ADXL322EB Просмотр технического описания (PDF) - Analog Devices

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ADXL322EB

Small and Thin ±2 g Accelerometer

Analog Devices 

THEORY OF OPERATION

The ADXL322 is a complete acceleration measurement system

on a single monolithic IC. The ADXL322 has a measurement

range of ±2 g. 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 measures static acceleration forces, such as

gravity, which allows it to be used as a tilt sensor.

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 inde-

pendent fixed plates and plates attached to the moving mass.

The fixed plates are driven by 180° out-of-phase square waves.

Acceleration deflects the beam and unbalances the differential

capacitor, resulting in an output square wave whose amplitude

is proportional to acceleration. Phase-sensitive demodulation

techniques are then used to rectify the signal and determine

the direction of the acceleration.

The demodulator’s 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.

ADXL322

PERFORMANCE

Rather than using additional temperature compensation

circuitry, innovative design techniques were used to ensure

built-in high performance. As a result, there is neither quanti-

zation error nor nonmonotonic behavior, and temperature

hysteresis is very low (typically less than 5 mg over the −20°C

to +70°C temperature range).

Figure 11 shows the zero g output performance of eight parts

(X- and Y-axis) over a −20°C to +70°C temperature range.

Figure 14 demonstrates the typical sensitivity shift over tem-

perature for supply voltages of 3 V. This is typically better than

±1% over the −20°C to +70°C temperature range.

Rev. 0 | Page 11 of 16

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