ADXL206 Analog Devices, ADXL206 Datasheet - Page 9

• Manufacturer Part Number: ADXL206
• Description: High Temperature iMEMS Accelerometer
• Manufacturer: Analog Devices

THEORY OF OPERATION
The ADXL206 is a complete acceleration measurement system
on a single, monolithic IC. The part contains a polysilicon, surface-
micromachined sensor and signal conditioning circuitry to imple-
ment an open-loop acceleration measurement architecture. The
output signals are analog voltages proportional to acceleration.
The ADXL206 is capable of measuring both positive and negative
accelerations to at least ±5 g. The accelerometer can measure
static acceleration forces such as gravity, allowing it to be used
as a tilt sensor.
The sensor is a surface-micromachined, polysilicon structure
built on top of the silicon wafer. Polysilicon springs suspend the
structure over the surface of the wafer and provide 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 beam and unbalances the differential capacitor, resulting in
an output square wave whose amplitude is proportional to accel-
eration. Phase-sensitive demodulation techniques are then used
to rectify the signal and determine the direction of the acceleration.
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The output of the demodulator is amplified and brought off chip
through a 32 kΩ resistor. At this point, the user can set the signal
bandwidth of the device by adding a capacitor. This filtering
improves measurement resolution and helps prevent aliasing.
PERFORMANCE
Rather than using additional temperature compensation circuitry,
innovative design techniques have been used to ensure that high
performance is built in. As a result, there is essentially no quantiza-
tion error or nonmonotonic behavior, and temperature hysteresis
is very low (typically less than 2 mg over the −40°C to +175°C
temperature range).
Figure 12 shows the 0 g output performance of eight parts over
the −40°C to +175°C temperature range.
Figure 11 and Figure 14 show the typical sensitivity shift over
temperature for V
V
S
= 5 V, but it is very good over the full supply voltage range.
S
= 5 V. Sensitivity stability is optimized for
ADXL206