基于陀螺仪和加速度惯性传感器的空中鼠标

Keywords: MEMS, Accelerometer, Gyroscope Sensors

APPLICATION NOTE 5830

ACCELEROMETER AND GYROSCOPES

SENSORS: OPERATION, SENSING, AND

APPLICATIONS

By: Majid Dadafshar, Senior Member of Technical Staff (Field Application Engineering)

Abstract: Microelectromechanical systems (MEMS) in consumer electronics are growing faster each year,

with increasing demands from the mobile market, which is dominating the growth for this emerging

technology. MEMS sensors are, in fact, becoming the key elements in designing differentiating products for

structures in the micrometer scale. They are formed by a combination of semiconductor and

microfabrication technologies using micro machine processing to integrate all the electronics, sensors, and

mechanical elements onto a common silicon substrate. Major components in any MEMS system are the

mechanical elements, sensing mechanism, and the ASIC or a microcontroller. This article presents an

overview of MEMS accelerometer sensors and gyroscopes. We discuss the principles of their operation,

their sensing mechanism, the growing variety of applications for them, and the profound impact they are

already having on our daily lives.

MEMS as Inertial Sensors

MEMS sensors have many applications in measuring either linear acceleration along one or several axis, or

angular motion about one or several axis as an input to control a system (Figure 1).

displacement of the resonating mass and its frame because of the Coriolis acceleration.

Newton’s Second law of motion says that the acceleration (m/s ) of a body is directly proportional to, and in

he same direction as, the net force (Newton) acting on the body, and inversely proportional to its mass

(gram).

Acceleration = Force (Newton)

(m/s ) Mass (gram)

(Eq. 1)

It is important to note that acceleration creates a force that is captured by the force-detection mechanism of

A common sensing approach used in accelerometers is capacitance sensing in which acceleration is related

to change in the capacitance of a moving mass (Figure 2). This sensing technique is known for its high

accuracy, stability, low power dissipation, and simple structure to build. It is not prone to noise and variation

with temperature. Bandwidth for a capacitive accelerometer is only a few hundred Hertz because of their

physical geometry (spring) and the air trapped inside the IC that acts as a damper.

Figure 2. Moving mass and capacitance.

The capacitance can either be arranged as single-sided or a differential pair. Let’s look at accelerometers

arranged as a differential pair (Figure 3). It is composed of a single movable mass (one planar surface),

small change in capacitance for proper detection (Equation 1). This mandates using multiple movable and

fixed electrodes, all connected in a parallel configuration. The configuration enables a greater change in

capacitance, which can both be detected more accurately, and ultimately makes capacitance sensing a

more feasible technique.

C = (ε × ε × A)/D (Farad)

(Eq. 2)