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A Sigma Delta micro accelerometer with 6 mu g/root Hz resolution and 130 dB dynamic range

This paper reports the implementation of a low noise, high dynamic-range I I" pound readout for low cost capacitive Micro-Electro-Mechanical Systems (MEMS) accelerometers. The readout circuit sets the bandwidth of the I I" pound loop through an extra feedback path, and hence allows the closed loop system to operate with the low noise characteristics similar to a second-order I I" pound analog-to-digital converter. A thorough noise analysis of the proposed accelerometer shows that the mechanical noise is the most significant source and quantization noise is mostly eliminated. Dynamic range (DR) of the system is improved by minimizing the circuit noise and increasing the full scale range (FSR) by high-voltage pulse feedback. Utilization of these techniques allows the implementation of low cost, low noise, and high DR navigation-grade accelerometers, by eliminating the need for large proof mass, large area MEMS sensors. The proposed system can achieve a minimum of 6.0 A mu g/aeHz noise floor, 3.2 A mu g bias instability, and a maximum of 130 dB DR at 1 Hz. A FSR of +/- 20 g is reported for 6.2 A mu g/aeHz noise floor. This range can be increased up to +/- 40 g at the cost of noise performance and DR.