MEMS数字麦克风基本知识课件

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MEMS麦克风

MEMS麦克风•MEMS（微型机电系统）麦克风是基于MEMS技术制造的麦克风，简单的说就是一个电容器集成在微硅晶片上，可以采用表贴工艺进行制造,能够承受很高的回流焊温度,容易与CMOS 工艺及其它音频电路相集成, 并具有改进的噪声消除性能与良好的RF 及EMI 抑制性能.MEMS麦克风的全部潜能还有待挖掘，但是采用这种技术的产品已经在多种应用中体现出了诸多优势，特别是中高端手机应用中。

目录•MEMS麦克风的发展前景MEMS麦克风的优势•目前，实际使用的大多数麦克风都是ECM(驻极体电容器)麦克风，这种技术已经有几十年的历史。

ECM 的工作原理是利用驻有永久电荷的聚合材料振动膜。

与ECM的聚合材料振动膜相比，MEMS麦克风在不同温度下的性能都十分稳定，其敏感性不会受温度、振动、湿度和时间的影响。

由于耐热性强，MEMS麦克风可承受260℃的高温回流焊，而性能不会有任何变化。

由于组装前后敏感性变化很小，还可以节省制造过程中的音频调试成本。

MEMS麦克风需要ASIC提供的外部偏置，而ECM没有这种偏置。

有效的偏置将使MEMS麦克风在整个操作温度范围内都可保持稳定的声学和电气参数，还支持具有不同敏感性的麦克风设计。

传统ECM的尺寸通常比MEMS麦克风大，并且不能进行SMT（表面贴装技术）操作。

在MEMS麦克风的制造过程中，SMT回流焊简化了制造流程，可以省略一个目前通常以手工方式进行的制造步骤。

在ECM麦克风内，必须添加进行信号处理的电子元件；而在MEMS麦克风中，只需在芯片上添加额外的专用功能即可。

与ECM相比，这种额外功能的优点是使麦克风具有很高的电源抑制比，能够有效抑制电源电压的波动。

另一个优点是，集成在芯片上的宽带RF抑制功能，这一点不仅对手机这样的RF应用尤其重要，而且对所有与手机操作原理类似的设备（如助听器）都非常重要。

MEMS麦克风的小型振动膜还有另一个优点，直径不到1mm的小型薄膜的重量同样轻巧，这意味着，与ECM相比，MEMS麦克风会对由安装在同一PCB上的扬声器引起的PCB 噪声产生更低的振动耦合。

