A Fully Differential Charge-Balanced Accelerometer for Electronic Stability Control

Abstract

An accelerometer for electronic stability control utilizes a two-mass mechanical sensor element to implement a fully-differential signal path, achieving robustness against electromagnetic interference (EMI) without the need for external shielding in the package. The EMI rejection is augmented further with a pseudo-random chopping scheme, which spreads the interference over a wide bandwidth, reducing its in-band portion to the level of the noise floor. The chopping function maintains zero-mean voltage waveforms across the sensor electrodes, which is also beneficial for the long-term offset stability of the device. A charge-balanced capacitance-to-voltage converter provides linear transduction for displacements of the proof-mass up to 70% of the gap and minimizes the residual electrostatic forces. A dual-axis design occupies 1.1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in 0.18- μm CMOS and consumes 820 μA from an internally regulated 1.9-V supply. The system achieves 380 μg/ √Hz noise floor and 84-dB dynamic range. The offset variation in the automotive temperature range of -40 to +140°C has a 3 σ range of ±11 mg.