(November 15, 2010) -- Jay Esfandyari, Roberto De Nuccio, Gang Xu, STMicroelectronics, introduce how MEMS gyroscopes work and their applications, the main parameters of a MEMS gyroscope with analog or digital outputs, practical MEMS gyroscope calibration techniques, and how to test the MEMS gyroscope performance in terms of angular displacement.
The significant size reduction of multi-axis MEMS gyroscope structures and their integration with digital interface into a single package of a few square millimeters of area at an affordable cost have accelerated the penetration of MEMS gyroscopes into hand-held devices.
MEMS gyroscopes have enabled exciting applications in portable devices including optical image stabilization for camera performance improvement, user interface for additional features and ease of use, and gaming for more exciting entertainment. Further applications such as dead reckoning and GPS assistance that require high sensitivity, low noise, and low drift over temperature and time are on the horizon.
Here, we discuss the methods and techniques of quickly getting meaningful information from a MEMS gyroscope in terms of angular velocity and angular displacement measurements.
MEMS gyroscope introduction
MEMS gyroscopes are making significant progress towards high performance and low power consumption. They are mass produced at low cost with small form factor to suit the consumer electronics market.
MEMS gyroscopes use the Coriolis Effect to measure the angular rate, as shown in Figure 1.
When a mass (m) is moving in direction v→ and angular rotation velocity ?→ is applied, then the mass will experience a force in the direction of the arrow as a result of the Coriolis force. And the resulting physical displacement caused by the Coriolis force is then read from a capacitive sensing structure.
Most available MEMS gyroscopes use a tuning fork configuration. Two masses oscillate and move constantly in opposite directions (Figure 2). When angular velocity is applied, the Coriolis force on each mass also acts in opposite directions, which result in capacitance change. This differential value in capacitance is proportional to the angular velocity ? > and is then converted into output voltage for analog gyroscopes or LSBs for digital gyroscopes.
When linear acceleration is applied to two masses, they move in the same direction. Therefore, there will be no capacitance difference detected. The gyroscope will output zero-rate level of voltage or LSBs, which shows that the MEMS gyroscopes are not sensitive to linear acceleration such as tilt, shock, or vibration.
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