ADXL330 Просмотр технического описания (PDF) - Analog Devices

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ADXL330

Digital Accelerometer

Analog Devices 

THEORY OF OPERATION

The ADXL330 is a complete 3-axis acceleration measurement

system on a single monolithic IC. The ADXL330 has a measure-

ment 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 accelera-

tion 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.

ADXL330

MECHANICAL SENSOR

The ADXL330 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 ADXL330. 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).

Figure 14, Figure 15, and Figure 16 show the zero g output

performance of eight parts (X-, Y-, and Z-axis) soldered to a

PCB over a −25°C to +70°C temperature range.

Figure 26, Figure 27, and Figure 28 demonstrate the typical

sensitivity shift over temperature for supply voltages of 3 V. This

is typically better than ±1% over the −25°C to +70°C

temperature range.

Rev. A | Page 11 of 16

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