New 2-Axis Accelerometers from STMicroelectronics Pack Increased Performance into Smaller, Thinner Package
Thursday September 29, 6:00 am ET
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The new devices incorporate in a single package both a robust, dual-axis MEMS sensor and a CMOS interface chip that provides two simultaneous, real- time analogue outputs: one for side-to-side (lateral) and one for forward- backward (longitudinal) directions. The sensor elements, which are fabricated using a dedicated process developed and optimized by ST for the production of inertial and rotational sensors, can measure both DC accelerations (static tilt) and AC accelerations with high resolution, can withstand shocks of up to 10,000g, and incorporate a built-in self-test capability that allows the user to verify functionality of the device. The interface chip incorporates all the multiplexer, charge amplifier, demultiplexer, sample-and-hold, and reference circuits required to provide the two analog output signals, with a typical bandwidth of 2.0kHz. To maximize robustness and immunity against external disturbances, the complete signal processing chain uses a fully differential structure, with a final stage converting the differential signal into a single-ended one to be compatible with the external world.
Key benefits of the new devices include: very low noise and consequent high resolution of 0.3mg (typical); a low power consumption (typically 850 microamps supply current at 3.3V), which makes the devices ideal for battery-operated applications; the small package, which reduces board space and therefore the system cost; high temperature stability and low offset, which eliminate the need for calibration in most applications; the ability to adjust the bandwidth via a single external capacitor per channel to optimize system performance, and operation over a -40 degrees to +85 degrees C temperature range.
Accelerometers based on silicon-micromachined MEMS technology are highly cost-effective because they provide high sensitivity, robustness, and precision with the economies of scale of the high volume wafer process used to make integrated circuits. ST's 2-axis acceleration sensors incorporate a suspended silicon structure that is able to move with two degrees of freedom above a silicon substrate, with movement along each axis producing a change in capacitance that is communicated to the interface chip. The interface chip converts these capacitance changes into calibrated analog voltages proportional to the movement. As a result, board mounting is much simpler than for two separate linear sensors. In addition, the interface chip is factory-trimmed to ensure repeatable performance without production-line adjustments in the end product.
The built-in Self-Test facility allows the user to verify both the mechanical and electrical parts of the device. Applying a logic signal to the Self-Test input pin causes an electric field to be established inside the device that has the same effect as a real physical acceleration, causing the sensor to move and generating a resulting change in capacitance that is detected and conditioned by the interface chip and then can be compared with the expected value.
The interface chip is factory calibrated for Sensitivity and Zero-g Offset. The trimming values are stored inside the device in a non-volatile structure. Whenever the device is turned on, the trimming parameters are downloaded into registers for use during operation. This allows the user to employ the device without further calibration.
Ideal for use in mobile terminals, gaming, and virtual-reality devices, free-fall detection for data protection in laptops and other portable equipment, inertial navigation and anti-theft systems, and a wide range of appliance, robotics, and other industrial applications, the LIS2L02AL and LIS2L06AL are available now at prices of US$2.80 and US$3.10, respectively, in quantities of 10,000 pieces.
This press release is also available at
http://www.st.com/stonline/press/news/year2005/p1678f.htm
... with links to further information on the LIS2L02AL and LIS2L06AL and ST's complete range of MEMS products.
About STMicroelectronics
STMicroelectronics is a global leader in developing and delivering semiconductor solutions across the spectrum of microelectronics applications. An unrivalled combination of silicon and system expertise, manufacturing strength, Intellectual Property (IP) portfolio and strategic partners positions the Company at the forefront of System-on-Chip (SoC) technology and its products play a key role in enabling today's convergence markets. The Company's shares are traded on the New York Stock Exchange, on Euronext Paris and on the Milan Stock Exchange. In 2004, the Company's net revenues were $8.76 billion and net earnings were $601 million. Further information on ST can be found at http://www.st.com.
Source: STMicroelectronics
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