Preliminary Technical Data

ADXL001

This information applies to an ongoing development. Its characteristics and specifications are subject to change without notice.

Analog Devices assumes no obligation regarding future manufacturing unless otherwise agreed to in writing. Patents pending.

Rev. PrA | Page 7 of 10

THEORY OF OPERATION

DESIGN PRINCIPLES

The ADXL001 accelerometer provides a fully differential sensor

structure and circuit path for excellent resistance to EMI/RFI

interference.

This latest generation SOIMEMS device takes advantage of

mechanically coupled but electrically isolated differential

sensing cells. This improves sensor performance and size as a

single proof mass generates the fully differential signal. The

sensor signal conditioning also uses electrical feedback with

zero-force feedback for improved accuracy and stability. This

force-feedback cancels out the electrostatic forces contributed

by the sensor circuitry.

Figure 5 is a simplified view of one of the differential sensor cell

blocks. Each sensor block includes several differential capacitor

unit cells. Each cell is composed of fixed plates attached to the

device layer and movable plates attached to the sensor frame.

Displacement of the sensor frame changes the differential

capacitance. On-chip circuitry measures the capacitive change.

MECHANICAL SENSOR

The ADXL001 is built using the Analog Devices, Inc., SOIMEMS

sensor process. The sensor device is micromachined in-plane

in the SOI device layer. Trench isolation is used to electrically

isolate, but mechanically couple, the differential sensing ele-

ments. Single-crystal silicon springs suspend the structure over

the handle wafer and provide resistance against acceleration forces.

UNIT

SENSING

CELL

MOVABLE

FRAME

FIXED

PLATES

UNIT

FORCING

CELL

ANCHOR

MOVING

PLATE

PLATE

CAPACITORS

ANCHOR

Figure 5. Simplified View of Sensor Under Acceleration