TABLE OF CONTENTS Michael Kraft
The objective of this chapter is to show how different systems level design solutions can be used to enhance the performance of inertial sensors. The technique that will be discussed in detail is the use of force feedback where the sensing element is incorporated in a closed loop control system, making the sensor a truly micro-electro-mechanical system (MEMS).
Micromachined inertial sensors have been the subject of extensive research and development effort for 25 years. A very wide range of research prototypes have been reported and many commercial sensors are available. They can be either classified by their fabrication technique or by the method of measuring the motion of the proof mass and converting it into an electrical signal (referred to in this book as the signal pick-off or interface electronics). The predominant fabrication techniques for inertial sensors are surface- or bulk-micromachining, with some sensors relying on a combination of both. The associated pick-off techniques are quite diverse but the dominant techniques are capacitive and piezoresistive; others include piezoelectric, tunnelling current, optical and thermal. For a detail survey on a variety of inertial sensor types the reader is referred to the review articles [1, 2].
Only sensors with capacitive pick-off will be considered here, as this approach lends itself particularly to force feedback, and in any case it is the pick off technique used in most integrated MEMS systems. The particular example around which the discussion will centre is a micromachined accelerometer. Various approaches for the control...
