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

To verify the effectiveness of a higher order electromechanical sigma–delta
modulator (SD M), a micromachined accelerometer is fabricated. The
in-plane sensor with fully differential structure has a mechanical noise floor
below 1 µgHz^−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
SDM, which only uses the sensing element as a loop filter, here it is
cascaded with additional electronic integrators to form a fifth-order
electromechanical SD 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
SD M loop was built and tested. The experimental data agree well with the
simulation results.