CN201066929Y

CN201066929Y - Capacitance microphone capable of filtering EMI noise

Info

Publication number: CN201066929Y
Application number: CNU2007201106441U
Authority: CN
Inventors: 陈恕华; 徐峰; 王廷华
Original assignee: NINGBO XINFENGTAI ELECTRICAL APPLIANCE CO Ltd
Current assignee: NINGBO XINFENGTAI ELECTRICAL APPLIANCE CO Ltd
Priority date: 2007-06-14
Filing date: 2007-06-14
Publication date: 2008-05-28
Anticipated expiration: 2017-06-14

Abstract

The utility model discloses a capacitor microphone which can filter out EMI noise. The utility model comprises a parallel plate capacitor and an electric signal processing component. The parallel plate consists of a vibration diaphragm support ring, a vibration diaphragm, an insulating washer and a back polar plate and is used for ultrasound-electricity conversion. The electric signal processing component consists of a field effect transistor FEF which is mounted on a printed circuit board PCB, a filter capacitor C1 and a filter capacitor C2. The two ends of the parallel plate capacitor are respectively connected with the grid G and the source cathode S of the FET. The filter capacitor C2 is paralleled between the source cathode S and the drain D of the FET. The drain D of the FET is connected with a connection terminal. The source cathode S of the FET is connected with the other end of connection terminal. The filter capacitor C1 is paralleled between the grid G and the source cathode S of the FET. The capacitor microphone can excellently filter out the EMI signal merged into the grid G and the drain D of the FET and then completely eliminate interference noises; in addition, the structure of the circuit is simple; filter components are few and the cost is low.

Description

The condenser microphone of energy filtering EMI noise

Technical field

The utility model relates to a kind of condenser microphone that is used for mobile phone, earphone, blue tooth products and automobile communication electronic product etc., specifically is a kind of condenser microphone of energy filtering EMI noise.

Background technology

At present, electronic product is fairly obvious to the trend of high frequency development, as the mobile phone of mobile communication from 800MHZ to 3GHZ, so just press for the ability that microphone possesses these electromagnetic interference of filtering.

And the condenser microphone that is used for mobile phone, earphone, blue tooth products and automobile communication electronic product etc. of prior art generally is divided into cavity type and SMD two kinds by its assembly structure:

The cavity type condenser microphone has comprised acoustic-electric transformation and the plane-parallel capacitor M that is made up of vibrating diaphragm support ring, vibrating diaphragm, insulating washer and back pole plate.Its printing board PCB is a single face, and it does not have filter elements such as electric capacity, and the volume ratio of field-effect transistor FET is bigger, easily receives the EMI interference signal, so this microphone can not filtering EMI interference noise.

Common SMD condenser microphone has comprised acoustic-electric transformation and the plane-parallel capacitor of being made up of vibrating diaphragm support ring, vibrating diaphragm, insulating washer and back pole plate equally, its printing board PCB generally adopts i.e. two laminates of the two-sided shoe copper of expoxy glass printed circuit board (PCB), compare with the cavity type condenser microphone, SMD condenser microphone field-effect transistor FET volume is less relatively, surface mount has filter capacitor, can filtering part EMI interference noise.But all filter elements of common SMD condenser microphone of prior art are to be mounted between the drain D of field-effect transistor FET and the source S, and have ignored the EMI noise filtering between field-effect transistor FET grid G and the source S.Its shortcoming is apparent: because FET itself is exactly the field-effect transistor of two PN junctions, after sealing in the TDMA radiofrequency signal process field-effect transistor FET of EMI signal such as gsm communication in the mobile phone of field-effect transistor FET grid G, under the detecting action of field-effect transistor FET, produce the modulated pulse signal in the audiorange and produced noise, and this noise is in the audiorange, the electric capacity of incorporating between the drain D of field-effect transistor FET and source S can not be with its filtering, if the words of filtering, the useful audio signal that receives also can be filtered out together, lost the effect of condenser microphone, so, the common SMD condenser microphone of prior art can not filtering seals in the EMI signal of field-effect transistor FET grid G, so still filtering EMI noise well of this kind microphone.

One tame electronics corporation of external some major company such as Korea S changes the design of printing board PCB into four laminates by two laminates, the centre is two-layer uses as screen, in circuit, form π type RC filter circuit by capacitor C 2, resistance R 1, capacitor C 3, come filtering EMI interference signal.But this circuit structure complexity, filter element is many, and cost greatly improves, moreover mounting so many electronic components can't do SMD condenser microphone product little.

The utility model content

The technical problems to be solved in the utility model is, overcome the shortcoming of above prior art, provide a kind of filtering effectively to seal in the EMI signal of field-effect transistor FET grid G and drain D, and then eliminate interference noise fully and circuit structure is simple, filter element is few, the condenser microphone of the energy filtering EMI noise that cost is low.

