Abstract: A single-loop fourth-order sigma–delta interface circuit for a closed-loop micromachined accelerometer is presented. Two additional electronic integrators are cascaded with the micromachined sensing element to form a fourth-order loop filter. The three main noise sources affecting the overall system resolution of a sigma–delta accelerometer, mechanical noise, electronic noise and quantization noise, are analyzed in detail. Accurate mathematical formulas for electronic and quantization noise are established. The ASIC is fabricated in a 0.5 μm two-metal two-poly n-well CMOS process. The test results indicate that the mechanical noise and electronic noise are 1 μg/Hz1/2 and 8 μV/Hz1/2 respectively, and the theoretical models of electronic and quantization noise agree well with the test and simulation results.

Key words: noise analysis