The Next Generation of MEMS Microphone Technology

Vesper's VM3011 intelligent MEMS microphone claim to fame is a power saving architecture that enables battery standby life that otherwise would be unattainable without the "smarts." This article discusses this and similar industry developments.

At the end of July 2020, audioXpress ran a product release on Vesper's VM3011 intelligent digital micro-electro-mechanical systems (MEMS) microphone. Its claim to fame is a power saving architecture that enables battery standby life that otherwise would be unattainable without the "smarts." There are another half-dozen developers working on integrating all sorts of capabilities within the MEMS mic package.

The component parts of the ubiquitous MEMS mic are the mic transducer element and an application-specific integrated circuit ("ASIC"), both stuffed into an SMT package. An application-specific integrated circuit is just that: the ASIC being just a simple mic preamp, or the semiconductor manufacturer can add a codec for digital output on the die. But why stop there? Advanced voice and audio processors, voice command, bio-monitors and authorized user ID are all areas rife for exploring.

Yet, as with any innovation, the greater the step forward, the greater the challenges to design wins. Let's take a look at why product designers have been reticent to embrace smart mics.

Today's product architectures have the signal processing further down the line - not at the mic. Smart mics are still just entering the market, with some coming from small start-ups without a second source - a high-risk design and purchasing decision.

The footprint of most MEMs mics follows the small industry-standard 3.76 mm x 2.95 mm x 1.3 mm package. Yet when packing more elements inside the interior of the SMT package, the air volume is reduced - and as this back volume shrinks, so does signal to noise. Vesper was in development of a superior doping process for their piezo MEMS mics to increase the signal to noise ratio - which was just in the nick of time to maintain performance of their latest VM3011.

The Vesper VM3011 digital microphone integrates both the ASIC and the piezoelectric MEMS transducer in the same package. Adaptive ZeroPower Listening (ZPL) technology automatically "learns" the acoustic characteristics of the environment in real-time, allowing the system to ignore background noise and only wake in response to keywords or other desired acoustic triggers.

The VM3011 builds on Vesper's VM1010 wake-on-sound mic. The VM1010 is a quiescent-sensing device with practically zero power drain and acoustic event-detection in microseconds, drawing just 3 µA of current while in listening mode. Quiescent-sensing is unique to piezo MEMS, as it uses the sound transduced to electrical energy by the piezo MEMS triggering itself to wake-up from full power-down - essentially energy harvesting from sound.

The Vesper VM3011 is targeted for some of the same applications as the Knowles IA61x family of "wake-on-voice" SmartMics. Knowles uses a 43 MHz Tensilica audio-optimized DSP in their SiSonic MEMS mic in a single, miniature, microphone package - the AISonic SmartMics family. The integrated programmable DSP was made available to third-party algorithms, enabling customization.

The VM3011 is intended for the low-power always-listening device market. Vesper's Adaptive ZeroPower Listening (ZPL) technology automatically "learns" the acoustic characteristics of the environment in real-time, ignoring background noise and only wakes in response to keywords or other desired acoustic triggers. By automatically adjusting the background threshold based on the acoustic level of the environment, this allows the system to hibernate over 90% of the time and extend battery life >10x. The VM3011 is a bottom port IP57 device, resistant to dust and moisture and can tolerate high acoustic levels without latch-up or mic element overload. When combined with the ultra-fast startup of piezo microphones, the VM3011 enables system power savings for voice-activated devices without compromising the acoustic performance.

The development of new products using smart MEMS is not an isolated process. Vesper has worked with industry partners to create a complete software and hardware support ecosystem for the Vesper VM3011.

The microphone is constantly listening to the environment with 10 μA of current consumption. In Wake on Sound (WoS) mode, a Digital Output pin (DOUT) outputs a single bit "Threshold Exceeded" flag when the acoustic input is greater than the set threshold. When the threshold is reached, an interrupt signal is sent to the external codec or voice processor - which "lights-up" anything and everything for a prescribed time frame. Adaptive Mode continuously measures the average sound level of the environment and adjusts the internal comparator until it converges to the threshold margin.

Matt Crowley, CEO of Vesper mentioned in a briefing with audioXpress that this technology "will power a new class of products such as always-listening far-field TVs, always-listening smartwatches, home security cameras and doorbells and many other system." It is available in volume production by Q4 2020, in a small industry-standard 3.76 mm x 2.95 mm x 1.3 mm package, and it's reflow solder compatible.

Read the complete article here, where I hinted at what else is coming.

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