Stability analysis of MEMS gyroscope drive loop based on CPPLL

Stability analysis of self-oscillation drive loop for MEMS gyroscope based on charge-pump PLL (CPPLL) is presented in this paper. The CPPLL-based driving loop could be realized at a regular voltage CMOS process by maximizing the oscillation amplitude. However, the driving loop has an unstable state at the beginning of the oscillation introduced by the harmonics of the square wave in driving stage. In order to solve this problem, a linear model of the driving loop is established for stability analysis. Based on the analysis, methods of pre-setting the control voltage of VCO and using a hysteresis comparator are proposed to prevent the unstable state occurring. The simulation results verified the validity of the theoretical stability analysis and the effectiveness of the two proposed methods.