High-Performance Closed-Loop Interface Circuit for High-Q Capacitive Microaccelerometers

High-Q sensory microsystems are desirable especially in low noise applications. However this makes implementation of the closed-loop control a great challenge. An in-depth investigation into high-performance closed-loop interface circuit design for high-Q capacitive microaccelerometers is presented. Focus is placed on an analogue force feedback scheme with proportional-derivative compensation. Such an approach is differing from the commonly used electromechanical Delta Sigma technique, since the latter one often suffers severe problems in balancing between the loop stability and other essential characteristics in the presence of high-Q sensing element. A comprehensive analysis concerning the system linearity and bandwidth is conducted, aiming for performance optimization. The adverse impact arising from several electronic noise sources in the system is studied in order for minimization. Accordingly, a prototype interface circuit is designed and fabricated in a commercial 0.35-mu m CMOS process. The chip measures 2.5 x 2.5 mm(2) and operates from a single 5 V supply. The quiescent current is about 10mA. The test results show that it offers a full scale acceleration of +/- 1.2 g correspondingly with integrated non-linearity (INL) of 6.6%, wide-band noise equivalent acceleration of nearly 1 mu g/root Hz over a signal bandwidth of about 1.2 kHz.