Design optimization of a piezoresistive pressure sensor considering the output signal-to-noise ratio

Abstract

Piezoresistive sensors often suffer from poor signal-to-noise ratios, limiting their use for measuring small pressure differentials. As the pressure range is reduced, and the sensitivity of the sensor increased, the effect of noise on the output signal becomes the limiting factor in the sensor design. In this paper, the optimization of the design to enhance the signal-to-noise ratio of a piezoresistive-type pressure sensor is performed considering different noise components commonly present with these types of sensors. The optimal design for the cases of constant voltage and current is achieved by maximizing the performance index, which is defined as the output signal versus noise. The output voltage and noise are separately analyzed and experimentally tested with respect to the geometric parameters of the piezoresistor and the applied voltage and current. Brownian, Johnson and flicker (1/f) noises are modeled, the latter two of which are dominant for piezoresistive sensors operated at low frequencies to dc. The experimental results show that the optimal design with respect to the resistor length, and number of turns is significantly different when noise is considered. For the special case of the piezoresistive sensor tested, the flicker noise required more turns and longer active elements than if only the effective and non-effective resistances were considered. The optimal Vout/Vnoise was over twice that of the sensor designed maximizing Vout alone.

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