KR200235869Y1 - Noise shield structure of electret capacitor microphone - Google Patents

Abstract

The present invention relates to a noise inflow prevention structure of a microphone in which noise blocking is designed to prevent high frequency noise (or electric noise) from being introduced into a PCB substrate on which a FET (field effect transistor) is mounted in a condenser microphone.

According to the present invention, in a microphone having a PCB installed at the end of the metallic case and mounted with an impedance conversion element (FET) on the surface, the PCB includes a three-layer including a noise blocking layer for blocking noise from the outside It is formed in a structure, preferably the noise blocking layer is to be built in the middle of the PCB.

Description

Noise introduction structure of microphone {NOISE SHIELD STRUCTURE OF ELECTRET CAPACITOR MICROPHONE}

The present invention relates to a noise inflow prevention structure of a microphone, and more specifically, to a printed circuit board (PCB) applied to an EC (Electret Capacitor) microphone for inputting a voice signal. It relates to a noise inflow prevention structure of the microphone designed a structure for blocking the.

As is well known, a microphone is provided in a communication device represented by a telephone for communication of voice or an audio device in which voice input processing is performed, and a microphone employed in such a phone or audio device is usually an electret. Wheel electrets having a vibratory diaphram formed in the form of a back electret, and a back electret type having an electret fixed by fusing to a fixed electrode, for example.

1 is a view showing an outline of a general back electret type condenser microphone, the microphone having a plurality of sound inlet holes (10a) in the front end surface while having a function to prevent external dust or foreign matter and to block electric noise. Inside the formed metallic case 10, a polar plate (Polar plate or back plate) 16 is disposed through a diaphragm 12 and an annular spacer 14.

Here, the diaphragm 12 and the bipolar plate 16 form a capacitor (capacitor) that is maintained at a predetermined interval spaced apart from each other by the spacer 14 is transmitted through the sound wave inlet (10a) When the diaphragm 12 vibrates by sound waves, the capacity set between the diaphragm 12 and the bipolar plate 16 is variable.

The bipolar plate 16 includes a plurality of equalization holes 16a interlocked with a cavity 18 defined behind the bipolar plate 16 to balance static pressure on both sides of the diaphragm 12. ) Is formed.

In addition, the cavity 18 is defined by a cup-shaped cylindrical support 20, in which a field effect transistor (FET) 22 employed for impedance conversion is disposed. .

That is, since the corresponding capacitor microphone has a small capacitance and high electrical impedance, and thus cannot be directly connected to a general amplifier, the FET 22 is employed as an impedance conversion element for matching with the input impedance required by the amplifier. .

The gate G of the FET 22 is connected to the bipolar plate 16 and electrically connected to corresponding terminals 24a and 24b on the PCB 24 according to the potential change of the gate G. The current value between D) and the source S is changed to obtain an electrical signal corresponding to the sound wave.

That is, referring to the equivalent circuit diagram of FIG. 1A illustrated in FIG. 1B, sound waves are transmitted to the diaphragm 12 through the sound wave inlet hole 10a formed on the front end surface of the metallic case 10, and the diaphragm 12. When this displacement occurs, a capacity change occurs between the diaphragm 12 forming the condenser 16b and the central portion of the bipolar plate 16.

The electrical output of the variable capacitor 16b, which is variable based on the action of the diaphragm 12, is amplified through impedance conversion by the FET 22, and the amplified output is output terminal OUT and ground terminal G. Will appear in between.

In the equivalent circuit diagram shown in FIG. 1B, the resistor indicated by 'R' is connected to the DC power supply (+ V) at one end thereof, and the other end thereof is connected to the drain D of the FET 22. One end of the capacitor denoted by C 'is connected to the output terminal OUT and the drain D of the FET 22.

2A is an exploded view and an assembled sectional view of a microphone (ie, a condenser microphone) according to a conventional example designed based on the outlines shown in FIGS. 1A and 1B.

Referring to the drawings, for example, the front cover member 32 having a plurality of sound wave penetration holes 32a is coupled to the front end of the metallic case 30 formed in a cylindrical shape by aluminum, and the coupling coupled to the case 30. Inside the front cover member 32, a diaphragm 34, a spacer member 36, and a bipolar plate 38 having a plurality of equalization holes 38a are disposed.

In addition, a PCB 46 on which the FET 44 is surface mounted is disposed on the cylindrical support 42 provided to define the cavity 40 in the case 20.

A cylindrical ring formed of a conductive material inside the cylindrical support 42 to electrically connect the gate 44G of the FET 44 mounted on the PCB 46 to the bipolar plate 38. A ring connector 48 is provided.

Accordingly, in the microphone, the gate 44G of the FET 44 mounted on the PCB 46 is electrically connected to the bipolar plate 38 via the ring connector 48 of the conductive material. .

By the way, in the microphone according to the conventional example, a pattern for mounting the FET 44 is designed on one or both surfaces of the PCB 46 around a base made of epoxy resin, but the PCB 46 is designed. In the part where the pattern (that is, the copper foil pattern) is executed, external noise is blocked by the pattern, but in the part where the pattern is not formed, there is a possibility that external high frequency noise (or electric noise) is introduced. Accordingly, high frequency electric noise is induced from the outside to the ring connector 48 and the bipolar plate 38 electrically connected to the gate 44G of the FET 44 constituting the corresponding microphone, so that the output terminal (+, Increasing electrical noise in-) degrades the signal-to-noise ratio of the microphone, resulting in overall performance degradation.

