CN202535535U - MEMS microphone - Google Patents

Abstract

The utility model discloses an MEMS microphone. An external packaging structure of the MEMS microphone is formed by a shell and a circuit board, and a pickup hole is formed in the packaging structure. Two or more MEMS acoustic transducers in series connection and an ASIC chip are arranged on the circuit board inside the packaging structure. According to the MEMS microphone, as the two or more MEMS acoustic transducers connected in series on the circuit board can shift a simultaneously sensed change in external sound pressure into an overall capacitance change, and the ASIC chip can detect the overall capacitance change and convert the overall capacitance change into an electrical signal for outputting, the overall sensitivity and the signal to noise ratio gain of the MEMS microphone are improved.

Description

A kind of MEMS microphone

Technical field

The utility model relates to a kind of MEMS microphone.

Background technology

Use at present more and microphone better performances is microelectromechanical-systems (Micro-Electro-Mechanical-System is called for short a MEMS) microphone, its encapsulation volume is littler than traditional electret microphone.The MEMS microphone is a kind of integrated microphone; Constitute the outer enclosure structure by shell and wiring board; Encapsulating structure is provided with sound channel; The inner wiring board of encapsulating structure is provided with a MEMS chip and an application-specific integrated circuit (ASIC) (Application Specific Intergrated Circuits is called for short ASIC) chip.This MEMS chip is made up of a MEMS acoustic transducer, comprises a rigid perforated back electrode and an elasticity vibrating diaphragm.Elasticity vibrating diaphragm on the MEMS chip is the variation of the extraneous acoustic pressure of perception effectively, and is converted into changes in capacitance, and asic chip detects this capacitance variations and is converted into signal of telecommunication output.

Because the MEMS microphone of existing structure only comprises a MEMS acoustic transducer, make the restriction that sensitivity that device is whole and signal to noise ratio will receive this single MEMS acoustic transducer.

The utility model content

The utility model provides a kind of can improve the whole sensitivity of device and the MEMS microphone of snr gain.

The MEMS microphone of the utility model; Constitute the outer enclosure structure of MEMS microphone by shell and wiring board; Said encapsulating structure is provided with the pickup hole, and the inner said wiring board of said encapsulating structure is provided with MEMS acoustic transducer and asic chip of two or more series connection.

Preferably, matched well between the MEMS acoustic transducer of said two or more series connection.

In one embodiment, the MEMS acoustic transducer of said two or more series connection constitutes independently MEMS chip respectively in substrate separately.

In one embodiment, the MEMS acoustic transducer of said two or more series connection constitutes an integral type MEMS chip in same substrate.

In one embodiment; Said asic chip comprises a buffer circuit and a DC-DC biasing circuit; After said two or more MEMS acoustic transducers were connected in series, an end was connected to said DC-DC biasing circuit output, and the other end is connected to the input of said buffer circuit.

In one embodiment, said pickup hole is arranged on the said shell.

In one embodiment, said pickup hole is arranged on the said wiring board.Wherein alternatively; This wiring board is the multi-layer sheet structure; Said pickup hole is arranged on the lower surface of said wiring board; And the upper surface at said wiring board is provided with and the corresponding a plurality of perforates of MEMS acoustic transducer number, and the equal correspondence of each perforate is positioned at the below of a MEMS acoustic transducer, in said wiring board, is provided with the raceway groove that buries that connects said pickup hole and said a plurality of perforates.

The MEMS microphone of the utility model; Through MEMS acoustic transducer and asic chip that two or more series connection are set in the circuit board; Since two or more MEMS acoustic transducers of being connected in series can perception simultaneously the variation of extraneous acoustic pressure convert the integral capacitor variation into; Detect this integral capacitor variation and be converted into signal of telecommunication output by asic chip, thereby realized the sensitivity of device integral body and the raising of snr gain.

Description of drawings

In order to be illustrated more clearly in the utility model embodiment or technical scheme of the prior art; To do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art below; Obviously, the accompanying drawing in describing below only is some embodiment of the utility model, for those of ordinary skills; Under the prerequisite of not paying creative work property, can also obtain other accompanying drawing according to these accompanying drawings.

