ADXL316

Data Sheet

Rev. 0 | Page 10 of 14

THEORY OF OPERATION

The ADXL316 is a complete 3-axis acceleration measurement

system. The ADXL316 has a measurement range of ±16 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 with an amplitude

proportional to acceleration. Phase-sensitive demodulation

techniques determine the magnitude and direction of the

acceleration.

A 32 kΩ resistor can amplify and bring the demodulator output

off-chip. The user then sets the signal bandwidth of the device

by adding a capacitor. This filtering improves measurement

resolution and helps prevent aliasing.

MECHANICAL SENSOR

The ADXL316 uses a single structure for sensing the X-, Y-, and

Z-axes. As a result, the three axes sense directions are highly

orthogonal with minimal cross axis sensitivity. Mechanical

misalignment of the sensor die to the package is the chief source

of cross axis sensitivity. Mechanical misalignment can be calibrated

out at the system level.

PERFORMANCE

Rather than using additional temperature compensation circuitry,

innovative design techniques ensure high performance is built-in

to the ADXL316. As a result, there is neither quantization error nor

nonmonotonic behavior, and temperature hysteresis is very low.