Sensors

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Freescale Semiconductor, Inc.

MMA7660FC

PRINCIPLE OF OPERATION

The Freescale Accelerometer consists of a MEMS capacitive sensing g-cell and a signal conditioning ASIC contained in a

single package. The sensing element is sealed hermetically at the wafer level using a bulk micro machined cap wafer. The

g-cell is a mechanical structure formed from semiconductor materials (polysilicon) using masking and etching processes.

The sensor can be modeled as a movable beam that moves between two mechanically fixed beams (Figure 4). Two gaps are

formed; one being between the movable beam and the first stationary beam and the second between the movable beam and the

second stationary beam.

The ASIC uses switched capacitor techniques to measure the g-cell capacitors and extract the acceleration data from the

difference between the two capacitors. The ASIC also signal conditions and filters (switched capacitor) the signal, providing a

digital output that is proportional to acceleration.

Figure 4. Simplified Transducer Physical Model

ACCELERATION