Fig. 1 shows and utilizes a plurality of voltage source series connection to improve the circuit diagram of signal to noise ratio;

Fig. 2 shows the circuit diagram that a plurality of element of transducers are connected in series to buffer circuit and DC-DC biasing circuit;

Fig. 3 shows the sectional block diagram of the MEMS microphone of the utility model;

The MEMS microphone that Fig. 4 shows the utility model is provided with two independently schematic perspective views of MEMS chip execution mode in the circuit board;

The MEMS microphone that Fig. 5 shows the utility model is provided with three independently schematic perspective views of MEMS chip execution mode in the circuit board;

The MEMS microphone that Fig. 6 shows the utility model is provided with four independently schematic perspective views of MEMS chip execution mode in the circuit board;

Fig. 7 shows the utility model is provided with pickup hole execution mode on shell generalized section;

Fig. 8 shows the utility model is provided with pickup hole execution mode on multilayer circuit board generalized section;

Fig. 9 shows the schematic perspective view that four MEMS acoustic transducers that the MEMS microphone of the utility model is provided with in the circuit board constitute an integral type MEMS chip execution mode.

Embodiment

For the purpose, technical scheme and the advantage that make the utility model is clearer, the utility model is described in detail below in conjunction with accompanying drawing and specific embodiment.Obviously, described embodiment only is the utility model part embodiment, rather than whole embodiment.Based on the embodiment in the utility model, those of ordinary skills are not making the every other embodiment that is obtained under the creative work prerequisite, all belong to the scope of the utility model protection.

At first to the utility model based on principle describe.

A plurality of voltage source series connection that utilize as shown in Figure 1 improve in the circuit diagram of signal to noise ratio n AC power V ₁, V ₂..., V _nSeries connection drives single load R _L, wherein each in n power supply all has source impedance Z _n, total output passes to load R _L, so output voltage V _OutCan calculate through accumulation principle:

V _out＝(V ₁+V ₂+......+V _n)*R _L/(R _L+Z ₁+Z ₂+......+Z _n)

When the source impedance matched well of each power supply, V ₁=V ₂=...=V _n=V ₀, Z ₁=Z ₂=...=Z _n, and consider for the internal resistance of source is anti-load R _LQuite big, so above-mentioned equality can be reduced to:

V _out＝n*V ₀

That is: output voltage V _OutEqual the supply voltage sum of n coupling power supply.

Consider the noise voltage of each voltage source again.Because phase place is irrelevant (being that free electron or air motion are rambling) in electronics thermal noise or the acoustic resistance noise, so the total system noise can be expressed as the independent noise power sum from each contribution source.

Suppose to have only the noise voltage source of two series connection, acting in conjunction is at a muting load R _LOn, the total noise power on this element equals the power sum that each noise source is done the time spent separately, and this is different with general sinusoidal ac circuit.Specify as follows:

The total noise power V of output can use a formulate, that is:

$V^2={\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HDA0000141066690000021.png,HDA0000141066690000042.png"\; state="\{\{state\}\}">V</figure-callout>}}_1^2+{\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="HDA0000141066690000021.png"\; state="\{\{state\}\}">V</figure-callout>}}_2^2+{2\mathrm{CV}}_1{\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="HDA0000141066690000021.png"\; state="\{\{state\}\}">V</figure-callout>}}_2.$

C in the formula is a coefficient correlation, and span is [1,1], and the size of C value is expressed V ₁, V ₂Degree of correlation, C=0 when both are independently irrelevant is the situation of random noise:

$V^2={\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HDA0000141066690000021.png,HDA0000141066690000042.png"\; state="\{\{state\}\}">V</figure-callout>}}_1^2+{\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="HDA0000141066690000021.png"\; state="\{\{state\}\}">V</figure-callout>}}_2^2={\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="HDA0000141066690000021.png,HDA0000141066690000042.png"\; state="\{\{state\}\}">V</figure-callout>}}_1^2[1+{\left(\frac{V_1}{V_2}\right)}^2]$

