Systematic measurement and optimization of a Universal Transducer Interface in resistive-bridge mode

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Abstract

The Universal Transducer Interface (UTI) is a mass-produced interface circuit which can realize the functions of measuring signals of various sensors such as capacitive sensors, resistive-bridge sensors and resistive sensors. For some of the front-ends, an instrumentation amplifier, which is implemented with dynamic-element-matching (DEM) for its feedback structure, is integrated in the chip. In certain UTI modes, this amplifier is used to amplify small output signals of a resistive-bridge sensor or a single resistive sensor before it enters the applied modulator. According to customers’ complaints, the UTI doesn’t work well. This thesis describes how with systematic investigations three problems have been identified. The first one is that undesired offset is introduced by the limited common-mode rejection ability of the instrumentation amplifier. The second one is that for input common-mode voltages higher than 3.4V, the On-resistances of the applied NMOS switches that control the DEM loop, cause the system to be out of function. The third one is that the electromagnetic interference can introduces unwanted noise in the wiring of the external resistive-bridge sensor. Two dynamic-offset-canceling techniques have been proposed and one of them has been realized on board. With these techniques, the offset has been successfully reduced from up to 200?V to about 7 ?V. The noise introduced by interference can be eliminated by applying proper shielding.