A novel accelerometer using MOS ring oscillators

Piezoresistive silicon accelerometers have many excellent performance characteristics such as high sensitivity, high reliability and low cost. In this paper, a novel piezoresistive silicon accelerometer using MOS ring oscillators is described and analysed. This accelerometer consists of two MOS ring oscillators, a mixer and a filter. Using a ring oscillator, the input acceleration changed into digital frequency output signal, this makes it easy to be used in digital world. The mechanical structure of this accelerometer is made up of one mass and four beams. Such structure can not only decrease cross-axis sensitivity, but also utilize the strain caused by input acceleration. Using finite-element analysis (FEA) software, we did strain simulation in order to analyse the stress distribution. The result of finite-element method simulation accorded with theory analysis very much. The MOS ring oscillator consists of an odd number of inverting gates connected in a ring and can be realized by CMOS, NMOS or PMOS circuits. The different kinds of MOS ring oscillator have different performances. Since MOS FET can realize the function of mixing frequency, the mixer is made up of MOS FET.