来自ST的MEMS麦克风使用指南,含参数计算

February 2017DocID025704 Rev 2 1/20 AN4426 Application note Tutorial for MEMS microphonesIntroductionThis application note serves as a tutorial for MEMS microphones, providing general characteristics of these devices, both acoustic and mechanical, as well as summarizing the portfolio available from ST. MEMS microphones target all audio applications where small size, high sound quality, reliability and affordability are key requirements.ST's MEMS microphones are designed, developed and manufactured within ST, creating an industry-unique, vertically integrated supply chain. Both analog and digital-input, top and bottom-port solutions are available.Our best-in-class AOP and SNR make ST’s MEMS microphones suitable for applications that require a very high dynamic range, improving the audio experience in any environment. Matching very tightsensitivity allows optimizing beamforming and noise cancelling algorithms for multi-microphone arrays. Low power consumption allows extending battery life.Contents AN4426 Contents1Mechanical specifications, construction details (4)2Acoustic parameters (11)2.1Sensitivity (11)2.2Directionality (11)2.3SNR (12)2.4Dynamic range and acoustic overload point (12)2.5Equivalent input noise (13)2.6Frequency response (15)2.7Total harmonic distortion (16)2.8PSRR and PSR (16)3MEMS microphone portfolio (17)4Revision history (19)2/20 DocID025704 Rev 2AN4426 List of figures List of figuresFigure 1: MEMS microphone inside package (4)Figure 2: MEMS transducer mechanical specifications (4)Figure 3: Capacitance change principle (5)Figure 4: 4 x 5 package (5)Figure 5: 3 x 4 metal cap package - bottom port (6)Figure 6: 3 x 4 package - top port (6)Figure 7: 2 x 3 package - bottom port (7)Figure 8: Faraday cage in ST’s MEMS microphones (7)Figure 9: RF immunity simulation (8)Figure 10: EMC test setup (8)Figure 11: RF test disturbance signal with sinusoidal pattern (9)Figure 12: RF immunity test results - MP34DT04 (9)Figure 13: RF test disturbance signal @ 217 Hz burst pattern (10)Figure 14: RF immunity of analog differential microphones (10)Figure 15: Omnidirectional microphone (11)Figure 16: A-weighted filter response (12)Figure 17: Acoustic and electrical relationship - analog (13)Figure 18: Acoustic and electrical relationship - digital (14)Figure 19: MP45DT02-M frequency response (15)Figure 20: MEMS microphone portfolio (17)Figure 21: MEMS microphone notation (17)DocID025704 Rev 2 3/201 Mechanical specifications, construction detailsA microphone is a dual-die device consisting of two components, the integrated circuit andthe sensor, which are housed in a package using techniques that are proprietary to ST.ASICintegratedThe sensor uses MEMS technology (Micro-Electrical-Mechanical Systems) and it isbasically a silicon capacitor. The capacitor consists of two silicon plates/surfaces. Oneplate is fixed while the other one is movable (respectively, the green plate and the grey oneshown in the following figure). The fixed surface is covered by an electrode to make itconductive and is full of acoustic holes which allow sound to pass through. The movableplate is able to move since it is bonded at only one side of its structure. A ventilation hole,allows the air compressed in the back chamber to flow out and consequently allows themembrane to move back. The chamber allows the membrane to move inside but also, incombination with the chamber created by the package will affect the acoustic performanceof the microphones in terms of frequency response and SNR.Figure 2: MEMS transducer mechanical specificationsSo basically the microphone MEMS sensor is a variable capacitor where the transductionprinciple is the coupled capacitance change between a fixed plate (back plate) and amovable plate (membrane) caused by the incoming wave of the sound.4/20 DocID025704 Rev 2Figure 3: Capacitance change principleThe integrated circuit converts the change of the polarized MEMS capacitance into a digital (PDM modulated) or analog output according to the microphone type. Finally the MEMS microphone is housed in a package with the sound inlet placed in the top or in the bottom part of the package, hence the top-port or bottom-port nomenclature of the package. ST manufactures microphones using industry-wide techniques, but also has developed innovative packaging to achieve improved performance of the microphones. Packaging techniques will be discussed in further detail.The 4x5 package is widely used to house the digital microphone MP45DT02-M. It is a common packaging technique in a top-port configuration where the ASIC is placed under the sound inlet with glue on top (glob top) in order to protect the circuit from light and the MEMS sensor is placed beside the integrated circuit. The two silicon components are fixed to the substrate and the pads of the device are on the bottom side. The resonant chambers are identified depending on the position of each chamber with respect to the membrane and the incoming sound. In this case, considering the incoming direction of the sound, the front chamber is created by the package and the chamber inside the MEMS, behind the MEMS membrane, is the back chamber. This configuration allows protecting the MEMS from dust and particles falling into the package but results in a low SNR and frequency response with a peak in the audio band.Figure 4: 4 x 5 packageThe 3x4 package is used in ST to produce both the bottom and the top-port digital microphones, MP34DB02 and MP34DT01-M, MP34DT04/-C1, and MP34DT05. Considering the bottom configuration first, this structure is depicted in the following figure. The ASIC and the MEMS sensor are fixed to the substrate and the pads of the device are on bottom side as well. The sound inlet is obtained by drilling the substrate according to the position of the MEMS sensor. The package encloses all the components. In this configuration the front chamber is the cavity of the MEMS sensor and the package creates the back chamber. This design optimizes the acoustic performance of the microphone in terms of SNR and also allows obtaining a flat response across the entire audio band. The drawback of this solution is represented by the assembly of this microphone. Usually theDocID025704 Rev 2 5/20bottom-port microphones are soldered on the PCB. The thickness of the board modifies thevolume of the front chamber, degrading the flat response of this type of microphone (referto AN4427, “Gasket design for optimal acoustic performance in MEMS microphones” fordetails). In order to minimize the artifacts caused by this environment, a flex cable isrecommended to be used. Additionally, the bottom-port microphones have a ringed metalpad around the hole. A very careful soldering process is required to avoid dust or solderingpaste from entering in the sound port, damaging the MEMS membrane.Figure 5: 3 x 4 metal cap package - bottom portThe 3x4 top-port configuration is basically a mirrored bottom-port microphone. The ASICand the sensor are placed close to each other, the sensor is still under the sound inlet butthese two components are attached to the top