Technical solution of the present utility model is, circuit structure to the SMD condenser microphone printed circuit board (PCB) of prior art improves, a kind of condenser microphone with energy filtering EMI noise of following structure is provided, comprise by an acoustic-electric transformation and by the vibrating diaphragm support ring, vibrating diaphragm, the plane-parallel capacitor M that insulating washer and back pole plate are formed, by the field-effect transistor FET and the filtering capacitor C1 that are mounted on the printing board PCB, the signal of telecommunication processing components that C2 constitutes, described plane-parallel capacitor M two ends connect grid G and the source S of field-effect transistor FET respectively, described filtering capacitor C2 is connected in parallel between the source S and drain D of field-effect transistor FET, the drain D of described field-effect transistor FET is connected with terminals, the source S of described field-effect transistor FET is connected with another terminals, and described filtering capacitor C1 is connected in parallel between the grid G and source S of field-effect transistor FET.

After adopting above structure, the condenser microphone of the utility model energy filtering EMI noise is compared with above-described prior art, has the following advantages:

Because filtering capacitor C1 is connected in parallel between the grid G and source S of field-effect transistor FET, compare with above-mentioned common SMD condenser microphone, effectively filtering comprise low frequency and mobile communication, high-frequency radio frequency during equipment such as Bluetooth communication use disturbs, filtering seals in the EMI signal of field-effect transistor FET grid G effectively, and and the former source S of field-effect transistor FET and the synergy of the filtering capacitor C2 between the drain D of being connected in parallel on, but the radio frequency interference noise of filtering wide region, can eliminate the interference noise in the microphone fully, obtain the effect of very desirable filtering EMI.

And compare with the SMD condenser microphone of above-mentioned four laminates, the condenser microphone circuit structure of the utility model energy filtering EMI noise is very simple, and filter element is few, and cost is low.

Simultaneously, because circuit structure of the present utility model is very simple, filter element is few, so can dwindle the volume of this condenser microphone is corresponding, as making the product of diameter below 4mm, to adapt to the needs of various device, make the utility model can filtering the use face of condenser microphone of EMI noise more extensive.

As improvement, described filtering capacitor C1 preferably adopts the electric capacity of 5PF～25PF, and its filtering EMI anti noise is better in this scope.

Description of drawings

Fig. 1 is the circuit theory schematic diagram of the cavity type condenser microphone of prior art.

Fig. 2 is the circuit theory schematic diagram of the common SMD condenser microphone of prior art.

Fig. 3 is the circuit theory schematic diagram of SMD condenser microphone of four layer printed circuit PCB of prior art.

Fig. 4 be the utility model can filtering a kind of overall structure cross-sectional schematic of specific embodiment of condenser microphone of EMI noise.

Fig. 5 is the circuit theory schematic diagram of the condenser microphone of the utility model energy filtering EMI noise.

Fig. 6 is the circuit working principle schematic of the condenser microphone of the utility model energy filtering EMI noise.

Embodiment

Below in conjunction with the drawings and specific embodiments the utility model is described in further detail.

In Fig. 1, the cavity type condenser microphone of prior art does not have filter elements such as electric capacity, plane-parallel capacitor M two ends connect grid G and the source S of field-effect transistor FET respectively, 1. the drain D of field-effect transistor FET is connected with terminals, and 2. the source S of field-effect transistor FET is connected with another terminals.Wherein dotted line is represented the shell of microphone, and the components and parts in the dotted line are (following all circuit theory diagrams and circuit working schematic diagram are all identical) all in the enclosure.

In Fig. 2, the plane-parallel capacitor M two ends of the common SMD condenser microphone of prior art connect grid G and the source S of field-effect transistor FET respectively, described filtering capacitor C1, C2 all are connected in parallel between the source S and drain D of field-effect transistor FET, 1. the drain D of described field-effect transistor FET is connected with terminals, and 2. the source S of described field-effect transistor FET is connected with another terminals.

In Fig. 3, the SMD condenser microphone of four layer printed circuit board PCB of prior art, form π type RC filter circuit by capacitor C 2, resistance R 1, capacitor C 3, that is: described plane-parallel capacitor M two ends connect grid G and the source S of field-effect transistor FET respectively, described filtering capacitor C1, C2, C3 all are connected in parallel between the source S and drain D of field-effect transistor FET, 1. be connected with terminals behind the drain D series resistance R1 of described field-effect transistor FET, 2. the source S of described field-effect transistor FET is connected with another terminals.

