KR20040011849A - An external bias type condenser microphone - Google Patents

Abstract

PURPOSE: A condenser microphone operated at low voltage is provided to supply a high sensitivity at a low voltage in comparison with a conventional condenser microphone by incorporating therein a high built in gain amplifier. CONSTITUTION: A condenser microphone(300) with applying a low voltage includes a diaphragm, a back plate, a spacer and a circuit device. The spacer is placed between the diaphragm and a back plate. The circuit device transmits the vibration signal between the back plate and the diaphragm to outside when the diaphragm is vibrated. The diaphragm is made of a thin film on which the metal film is deposited. A low bias voltage is applied to the diaphragm. The back plate is made of a metal plate and the signal input terminal of the circuit device is connected to the back plate. And, the amplifier(310) is connected to the outside through the output terminal and the ground terminal.

Description

Low voltage condenser microphone {An external bias type condenser microphone}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to condenser microphones for converting sound into electrical signals, and more particularly to low voltage applied condenser microphones capable of applying a low voltage external bias.

In general, the microphone is a magnetic field of the diaphragm equipped with a carbon-type using the electrical resistance characteristics of the carbon particles, the crystalline form using the piezoelectric effect of the shell salt (coil) according to the method of converting the mechanical vibration into an electrical signal magnetic field Movable coil type that vibrates inside to generate induction current, Velocity microphone that uses the induced current to generate when the metal film installed in the magnetic field vibrates by receiving sound waves, and condenser using the change of capacitance due to vibration of the film by sound waves Type and the like.

A typical condenser microphone consists of a voltage bias element, a diaphragm / backplate pair forming a capacitor C that changes in response to sound pressure, and a field effect transistor (JFET) for buffering the output signal.

As shown in FIG. 1, the conventional condenser microphone is divided into an acoustic part and a PCB circuit part and is integrally assembled by one housing 108. The diaphragm 106 and the back plate 104 face each other with a spacer 105 therebetween, and the diaphragm 106 has a case 108 in which a sound hole 109 is formed through the polar ring 107. Supported on the side, the backplate 104 is supported on the PCB substrate 101 by the instrument 103. The JFET 102 is mounted on the PCB substrate 101. Here, the diaphragm 106 and the back plate 104 are a metal plate.

Looking at the operation of the condenser microphone as described above, when the sound pressure introduced through the sound hole 109 is applied to the diaphragm 106, the diaphragm 106 vibrates and the distance to the back plate 104 is changed. When the interval is changed by the sound pressure, the capacitance formed by the diaphragm 106 and the back plate 104 is changed to obtain a change in the electrical signal (voltage) according to the sound wave, and this signal causes the JFET 102 to change. It is delivered to the outside. That is, the total charge amount Q formed by the diaphragm 106 and the back plate 104 is defined as in Equation 1 below, and the capacitance C is defined as in Equation 2 as follows. In this case, since the capacitance C and the voltage V have an inverse relationship with each other, when the distance d is changed by sound pressure, the capacitance changes, thereby causing a change in voltage.

However, such a conventional condenser microphone has a problem that it is inconvenient to use a high pressure of several tens of volts for biasing because the back plate and the diaphragm are made of a metal plate.

In order to solve the above problems, an object of the present invention is to provide a condenser microphone in which a diaphragm is a film formed by sputtering metal on both sides of an organic or inorganic thin film, and is operable at a low voltage by incorporating an amplifier.

1 is a schematic diagram showing the structure of a conventional condenser microphone;

2 is a view showing a main section of the condenser microphone according to the present invention;

3 is a circuit diagram of a condenser microphone according to the present invention.

* Explanation of symbols for main parts of the drawings

200: sound unit 210: back plate

220: diaphragm 222: thin film

224,226 metal film 230 spacer

300: microphone 310: built-in amplifier

320: resistance

In order to achieve the above object, the microphone of the present invention forms a space in which a diaphragm and a back plate face each other with spacers therebetween, and when the diaphragm vibrates according to sound pressure, a change signal between the diaphragm and the back plate is achieved. In the condenser microphone such that the circuit element is transmitted to the outside,

The diaphragm is a metal film deposited on both sides of the thin film, a low voltage bias voltage is applied, the back plate is a metal plate, and the circuit element has a signal input terminal connected to the back plate, and an output terminal and a ground terminal. It is characterized by consisting of an amplifier connected to the outside through.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a view showing a main section of the condenser microphone according to the present invention, Figure 3 is a circuit diagram of the condenser microphone according to the present invention.

