The hottest MEMS microphone can effectively improv

2022-07-23
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MEMS microphones can effectively improve sound quality

more and more mobile devices, such as, headphones, cameras and MP3 players, have adopted advanced noise reduction technology to eliminate background sound and improve sound quality. To put this advanced technology into practice, the microphones used must not only have the ability to resist RF and EMI, but also have a very small size. The MEMS microphone produced by EPCOS is an ideal solution to meet this requirement. As the smallest microphone in the market, MEMS microphone not only provides excellent audio quality, but also has excellent anti electromagnetic interference function

excellent performance and small footprint

in May, 2009, a series of highly innovative MEMS products were put into the silicon microphone market due to the use of technitrol's MEMS (micro electro mechanical system) microphone technology. The first batch of products to be launched are apotheker t4000 and t4010 series, which have gathered the design capability of advanced MEMS and ASIC technologies, in-depth understanding of applications and various patents

now, a microphone with digital output, namely t4030, has been added to the product line. The new product is small in size, with a sensitivity of -26db fs (full range) and a signal-to-noise ratio of 60dbA. Even if the sound level is 100dB, the distortion is less than 1%. Its frequency response is characterized by high bandwidth and low amplitude fluctuation that will be officially operated at the end of this month (see Figure 1). Since PDM (pulse density modulation) output is adopted, t4030 basically has no response to electromagnetic interference. Power supply noise suppression is -82db FS. Two channel transmission via one signal line makes stereo or multi microphone applications easier than analog technology. The power supply voltage is between 1.64v and 2.86v. Power consumption is 650 μ A. Less than 10 in standby mode μ A。

Figure 1: frequency response curve

the product is compact

t4030 has excellent performance and small size. It is most suitable for noise reduction in mobile devices, because space occupation is often the primary consideration in these devices. A good example of this is the jetbrand stone Bluetooth headset developed by GN Netcom when the chain segment is heated to sufficient activity. Greater northern Europe is a Danish headphone manufacturer whose products are used in, contact centers and offices (see Figure 2 for product quality stability improvement). Jabulan stone is a very compact earphone, which is characterized by finding the best balance between noise elimination and natural sound, providing perfect sound quality. To achieve this effect, only dual microphones are used to capture sound, and only background noise is intelligently filtered. For this purpose, the manufacturer chose t4000 series products with small size and excellent performance

Great Northern Europe believes that jabulan stone is a revolutionary product, which will certainly overturn the inherent view of consumers on Bluetooth headsets. "It has a unique shape, advanced noise reduction technology, and does not need a cross arm. It is a new product concept," said Anna R. rasmusser, vice president of the greater northern Europe mobile communication department

Figure 2: jetbrand stone Bluetooth headset produced in northern Europe

advanced noise reduction technology

noise elimination is increasingly becoming a standard requirement in medium and high-end mobile devices. In the receiving path and the transmission path, the two noise reduction functions can be combined (see Figure 3). As shown in the following figure, in the receiving path (blue), microphone 1 is located next to the horn to receive noise, which is added to the incoming sound after being inverted. The inverted noise signal cancels the surrounding noise signal. In this way, users can understand each other's voice more clearly, even in a noisy environment

Figure 3: noise elimination in the receiving and transmission path

in the transmission path (yellow), microphone 2 faces away from the mouth and receives surrounding noise. Microphone 3 is facing the mouth, and it receives the surrounding noise and the voice of the speaker at the same time. Here, by adding an inverse noise signal, the noise is eliminated. At this time, the noise interference of the other party will be reduced

with more than three microphones, a more powerful and complex noise reduction system can be designed. As more microphones are embedded in small mobile devices, the size of products has become more and more important. Figure 4 shows two small t4000 microphones mounted on a circuit board. At the same time, users have higher expectations for sound quality. In the future, the signal-to-noise ratio (SNR) of the microphone will reach 62db, dB higher than today's general level. Today, EPCOS' t4020 MEMS has excellent performance, and its signal-to-noise ratio has reached 62db, and products with higher signal-to-noise ratio are under development

figure 4:the circuit board of the stone earphone is installed with two MEMS microphones

the cutting-edge packaging technology

avoiding electromagnetic interference and radio frequency interference has always been an important issue for SAW filters. SAW filters work in the GHz range. After the antenna receives the RF signal, it is usually the first component in the signal path. For this reason, in order to maintain very weak signals, extremely reliable shielding must be adopted. This requirement led to the birth of CSSP (i.e. "chip size saw packaging") technology. This technology is a very small package with shielding function, and its maturity has been proved by its application to billions

mems microphones are produced based on the same packaging technology dedicated to MEMS (CSMP, that is, chip size MEMS packaging) (see Figure 5). This technology benefits from the mature EPCOS production process and 15 years of experience in developing MEMS microphones. MEMS microphone complies with ROHS directive and is suitable for SMD lead-free reflow soldering process

Figure 5: solid package of MEMS microphone

complete test

tdk-epc company also uses mature saw production technology for final electroacoustic measurement. By designing a specific test head, the problem of measuring electroacoustic characteristics is solved. Before leaving the factory, each microphone will undergo complete measurement according to relevant specifications, including basic electroacoustic performance test. Specific test items are as follows:

* sensitivity at 1kHz and narrow-band noise

* broadband frequency response

* broadband noise

* power penetration

* harmonic distortion

* power consumption

100% testing makes MEMS microphones reliably show excellent performance in applications

table: key technical parameters

mems microphone has compact structure and excellent electrical performance. It can also be used in fields requiring high sound quality, including high-quality video and VoIP (interconnection) systems, conference systems and beam forming systems. Mass production of t4000 series products has begun. At present, engineering samples of t4020 and t4030 series can be obtained. (end)

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