$V=V_1{[1+{\left(\frac{V_1}{V_2}\right)}^2]}^{\frac{1}{2}}$

Take the logarithm

$20\mathrm{lgV}=20\mathrm{<figure-callout\; id="1"\; label="lg\; V"\; filenames="HDA0000141066690000021.png,HDA0000141066690000042.png"\; state="\{\{state\}\}">lg</figure-callout>}{V}_{}{}_1+10\lg [1+{\left(\frac{V_1}{V_2}\right)}^2]$

During the voltage source coupling, V ₁=V ₂, have

20lgV＝20lgV ₁+3dB

It is thus clear that the overall noise magnitude of voltage of two mutual incoherent constant amplitude noise source series connection outputs equals single noise voltage value and adds 3dB.If the irrelevant thermal noise signal source of a plurality of mutual independences, and their amplitudes are when equating basically, and similar the derivation obtains total noise source voltage dB numerical value and do

20lgV＝20lgV ₁+10lgn

(Signal to Noise Ratio SNR) can pass through output voltage V to signal to noise ratio _OutCalculate with the ratio of total noise voltage V.When voltage source mated, signal to noise ratio was sqrt (n).Particularly, the series connection signal source, coherent signal has obtained gain from cumulative signal, and it is n*V that overall signal increases, and makes total uncorrelated noise increase sqrt (n) simultaneously, and total thus signal to noise ratio snr gain is sqrt (n).Hence one can see that, can increase signal to noise ratio through Correlated Signals is sued for peace.

Fig. 2 shows the circuit diagram that a plurality of element of transducers are connected in series to buffer circuit and DC-DC biasing circuit.As shown in Figure 2; A plurality of element of transducer series connection; Each element of transducer is depicted as variable capacitor, and buffer circuit is used between high impedance element of transducer and user interface circuit, impedance matching being provided, and the DC-DC biasing circuit is used to each element of transducer bias voltage is provided.

According to above-mentioned derivation, if under the situation of the element of transducer of n matched well series connection, can access the result that total signal to noise ratio snr gain increases sqrt (n) on the one hand, this representative utilizes the theoretical maximum of the snr gain of a plurality of series connection element of transducers; The capacitance variations of whole output is n times that single transducer element output capacitance changes on the other hand, i.e. sensitivity has improved n doubly, will bring the sensitivity of system and the raising of snr gain after therefore a plurality of element of transducer series connection.And can know, under the situation of using a plurality of series connection element of transducers that not too mate, also can bring the result who improves sensitivity and snr gain.Need to prove that above-mentioned derivation is to be based upon each element of transducer to be under the normal bias condition and to obtain, therefore for keeping each element of transducer to be operated in normal condition, the output voltage of so supporting DC-DC biasing circuit should be n*V _Bias

Be based on the embodiment of the utility model that above-mentioned principle provides below.

Fig. 3 shows the sectional block diagram of the MEMS microphone of the utility model.The MEMS microphone of present embodiment; Constitute the outer enclosure structure of MEMS microphone by shell 2 and wiring board 1; Wherein, shell 2 can adopt the material of metal or plating to constitute, and can carry out bonding through scolding tin or conducting resinl between shell 2 and the wiring board 1; Make to guarantee between shell 2 and the wiring board 1 that circuit connects preferably, and realize the effectiveness that the MEMS microphone needs.Shell 2 is provided with the pickup hole 21 that receives the external sound signal, and the inner wiring board 1 of encapsulating structure is provided with the MEMS acoustic transducer 3 of an asic chip 4 and two or more series connection.

Two or more MEMS acoustic transducers are set on a wiring board can pass through cutting and separating technology, the MEMS acoustic transducer cutting and separating of desired amt is realized on different base.Each MEMS acoustic transducer constitutes independently MEMS chip respectively, and each independently realizes series connection through mutual lead-in wire between the MEMS chip.

