AD22284-A Analog Devices Inc, AD22284-A Datasheet - Page 7

• Manufacturer Part Number: AD22284-A
• Manufacturer: Analog Devices Inc

Specifications of AD22284-A

• Family Name: AD22284
• Package Type: CLLCC
• Operating Supply Voltage (min): 4.75V
• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (max): 5.25V
• Operating Temperature (min): -40C
• Operating Temperature (max): 105C
• Operating Temperature Classification: Industrial
• Product Depth (mm): 5mm
• Product Height (mm): 1.98mm
• Product Length (mm): 5mm
• Mounting: Surface Mount
• Pin Count: 8
• Lead Free Status / Rohs Status: Compliant

THEORY OF OPERATION
The ADXL278 provides a fully differential sensor structure and
circuit path, resulting in the industry’s highest resistance to
EMI/RFI effects. This latest generation uses electrical feedback
with zero-force feedback for improved accuracy and stability.
The sensor resonant frequency is significantly higher than the
signal bandwidth set by the on-chip filter, avoiding the signal
analysis problems caused by resonant peaks near the signal
bandwidth.
Figure 5 is a simplified view of one of the differential sensor
elements. Each sensor includes several differential capacitor
unit cells. Each cell is composed of fixed plates attached
to the substrate and movable plates attached to the frame.
Displacement of the frame changes the differential capacitance,
which is measured by the on-chip circuitry.
Complementary 200 kHz square waves drive the fixed plates.
Electrical feedback adjusts the amplitudes of the square waves
such that the ac signal on the moving plates is 0. The feedback
signal is linearly proportional to the applied acceleration. This
unique feedback technique ensures that there is no net
electrostatic force applied to the sensor. The differential
feedback control signal is also applied to the input of the filter,
where it is filtered and converted to a single-ended signal.
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CAPACITORS
Figure 5. Simplified View of Sensor Under Acceleration
SENSING
PLATE
CELL
UNIT
ANCHOR
MOVING
PLATE
FIXED
PLATES
ANCHOR
ADXL278
MOVABLE
FRAME
UNIT
FORCING
CELL