It’s difficult to overstate the impact of battery electric vehicles (BEVs) on automotive electronic design requirements. Indeed, while cars have traditionally been defined by engine performance, exterior design, and powertrains, carmakers are now focused on such things as further attenuating in-cabin noise from electric vehicles (EVs), already intrinsically less noisy than their internal-combustion-engine ICE) cousins.
To do so, manufacturers are focusing on wheel rotation noise and chassis vibration. These efforts aim to allow passengers to better enjoy the journey in a quieter ambient environment.
RNC Sensor Leverages ANC
With its new sensor for road-noise cancellation (RNC) through active-noise-control (ANC) techniques, STMicroelectronics is enabling more acoustically comfortable cars. Noise-cancellation algorithms, working with an array of sensors installed throughout the vehicle, measure the ambient sounds and eliminate vibration using noise-cancelling waveforms that act as anti-vibration (cancelling) sounds.
Optimized for sensing road noise and related vibration, the AIS25BA is said by ST to be a best-in-class automotive MEMS accelerometer for accuracy in controlling and quieting in-cabin acoustic environment.
The AIS25BA has a dedicated time-division-multiplexing (TDM) interface designed to address automotive non-safety applications, particularly wideband ANC and vibration monitoring. TDM is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line. As a result, each signal appears on the line for only a fraction of time in an alternating pattern. This method allows for transmission of two or more digital signals or analog signals over a common channel.
In addition to the TDM interface for the sensor data, the AIS25BA has a user-selectable full-scale range of ±3.85/±7.7 g, and an I²C interface for device configuration.
“In today’s digital age, canceling—not deadening—unwanted sounds is the smart way to ensure a quieter cabin for safer, more enjoyable journeys,” said Simone Ferri, MEMS Sub-Group General Manager of Marketing, Analog, MEMS and Sensors Group, STMicroelectronics. “With the transition to hybrid and electric vehicles, which can be strongly affected by road noise, our AIS25BA accelerometer delivers superior value for system designers.”
Higher Accuracy via MEMS Tech
ST has leveraged its competencies in microelectromechanical-system (MEMS) ICs to give the AIS25BA superior characteristics for enhancing RNC system accuracy. According to the company, the sensor has the lowest electrical noise in the market, which helps vehicle engineers achieve the calmest possible in-car environment.
On the other hand, it has the fast response/low latency needed by the RNC system to calculate corrective waveforms in real-time as well as wide bandwidth to capture disturbances across the full spectrum of sound frequency relevant for the application. Its wide temperature range and mechanical robustness is said to enable placement in the harshest places of today’s vehicles—near the engine or electric drive as well as close to the wheels and suspension.
The AIS25BA 3-axis accelerometer is engineered to prioritize RNC system accuracy. At 30 µg/√Hz in X and Y axes and 50 µg/√Hz in the Z axis, it maintains extremely low noise density, which is claimed to be up to 58% better than the closest competing alternative.
With this noise performance, frequency response covers all of the spectrum relevant for in-car noise cancellation. Similarly, the total sensor latency of 266 µs is engineered to leave the system plenty of time to generate noise-cancellation signals in real-time.
What’s more, the TDM digital interface makes it possible for the system to synchronize the outputs from multiple accelerometers installed to measure vibrations throughout the vehicle. This audio-friendly interface also allows for easy connection to other types of data buses widely adopted in automotive applications. The full-scale measurement range is selectable up to ±7.7 g, giving plenty of margin with respect to the intense vibrations typical of the application. Supply-voltage range is 1.71 to 1.99 V.
AIS25BA Eval Kit
To help engineers get started, STMicroelectronics offers the STEVAL-MKI226KA evaluation kit that’s based on the AIS25BA 3-axis digital accelerometer. The kit is connected to a generic adapter board (STEVAL-MKIGI03B) through a flat cable, to make it compatible with the STEVAL-MKI109V3.
The STEVAL-MKIGI03B can be plugged into a standard DIL 24 socket. The kit provides the complete AIS25BA pinout and comes ready-to-use with the required decoupling capacitors on the VDD power-supply line.
The STEVAL-MKI109V3 motherboard supports this adapter. The board includes a 32-bit microcontroller functioning as a bridge between the sensor and a PC.
It’s possible to use the downloadable graphical user interface (Unico-GUI) or dedicated software routines for customized applications.
The AEC-Q100-compliant AIS25BA is available now in a 14-lead, 2.5- × 2.5- × 0.86-mm LGA package. It’s guaranteed to operate over an extended temperature range from -40 to +125°C and is priced from $3.90 for orders of 1,000 pieces.