Fig. 4 to Fig. 6 shows the utility model MEMS microphone respectively the independently stereogram of MEMS chip of two, three and four is set in the circuit board.A plurality of MEMS chips 3 are positioned at the phase adjacent locations on the wiring board 1, and series connection (series line is not shown in the drawings) each other, and asic chip 4 is near one or more MEMS chips 3.MEMS chip and asic chip can be located in the circuit board through solid brilliant, mounted on surface or other common technologies of this area, being connected and can realizing through the mode of wire-bonded between connection between the MEMS chip and MEMS chip and the asic chip.

Through the MEMS acoustic transducer of two or more series connection is set in the circuit board; Making the elasticity vibrating diaphragm of MEMS chip 3 of two or more series connection to convert the variation of the extraneous acoustic pressure of perception simultaneously into integral capacitor changes; Detect this integral capacitor by asic chip and change, and be converted into signal of telecommunication output.Derive and to know according to above-mentioned theory; The sensitivity of MEMS microphone and signal-to-noise performance will improve along with the increase of the MEMS number of chips that is provided with on the wiring board, and 2-4 the series connection MEMS chip extremely shown in Figure 6 more than Fig. 4 can reach higher sensitivity and signal-to-noise performance.

In one embodiment; Asic chip 4 can comprise a buffer circuit and a DC-DC biasing circuit; After said two or more MEMS acoustic transducers were connected in series, an end was connected to said DC-DC biasing circuit output, and the other end is connected to the input of said buffer circuit.Wherein DC-DC biasing circuit each MEMS chip of being used to series connection provides the bias voltage of operate as normal, and buffer circuit is used to high impedance MEMS chip and the subsequent applications interface circuit provides impedance matching, avoids the loss of transmission signals in transmittance process.

In one embodiment, referring to Fig. 7, Fig. 7 shows the utility model is provided with pickup hole execution mode on shell generalized section.When the external sound signal imports into through the pickup hole 21 that on shell 2, is provided with; Because the MEMS chip size is very little; Be about 1mm*1mm, can think that therefore the MEMS chip of two or more series connection of setting can receive this external sound signal simultaneously in the circuit board.The elasticity vibrating diaphragm of two or more MEMS chips 3 of series connection converts the variation of the extraneous acoustic pressure of simultaneously effective perception into the integral capacitor variation, is detected the integral capacitor variation of this series connection MEMS chip and be converted into the signal of telecommunication by asic chip 4 to export the subsequent applications interface circuit to.

Can also offer sound channel in the circuit board.Referring to Fig. 8, Fig. 8 shows the generalized section that the utility model is provided with pickup hole execution mode in the circuit board.As shown in Figure 8; Wiring board 1 is the multi-layer sheet structure; Lower surface at wiring board 1 is provided with pickup hole 11; Upper surface at wiring board 1 is provided with and the corresponding a plurality of perforates 12 of MEMS chip number; Each perforate 12 all is positioned at the below of a MEMS chip, be connected through the raceway groove 13 that buries in the wiring board 1 between pickup hole 11 and the perforate 12, like this by pickup hole 11, bury and constitute a long and narrow sound channel between raceway groove 13 and a plurality of perforate 12; The external sound signal that gets into from pickup hole 11 directly clashes into the elasticity vibrating diaphragm of each MEMS chip via a plurality of perforates 12 again after burying raceway groove 13, thereby the integral capacitor that causes the MEMS chip 3 of two or more series connection on wiring board 1 changes.Asic chip 4 will detect this integral capacitor variation equally and be converted into the signal of telecommunication and export the subsequent applications interface circuit to.

Need to prove that the utility model is not defined as multi-layer sheet structure wiring board shown in Figure 8, on the wiring board of two-ply and lamina structure, can realize long and narrow sound channel equally.

