ADXL335 View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

ADXL335

Small, Low Power, 3-Axis ±3 g Accelerometer

Analog Devices 

ADXL335

THEORY OF OPERATION

The ADXL335 is a complete 3-axis acceleration measurement

system. The ADXL335 has a measurement range of ±3 g mini-

mum. 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 meas-

ured 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.

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.

MECHANICAL SENSOR

The ADXL335 uses a single structure for sensing the X, Y, and

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

orthogonal and have little cross-axis sensitivity. Mechanical

misalignment of the sensor die to the package is the chief

source of cross-axis sensitivity. Mechanical misalignment

can, of course, be calibrated out at the system level.

PERFORMANCE

Rather than using additional temperature compensation circui-

try, innovative design techniques ensure that high performance

is built in to the ADXL335. As a result, there is no quantization

error or nonmonotonic behavior, and temperature hysteresis

is very low (typically less than 3 mg over the −25°C to +70°C

temperature range).

Rev. B | Page 10 of 16

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