The ADXL335 is a complete 3-axis acceleration measurement
system. The ADXL335 has a measurement range of ±3 g minimum.
It contains a polysilicon surface-micromachined sensor
and signal conditioning circuitry to implement an open-loop
acceleration measurement architecture. The output signals are
analog voltages that are proportional to acceleration. The
accelerometer can measure the static acceleration of gravity
in tilt-sensing applications as well as dynamic acceleration
resulting from motion, shock, or vibration.
The sensor is a polysilicon surface-micromachined structure
built on top of a silicon wafer. Polysilicon springs suspend the
structure over the surface of the wafer and provide a resistance
against acceleration forces. Deflection of the structure is measured
using a differential capacitor that consists of independent
fixed plates and plates attached to the moving mass. The fixed
plates 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.