Analog and Direct-Digital Front-End Circuits Suitable for Low-Valued Resistive Sensors

Two simple and efficient electronic front-ends suitable for low-valued resistive sensors are presented in this paper. The first front-end is a low-cost two-opamp based circuit which gives a linear zero-offset transfer characteristic. This circuit also does not employ any expensive parts (e.g., instrumentation amplifier) in its architecture. The second circuit, based on modified dual-slope architecture, acts as a linearizing direct-digital converter for low-valued resistive sensors. It also gives excellent immunity to many circuit nonlinearities, including ON resistance of the switches employed. Both these front-ends are designed with a provision to set the current through the sensors. The working principle of these front-ends have been derived mathematically and reported. Performance of these schemes has been studied through simulation as well as some experimental studies. The schemes were shown to possess fair performance parameters (linearity, zero offset, etc.).