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Advantage of MEMS microphone applications replace the traditional electret microphone

    Vision: Fully integrated single-chip high-level microphone audio system.

    Imagine the size of size less than a watch with integrated microphone, single-chip micro-phone. Imagine a single-chip Bluetooth built-in micrbooster cables ophone headset.

    Imagine much smaller than ordinary microphones with integrated echo cancellation and noise cancellation system microphone.

    New MEMS (micro electromechanical systems) technology, market potential,battery clip including the microphone has yet to be excavated. But the first products using this technology, such as MEMS microphones have been reflected in a variety of applications, many advantages,tow rope especially in the high-end mobile phones.

    Alternative to traditional sensor and semiconductor sensors open up new fields of application.

    MEMS and other semiconductor systems including optical, electromagnetic, ratchet tie dowm radio frequency, mechanical and microfluidics work. These systems are based on temperature sensors, magnetic field, fingertips, acceleration, pressure or flow sensors.

    Pressure sensor based on MEMS technology, including complex automotive tire pressure monitoring system, simple for the altimeter and consumer devices MEMS pressure sensor microphone.

    Semiconductor sensors not only replaces the traditional sensor, but also opened new application areas such as consumer devices (game consoles or mobile phones) in the acceleration sensor.

    MEMS microphones not only replace the existing microphone, but also brings new value applications.

    MEMS microphone works is a miniature capacitor etched into the semiconductor.

    Infineon microphone SMM310 contains two chips: MEMS chip and ASIC (application specific integrated circuit) chip. Two chips are packaged in a surface mount device. Figure 1. MEMS chip consists of a rigid, perforated back electrode and a flexible silicon membrane.

    MEMS chip for capacitance, the sound pressure is converted to capacitance changes. MEMS chip cross-section shown in Figure 2. In the design of Infineon, the silicon membrane is about a typical diameter of 900μm. In this design, flexible silicon membrane in the total chip area of the surface is greatest. Therefore, the optimized signal to noise ratio on a particular chip size.

    MEMS ASIC chip for detecting changes in capacitance and converts it to electrical signals, is passed to the appropriate processing devices, such as the baseband processor or amplifier. ASIC chip is a standard IC technology. Therefore, this two-chip approach can quickly add additional features to the ASIC. This feature can be either additional components, such as audio signal processing, RF shielding, can also be integrated in any standard IC's functionality.

    MEMS microphone, small size, powerful, and can be reflow soldering without reducing sensitivity.

    Today we use most of the microphones are electret condenser microphone (ECM), this technology has been for decades. ECM works is to use a permanent polymer charge isolation diaphragm.

    Polymer materials with the ECM than the diaphragm, MEMS microphone performance at different temperatures are very stable, not affected by temperature, vibration, humidity and time effects. As heat and strong, MEMS microphones can withstand 260 ℃ high temperature reflow, and there will be no change in sensitivity.

    MEMS microphones require ASIC to provide an external bias. The ECM is not such a bias. Will effectively offset the entire operating temperature range can be stable acoustic and electrical parameters.

    Usually higher than the traditional ECM MEMS microphone the size of a large, and can not be SMT operation. SMT reflow simplifies the manufacturing process, a manufacturing step can be omitted, and this step is usually carried out manually. The microphone is now standard SMT components, the same as other SMT components, it does not require special treatment.
    Advantages of this accessibility can be integrated into ASIC on. Compared with the standard ECM, the amount of auxiliary functions that the microphone has the additional advantage of the ESD protection and high power supply rejection ratio. That is, if the power supply voltage fluctuations, will be the way to the audio output is effectively suppressed.

    Microphone ASIC chip design makes it a very low power consumption, only the standard ECM 1 / 3 (in 1.5V ~ 3.3V supply voltage, the current consumption of Infineon SMM310 is ~ 80μA, as Table 1 SMM310 the technical specifications).

    Another advantage is integrated in the IC on the broadband RF (Radio Frequency) rejection. SMM310 has a metal cover that can be shielded against RF. Integrated broadband inhibition in the ASIC on the performance of not only specific frequency bands, and UMTS and GSM frequency bands, including all areas.

    MEMS microphone diaphragm has another advantage of small, less than 1mm in diameter smaller films with the same light weight. This means that, compared with the ECM, MEMS microphones will be installed on the same PCB by the speaker on the PCB due to vibration coupling produces lower noise. This is a special case of spring installation cost savings.

    PCB in the application of MEMS microphone allows the other side of the opposite mount.

