Noise Consideration for Micromachined Digital Accelerometers

Three noise sources are present in a sigma-delta modulator (SigmaDeltaM) type system applied to a micromachined accelerometer: mechanical noise due to Brownian motion, electronic noise introduced by the interface circuit due to thermal noise sources in the electronic devices and quantisation noise due to the analog to digital conversion process. Based on theory of limit cycles in nonlinear closed loop systems, the mathematical model and formulae for power spectral density calculation of a micromachined accelerometer are derived in this paper. The theoretical considerations agree well with the simulation results in Matlab SIMULINK