Because the manufacturing of MEMS chip can be adopted and similar mature technology of integrated circuit manufacturing or technology; Therefore the MEMS chip that produces is very high in the consistency of aspect of performances such as sensitivity, signal to noise ratio, and the MEMS chip that can be considered same batch is a matched well.Adopt the MEMS chip of a plurality of matched well to promote so that the sensitivity of the MEMS microphone of the utility model and signal-to-noise performance obtain the best.Certainly, the MEMS chip of two or more series connection does not need matched well in the utility model MEMS microphone, nonetheless, still can improve device whole sensitivity and snr gain.

In another execution mode, can design chip structure with two or more MEMS acoustic transducers, the chip internal that is connected in series between each acoustic transducer is realized.As shown in Figure 9, Fig. 9 shows the schematic perspective view that four MEMS acoustic transducers that the MEMS microphone of the utility model is provided with in the circuit board constitute integral type MEMS chip execution mode jointly.Four MEMS acoustic transducers constitute an integral type MEMS chip in same substrate.In this execution mode between each MEMS transducer owing to need not connect through the wire-bonded mode of outside, thereby reduced the quantity of postorder wire-bonded, the cabling that guarantees MEMS microphone inner lead has reduced the probability that interference signal imports freely.This execution mode of while has also reduced the chip of reserving on the wafer to be cut apart, and helps the more acoustic transducers of preparation on the wafer of same size.Therefore this execution mode can provide production efficiency and more low production cost more efficiently.

Need to prove; The MEMS acoustic transducer of two or more series connection that the MEMS microphone of the utility model is provided with in the circuit board; It also can be the combination of above-mentioned two kinds of execution modes; That is: a plurality of MEMS acoustic transducers of part constitute integral type MEMS chip in same substrate, and remainder MEMS acoustic transducer is constituting independently MEMS chip respectively in the substrate respectively separately.

In sum; The MEMS microphone of the utility model; Through MEMS acoustic transducer and asic chip that two or more series connection are set in the circuit board; Since two or more MEMS acoustic transducers of being connected in series can perception simultaneously the variation of extraneous acoustic pressure convert integral capacitor into and change, detect this integral capacitor by asic chip and change and be converted into signal of telecommunication output, thereby realized the sensitivity of device integral body and the raising of snr gain.

The above; Be merely the embodiment of the utility model; But the protection range of the utility model is not limited thereto; Any technical staff who is familiar with the present technique field can expect changing or replacement in the technical scope that the utility model discloses easily, all should be encompassed within the protection range of the utility model.

Claims (8)

1. MEMS microphone; Constitute the outer enclosure structure of MEMS microphone by shell and wiring board; Said encapsulating structure is provided with the pickup hole; It is characterized in that the inner said wiring board of said encapsulating structure is provided with MEMS acoustic transducer and asic chip of two or more series connection.

2. MEMS microphone according to claim 1 is characterized in that, matees between the MEMS acoustic transducer of said two or more series connection.

3. MEMS microphone according to claim 1 is characterized in that, the MEMS acoustic transducer of said two or more series connection constitutes independently MEMS chip respectively in substrate separately.

4. MEMS microphone according to claim 1 is characterized in that, the MEMS acoustic transducer of said two or more series connection constitutes an integral type MEMS chip in same substrate.

5. MEMS microphone according to claim 1; It is characterized in that; Said asic chip comprises a buffer circuit and a DC-DC biasing circuit; After said two or more MEMS acoustic transducers were connected in series, an end was connected to said DC-DC biasing circuit output, and the other end is connected to the input of said buffer circuit.

6. according to each described MEMS microphone of claim 1-5, it is characterized in that said pickup hole is arranged on the said shell.

7. according to each described MEMS microphone of claim 1-5, it is characterized in that said pickup hole is arranged on the said wiring board.

8. MEMS microphone according to claim 7; It is characterized in that; Said wiring board is the multi-layer sheet structure, and said pickup hole is arranged on the lower surface of said wiring board, and is provided with the perforate with the consistent quantity of MEMS acoustic transducer number at the upper surface of said wiring board; And each perforate all is positioned at the below of its corresponding MEMS acoustic transducer, in said wiring board, is provided with the raceway groove that buries that connects said pickup hole and said perforate.

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