E-compass chip for precision dead-reckoning navigation
Integration of a high-performance MEMS accelerometer saves space and power compared to existing alternatives, ST adds. Fitness-tracking smartphone apps, smartwatches, and bands need continuous location data for mapping and recording, and accuracy is critical for wearers who like to monitor their progress and share achievements online. A built-in eCompass helps calculate location when satellite signals are unavailable, such as inside buildings or when running or cycling under tree cover. However, current solutions can give errors of about 10° in latitudes such as Northern Italy or Northern California. This can put the user off course by 150m or more in every km travelled.
ST’s LSM303AGR eCompass cuts the heading error to less than 4°, using the company’s technology for manufacturing high-accuracy magnetic sensors. This enhanced accuracy, combined with ultra-low-power operation consuming up to 50% less than competing devices when in low-power mode, is offered for high-precision Pedestrian Dead Reckoning (PDR) on mobile devices.
The LSM303AGR also enhances dead-reckoning accuracy in applications such as automotive navigation, and maintains accuracy over the full temperature range from -40°C to 85°C, whereas competing devices can vary by as much as 35% or more over small intervals such as between normal room temperature and human-body temperature.
As an all-in-one eCompass IC fabricated on a single die, the LSM303AGR combines a 3-axis MEMS accelerometer leveraging ST’s ThELMA technology and a very compact 3-axis Anisotropic Magneto-Resistive (AMR) sensor that delivers higher sensitivity and lower noise than conventional Hall sensors. ThELMA abbbreviates Thick Epi-Poly Layer for Microactuators and Accelerometers; one of ST’s processes for the creation of MEMS mechanisms, using wafer-to-wafer bonding and a protective silicon cap. ST’s own AMR manufacturing process technology gives the LSM303AGR superior temperature stability compared to Giant Magneto-Resistive (GMR) or Tunnel Magneto-Resistive (TMR) technology. ST’s AMR sensor also has high dynamic range, which further contributes to the device’s accuracy by preventing magnetic saturation in areas of high ambient-field strength.
ST adds that it has tested the LSM303AGR’s magnetic-sensing accuracy at various latitudes and recorded superior accuracy and temperature stability over current eCompass ICs and pure magnetic sensors from competing manufacturers.
ST’s LSM303AGR eCompass is packaged as a 2 x 2 x 1 mm 12-lead LGA, priced from $1.485 (1000).
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