A monolithically integrated three-axis accelerometer using CMOS compatible stress-sensitive differential amplifiers

In this paper, the development of a bulk-micromachined CMOS integrated three-axis accelerometer which includes analog signal conditioning circuits is presented. The accelerometer was designed to simplify the signal processing tasks by incorporating a set of circuits for three-axis signal conditioning, This approach resulted in a 25% reduction of the circuit area. Stress-sensitive differential amplifiers (SSDA's) have been used as signal transducers, because they can be conveniently formed in a small area. The sensitivity and resolution of the fabricated devices realized in 8 x 8 mm(2) die area were 192 mV/g and 0.024 g for Z-axis acceleration, and 23 mV/g and 0.23 g for X and Y axis acceleration, respectively. The electrical noise component in the analog CMOS circuits was reduced by using a chopper stabilization technique. It was observed that there is a proper chopping clock frequency range to maximize the noise reduction effect. The noise of the SSDA was found to be related with the characteristics of CMOS differential amplifiers used. Typical temperature coefficient of sensitivity was about -2000 ppm/degrees C, which could be reduced to -320 ppm/degrees C or less by selecting a proper bias condition.