ADXL337 데이터 시트보기 (PDF) - Analog Devices

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ADXL337

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

Analog Devices 

ADXL337

THEORY OF OPERATION

The ADXL337 is a complete 3-axis acceleration measurement

system. The ADXL337 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.

The demodulator output is amplified and brought off chip

through a 32 kΩ resistor. The user then sets the signal bandwidth

(BW) of the device by adding a capacitor. This filtering improves

measurement resolution and helps prevent aliasing.

MECHANICAL SENSOR

The ADXL337 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 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 that high performance is built

into the ADXL337. 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 +85°C temperature

range).

Rev. 0 | Page 10 of 16

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