of the structure, in other words, the ASICand MEMS are fixed to the package lid, not to the substrate. The pads are on the substrateand thus on the bottom side of the microphone. This configuration, covered by ST patents,allows optimizing all the benefits of the bottom-port microphone in terms of acousticperformance (i.e. maximized SNR and flat band) and all the benefits related to the top-portconfiguration during the assembly process.Figure 6: 3 x 4 package - top port6/20 DocID025704 Rev 2A smaller package, 2.5 x 3.35 mm, has been introduced in ST's product portfolio (for simplicity referred to as 2x3, see Figure 7: "2 x 3 package - bottom port"). This package is a bottom-port configuration with the same internal construction as the 3 x 4 bottom-port package and it is used for the analog differential microphones MP23AB01DM/DH and analog single-ended microphone MP23AB02B. As a result of the 2x3 bottom-port package and differential output configuration, the MP23AB01DH is the best microphone provided by ST in terms of SNR and AOP.Figure 7: 2 x 3 package - bottom portMEMS microphones housed in a plastic package are protected from radiated disturbances by embedding in the plastic package a metal shield which serves as a Faraday cage. The model in the following figure shows how the Faraday cage is implemented in ST’s plastic packages.Figure 8: Faraday cage in ST’s MEMS microphonesThe next figure shows the simulation of an electric field in open space. By applying an electric field source outside the microphone package, the Faraday cage is able to considerably attenuate the field inside the microphone structure. The temperature grade of the E field is an easy way to plot the results.DocID025704 Rev 2 7/20Figure 9: RF immunity simulationIn addition to the simulation, ST has a dedicated test to evaluate immunity, “Microphonedurability to EMC disturbances”.Microphones are subjected to RF disturbances using a proper jig with the following setup.Basically the test consists of placing the microphone under an antenna radiating adisturbance signal of 1 kHz AM modulated in the range [0.8, 3] GHz. The RF amplitudediffers depending on the frequency range according to the following criteria:•+33 dBm in the range [0.8, 2.4]•+17 dBm in the range [2.4, 3.0]8/20 DocID025704 Rev 2Figure 11: RF test disturbance signal with sinusoidal patternThe carrier of the disturbance is 1 kHz since it is an audio signal. Hence, the RF immunity of the microphone is evaluated by measuring the residual of the carrier at the output of the microphone. The next figure shows the result of the peak at 1 kHz measured when applying the RF disturbance on top of an MP34DT04.In parallel with the sinusoidal pattern, another 217 Hz burst pattern used to test the RF immunity is shown in the following figure.•The RF amplitude (power): +33 dBm•Carrier frequency: 700 MHz ~ 2.5 GHz•GSM burst frequency: 217 Hz pattern (see below)DocID025704 Rev 2 9/20Figure 13: RF test disturbance signal @ 217 Hz burst patternFigure 14: RF immunity of analog differential microphones10/20 DocID025704 Rev 2AN4426Acoustic parametersDocID025704 Rev 211/202Acoustic parameters2.1SensitivityThe sensitivity is the electrical signal at the microphone output to a given acoustic pressure as input. The reference of acoustic pressure is 1 Pa or 94 dBSPL @ 1 kHz. The sound pressure level, expressed in decibel, dBSPL=20*Log(P/Po) where Po = 20 µPa is the threshold of hearing. 20*Log(1Pa/20µPa) = 94 dBSPL • For analog microphones the sensitivity is expressed in mV RMS /Pa or dBV/Pa •For digital microphones the sensitivity is expressed in dBFSdBV ≠ dBFS. It is not correct to compare different units. As given in the above equations, dBV is in reference to 1V RMS instead of dBFS where the reference is the digital full scale.2.2 DirectionalityThe directionality indicates the variation of the sensitivity response with respect to thedirection of the arrival of the sound. MEMS microphones from ST are omnidirectional which means that there is no sensitivity change to every different position of the source of thesound in space. The directionality can be indicated in a Cartesian axis as sensitivity drift vs. angle or in a polar diagram showing the sensitivity pattern response in space.The following figure depicts the directionality in these two reference systems.Figure 15: Omnidirectional microphoneAcoustic parametersAN442612/20DocID025704 Rev 22.3 SNRThe signal-to-noise ratio specifies the ratio between a given reference signal to the amount of residual noise at the microphone output. The reference signal is the standard signal at the microphone output when the sound pressure is 1Pa @ 1 kHz (microphone sensitivity). The noise signal (residual noise) is the microphone electrical output at silence.This parameter includes both the noise of the MEMS element and the ASIC. Concerning this sum, the main contribution to noise is given by the MEMS sensor, the integrated circuit contribution can be considered negligible. Typically, the noise level is measured in an anechoic environment and A-weighting the acquisition. The A-weighted filter corresponds to the human ear frequency response.Figure 16: A-weighted filter response2.4 Dynamic range and acoustic overload pointThe dynamic range is the difference between the minimum and maximum signal that the microphone is able to generate as output. • The minimum signal is the smallest audio signal that the microphone can generate distinctly from noise. In other words, the minimum signal is equivalent to the residual noise.•The maximum audio signal is that which the microphone can generate withoutdistortion. It is also called acoustic overload point (AOP). Actually, the specification allows up to 10% in terms of distortion at the acoustic overload point.AN4426 Acoustic parameters2.5 Equivalent input noiseA microphone is a sound-to-electricity transducer which means that any output signalcorresponds to a specific sound as input. The equivalent input noise (EIN) is the acousticlevel, expressed in dBSPL, corresponding to the residual noise as output.For example, a digital microphone with a sensitivity of -26 dBFS and a 63 dB as SNR:Residual noise = -26 - 63 = -89 dBFS this sum transposed in the acoustic domain is:EIN = 94 - 63= 31 dBSPLThe following figures summarize the relationship between the acoustic and electricdomains related to each of the parameters listed above. Figure 17: "Acoustic and electricalrelationship - analog" and Figure 18: "Acoustic and electrical relationship - digital" illustratethis for analog and digital microphones, respectively.Figure 17: Acoustic and electrical relationship - analogDocID025704 Rev 2 13/20Acoustic parametersAN442614/20DocID025704 Rev 29030-90-3094dBSPL AOPS N R =63d B-26dBFSD y n a m i c R a n g e =89d BSensitivity EIN Residual noiseAN4426 Acoustic parameters 2.6 Frequency responseThe frequency response of a microphone in terms of magnitude indicates the sensitivityvariation across the audio band. This parameter also describes the deviation of the outputsignal from the reference 0 dB. Typically, the reference for this