Motion Processing for CE Applications
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Motion processing characterizes measures and intelligent processing of three dimensional (3D) movements. Motion processing technology has become the technological milestone that drives User Interface (UI) innovations in Consumer Electronic (CE) product design. Motion processing function promises to become the “must have” feature able to convert any standard handset into 3D intelligent equipment extending the means of how the user can interact with the mobile device. Adaptation of motion processing technology delivers new user experiences and functions to mobile handsets through enhancing web and multimedia navigation, providing Optical Image Stabilization (OIS), Location Based Services (LBS), mobile 3D gaming, and many other applications.
Motion Processing Implementations
Common methodology used for motion processing applications assumes measurements and processes of linear and rotational movements with use of accelerometer, magnetometer or a gyroscope. Accelerometers provide information about linear movement as a sum of linear and centripetal acceleration affected by the gravity and vibration. Extraction of a single element from the linear motion information given by accelerometer requires an addition of device able to provide detailed information about rotational movement. The most intuitive solution providing rotational movement information required for complete motion processing solution is magnetometer. Unfortunately its’ output data is relative to magnetic north. Moreover magnetometer is prone to be affected by external magnetic fields sources and has limited ability to respond to fast rotational movements. Thus the key technology commonly used for measurement of angular rate of rotation is a gyroscope. The gyroscope is the only inertial sensor providing accurate and latency free rotational movement information without being affected by gravitational, magnetic or other external factors.
Application Note: InvenSense ARM Reference Board
CE Targeted Gyroscope
The only technology feasible for measures of absolute rate of rotation suitable for consumer grade products is the gyroscope based on Micro-ElectroMechanical Systems (MEMS) technology. Only MEMS device can overcome limitations such as large dimension and fragile structure of the conventional attitude indicator. Another factor making MEMS devices very attractive for CE market is relatively low price of MEMS based gyroscope with accuracy comparable with the conventional rotating one. Typical MEMS implementations use miniaturized structures vibrating in the plane which will be rotated. The Coriolis effect implicates an acceleration of the vibrating proof masses during rotation. This causes out of plane motion (deflection) of vibrating structure during rotation which is detected by transducer. The resulting signal produce voltage that is proportional to the angular rate. It is that so because detected Coriolis acceleration arising in a rotating reference frame is proportional to the angular velocity which specifies the angular speed and the axis about which the object is rotating.
State of the art CMOS-MEMS Fabrication Process
The foundation of InvenSense motion processing solution is proprietary Nasiri fabrication process. Nasiri fabrication combines CMOS and MEMS (CMOS-MEMS) technologies in a single, small and cost effective standard package. Through combining standard CMOS and MEMS wafers InvenSense has pioneered a technological breakthrough in manufacturing low cost MEMS motion processing solutions. This unique fabrication technology allows combining mixed signal IC with MEMS based motion sensor simultaneously guaranteeing the reduction of manufacturing steps, wafer level testing procedures and use of chip scale packaging. Thanks to Nasiri fabrication process InvenSense is able to provide MEMS sensors with industry leading form factor, performance, reliability, integration and lowest cost.
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InvenSense Motion Processing Technology
InvenSense 3-axis MEMS gyroscopes are the world’s first single-chip and digital-output devices optimized for CE applications. Each motion processing device is equipped with 16-bit Analog-to-Digital-Converters (ADC) used for digitizing the gyroscope sensor outputs, a low-pass filter with user-selectable bandwidth and fast mode (400kHz) I2C or SPI interfaces. These digital-output gyroscopic sensors provide a full-scale range up to ±2000 degrees per second (dps) and low power operation (2.1V up-to 3.6V). Additional features include internal oscillator and embedded temperature sensor for enhancing sensor temperature stability. All devices in the family are available in a very small 4x4x0.9mm QFN packages providing dramatic package size reduction compared with competing multi-chip solutions. InvenSense family of motion processing devices includes ITG-3200, IMU-3000 and MPU-3000.
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The ITG-3200 provides raw 3-axis gyroscope data output to serial communications bus. The MPU and IMU devices have extended functionality through addition of an embedded Digital Motion Processor™ (DMP), a 512 byte FIFO and a secondary I2C master bus which could be used for communication with third party accelerometers. Combination of 3-axis gyroscope and accelerometer data provides 6-axis fusion output of processed acceleration and rotational rate information within one motion processing device. The on-chip FIFO and external sensor bus provide the host processor the ability for burst read of the sensor data for more reliable use of available Microcontroller (MCU) resources. This feature could also significantly lower the power consumption as system MCU could enter the sleep mode while IMU or MPU collects motion information using secondary sensor bus and on-chip FIFO.
The on-chip DMP hardware accelerator engine can be programmed to provide advanced UI functionality for such an applications as AirSign™ signature authentication, TouchAnywhere™ application, navigation control or MotionCommand™ gesture shortcuts. In order to speed-up time-to-market of a new CE device equipped with MPU-3000 or IMU-3000 InvenSense provides a Motion Processing Library (MPL). MPL contains the implementation of motion processing algorithms and provides an Application Programming Interface (API) layer simplifying the usage of these core algorithm engines. Moreover the availability of sample motion processing applications such as image stabilization or gesture recognition could significantly reduce the time required for development of new CE products. Evaluation Kits (EVK) are available for all the triple-axis devices.
