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LIS3L02DQ

3

FUNCTIONALITY

3.1 Sensing element

The THELMA process is utilized to create a surface micro-machined accelerometer. The technology al-

lows to carry out suspended silicon structures which are attached to the substrate in a few points called

anchors and free to move on a plane parallel to the substrate itself. To be compatible with the traditional

packaging techniques a cap is placed on top of the sensing element to avoid blocking the moving parts

during the molding phase.

The equivalent circuit for the sensing element is shown in the below figure; when a linear acceleration is

applied, the proof mass displaces from its nominal position, causing an imbalance in the capacitive half-

bridge. This imbalance is measured using charge integration in response to a voltage pulse applied to the

sense capacitor.

The nominal value of the capacitors, at steady state, is few pF and when an acceleration is applied the

maximum variation of the capacitive load is few tenth of pF.

Figure 4. Equivalent electrical circuit

S1x

rot

S2x

S1y

S2y

S1z

S2z