measurement is exactly thesensitivity of the microphone @ 0 dB = 94 dBSPL @ 1 kHz. The frequency response of amicrophone can vary across the audio frequency band depending on three parameters: theventilation hole, the front chamber geometry, and back chamber geometry. The ventilationhole and the back chamber geometry have an impact on the behavior at low frequencieswhile the behavior at high frequencies depends on the geometry of the front chamber only.Behavior at high frequencies can be a resonance peak caused by the Helmholtz effect.This resonance is the phenomenon of air resonance in a cavity. As a matter of fact, itdepends on the dimension of the front chamber of the microphone, representing the soundcavity in which the air resonates. A microphone with a flat frequency response is suitablewhen natural sound and high intelligibility of the system is required. The following figureshows the response of the MP45DT02-M. It shows a roll-off at low frequencies and a peakaround 18 kHz caused by the large front chamber of this microphone.Figure 19: MP45DT02-M frequency responseThe frequency response of a microphone in terms of phase indicates the phase distortionintroduced by the microphone. In other words, the delay between the sound wave movingthe microphone membrane and the electrical signal at the microphone output results in thatthis parameter includes both the distortion due to the membrane and the ASIC.DocID025704 Rev 2 15/20Acoustic parametersAN442616/20DocID025704 Rev 22.7 Total harmonic distortionTHD is the measurement of the distortion affecting the electrical output signal of themicrophone given an undistorted acoustic signal as input. THD+N is expressed as a ratio of the integer in a specified band of the power of the harmonics plus the power of noise and the power of the undistorted signal (fundamental). Equation 1TTTTTT +NN (%)=∑PPPPPPPPPP (TTHHPPHHPPHHHH HH HH )+PPPPPPPPPP (NNPPHH HH PP )NN nn−1PPPPPPPPPP (FFFFHHFFHHHHPPHHFFHHFF )Typically ST indicates the THD+N measured in the (50 Hz - 4 kHz) band for a given undistorted signal 1 kHz @ 100 dBSPL.2.8 PSRR and PSRPSRR indicates the capability of the ASIC to reject noise added to the supply voltage. To evaluate this parameter, a tone of V IN = 100 mVpk-pk @ 217 Hz (GSM switching frequency in phone applications) is added to the power supply and then the amplitude of the output is measured. The added noise can be either a square wave or sinusoidal wave. Typically the square wave is preferred since it is the worst case.PSRR is the ratio of the residual noise amplitude at the microphone output (V OUT @ 217 Hz) to the added spurious signal on the supply voltage. It is typically expressed in dB as given in the equation below: Equation 2PPPPPPPP =20 xx log �(VV OOOOOO @217TTHH )(VV IINN @217TTHH )�The capability of the integrated circuit to reject noise added to the supply voltage can also be expressed with another parameter that is the PSR. Basically it is simply a measurement of the output when noise of 100 mVpk-pk @ 217 Hz is superposed to the supply voltage. Consequently expressed in dB as given in the equation below: Equation 3 PPPPPP =20 xx log[VV OOOOOO @217TTHH ]To evaluate either the PSRR or PSR, proper sealing of the sound inlet or measurements performed in an anechoic chamber are recommended to avoid mixing the superimposed noise with that of the noise floor of the output. Finally, in the microphone datasheets PSR is commonly given instead of PSRR.AN4426 MEMS microphone portfolio3 MEMS microphone portfolioFigure 20: MEMS microphone portfolioST’s portfolio includes digital and analog microphones. The commercial products arenamed using the notation depicted in the following figure.Figure 21: MEMS microphone notationDocID025704 Rev 2 17/20MEMS microphone portfolio AN442618/20DocID025704 Rev 2The following table provides a complete overview of the microphones offered by ST. Additionally it serves as a summary for selecting the appropriate microphone among the ST portfolio as the features of both digital and analog microphones are given.Table 1: Features of MEMS microphonesParameter MP45DT02-M MP34DB02 MP34DT01-M MP34DT04 MP34DT04-C1 MP34DT05 MP23AB02B MP23AB01DM MP23AB01DH Sensitivity -26 dBFS -26 dBFS -26 dBFS -26 dBFS -26 dBFS -26 dBFS -38 dBV -38 dBV -38 dBV Directivity OmnidirectionalOmnidirectional OmnidirectionalOmnidirectionalOmnidirectionalOmnidirectionalOmnidirectionalOmnidirectionalOmnidirectionalSNR 61 dB 62.5 dB 61 dB 64 dB 64 dB 64 dB 64 dB 64 dB 65 dB AOP 120 dBSPL 120 dBSPL 120 dBSPL 120 dBSPL 120 dBSPL 122 dBSPL 125 dBSPL 130 dBSPL 135 dBSPL EIN 33 dB 31.5 dB 33 dB 30 dB 30 dB 30 dB 30 dB 30 dB 29 dB THD+N <5% @ 115 dBSPL <5% @ 115 dBSPL <2% @ 115 dBSPL <5% @ 115 dBSPL <5% @ 115 dBSPL <6% @ 120 dBSPL <2% @ 120 dBSPL <10% @ 130 dBSPL <5% @ 130 dBSPL PSR -70 dB -86 dB -70 dB -70 dB -70 dB -72 dB -70 dB -85 dB -100 dB Max. current consumption 650 µA 650 µA 600 µA 700 µA 700 µA 650 µA 220 µA 250 µA 250 µA Package dimensions 3.76x4.76x1.25mm3x4x1mm 3x4x1.06mm 3x4x1.095mm 3x4x1.095mm 3x4x1mm 2.5x3.35x0.98mm 2.5x3.35x0.98mm 2.5x3.35x0.98mm Port location Top port Bottom port Top port Top port Top port Top port Bottom port Bottom port Bottom port Operating temperature-30°C<T<+85°C-40°C<T<+85°C-40°C<T<+85°C-40°C<T<+85°C-40°C<T<+85°C-40°C<T<+85°C-40°C<T<+85°C-40°C<T<+85°C-40°C<T<+85°CAN4426Revision historyDocID025704 Rev 219/204 Revision historyTable 2: Document revision historyDate RevisionChanges09-Jan-20141Initial release14-Feb-2017 2Updated part numbers throughout documentUpdated "Introduction" and Section 1: "Mechanical specifications, construction details"Updated Figure 5: "3 x 4 metal cap package - bottom port", Figure 20: "MEMS microphone portfolio", Figure 21: "MEMS microphone notation"Added Figure 7: "2 x 3 package - bottom port",Figure 13: "RF test disturbance signal @ 217 Hz burst pattern", Figure 14: "RF immunity of analog differential microphones" Updated Table 1: "Features of MEMS microphones"AN4426IMPORTANT NOTICE – PLEASE READ CAREFULLYSTMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, enhancements, modifications, and improvements to ST products and/or to this document at any time without notice. Purchasers should obtain the latest relevant information on ST products before placing orders. ST products are sold pursuant to ST’s terms and conditions of sale in place at the time of order acknowledgement.Purchasers are solely responsible for the choice, selection, and use of ST products and ST assumes no liability for application assistance or the design of Purchasers’ products.No license, express or implied, to any intellectual property right is granted by ST herein.Resale of ST products with provisions different from the information set forth herein shall void any warranty granted by ST for such product.ST and the ST logo are trademarks of ST. All other product or service names are the property of their respective owners.Information in this document supersedes and replaces information previously supplied in any prior versions of this document.© 2017 STMicroelectronics – All rights reserved20/20 DocID025704 Rev 2。