Fig. 4 show the utility model can filtering a kind of overall structure of specific embodiment of condenser microphone of EMI noise: the vibration component that vibrating diaphragm support ring 2 and vibrating diaphragm 3 constitute is located in the metal shell 1, vibrating diaphragm 3 usefulness glue curing are on support ring 2, be close to insulating washer 4 above the vibrating diaphragm 3, be close to back pole plate 5 above the insulation spacer 4.Vibrating diaphragm support ring 2, vibrating diaphragm 3, insulating washer 4 and back pole plate 5 have been formed the plane-parallel capacitor M of acoustic-electric transformation.Back pole plate 5 close-fittings are in ring 6 is moulded in insulation, be close to polar ring 7 above the back pole plate 5, the gap that can leave between ring 6 the interior circle in 5 is moulded in the cylindrical of polar ring 7 and insulation, be close to printing board PCB above the polar ring 7, the printing board PCB inner surface is pasted with field-effect transistor FET and filtering capacitor C1, C2.In Fig. 4, field-effect transistor FET is labeled as 50, and C2 is labeled as 60, and capacitor C 1 is labeled as 61, and printing board PCB is labeled as 8.Printing board PCB generally adopts i.e. two laminates of the two-sided shoe copper of expoxy glass printed circuit board (PCB).The field-effect transistor FET and filtering capacitor C1, the C2 that are mounted on the printing board PCB constitute signal of telecommunication processing components.Following plane-parallel capacitor M two ends connect grid G and the source S of field-effect transistor FET respectively, and described connection is connected with printing board PCB by polar ring 7, and the connection of other element in the following shell connects by printing board PCB.The sound hole face of the shell 1 i.e. bottom surface of the shell 1 among the figure posts one deck water proof and dust proof non woven fabric 9.

As shown in Figure 5, described plane-parallel capacitor M two ends connect grid G and the source S of field-effect transistor FET respectively, described filtering capacitor C2 is connected in parallel between the source S and drain D of field-effect transistor FET, 1. the drain D of described field-effect transistor FET is connected with terminals, 2. the source S of described field-effect transistor FET is connected with another terminals, and described filtering capacitor C1 is connected in parallel between the grid G and source S of field-effect transistor FET.Described filtering capacitor C1 can adopt the electric capacity of 5PF～25 PF.Representative instance of the present utility model is the multilayer ceramic capacitor (MLCC) that adopts 10PF.Described filtering capacitor C2 can adopt the electric capacity of 33PF～10NF.

As shown in Figure 6, operation principle of the present utility model is as follows:

2. 1. external circuit be connected with the circuit of this condenser microphone printing board PCB with terminals by terminals, and external circuit puts on the 2.0V direct voltage between the drain D and source S of field-effect transistor FET by load resistance RL.Cause its vibration when the outside sound signal passes on the vibrating diaphragm 3, vibration has changed the appearance value of plane-parallel capacitor M, has just produced the signal of telecommunication that changes at the two ends of plane-parallel capacitor M, has so just realized by the conversion of sound to the signal of telecommunication.The signal of telecommunication passes to the grid G of field-effect transistor FET, carrying out impedance conversion and electric current amplifies, like this in the drain D of field-effect transistor FET and the electric current between the source S input electrical signal real-time change along with grid G, the electric current that changes has formed the voltage that changes at drain D and the source S two ends of field-effect transistor FET, by capacitor C 1 this signal of telecommunication of output.If extraneous EMI signal will seal in the grid G of field-effect transistor FET, will be filtered by C1, if seal in, will be filtered by capacitor C 2 from the drain D of field-effect transistor FET, realized the purpose of filtering EMI noise.Described EMI, general is interpreted as: the interference phenomenon that electromagnetic wave and electronic component interaction produce is called EMI.

Claims

1. the condenser microphone of an energy filtering EMI noise, comprise by an acoustic-electric transformation and by vibrating diaphragm support ring (2), vibrating diaphragm (3), the plane-parallel capacitor M that insulating washer (4) and back pole plate (5) are formed, by the field-effect transistor FET (50) and the filtering capacitor C1 (61) that are mounted on the printing board PCB (8), the signal of telecommunication processing components that C2 (60) constitutes, described plane-parallel capacitor M two ends connect grid G and the source S of field-effect transistor FET (50) respectively, described filtering capacitor C2 (60) is connected in parallel between the source S and drain D of field-effect transistor FET (50), the drain D of described field-effect transistor FET (50) is connected with terminals, the source S of described field-effect transistor FET (50) is connected with another terminals, it is characterized in that: described filtering capacitor C1 (61) is connected in parallel between the grid G and source S of field-effect transistor FET (50).

2. the condenser microphone of energy filtering EMI noise according to claim 1, it is characterized in that: described filtering capacitor C1 (61) adopts the electric capacity of 5PF～25PF.

3. the condenser microphone of energy filtering EMI noise according to claim 2, it is characterized in that: described filtering capacitor C1 (61) adopts the electric capacity of 10PF.