#Mems gyroscope serial
That parallel data stream can then be transformed using a serial protocol like I 2C or SPI before it is sent to the host for further processing ( Figure 5).įigure 5. The serial digital bit stream from the ADC is then passed to a FIFO buffer that converts the serial signal into a parallel data stream. The analog mass voltage will go through charge amplification, signal conditioning, demodulation, and lowpass filtering before it gets converted into a digital domain using a sigma-delta ADC. Acceleration associated with multiple moving masses. V1 and V2 are electrical connections to each side of the capacitors and form a voltage-divider with the center point as the voltage of our mass.įigure 4. Now, placing multiple electrodes in parallel allows a larger capacitance, which will be more easily detected ( Figure 4). Force causes a displacement of the mass which, in return, causes a capacitance change. The configuration enables a greater change in capacitance, which can both be detected more accurately, and ultimately makes capacitance sensing a more feasible technique. This mandates using multiple movable and fixed electrodes, all connected in a parallel configuration.
The displacement of the movable mass (micrometer) is caused by acceleration, and it creates an extremely small change in capacitance for proper detection (Equation 1). Acceleration associated with a single moving mass. By calculating the difference between C2 and C1 we can derive the displacement of our mass and its direction.įigure 3. It is obvious that the movement of the mass (Motion x) is relative to the fixed electrodes (d1 and d2), and causes a change in capacitances (C1 and C2). It is composed of a single movable mass (one planar surface), that is placed along with a mechanical spring between two, fixed, reference silicon substrates or electrodes (another planar surface). Let’s look at accelerometers arranged as a differential pair ( Figure 3). The capacitance can either be arranged as single-sided or a differential pair. Ε r = Relative material permitted between plates 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.
It is not prone to noise and variation with temperature. This sensing technique is known for its high accuracy, stability, low power dissipation, and simple structure to build. The Accelerometer's Sensing MechanismĪ 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). Accelerometers are fabricated in a multilayer wafer process, measuring acceleration forces by detecting the displacement of the mass relative to fixed electrodes. So the accelerometer really measures force, not acceleration it basically measures acceleration indirectly through a force applied to one of the accelerometer's axes.Īn accelerometer is also an electromechanical device, including holes, cavities, springs, and channels, that is machined using microfabrication technology. It is important to note that acceleration creates a force that is captured by the force-detection mechanism of the accelerometer. Newton’s Second law of motion says that the acceleration (m/s 2) of a body is directly proportional to, and in the same direction as, the net force (Newton) acting on the body, and inversely proportional to its mass (gram). Gyroscopes, however, measure both the displacement of the resonating mass and its frame because of the Coriolis acceleration. That measurement is then converted into a digital electrical signal through an analog-to-digital converter (ADC) for digital processing. 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).Īll MEMS accelerometer sensors commonly measure the displacement of a mass with a position-measuring interface circuit. 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. This article presents an overview of MEMS accelerometer sensors and gyroscopes.
Major components in any MEMS system are the mechanical elements, sensing mechanism, and the ASIC or a microcontroller. 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. Microelectromechanical systems (MEMS) combine mechanical and electrical components into small structures in the micrometer scale. A similar version of this article appeared March 2014 in EDN.