数字麦克风基础知识PPT课件

9
10
01010
A
11
ห้องสมุดไป่ตู้
01011
B
12
01100
C
13
01101
D
14
01110
E
15
01111
F
2.2 码制
不同的数码不仅可以表示数量的不同大小，而且还能用来表示不同的事物。在后一种情况下，这些数码已没有数量的含义，只是表示不同事物的代号而已。这些数码称为代码。
例如在举行长跑比赛时，为便于识别运动员，通常给每个运动员编一个号码。显然这些号码仅仅表示不同的运动员，已失去了数量的大小的含义。
43.5=4×101+3 ×100+5 ×10-1 所以任何一个十进制数都可以用式(1)表示:
D=∑Ki ×10i ……………式(1)
2.1 数制
2.1.2 二进制目前在数字电路中应用最广的是二进制。在二
进制数中，每一位仅有0和1两个可能的数码，所以计数基数为2。低位和相临高位的进位关系是“逢二进一”，故称为二进制
在数字电路中经常使用的计数进制除了十进制外，还经常使用二进制和十六进制。
2.1 数制
2.1.1 十进制十进制是日常生活和工作中最常使用的进位计数
制。在十进制中，每位有0~9十个数码，所以计数的基数是十。超过9的数必须用多位数表示，其中低位和相临的高位之间的关系是“逢十进一”，故称为十进制。例如：
为了便于记忆和处理，在编制代码时总要遵循一定的规则，这些规则就叫做码制。通常将这些代码称为二—十进制代码，简称BCD码，通常所用的BCD码有8421 码，余3码， 2421码，5211码和余3循环码。
2.2 码制