The condenser microphone 300 of the present invention comprises an acoustic portion and a circuit portion. The acoustic portion uses a diaphragm of an organic material or an inorganic material sputtered with gold on both sides instead of a metal plate, and an amplifier (Built-in) instead of a JFET in the circuit portion. -Gain: 310 in FIG. 3 is used.

Referring to FIG. 2, the condenser microphone acoustic part 200 of the present invention faces the diaphragm 220 and the back plate 210 with the spacer 230 interposed therebetween, and the diaphragm 220 may be formed of organic or inorganic materials. Metals (eg, gold, nickel, nichrome, etc.) are deposited on both surfaces of the thin film 222 by sputtering to form metal films 224 and 226. At this time, it is preferable to use sputtering as a method of depositing gold. The thickness d of the spacer 230 is made lower than the existing thickness (38 μm), and the back plate 210 is a metal plate without an organic film as in the prior art.

As described above, since the diaphragm 220 is a thin film sputtered with metal on organic or inorganic material instead of a metal plate, which is stressed a lot, the external bias voltage can be reduced. .

3 is a circuit diagram of a condenser microphone according to the present invention.

Referring to FIG. 3, the acoustic unit 200 of the condenser microphone of the present invention forms a space while the diaphragm 220 and the back plate 210 face each other with the spacer 230 interposed therebetween. In addition, when the input of the amplifier 310 is connected to the back plate 210 of the acoustic unit 200 and the diaphragm 220 vibrates according to sound pressure, a change in capacitance between the diaphragm 220 and the back plate 210 may occur. It is designed to sense and amplify corresponding voltage fluctuations.

At this time, the diaphragm 220 is made of metal films 224 and 226 deposited on both sides of the thin film 22, and a low voltage bias voltage is applied, the back plate 210 is made of a metal plate, and the amplifier 310 is a signal input terminal ( An input is connected to one end of the sound unit 200 and is connected to the outside through an output terminal and a ground terminal GND. The sensitivity is determined by changing the bias voltage by applying about + 2V between the output terminal of the amplifier and ground (GND) and applying a + bias voltage (+ Vb) to the other end of the acoustic unit 200. The loss is a three-port condenser microphone. In addition, to reduce noise, a resistor G of several GΩs or a reverse biased diode is used between input and ground (GND).

Subsequently, the operation of the low voltage application type condenser microphone of the present invention configured as described above will be described.

The terminal of the low voltage application type condenser microphone according to the present invention is connected to an external device, and a predetermined + bias voltage is applied to the bias terminal. When a bias voltage is applied, the sound unit forms an electric field.

When the user utters a voice in such a state, the sound wave is transmitted to the sound unit inside the microphone through the sound hole of the case, and the diaphragm vibrates by the sound wave. When the diaphragm vibrates, the capacitance of the capacitor consisting of the diaphragm and the back plate changes, and thus a voltage change corresponding to an acoustic signal is generated at an input terminal of the amplifier. The amplifier amplifies this weak input signal with high gain and outputs it to an external device through the output terminal.

As described above, in the conventional condenser microphone, since a JFET is used as a preamplifier, an amplifier for amplifying the microphone signal is required outside of the microphone. However, in the present invention, an amplifier having a high gain is introduced into the microphone's internal circuit. This makes it possible to provide higher sensitivity at lower voltages than conventional condenser microphones. In addition, the microphone of the present invention can be applied to the surface mounting technology (SMD) is low production cost and good high temperature characteristics because of the simple configuration, there is a strong advantage in the change of the external environment. In particular, the circuit design is easy because it can be driven at a lower voltage than the conventional condenser microphone.

Claims (4)

A condenser microphone in which a diaphragm and a back plate face each other with a spacer therebetween to form a space, and when the diaphragm vibrates according to sound pressure, a circuit element transmits a change signal between the diaphragm and the back plate to the outside. The diaphragm is A low voltage bias voltage is applied to the metal film deposited on both sides of the thin film, The back plate is made of a metal plate, The circuit element is a low voltage application type condenser microphone, characterized in that the signal input terminal is connected to the back plate, the output terminal is connected to the outside through the ground terminal. The low voltage application type condenser microphone of claim 1, wherein the diaphragm has high sensitivity even when a low voltage bias is applied by sputtering gold on a thin film of an organic material or an inorganic material having less stress than a metal film. The low voltage application type condenser microphone of claim 1, wherein the condenser microphone suppresses generation of noise by connecting a high resistance or reverse biased diode between ground and an input terminal of the amplifier. The condenser microphone of claim 1, wherein the condenser microphone can provide a high sensitivity at a voltage lower than that of a condenser microphone that is used by fabricating an amplifier having a high gain into a microphone internal circuit. Low voltage application type condenser microphone.