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Enabling superior performance in emerging automotive applications


Ken Waurin, strategic marketing manager at Analog Devices Inc., Dietmar Ruwisch, senior audio technologist at Analog Devices Inc. and Yu Du, senior principal acoustic engineer at Harman International Industries explore how automotive audio bus (A2


B) and digital microphones enable superior performance in emerging automotive applications W


ithin the automotive in-cabin electronics segment, it’s becoming increasingly clear that the universe of audio-, voice-


and acoustics-related applications is rapidly expanding as car manufacturers attempt to differentiate their vehicles from the competition. Additionally, as average consumers become more tech savvy, their expectations related to both the “driving experience” and level of personal interaction with the vehicle are expanding significantly. Home theater quality sound systems are commonplace across all vehicle price points and are now being augmented by sophisticated Hands-free (HF) and In-Car Communications (ICC) Systems. Additionally, Active and Road Noise Cancellation (ANC/RNC) systems, historically deployed in only the top-level premium vehicles, are now making their way into more mainstream, affordable segments. Looking to the future, audible or acoustics-based techniques will become a critical component in Level 4/5 autonomous vehicle Engine Control Units (ECUs) as they attempt to detect the presence of emergency vehicles. The common thread binding all these legacy and emerging


applications is the dependency on high performance acoustic sensing technology such as microphones and accelerometers. And since nearly all emerging applications require multiple acoustic sensors like microphones (or mic arrays) to achieve best system level performance, a simple cost-effective interconnect technology is required to ensure that total system costs are minimised. Historically, the lack of a microphone-optimised interconnect technology has been a significant pain point for the car manufacturers, as each microphone would need to be directly connected to the processing unit using expensive and heavy shielded analogue cable. These added costs, primarily in terms of actual wiring, but secondarily in terms of added weight and reduced fuel efficiency, have in many cases prevented the widespread adoption of these applications – or at least limited them to only the super-premium segments. Recent advances in both digital microphone and connectivity technologies are game-changers for future generations of vehicle infotainment systems.


12 OCTOBER 2021 | ELECTRONICS TODAY


Digital MEMs microphones Micro-Electro Mechanical System (MEMS) technology is swiftly becoming the new industry standard for microphones, as it offers many advantages over traditional Electret Condenser Microphones (ECM). First and foremost, MEMS enables a much smaller form factor sound sensor than ECM capsules. Additionally, integrating a MEMS sensor with an analogue-to-digital converter results in a digital microphone in a single IC package. Analogue-ported MEMS microphones without an integrated A/D


converter are also available; but they share many of the same disadvantages as analogue ECM microphones and even require more complex amplifier circuitry than ECMs if operated on the traditional two-wire analogue interface. It is only with an all-digital interface technology that the interference and SNR problems inherent to analogue wires can be significantly alleviated. Also, from a production perspective, MEMS is preferred because MEMS mics can be produced with a much tighter specification variance than ECM capsules, which is important for beamforming (BF) algorithms. Lastly, with MEMS IC microphones, the manufacturing process is greatly simplified because automated mounting techniques can be utilised, which reduces overall production costs. From an application perspective, the smaller form factor is the largest advantage; and, due to very small sound-entry portholes, MEMS mic arrays can be made virtually invisible. The porthole and the sound channel to the sensor require great care in terms of design and production quality. If the acoustic seal is not tight, noise from the inner structure may


reach the sensor and leakage between two sensors may degrade the performance of the BF algorithm. Different from typical ECM capsules that can be designed and manufactured to be either omnidirectional or directional, MEMS microphone elements are almost always manufactured to be omnidirectional (i.e., they have no intrinsic directionality of sound reception). As such, MEMS microphones are phase-true omnidirectional sound pressure sensors that deliver ideal signals for advanced BF algorithms, where attenuation directions and beam widths can be user-configurable via software.


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