MEMS accelerometers for convenience and positioning
The dawn of the first-generation iPhone marked a pivotal moment in technology – it showcased the remarkable power of accelerometers. These sensors, abbreviated as MEMS (Micro Electronic Mechanical Systems) accelerometers, have since infiltrated diverse electronic design realms. This article delves into the world of MEMS accelerometers, unveiling their wide-ranging applications and highlighting their significance in modern electronics.
The Motivation Behind MEMS Development
To understand the essence of MEMS development, one can turn to Kovacs's seminal work, "Micromachined Transducers Sourcebook". While primarily focused on manufacturing processes, the book encapsulates the core motivation behind MEMS advancement: "… micromachined transducers are generally those that are fabricated using tools and techniques intended for the integrated circuit industry..."
Excursus: MEMS technology is more
Though this article predominantly explores accelerometers, the domain of MEMS technology is expansive, encompassing microphones, barometers, optical switches, mirror-based displays, and even more innovative applications. MEMS microphones, for instance, have undergone revolutionary construction, resulting in size reduction and enhanced Signal-to-Noise Ratio (SnR). This trend mirrors the progress in MEMS accelerometers, with the only drawback being the need for higher sensitivity amplifiers due to the comparatively lower signal voltage.
Figure 1: This compares an Infineon IM73A135V01 with a BCM9745-44
Due to the closeness of the fabrication processes, MEMS vendors often integrate analog or digital circuitry onto the MEMS die. A great example is the ADXL213 die shot provided by Richard Kaussler – the MEMS element is in the middle. Circuit designers benefit from this as the systems can often interface with the MEMS sensors using a digital bus such as SPI or I2C.
Accelerometers, Gyroscopes, Magnetometers, and IMUs
Navigating the realm of accelerometer measurement involves grappling with four frequently interchanged terms – accelerometers, gyroscopes, magnetometers, and IMUs (Inertial Measuring Units). Each serves distinct functions. An accelerometer measures an object's proper acceleration, with zero in freefall and 'g' on the earth's surface. Gyroscopes detect circular motion, while magnetometers ascertain orientation with respect to the Earth's magnetic field. IMUs amalgamate accelerometers, gyroscopes, and more for comprehensive navigation, facilitated by miniaturization in MEMS IMUs.
How to Integrate Accelerometers into Circuits
Harnessing accelerometer data necessitates combating noise and drift, often through intricate algorithms provided by sensor vendors. Integrating accelerometers is typically straightforward, illustrated by linking an LSM6DS3USTR to an OrangePi process computer. Standard interfaces facilitate this integration, employing Java and hardware access libraries for seamless software interaction.
Prudent Usage to Avoid Oversampling
Beware the pitfall of oversampling – modern IMUs can flood communication channels with data packets, resulting in bus contention and amplified power consumption. The strategic delegation of accelerometers to plugin PCBs during component procurement offers flexibility, especially during semiconductor shortages.
PCB Layout Strategies for Accuracy
Careful PCB layout is paramount to maintain accelerometer accuracy. Placing components away from stress-prone PCB areas (near mounting holes or "mouse bites") prevents accuracy loss. Ensuring a 15mm buffer around these elements and avoiding close vias safeguards precision.
Tackling Resonance and Inaccuracy
Resonance-induced inaccuracy stemming from signals, including audio circuits and switch mode power supplies, requires vigilance. Avoid routing critical traces near components, maintain spatial separation from SMPS components, and leverage filter capacitors to mitigate this challenge.
For example, TDK specifies signals in the range of 25 to 29 KHz to be especially critical in their version of the application.
During prototyping, hand soldering of IMUs is not recommended due to the uneven heat application. Using a prototyping vendor or a prototyping board can be economically beneficial if no reflow oven is available. Most accelerometer manufacturers provide application notes with further information; these should be obeyed to get maximum accuracy.
Embracing Artificial Intelligence in Accelerometers:
A recent breakthrough involves AI-capable IMUs with signal conditioning logic. This revolutionizes data processing, curbing data transfer volume and reducing the risk of bus contention. Moreover, optimized power consumption and advanced algorithms embedded in AI-capable IMUs elevate performance, albeit with challenges of supply flexibility due to its proprietary nature.
Conclusion
MEMS accelerometers have redefined modern electronics, influencing convenience, positioning, and design efficiency. From the inception of MEMS development to the adoption of AI-capable IMUs, their journey has been marked by innovation and progress. As we navigate this dynamic landscape, MEMS accelerometers continue to shape the future of technology.