    Another advantage of MEMS microphones can be installed in the PCB opposite. Figure 3 shows examples of the opposite to install the microphone. MEMS microphones can be installed in a hole on the back of PCB. In this way, PCB components to the top no longer needed. Application of PCB can be directly exposed to consumer devices of the shell, make the design even more clever.

    RF MEMS microphone low distortion, high reliability, simplifying design.

    Taking into account the many advantages of silicon microphones, and system cost, silicon microphone for those on the size, heat, vibration and very high RF and high-end application requirements, will have great appeal, for example, as shown in Figure 4 application examples.

    Size refers not only to the microphone device footprint, also refers to a higher degree of integration through the ASIC can save the size of discrete devices. The opposite of the PCB through the installation can also be greater design freedom.

    Before and after the assembly process slightly increased the sensitivity of the system not only saves the audio adjustment of manufacturing costs, but also allows the audio path in the remaining lower cost components, while the sensitivity of the system growing.

    Better in terms of RF suppression for mobile phones is becoming increasingly important: to SAR (specific absorption rate) is reduced to the minimum, usually on the phone's antenna, the lower end of the phone, that is, the location of the microphone. In these designs, the distance between the microphone and the antenna is small, the location of the microphone, radio frequency radiation levels increased significantly.

    With internal rechargeable polymer with the working conditions of the working principle and performance degradation characteristics of deterioration compared, MEMS microphones because of the external bias, with stable quality, reliability and durability. In the harsh environment can ensure that this very stable performance. Examples include air-conditioned rooms in operation for a while, and then on the outside of the hot and humid environment operations.

    With the requirements of applications include: high-end mobile phones, digital cameras, personal digital assistant (PDA) or game consoles.

    Accessibility and the best performance is now being gradually realized.

    With a digital interface through a microphone, the audio signal to interference will not because of RF noise and distortion. This is in terms of mobile phones and laptop computers are an advantage.

    For accessibility, you need digital interface, voice processing or filtering functions on IC. This two-chip solution ASIC technology has been adopted. ASIC can be placed on any additional features can be easily integrated into the microphone. In the electret, you must add the IC, MEMS microphone in, just add an extra special IC features can be.

    For notebook computers, the silicon microphone has another advantage. The growing popularity of IP voice in the promotion, the notebook computer can use as a phone. Using the microphone array software can near the computer or the entire space (such as conference rooms) to adjust the directional sensitivity. However, from an array to calculate the delay of the microphone signals of different sound direction, you need to have a very stable performance of the microphone, such as MEMS microphones.

    In addition to consumer applications and data processing applications, but for industrial, medical and automotive industry is the preferred program. From the machine monitoring, hearing aids to have a speakerphone may be used in applications such as MEMS microphones. Application of high-end system costs roughly the same.

    System costs start approaching, and component cost reduction is just beginning.

    Although MEMS ECM components cost more than high-end applications in the system cost about the same. But siliconMEMS there is great potential for development microphone. And reduce the cost of other semiconductors (in the mass production from the beginning of the process design to achieve) than expected in the next few years, the cost will be drastically reduced.

    Infineon MEMS microphone.

    Infineon is the end of 2006 new product line - siliconMEMS (MEMS) microphone. The product line is the first product in the SMM310 - SMT analog output single-ended microphone. It is in volume production in 2007. Today, Infineon is expanding its product line.

    Semiconductor manufacturers have to manufacture the product line's core competencies. First, MEMS design and manufacturing capabilities, followed by the ASIC design and manufacturing capabilities. Finally, low-cost high-capacity packaging capacity. So far, the audio has been dominated almost the entire company MEMS microphone market. Audio semiconductor foundry companies must rely on to provide relevant technology and share profits with them. Now, Infineon's entry means that the market has a new option, and reduce the risk of component buyers.

    The future of MEMS microphone may have improved sound.

    Effect, accessibility, and further reduce the size.

    Infineon SMM310 is the first new product line of products. Infineon is on three dimensions of innovation: size reduction, additional features and enhanced interface and sound effects.

    Size will be further reduced, the standard manufacturing process will be automated placement tool restrictions. In fact, limits itself mainly from the MEMS. Shown in Figure 1, MEMS microphones the size of less than half of today's ordinary.

    ASIC will integrate more functions, A / D conversion and digital output is the first step. There is also the use of standard components, such as wind noise signal filter components. Specific interface and signal preprocessing will become a big application areas.

    In the audio side, there will be many changes. SMM310 is optimized for the human voice, and other products will be optimized for other applications such as digital cameras - most cell phones are beginning to become a digital camera.

    Difficult to predict when it will appear with integrated stereo microphone and can record wonderful video single-chip phone, but there is no doubt that we are moving in this direction.

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