MEMS麦克风的基本原理教学教材

•声学过载点(AOP)
•在麦克风声压级开始接近声学过载点之前，失真通常不会随着声压级升高而大幅增加。但是，当达到过载点时，失真开始快速升高。麦克风声学过载点通常是指失真达到10%时的声压级。
频响 MEMS麦克风频响是在不同频率时指灵敏度的变化。麦克风频响通常在1 kHz 时设为0 dB，对不同频率下的灵敏度进行归一化处理。大多数MEMS麦克风的灵敏度都低于100Hz，在出现Helmholtz谐振后开始上升，达到大约4kHz至6kHz之间。这就是许多MEMS麦克风将频响指定在100Hz至10kHz之间的原因。不过，高性能的MEMS麦克风在20Hz至20kHz全音频带内拥有较平坦的频响曲线。
• 除输出、地和VDD引脚外，大多数数字麦克风还有时钟输入和L/R控制输入。时钟输入用于控制Δ-Σ 调制器，将传感器的模拟信号转换成PDM数字信号。数字麦克风的典型时钟频率通常在1MHz至 3.5MHz之间。麦克风输出信号在所选时钟边沿进入适合的逻辑状态，在另半个时钟周期进入高阻抗状态。这个两个数字麦克风的输入共用一条数据线。L/R输入确定有效数据是在哪一个时钟边沿上。
MEMS麦克风封装
• MEMS麦克风采用由基板和封装盖组成的空心封装，内部组件包括声学传感器和接口ASIC。封装基板下面是焊盘，用于将麦克风焊接在电路板或挠性电路上。在大多数MEMS麦克风的内部，MEMS声学传感器和接口ASIC是两颗独立的芯片，为制作能够移动的结构，声学传感器的制造工艺经过优化改良，而 ASIC芯片则采用工业标准的CMOS制造工艺。ASIC通过引线键合方法连接到传感器和基板，然后将封装盖扣在基板上并进行密封处理。
MEMS麦克风性能评测
•帕斯卡(Pa)是压力的线性国际单位制，表示单位面积上的压力(1Pa = 1N/m2)。不过，对数单位制更适用研究声压级（SPL），因为人耳动态范围大，能够察觉从最低20微帕到高达20帕的声压。因此，麦克风的关键性能指标通常用分贝 (dB)表示，0dB SPL等于20µPa，1 Pa等于94dB SPL。下面的参数通常是最重要的麦克风性能指标：

数字麦克风应用指南

0.1uF GND
VDD
L/R
0.1uF GND
DATA2 MIC GND VDD
DATA1 MIC
L/R
GND
Dual MIC
CLOCK DATA
DSP
VDD
0.1uF
GND
DATA1
L/R
GND
CLOCK DATA
DSP
Single MIC
图 5: 单/双声道应用电路
2.麦克风系统及性能
2.4 频响及超声应用
Peak Temperature
Time Within +5°C of Actual Peak Temperature
Ramp-Down Rate
Time +25°C (t25°C) to Peak Temperature
Reference Specification
TL to TP 3°C/sec max
数字麦克风应用指南
Date：201901
目录
❖ 1 MEMS麦克风封装介绍 ❖ 2 麦克风系统及性能 ❖ 3 设计推荐 ❖ 4 产线应用注意事项 ❖ 5 产品存储注意事项 ❖ 6 数字MEMS麦克风选型表
1.MEMS麦克风封装介绍
MEMS麦克风封装结构介绍
根据音孔位置，MEMS麦克风可分为Top、Bottom两种封装结构。其中，音孔在外壳上的为Top结构，适合普通产品结构和胶套/密封垫片设计；音孔在PCB上的为Bottom结构，适合超薄产品设计，麦克风与其他电子器件贴装在PCBA与音孔相反的一面。
MEMS die
VDD
IN+ Vmic
LDO
Charge Pump
Mode Detector

MEMS(数字)麦克风基本知识

MEMS Microphone Wafer & MEMS Die
MEMS Wafer
MEMS Die
MEMS Microphone 产品简介
MEMS Microphone Profile
Acoustic port hole
W
H
4
1
L
3
2
PIN# FUNCTION 1.OUTPUT, 2.NO CONNECTION 3.GROUND, 4.POWER
Stage
Temperature Profile
Time (Maximum)
Pro-head
170~180 ℃
120sec.
Solder Melt
Above 230 ℃
100sec.
Peak
260 ℃ Maximum
30sec.
Production Process
Wafer Fabrication
>58dB
RF-filtering capacitance
10pF, 33pF, both or none
Change in sensitivity(电压特性) <1dB across voltage range
Standard operating temperature -40℃ to + 100℃
Packaging/Cutting
Testing / Marking / Taping
Shipping Inspection
Packing
Reliability Test
MEMS Microphone 产品简介
Application of Product
MEMS Wafer Fab. < MEMS Microphone >

硅麦产品介绍 PPT

硅麦的结构
MEMS声压传感器
MEMS声压传感器
MEMS剖面示意图
MEMS声压传感器实际上是一个由硅振膜和硅背极板组成的微型电容器，硅振膜能感测声压的变化，将声压转化为电容变化。
MEMS主要加工流程1
大家学习辛苦了，还是要坚持
继续保持安静
MEMS主要加工流程2
硅麦的工作过程
声压ΔP作用到振膜上将产生一个是使振膜移动的推力ΔF 振膜相当于一个弹簧，将推力ΔF转化为位移量ΔX 振膜与背极板构成一个微电容， ΔX导致微电容变化ΔC ASIC将电容变化ΔC转化为ΔV 整个感应过程： ΔP → ΔF → ΔX → ΔC → ΔV
抗RF干扰
金属盖子和带屏蔽层的四层封装基板构成一个全包围PUT引脚上内置对地RF滤波电容。 ASIC的输出阻抗小于200Ω，抗RF干扰能力强，而ECM的输出阻抗大于1.5KΩ
AW8610介绍及应用
我们的合作伙伴
采用Infineon全套MEMS MIC芯片全球第二大MEMS MIC供应商 2012年总出货量6亿多片，占总份额的31% 产品素以高可靠性、卓越质量和创新性著称
全球领先的封测供应商 MEMS MIC全自动封装测试生产线产品以LGA，BGA，FC，CSP等高端封装为主
AW8610：高性能、超强RFI抑制、上进音模拟硅麦
主要特性：
采用Infineon MEMS晶圆支持SMT贴片优异的一致性，显著增强双MIC降噪效果平坦的频率响应，使语音清晰逼真超强RFI抑制高信噪比：59dB 灵敏度：-42 dBV/Pa 上进音，全向模拟硅麦 3.76mm*2.95mm*1.1mm LGA封装
硅麦功能框图
灵敏度
灵敏度：在压强为1Pa或94dB SPL，频率为1KHz的声压下，硅麦输出多少dBV的电压，单位是dBV/Pa，反映硅麦的声电转化效率。

