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ST's latest acceleration sensors

Posted: 04 Oct 2005 ?? ?Print Version ?Bookmark and Share

Keywords:stmicroelectronics? st? acceleration sensor? lis2l02al? lis2l06al?

Sensors offer tighter offset tolerances

STMicroelectronics (ST) extended its range of dual-axis acceleration sensors with the introduction of two new devices housed in the tiny, lead-free LGA (Land Grid Array) package measuring 5-by-5-by-1.5mm.

The LIS2L02AL and LIS2L06AL are 2-axis ultra-compact linear accelerometers that complement the company's existing 'low g' accelerometers, while offering tighter offset tolerances, improved temperature drift performance, and a package whose smaller footprint and height is suitable to mobile phones, PDAs, laptops and PCMCIA cards characterized by slim product form factors. The LIS2L02AL provides a full-scale output range of 20g (typical), while the LIS2L06AL provides a dynamically selectable choice of 2g and 6g.

These 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 2kHz. 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.

According to ST, key benefits of its new products include very low noise and consequent high resolution of 0.3mg (typical); a low power consumption (typically 850?A supply current at 3.3V); the small package, which reduces board space and therefore the system cost; high temperature stability and low offset; the ability to adjust the bandwidth via a single external capacitor per channel to optimize system performance; and operation over a -40C to 85C temperature range.

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 than can be compared with the expected value.

The interface chip is factory calibrated for Sensitivity and Zero-g Offset, and 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, explained ST.

Already available, the LIS2L02AL and LIS2L06AL sensors are priced at $2.80 and $3.10 in quantities of 10,000 pieces, respectively.

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