STMicro Rolls All-in-one Motion and Bone-conduction Sensor for Hearables

March 06, 2023 by Jake Hertz

With its new sensor IC, STMicroelectronics hopes to enable a new class of hearables for applications like true wireless stereo (TWS).

The audio segment ranks among the biggest fields of the consumer electronics industry. Within this, hearables—or wearable audio devices like earbuds and headsets—are amongst the most popular devices on the market.

However, achieving top performance and functionality out of a tiny, battery-powered hearable device can often be a significant design challenge. Today, STMicroelectronics (ST) released a new highly integrated sensor aimed at delivering a range of functionality to hearables for applications like true wireless stereo (TWS).

In this article, we’ll take a look at TWS, the need for monolithic integration in this context, and ST’s new sensor offering.


What is True Wireless Stereo?

In the world of hearables, one of the most sought-after use cases is that of TWS. At a high level, the idea behind TWS is that TWS-enabled devices transfer sound and data entirely through wireless connectivity.

Unlike traditional wireless offerings where both earbuds are connected together through a single wire, TWS offerings essentially treat each earbud as an individual device.


TWS can connect simultaneously or through a primary/secondary connection.

TWS can connect simultaneously or through a primary/secondary connection. Image used courtesy of Telink


In general, this can either be implemented by having a simultaneous connection between both earbuds and the source device or through a primary and secondary connection. In a simultaneous connection, the two earbuds do not connect with each other, but instead, receive the same signal directly from the source.

In a primary/secondary configuration, both earbuds are connected to one another. Here, a single primary earbud will interface with the source and then relay any information directly to the secondary as needed.

The primary advantage of a TWS system is that it requires no cabling at all, making the hearable experience less cumbersome, easier to use, and more convenient. 


The Need for Integration

One of the major challenges with the design of TWS hearables is being able to fit all of the desired functionality and performance. By nature, TWS hearables are standalone, battery-powered devices that are expected to be small, comfortable, and offer long battery lives. 

At the same time, competitive TWS earbuds offer a wide array of functionality including Bluetooth connectivity and high audio quality along with features like active noise canceling, head tracking, battery charging, and more. Implementing all of this requires an array of dedicated circuit blocks, requiring significant amounts of area and power consumption.


A standard TWS hearable block diagram.

A standard TWS hearable block diagram. Image used courtesy of from STMicroelectronics (Click image to enlarge)


To balance the wide array of functionality required by TWS hearables with the demands for small size and long battery life, designers have turned to greater device integration. By offering single ICs that encompass multiple functions, such as DSP, Bluetooth, and battery management on the same chip, hearable designers can successfully achieve products that are low-power and small but still offer competitive features.


Sensor with IMU for Hearables

Feeding the needs of TWS hearables, today’s announcement from STMicroelectronics unveils its new highly-integrated sensor solution for hearables. The new product, the LSM6DSV16BX, is a system-in-package (SiP) solution that centers around an inertial measurement unit (IMU). 

Along with the IMU,  the device also integrates a 3-axis digital accelerometer as well as a 3-axis digital gyroscope, the acceleration and angular rate data from which can be processed to better perform head and motion tracking to deliver greater spatial audio experiences.

Importantly, this chip also features a vibration sensor which is to be applied to bone conduction applications, where vibrations of the wearer’s bone caused by audio can be detected and used in a feedback loop to improve the auditory experience.


Block diagram of the filters in the LSM6DSV16BX.

Block diagram of the filters in the LSM6DSV16BX. Image used courtesy of STMicroelectronics. (Click image to enlarge)


Other features integrated into the LSM6DSV16BX include dedicated features and data processing for motion processing like a finite state machine (FSM), sensor fusion low power (SFLP) block, adaptive self-configuration (ASC), and machine learning core (MLC). 

Importantly, the device is also low power and of a small form factor, with a high-performance power draw of 0.95 mA and a package size of 2.5 mm × 3.0 mm × 0.71 mm. More information is available in the LSM6DSV16BX datasheet.

With the combination of functionality, low power, and small form factor, STMicro believes their new device is perfectly suited for applications like TWS hearables.