ADXL323 データシートの表示（PDF） - Analog Devices

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ADXL323

Small, Low Power, 2-Axis ±3 g iMEMS® Accelerometer

Analog Devices 

THEORY OF OPERATION

The ADXL323 is a complete 2-axis acceleration measurement

system on a single, monolithic IC. The ADXL323 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.

ADXL323

MECHANICAL SENSOR

The ADXL323 uses a single structure for sensing the X-axis and

Y-axis. As a result, the sense directions of the two axes 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, of

course, be calibrated out at the system level.

PERFORMANCE

Rather than using additional temperature compensation

circuitry, innovative design techniques ensure that high

performance is built in to the ADXL323. 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 13 and Figure 16 show the zero g output performance of

eight parts (X-axis and Y-axis) soldered to a PCB over a −25°C

to +70°C temperature range.

Figure 25 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. 0 | Page 11 of 16

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