MEMS sensors have revolutionized the way we interact with everyday technology, making it easier and more user-friendly. MEMS sensors are providing functions such as 2- and 3-axis linear accelerometers as well as single- and multi-axis gyroscopes Manufacturers such as STMicroelectronics have now introduced a 6D digital geomagnetic module that combines a 3-axis accelerometer and 3-axis magnetometer in a single package.
The consumer market is driving the demand for tiny, inexpensive, low-voltage and low-power devices with MEMS sensors built in.
Handheld devices such as mobile phones, Mp3 and Mp4 players, and portable PCs are all battery operated and are becoming smaller and thinner. The supply voltage goes down to 1.8 V, and the electrical current has to be lower than 100 μA. Additionally, customers have come to expect a power-down feature as well as multiple interrupt pin functions to simplify product integration in the final consumer product.
Newest MEMS product families
Ultra-low power 3-axis accelerometers
MEMS accelerometer portfolios have been extended with a new 3-axis digital-output accelerometer that has a significant 90 percent power reduction compared to currently available solutions on the market. They also feature a miniature footprint and enhanced functionalities. With operating current consumption as low as 2 μA, the 3 mm x 3 mm x 1 mm accelerometer is a perfect fit for motion-sensing features and applications in space- and power-constrained consumer devices such as mobile phones, games, and remote controllers.
The sensor provides accurate output across selectable full-scale ranges of ±2g/±4g/±8g/±16g with excellent offset and sensitivity stability over time and temperature.
The accelerometers have an embedded temperature sensor and three analog-to-digital converter channels for easy integration with companion chips such as gyroscopes. It embeds a host of enhanced features, including click and double-click recognition, 4D/6D orientation detection, and a power-saving mode.
A programmable FIFO (first-in first-out) memory block and two programmable interrupt signals that enable immediate notification of motion detection, click/double-click events, and other conditions have been added.
3-axis digital output gyroscope
The MEMS gyroscope portfolio has been extended with a high performance, 3-axis, digital-output gyroscope that embeds a FIFO (first-in first-out) memory block for smarter power management.
New gyroscope chips integrate a FIFO memory block that stores up to 96 levels, split in 32 sample sets of x-, y-, and z-axis data. This feature removes the need of continuous communication for angular rate data acquisition between the sensor and the host processor so that the host processor can then spend more time in a sleep mode to dramatically decrease the overall system power consumption.
Application designers can program the FIFO to work at several different operating modes. A dedicated watermark (reference) interrupt can be generated when the memory is filled to that watermark level. Many MEMS gyroscopes employ the concept of a single sensing structure for motion measurement along all three orthogonal axes. This design approach eliminates the interference between each axis and significantly increases the accuracy and reliability in a wide range of consumer and industrial applications, including advanced user interface for gaming and portable devices, motion tracking, and camera image stabilization.
The newest MEMS gyroscope boosts excellent zero-rate level and sensitivity stability over time and temperature, removing the need of further calibration on the customer side depending on applications. With advanced filtering capabilities for improved noise reduction and application flexibility, users are able to set the desired bandwidth through embedded high- and low-pass filters. The sensor and ASIC interface are housed inside an ultra-small 4 mm x 4 mm x 1 mm package, addressing the size constraints of current and future consumer applications. The gyroscope outputs 16-bit data on three axes with a wide set of user-programmable, full-scale ranges up from ±250 dps up to ±2000 dps, while low full-scale range can be used to detect and measure fast gestures and movements.
GEO-magnetic module digital compass
MEMS technology contributed to the integration of a 3-axis digital accelerometer with a 3-axis digital magnetic sensor in a single module. The digital compass module combines high accuracy with small form factor and low power consumption at a competitive cost, meeting the growing market demand for advanced navigation capabilities and emerging smart location-based services.
The high-performance system-in-package digital compass uses magneto-resistive technology from Honeywell and aims to accelerate the adoption of the enhanced tilt-compensated digital compass in portable consumer applications, including direction finding, map/display orientation, location-based services, and pedestrian dead reckoning. The combination of high-performance motion and magnetic sensing enhances the mobile user experience in a number of ways. Modules add forward direction orientation that enables application developers to improve the use of limited phone/PDA display size for maps by putting the current user position at the bottom of the map with the rest of the display in the forward (“up ahead”) direction. The digital compass provides accurate heading information to indicate the direction in which a person or vehicle is moving. It also supports dead-reckoning applications, including pedestrian navigation in places where GPS is not available.
Compass modules in handsets open new possibilities for advanced location-based services. With compassing and GPS capabilities, consumers will be able to identify and retrieve information on nearby points of interest such as restaurants or shops by simply pointing their mobile devices in the directions of the objects concerned. High-precision sensing couples with smart embedded features, including wakeup/power-down function and 6D orientation recognition, which signals if the device is up or down along all three axes (x, y, z). The device has a linear acceleration full-scale of ±2/±4/±8 g and a magnetic field full-scale from ±1.3 up to ±8 gauss, both fully selectable by the user. The magnetic sensing element that measures the strength and direction of the Earth’s magnetic field and determines the heading relative to magnetic north is based on Honeywell’s anisotropic magneto-resistive (AMR) technology. This technology combines best-in-class accuracy in compass calculations with low power consumption, which is crucial in battery-hungry portable devices. The AMR technology provides the same sensitivity on the z-axis as it does on the x- and y-axes, eliminating the need for flux concentrators used in Hall-effect type sensors that can shift the sensor offset after it has been magnetized.
This market-unique, three-axis sensing approach reduces measurement errors in ultra-low magnetic field strength environments such as metal buildings, automobiles, or in higher latitudes like Canada or Northern Europe. Moreover, Honeywell’s magnetic sensor design includes a built-in offset cancellation circuit to minimize the need for calibration and patented set/reset straps that degauss or demagnetize the sensor for each measurement to improve the heading accuracy.
Single- and dual-axis gyroscopes
MEMS motion sensors have shrunk in size over previous devices and reduced power consumption. New, high-performance angular-motion sensors open the way to a wide range of innovative consumer applications, including motion tracking, motion-based user interface, gesture-controlled gaming and 3D pointing devices, image stabilization in digital video and still cameras, and navigation and GPS assistance.
The newest single-axis (yaw) and two-axis (pitch-and-roll, pitch-and-yaw) MEMS gyroscopes fit in miniature packages to address the size constraints of consumer applications. Power consumption is another key factor, especially in battery-operated devices. Some gyroscopes include a power-down mode (when the entire device is switched off) and a sleep mode in which part of the circuitry is turned off to significantly reduce power consumption, allowing very fast turn-on time and smart power cycling.
