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ADXL335
(Rev.:2008)

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

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 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 band-

width of the device by adding a capacitor. This filtering improves

measurement resolution and helps prevent aliasing.

Preliminary Technical Data

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 with little cross axis sensitivity. Mechanical mis-

alignment 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

circuitry, innovative design techniques ensure high

performance is built-in to the ADXL335. As a result, there is

neither quantization error nor nonmonotonic behavior, and

temperature hysteresis is very low (typically less than 3 mg over

the −25°C to +70°C temperature range).

Rev. PrA | Page 6 of 11

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