發布日期：2022-04-17 點擊率：66
Some of the most amazing features integrated in today’s mobile consumer electronics devices are thanks to accelerometers. Just think – the popularity of the Nintendo Wii and Apple’s iPhone and iPad probably wouldn’t have happened without the help of this motion-sensing technology.
The market used to be very automotive focused, consuming mostly one- and two-axis accelerometers, said Jérémie Bouchaud, director and principal analyst for MEMS at market research firm iSuppli Corp. Now that consumer electronics and cell phones have become the major driver of unit growth and revenue for accelerometers, the supply chain has shifted to three-axis devices, he said.
iSuppli Corp. expects accelerometers to account for 44 percent of total motion sensor revenue for cell phones in 2014. The number of cell phones incorporating accelerometers is expected to claim a 65 percent market share, up from 28 percent in 2009.
iSuppli projects that shipments of motion sensors – including accelerometers, compasses, gyroscopes, and pressure sensors – for cell phones will reach 2.2 billion units in 2014, up from 435.9 million in 2009. This translates into a more than $1 billion market in 2014, up from $316 million in 2009.
Bouchaud attributes some of this significant growth to the Chinese gray handset market, which consumed nearly 20 percent of the global shipments of accelerometers for cell phones last year. “It’s also a different market because it’s not in the hands of a few OEMs. It is a market with hundreds of independent design houses that are manufacturing these phones,” he said.
Lower average selling prices are also fueling growth, said iSuppli. The market research firm projects that pricing for low-end 6-bit three-axis accelerometers will fall to 34 cents by 2014, down from 90 cents in 2008.
Bouchaud said prices have been dropping fast. ASPs have fallen from $2 in 2007 to $1 in 2008 to 70 cents in 2009.
However, the share of higher-end 12- to 14-bit accelerometers will increase, because they will be used by designers for more sophisticated hand gesture recognition and navigation applications, according to iSuppli.
To meet growing demand for more sophisticated functionality in mobile devices, several top suppliers of three-axis accelerometers – including Analog Devices, Bosch Sensortec, Freescale, and STMicro – have beefed up their product portfolios over the past year with some significant enhancements aimed at lower power consumption, higher resolution, and smaller packaging.
Designing for energy efficiency started early last year with the introduction of the ADXL345 from Analog Devices, Inc. (Norwood, Mass.). The ultra-low-power three-axis iMEMS digital accelerometer was designed to boost power efficiency in mobile devices. 
ADI claimed the ADXL345 was the lowest-power device in its class, achieving an 80 percent power savings compared to competing three-axis inertial sensors. The device features an on-chip FIFO (first-in/first-out) memory block that stores up to 32 sample sets of X, Y, and Z data that helps save additional system power. Other key specs include up to 13-bit resolution and SPI and I2C digital interfaces.
The accelerometer also provides an output data range that scales from 0.1Hz to 3.2kHz, which allows portable system designers to better manage energy consumption by precisely allocating power for a given system function and reserving unused power for other uses.
In addition, ADI simplifies hardware configurations by incorporating an on-chip analog-to-digital converter (ADC) in the ADXL345.
New product development is focused on getting the devices smaller, reducing power consumption, and improving price, said Dr. Frank Melzer, CEO for Bosch Sensortec GmbH (Reutlingen, Germany).
As an example, the company’s last development is the 2mm x 2mm LGA package for acceleration sensors, targeting space-constrained applications. The package delivers a 55 percent reduction in surface area compared to the 3mm x 3mm LGA housings.
Bosch Sensortec’s BMA220 3-axis MEMS sensor measures 2mm x 2mm x 0.98mm and is the first be housed in the LGA package. The company said the smaller size does not impact its functionality.
The triaxial g-sensor with digital data output offers four programmable ranges from +/-2g to +/-16g and integrated evaluation electronics for recognizing specific motion patterns, which eliminate the need for extensive signal evaluation by the host application’s microcontroller, thus reducing energy use and extending battery life in end products.
Bosch also introduced a highly sensitive accelerometer last year. Melzer said the BM180 is very accurate and can detect movements up to 0.00025g/0.25-degree tilt change and offers 14-bit resolution. He believes it’s the best rating for devices aimed at consumer electronics applications.
The latest advances from STMicroelectronics (Geneva, Switzerland), the number one supplier of accelerometers in the consumer electronics market, includes next-generation devices housed in 2mm x 2mm packages – similar to Bosch’s offering – and reduced current consumption below 10 microamps at a sampling rate of 100Hz.
ST also said these valves can further shrink to just a few microamps at lower data rates. ST’s accelerometers also embed a host of enhanced features, including click and double-click recognition, motion-detection/wake-up, and 4D/6D orientation detection. They incorporate a temperature sensor and three ADC channels for easy integration with companion chips such as gyroscopes. Other features include a programmable FIFO and two programmable interrupt signals that enable immediate notification of motion detection, click/double click events, and other conditions.
The new family is pin-to-pin and software-compatible with ST’s current 3mm x 3mm three-axis digital accelerometers, so it’s easier for designers to hot swap and protect their investment in application development. These three-axis accelerometers will be available in volume production in the third quarter of 2010.
ST’s announcement was followed by the introduction of an energy-efficient three-axis accelerometer from Freescale Semiconductor (Austin, Texas) with embedded features that detect precise movement via highly sensitive gesture and orientation detection capabilities. 
The MMA8450Q accelerometer, housed in a 3mm x 3mm x 1mm package, features 12-bit digital resolution and an internal 32-sample/axis (X-, Y-, and Z-axis) FIFO memory buffer to improve overall system power savings and response time by offloading functions from the host processor.
The +/-2-, +/-4-, and +/-8-g three-axis digital accelerometer with I2C also features configurable power-saving modes and auto-wake/sleep capability for optimal current consumption.
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