JPH0329499A - Static condenser type microphone - Google Patents

Abstract

PURPOSE:To obtain an electrostatic capacity type microphone with excellent S/N by providing a vibration electrode to both faces of a back electrode, using one diaphragm electrode face for a sound wave reception and the other for a dummy not receiving the sound wave and receiving signals from the two diaphragm electrodes differentially. CONSTITUTION:Diaphragm electrodes 13, 14 are formed to the surrounding of both faces of a back electrode 11 via an insulator 12. Moreover, a couple of electrodes 11, 13 form a microphone and a couple of electrode 11, 14 form other microphone. One 15 of the two microphones obtained in this way can receive a sound wave externally and the other 16 is subject to housing to the cover so as not to receive the sound wave. Then a bias is applied to the microphone 15 and the dummy microphone 16 with a DC bias section 17 and respective outputs are inputted to a preamplifier 18. Thus, the two outputs are received differentially to eliminate common mode electromagnetic noise or power noise or the like thereby improving the S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a microphone for audible audio equipment or an ultrasonic band microphone for distance measurement.

(Prior technology) “A capacitive microphone generally has a structure in the form of a capacitor, consisting of a back electrode and a vibrating electrode with an air layer in between.The vibrating electrode vibrates due to sound waves incident from the outside, As a result, the capacitance of the capacitor changes, resulting in an acoustoelectric transducer that converts the capacitance change into an electrical signal.

This type of microphone has a vibrating electrode that is made of a very light and highly rigid material, so it has good impedance matching with the air, and has a wide frequency band and excellent transient response characteristics. However, it is necessary to apply a DC bias voltage between both electrodes during driving, and the sensitivity of the microphone is proportional to the DC bias voltage.
There are drawbacks such as the fact that a voltage higher than aoov must be applied as the DC bias voltage to achieve high sensitivity, and the structure has high impedance and tends to pick up electromagnetic noise. FIGS. 2(a) and 2(b) show a conventionally used acoustoelectric transducer. 2(a) is based on transformer coupling, and FIG. 2(b) is the one in which the DC bias voltage is cut by a coupling capacitor and then the impedance is converted by an FET. In FIGS. 2(a) and 2(b), 21 is a microphone section for receiving sound waves, and 22 is a DC bias.

(Problems to be Solved by the Invention) As mentioned above, capacitive microphones inherently have high impedance due to their structure, and the incident signal is very weak, so they are extremely susceptible to electromagnetic noise and noise coming from the power supply. weak to

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art, and to
The objective is to provide a capacitive microphone with a good ratio.

(Means for Solving the Problems) According to the present invention, vibrating electrodes are provided on both sides of a back electrode in a capacitive microphone, one vibrating electrode surface is used for receiving sound waves, and the other side is used to prevent sound waves from entering. Thus, a capacitive microphone characterized in that it receives signals from two vibrating electrodes differentially can be obtained.

(Function) The capacitive microphone of the present invention has two microphones in its structure, one of which is a microphone in the original sense of receiving sound waves, and the other is a dummy. By receiving these two outputs differentially,
Electromagnetic noise, power supply noise, etc. that come in the same phase can be removed, and the S/N ratio can be improved.

(Example) Hereinafter, an example of the present invention will be described using FIG. 1. 1st
As shown in Figure (a), vibrating electrodes 13. Shape 14.

11. One microphone with 13 pairs of electrodes, 1
Another microphone is used at 1 and 14. One of the two microphones thus obtained is designed to allow sound waves to enter from the outside, and the other is housed so that sound waves do not enter the surface of the microphone. In other words, one microphone is provided with a protective cover with holes (a net-like one if kept), and the other microphone is provided with a protective cover without holes. In order to distinguish between the two microphones, the microphone mounted in such a way that no sound waves enter the surface is referred to here as a dummy microphone. These two microphones are connected as shown in the circuit diagram of FIG. 1(b). That is, a DC bias section 17 applies a bias to the microphone microphone 15 and the dummy microphone 16, and their respective outputs are input to the preamplifier 18.

When the microphone thus obtained was input into a commercially available microphone amplifier and amplified, it was found that the common mode noise was removed and the S/N ratio was improved by about three times.

(Effects of the Invention) As described above, in the capacitive microphone of the present invention, electromagnetic noise and noise leaking from the power supply section are removed, and as a result, the sensitivity is improved. Further, by adopting such a differential structure, a coupling capacitor with a large dielectric strength voltage can be omitted, and a small amplifier can be built into the microphone, which is an advantage.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention. (a) is a schematic cross-sectional view of the capacitive microphone of the present invention, (b)
is a diagram of the circuit section. Figures 2 (a) and (b) are
FIG. 2 is a diagram of a signal output circuit of a conventional microphone. The numbers in the figure indicate the following. 11... Back electrode, 12... Insulator, 13. 14
... Vibrating electrode, 15. ．． ．． Microphone, 16... dummy microphone,

Claims (1)

[Claims] In a capacitive microphone, vibrating electrodes are provided on both sides of the back electrode, and one vibrating electrode surface is used for receiving sound waves.
The other is a capacitive microphone that prevents sound waves from entering and receives signals differentially from two vibrating electrodes.