MEMS (micro electromechanical systems) microphones are smaller in appearance and have stronger heat resistance, vibration resistance and radio frequency interference resistance than the currently widely used electret microphones. Due to their strong heat resistance, MEMS microphones use a fully automated surface mount (SMT) production process, while most electret microphones require manual welding. This not only simplifies the production process and reduces production costs, but also provides higher design freedom and system cost advantages.
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Just imagine it Half the size of an ordinary microphone and with integrated audio signal processing, MEMS microphones can be used as an integrated part of a single-chip mobile phone. The full potential of the new MEMS microphones has yet to be tapped, but the first products using this technology are already showing many advantages in a variety of applications, especially mid- to high-end mobile phones.
Working principle
Infineon microphone SMM310 contains two chips: MEMS chip and ASIC chip. The two chips are packaged in a surface mount device. The MEMS chip consists of a rigid perforated back electrode and a flexible silicon membrane. The MEMS chip acts as a capacitor, converting sound pressure into changes in capacitance. ASIC chips are used to detect changes in MEMS capacitance, convert them into electrical signals, and pass them to related processing devices, such as baseband processors or amplifiers. ASIC chips are standard IC technology. Therefore, this two-chip approach can quickly add additional functionality to the ASIC. This functionality can be additional building blocks such as audio signal processing, RF shielding, or anything that can be integrated on a standard IC.
Performance Features
Most of the microphones we use today are electret condenser microphones (ECM), a technology that has been around for decades. The ECM works by utilizing a diaphragm of polymeric material with permanent charge isolation.
Compared with ECM's polymeric material diaphragm, MEMS microphone performance is very stable at different temperatures and will not be affected by temperature, vibration, humidity and time. Due to its strong heat resistance, MEMS microphones can withstand high-temperature reflow soldering at 260°C without any change in performance. This can even save audio debugging costs during manufacturing due to minimal changes in sensitivity before and after assembly.
MEMS microphones require external biasing from the ASIC, while ECM does not require this biasing. Effective biasing will maintain stable acoustic and electrical parameters over the entire operating temperature range. External biasing of MEMS chips also enables the design of microphones with different sensitivities.
Traditional ECMs are usually larger in size than MEMS microphones and cannot be operated by SMT. SMT reflow simplifies the manufacturing process and can eliminate a manufacturing step that is now typically performed manually.
There is no difference between the signal processing electronics in IC and electret condenser microphones, but this is a technology that is already in use. In an electret, an IC must be added, whereas in a MEMS microphone, additional specialized functions are simply added to the IC. The advantage of this extra functionality is that it gives the microphone a high power supply rejection ratio compared to ECM. In other words, if the power supply voltage fluctuates, it will be effectively suppressed.
The smart ASIC design of SMM310 makes its power consumption very low, only one-third of the standard ECM (at a power supply voltage of 1.5-3.3 V, the current consumption of SMM310 is ￣70? A, as shown in Table 1).
Table 1: Characteristic parameters of the new SMM310 silicon-based MEMS microphone.
Another advantage is the broadband RF rejection performance integrated on the IC, which is especially important not only for RF applications such as mobile phones, but also for all devices that work similarly to mobile phones (such as hearing aids). Very important. The SMM310 has a metal cover that provides RF shielding.
The small diaphragm of MEMS microphones has another advantage. Small diaphragms with a diameter of less than 1mm are equally lightweight, which means that, compared to ECMs, MEMS microphones will be mounted on the same PCB. The speaker-induced PCB noise produces lower vibration coupling.
Wide range of applications
Considering the many advantages and system costs of silicon-based microphones, silicon-based microphones have high requirements for size, heat resistance, vibration and RF Mid-to-high-end applications will be very attractive, such as the application example shown in Figure 1.
Figure 1: Example of mobile phone application with additional 30pF capacitor for mode suppression
Size refers not only to the footprint of the microphone device, but also to those that can be updated via the ASIC A high degree of integration eliminates the size of discrete components. Applications with the above requirements include: mid-to-high-end mobile phones, digital cameras, PDAs or game consoles, etc.
A/D converters can be easily integrated into ASICs. By equipping the microphone with a digital interface, the audio signal will not be distorted by RF noise interference. This is an advantage for both mobile phones and laptops.
For laptops, silicon-based microphones have another advantage. With VoIP becoming increasingly popular, laptops can be used as phones. Using microphone array software, directional sensitivity can be adjusted near a laptop or throughout a space, such as a conference room. But to calculate the sound direction of delayed signals from different microphones in an array, you need microphones with very stable performance, such as MEMS microphones.
In addition to consumer applications and data processing applications, MEMS microphones are also very attractive to the industrial, medical and automotive industries, and may be used in applications ranging from machine monitoring, hearing aids to vehicle hands-free devices. MEMS microphone. System costs for mid- to high-end applications are roughly the same. However, MEMS microphones still have great potential for development. Now might be a good time to learn about this new technology so you can benefit from it in the future.
Technology Outlook
Infineon launches new product series? Silicon-based MEMS microphone, the first product in this product series is SMM310? SMT analog output single-ended microphone. Semiconductor manufacturers have the core capabilities to manufacture this product family. The first is MEMS design and manufacturing capabilities, followed by ASIC (Application Specific Integrated Circuit) design and manufacturing capabilities, and finally high-volume, low-cost packaging capabilities. Until now, audio companies have dominated nearly the entire MEMS microphone market. Audio companies must rely on semiconductor foundries to provide relevant technology and share profits with them. Now, the entry of semiconductor companies like Infineon means that the market has new options and reduces risk for component buyers.
Further size reduction will be limited by standard automated placement tools in the manufacturing process because the audio ports cannot be operated with vacuum tools. In fact, the limitation mainly comes from the size of MEMS itself, which is less than half the size of today's ordinary microphones.
More functions will be integrated into ASICs, with A/D conversion and digital output being the first step. In addition, standard components such as wind noise signal filtering components can be utilized. Specialized interfaces and signal preprocessing will also become a large application area. RF shielding will also be further improved.
On the audio side, there will be a lot of changes, too. The SMM310 is optimized for human voices, but has higher acoustic sensitivity in the frequency range of 20Hz-20kHz. It's hard to predict when a single-chip video phone with an integrated microphone and the ability to record beautiful stereo sound will be available, but there's no doubt we're moving in that direction.