Thus, it becomes possible to provide an extremely good electret capacitor type transducer that has been improved to improve distortion characteristics and sensitivity.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram showing a conventional electret condenser microphone, Fig. 2 is a curve diagram showing the surface charge distribution of the fixed electret pole used in Fig. 1, and Fig. 3 is an electret condenser according to the present invention. FIG. 4 is a diagram showing the principle configuration of an example of a type transducer applied to a microphone. FIG. 4 is a curve diagram showing the surface electric field distribution of the fixed electret pole used in FIG. 3. FIGS.
The figures are a plan view and a sectional view showing a specific example of the electret fixed pole used in FIG. 3. 21...Electret fixed pole, 22...Spacer, 23...Support ring, 24...Movable pole.

Claims (1)

[Claims] 1. An electret is used for either the fixed pole or the movable pole, which are arranged opposite to each other with a predetermined gap, and the surface charge of the electret is formed in a distribution such that the center part is smaller than the peripheral part. electret capacitor type transducer.