Planar-assembly triaxial microaccelerometer with electromechanical sigma-delta ADCs

By combination of two LIGA-fabricated micromechanical acceleration sensors with a Z-axis sensitive acceleration sensor element, a planar assembly of a triaxial microaccelerometer can be put into practice. In our readout system, each channel consists of a dedicated full-custom ASIC electromechanical sigma-delta modulator and a digital sinc(3)(f) decimation filter. The output data interface is intended for readout by microcontrollers and digital signal processors (DSPs). Software-programmable reference voltages facilitate self-test and software-controlled range and offset adjustment. Temperature compensation can be performed by reading the output of a temperature-sensing circuit on the sensor head. The measured noise level is 5 mu g Hz(-1/2) at a measuring range of +/-1.5g. Simulations with a dedicated high-level simulator have shown that the sensitivity can be increased by at least one order of magnitude by optimizing the sigma-delta modulators. As an example for application, an acceleration data logger will be described. Finally, we present the design of an improved accelerometer chipset which consists of a single sensor head chip and an enhanced decimation filter interface.