Design and Optimization of Wheatstone Bridge Adjustment Circuit for Resistive Sensors

A novel Wheatstone bridge adjustment circuit with both rough-tuning and fine-tuning functions is designed for balancing the Wheatstone bridge in this article. Firstly, the parametric circuit structure is constructed to facilitate the design of rough-tuning and fine-tuning sub-circuit parameters; Secondly, the quantitative index of Wheatstone bridge imbalance is defined, and the parameter design flow of the rough-tuning sub-circuit, which consists of two sets of series-parallel-resistor (SPR) structures that are, respectively, connected in parallel with the two branches of one half-bridge, is given to directly weaken the initial bridge imbalance in the manufacturing stage. Theoretical analysis results show that the SPR structure can effectively approach any expected value and reduce the number of fixed resistor types. Thirdly, parameters of the fine-tuning sub-circuit, which consists of a resistor and a digital-to-analog converter (DAC), are optimized based on any expected adjustable range. Adjusting the DAC input to seek the middle value of an analog-to-digital converter (ADC) output, indirectly eliminates the additional bridge imbalance caused by mechanical assembly stress, gravity, ambient temperature, etc., in the application stage. Then the influence of the fine-tuning parameters on linear fitting coefficients of the output versus input of the Wheatstone bridge is analyzed theoretically. The results show that the DAC output voltage only has a significant linear impact on the intercept coefficient, while its impact on the scale coefficient is negligible. Finally, the effectiveness of the adjustment circuit is verified on a six-axis force/torque sensor that is developed for an Experimental Module Manipulator (EMM) in the Chinese Space Station (CSS).