In addition, since the gate of the FET 44 applied to the microphone is open and its input impedance is several tens of kHz, it reacts to minute electrical noise of, for example, -100 dB or less. Anomalies may occur, causing poor currency.

Therefore, the present invention was made in view of the above-described prior art, and further designed a noise blocking layer for blocking external noise inflow in the middle of the PCB provided in the microphone so that external noise does not flow through the PCB. The purpose is to provide a noise inflow prevention structure of the microphone to prevent.

In order to achieve the above object, according to a preferred embodiment of the present invention in the microphone having a PCB mounted on the surface of the impedance conversion element (FET) is installed at the end of the metallic case, the PCB is the noise introduced from the outside A noise inflow preventing structure of a microphone formed in a three-layer structure including a noise blocking layer for blocking is provided.

Preferably, the noise blocking layer is formed by a thin copper plate disposed entirely on the intermediate layer of the corresponding PCB board, and the noise blocking layer is grounded to the ground potential of the corresponding PCB board.

According to the noise intrusion prevention structure of the microphone according to the present invention, while designing a three-layer PCB PCB mounted FET in the microphone, the intermediate layer is formed as a noise blocking layer and a ring connector electrically connected to the gate of the FET; External high frequency noise (or electric noise) is not induced to the bipolar plate.

1A is a view for explaining an outline of a general capacitor microphone;

1B is an equivalent circuit diagram of the microphone shown in FIG. 1A;

2A is a cross-sectional view showing an assembly structure of a microphone according to a conventional example;

FIG. 2B is a schematic diagram illustrating a state in which external noise flows into the microphone through the PCB illustrated in FIG. 2A;

3 is a cross-sectional view showing an assembly structure of a microphone to which a noise inflow preventing structure is applied according to a preferred embodiment of the present invention;

4 is a view illustrating an external noise blocking state by a PCB in which the noise inflow preventing structure shown in FIG. 3 is designed;

Figure 5a is a graph showing the high frequency noise induced frequency response characteristics of the microphone according to the conventional example shown in Figure 2a,

5B is a graph showing the high frequency noise induced frequency response characteristics of the microphone to which the noise inflow preventing structure according to the present invention shown in FIG. 3 is applied.

* Description of the symbols for the main parts of the drawings *

30: metallic case, 32: front cover member,

34: diaphragm, 36: spacer member,

38: bipolar plate, 44: FET,

46: PCB, 46b: noise blocking layer.

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

3 is a cross-sectional view illustrating an assembly structure of a microphone to which a noise inflow preventing structure is applied according to a preferred embodiment of the present invention.

Referring to the drawings, the overall configuration is the same as or similar to that of the microphone shown in FIG. 2A, and the PCB 46 is designed in a three-layer structure 46a, 46b, 46c.

That is, the PCB 46 is a ring connector electrically connected to the gate 44G of the FET 44 by designing an intermediate layer 46b positioned between the upper layer 46a and the lower layer 46c as a noise blocking layer. High frequency noise or electric noise induced by the 48 and the bipolar plate 38 is blocked (see FIG. 4).

Preferably, the noise blocking layer 46b of the PCB 46 arranges a thin copper plate as a whole in the middle of the epoxy resin forming the base of the corresponding PCB 46, and through-holes for the copper foil are provided. It is formed in such a way that the ground plane is made by connecting to the ground potential of the PCB 46 (for example, the '-' terminal of the FET 44) through a hole), and thus high frequency noise (or electric noise) introduced from the outside. ) Is blocked by the noise blocking layer 46 by about 99%.

That is, referring to the graph of FIG. 5A, in the microphone according to the conventional example illustrated in FIG. 2A, high frequency noise (or electric noise) is introduced through the PCB 46 to deteriorate response characteristics, but the response of the microphone shown in the graph of FIG. In the case of the microphone according to the present invention, it can be seen that the high frequency noise (or the electric noise) is blocked by the noise blocking layer 46c of the PCB 46, so that the response characteristic is improved.

As described above, according to the noise inflow prevention structure of the microphone according to the present invention, a high-frequency noise (or electric noise) induced by a ring connector and a bipolar plate connected to a gate of a FET mounted on the PCB by a noise blocking layer designed on the PCB. ), The signal-to-noise ratio of the corresponding microphone is remarkably improved, so that the sound quality of the communication device or audio device employing the microphone is ensured.

Claims (2)

A microphone having a PCB installed at an end of a metallic case and mounted with an impedance conversion element (FET) on its surface, The PCB is noise intrusion prevention structure of the microphone, characterized in that formed in a three-layer structure including a noise blocking layer for blocking the noise flowing from the outside. 2. The noise inflow preventing structure of a microphone according to claim 1, wherein the noise blocking layer is formed by a thin copper plate disposed entirely on the intermediate layer of the PCB, and the noise blocking layer is grounded to the ground potential of the PCB. .