MIC基础知识 ppt课件

数字麦克风便是将采集到的声压这一连续变化的模拟物理量，直接转换为特定编码格式的数字脉冲信号输出，供IT应用设备进行加工处理。
阮宏飞
NeoMEMs
模拟麦克风输出信号波形
阮宏飞
数字麦克风输出脉冲信号
NeoMEMs
引脚
与传统麦克风的两只引脚结构不同，数字麦克风一般具有4～5 只引脚，其功能分别为Vdd-电源输入、GND-地线、 CLK-时钟输入、DATA-数据输出、L/R-左右声道输出信号选择。根据客户需求，也可将L/R 选择端采取内部连接而形成4 引脚结构，也有的IC芯片厂家同时供应不同型号的L或R声道芯片供客户选用。
频率响应又称带宽(frequency range)，是指麦克风感应声波频率的范围，并将声波能量忠实的转换为电子讯号的能力。麦克风接受到不同频率声音时，输出信号会随着频率的变化而发生放大或衰减。一般以频率响应曲线图标之。
阮宏飞
NeoMEMs
阮宏飞
NeoMEMs MIC基础知识
灵敏度代表麦克风将声音能量转换成电压后所产生的输出讯号强度，是在麦克风单位声压激励下输出电压与输入声压的比值。当输入信号固定时(1kHz)，输出讯号越强识
阮宏飞
NeoMEMs MIC基础知识
Diaphragm
Resistance
Sound waves
Signal
阮宏飞
Back Plate
Battery
NeoMEMs MIC基础知识
传统ECM是在一个金属壳体内，包括一片可移动的永久充电振膜（高分子聚合材料振动膜）和一片与之平行的刚性背极板以及场效应晶体管(FET)构成，声波使振膜弯曲，改变振膜和背极板之间的气隙间距，从而使振膜和背板之间的电容发生改变，这种改变以交变电压信号的形式输出，可以反映出入声口处声波的频率和幅度变化。

MEMS麦克风的基本原理PPT课件

.
• 大多数MEMS麦克风的灵敏度随频率升高而
提高，这是声孔的空气与麦克风前室的空
气相互作用的结果。这种交互作用产生了
Helmholtz谐振，这与吹瓶产生的声音的现
象相同。像吹瓶子一样，空气容积越小，
谐振频率越高；反之，空气容积越大，谐
振频率越低。下置声孔麦克风将声学传感
器直接置于声孔之上，这样设计导致前室
.
频响 MEMS麦克风频响是在不同频率时指灵敏度的变化。麦克风频响通常在1 kHz 时设为0 dB，对不同频率下的灵敏度进行归一化处理。大多数MEMS麦克风的灵敏度都低于100Hz，在出现Helmholtz谐振后开始上升，达到大约4kHz至6kHz之间。这就是许多MEMS麦克风将频响指定在100Hz至10kHz之间的原因。不过，高性能的MEMS麦克风在20Hz至20kHz全音频带内拥有较平坦的频响曲线。
• 顾名思义，数字MEMS麦克风的输出为数字信号，可在高低逻辑电平之间转换。大多数数字麦克风采用脉冲密度调制技术 (PDM)，生成过采样率较高的单个比特的数据流。脉冲密度调制麦克风的脉冲密度与瞬间空气压力级成正比。脉冲密度调制技术与D类功放所用的脉宽调制（PWM）技术相似，不同之处是，脉宽调制技术的脉冲间隔时间是定量，使用脉宽给信号编码，而脉冲密度调制则相反，脉宽是定量，使用脉冲间隔时间给信号编码。
• 数字麦克风输出相对来说具有较高的抗噪性，但是信号完整性却是一个令人们关心的问题，因为寄生电容以及麦克风输出与系统芯片之间的电感导致信号失真。阻抗失匹也会产生反射问题，若数字麦克风与系统芯片间隔较大，反射现象将会导致信号失真。
• 虽然数字麦克风不需要编解码器，但是，脉冲密度调制输出的单比特PDM格式在大多数情况下必须转转换成多比特脉冲代码调制(PCM)格式。很多编解码器和系统芯片都有PDM输入，其内部滤波器负责将PDM数据转换成PCM格式。微控制器也使用同步串行接口捕获数字麦克风的PDM数据流，然后通过软件滤波器将其转换成PDM格式。

