Analysis of Wheatstone Bridge Sensitivity for Applications in Integrated Piezoresistive Stress Sensors

The Wheatstone bridge configuration of sensing elements is often used in stress measurements due to its simple architecture and relatively high linearity and sensitivity when used in a full-bridge configuration. The sensitivity of the Wheatstone bridge is influenced by several factors: the initial mismatch between the resistances of the sensing elements, the inevitable resistance of the bias voltage lines, and the ratio between the sensing and bias resistances. In this paper, the effects of the aforementioned factors on the sensitivity of the Wheatstone bridge are analysed and compared to the ideal case. The bias resistances in this work originate from the transmission gates in the bias voltage lines. They are included because the sensors are intended to be used for stress mapping as elements of a matrix. Here, each sensor can be addressed individually and must be disconnected when not in use. The analysis results are confirmed by simulations that show the response of such a sensor to stress. The analysis and simulations lead to design rules and measurement methods that ensure minimum degradation of sensitivity due to the resistances in the bias voltage lines.