Datasheet ADXL327 (Analog Devices) - 11

ADXL327 THEORY OF OPERATION
The ADXL327 is a complete 3-axis acceleration measurement
MECHANICAL SENSOR
system. The ADXL327 has a measurement range of ±2 g minimum. The ADXL327 uses a single structure for sensing the X, Y, and Z axes. It contains a polysilicon surface micromachined sensor and signal As a result, the three axes sense directions are highly orthogonal conditioning circuitry to implement an open-loop acceleration with little cross-axis sensitivity. Mechanical misalignment of the measurement architecture. The output signals are analog voltages sensor die to the package is the chief source of cross-axis sensitivity. that are proportional to acceleration. The accelerometer can Mechanical misalignment can, of course, be calibrated out at measure the static acceleration of gravity in tilt sensing applications, the system level. as well as dynamic acceleration, resulting from motion, shock, or vibration.
PERFORMANCE
The sensor is a polysilicon surface micromachined structure Rather than using additional temperature compensation circuitry, built on top of a silicon wafer. Polysilicon springs suspend the innovative design techniques ensure that high performance is structure over the surface of the wafer and provide a resistance built-in to the ADXL327. As a result, there is neither quantization against acceleration forces. Deflection of the structure is measured error nor nonmonotonic behavior, and temperature hysteresis is using a differential capacitor that consists of independent fixed very low (typically <3 mg over the −25°C to +70°C temperature plates and plates attached to the moving mass. The fixed plates range). are driven by 180° out-of-phase square waves. Acceleration deflects the moving mass and unbalances the differential capacitor resulting in a sensor output whose amplitude is proportional to acceleration. Phase-sensitive demodulation techniques are then used to determine the magnitude and direction of the acceleration. The demodulator output is amplified and brought off-chip through a 32 kΩ resistor. The user then sets the signal bandwidth of the device by adding a capacitor. This filtering improves measurement resolution and helps prevent aliasing. Rev. 0 | Page 10 of 16 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION MECHANICAL SENSOR PERFORMANCE APPLICATIONS INFORMATION POWER SUPPLY DECOUPLING SETTING THE BANDWIDTH USING CX, CY, AND CZ SELF TEST DESIGN TRADE-OFFS FOR SELECTING FILTER CHARACTERISTICS: THE NOISE/BW TRADE-OFF USE WITH OPERATING VOLTAGES OTHER THAN 3 V AXES OF ACCELERATION SENSITIVITY LAYOUT AND DESIGN RECOMMENDATIONS OUTLINE DIMENSIONS ORDERING GUIDE