数字麦克风应用指南

4.产线应用注意事项
4.1 SMT回流曲线推荐
表2: 回流温度设置
Parameter Average Ramp Rate Minimum Temperature Preheat Maximum Temperature Time TSMIN to TSMAX Ramp-Up Rate Time Maintained Above Liquidous Liquidous Temperature Reference Specification TL to TP TSMIN TSMAX tS TSMAX to TL tL TL 3°C/sec max 150°C 200°C 60 sec to 180 sec 1.25°C/sec 60 sec to 150 sec 217°C 260°C +0°C/−5°C 20 sec to 40 sec 6°C/sec max 8 min max
1.5
丝来保证PCBA在Z轴可以完全被压住
应用范围：进音通道可以适当加长的双面板
1
2 3 4
3.设计推荐- PCBA固定方式及通道参数推荐
方案四
≤4
序号 1 2
部件名称上壳密封双面胶
Z向公差标准 ±0.05 ±0.05
3
PCBA
±10%
0.2
1.PCBA建议开孔直径0.5-0.8mm 2.PCBA通过一层0.2mm厚度的双面胶粘贴固定在上壳内部，在 MIC的进音位置开孔避让，其他地方密封，双面胶最窄位置不得小于1.5mm，可以保证MIC进音通道的密封，装配时需要用保压工装保证双面胶粘贴到位应用范围：尺寸比较小的单面板
1.5
1
2 3
3.设计推荐
3.2 PCBA焊盘设计

MEMS麦克风ppt课件

ADI MEMS Microphones Key Performance
THD @ 115dBL <10% SNR 61dBA Typical PSRR: Analog 70dBV; Digital 80dBFS Frequency Response FLAT 100Hz to
15kHz,no resonant peak Shock Resistance >20k G-force >160dB sound pressure shock Power Consumption:Analog
ECM
电容式麦克风工作原理
PFxV
电容式麦克风的工作原理
Microphone vs. pressure sensor: Pressure sensor messure high(kPa) static
pressure Microphones messure low(mPa)alternating
一、工作原理
MEMS麦克风是通过微机电技术在半导体上蚀刻压力感测膜片而制成的微型麦克风，其工作原理与ECM麦克风完全相同，工艺好比在单一硅晶片上制作传统麦克风的各个零部件，所集成的半导体元件有信号放大器、模数转换器（ADC）和专用集成电路（ASIC）。
一、工作原理
新型麦克风内含两个晶片：MEMS晶片和ASIC晶片，两颗晶片被封装在一个表面贴装器件中。MEMS晶片包括一个刚性穿孔背电极（fixed backplate）和一片用作电容器的弹性硅膜（flexible membrane）。该弹性硅膜将声压转换为电容变化。ASIC 晶片用于检测电容变化，并将其转换为电信号，传送给相关处理器件，如基带处理器或放大器等。
二、Module Structure

MEMS(微型机电系统) 麦克风

∙MEMS（微型机电系统）麦克风是基于MEMS技术制造的麦克风，简单的说就是一个电容器集成在微硅晶片上，可以采用表贴工艺进行制造,能够承受很高的回流焊温度,容易与 CMOS 工艺及其它音频电路相集成, 并具有改进的噪声消除性能与良好的RF 及EMI 抑制性能.MEMS麦克风的全部潜能还有待挖掘，但是采用这种技术的产品已经在多种应用中体现出了诸多优势，特别是中高端手机应用中。

目录∙MEMS麦克风的优势∙MEMS麦克风的主要参数∙MEMS麦克风的发展前景MEMS麦克风的优势∙目前，实际使用的大多数麦克风都是ECM(驻极体电容器)麦克风，这种技术已经有几十年的历史。

ECM 的工作原理是利用驻有永久电荷的聚合材料振动膜。

与ECM的聚合材料振动膜相比，MEMS麦克风在不同温度下的性能都十分稳定，其敏感性不会受温度、振动、湿度和时间的影响。

由于耐热性强，MEMS麦克风可承受260℃的高温回流焊，而性能不会有任何变化。

由于组装前后敏感性变化很小，还可以节省制造过程中的音频调试成本。

MEMS麦克风需要ASIC提供的外部偏置，而ECM没有这种偏置。

有效的偏置将使MEMS麦克风在整个操作温度范围内都可保持稳定的声学和电气参数，还支持具有不同敏感性的麦克风设计。

传统ECM的尺寸通常比MEMS麦克风大，并且不能进行SMT（表面贴装技术）操作。

在MEMS麦克风的制造过程中，SMT回流焊简化了制造流程，可以省略一个目前通常以手工方式进行的制造步骤。

在ECM麦克风内，必须添加进行信号处理的电子元件；而在MEMS麦克风中，只需在芯片上添加额外的专用功能即可。

与ECM相比，这种额外功能的优点是使麦克风具有很高的电源抑制比，能够有效抑制电源电压的波动。