A high-performance accelerometer with a fifth-order sigma-delta modulator

To verify the effectiveness of a higher order electromechanical sigma-delta modulator (Sigma Delta M), a micromachined accelerometer is fabricated. The in-plane sensor with fully differential structure has a mechanical noise floor below 1 mu g Hz(-1/2), static sensitivity 16 pF g(-1) and resonant frequency 325 Hz. FEM analyses are performed to verify these key parameters. The silicon-on-glass sensor is fabricated by deep reactive ion etching (DRIE) and anodic bonding. Compared with a second-order electromechanical Sigma Delta M, which only uses the sensing element as a loop filter, here it is cascaded with additional electronic integrators to form a fifth-order electromechanical Sigma Delta M, which leads to better signal to quantization noise ratio (SQNR). This novel approach is analysed and system level simulations are presented. A printed circuit board (PCB) prototype of this high-order Sigma Delta M loop was built and tested. The experimental data agree well with the simulation results.