In this letter, we evaluate the parasitic capacitance of an LCD touch panel, the description and implementation of a differential input sensing circuit, and an algorithm suitable for large LCDs with integrated touch function. When projected capacitive touch sensors are integrated with a liquid crystal display, the sensors have a very large amount of parasitic capacitance with the display elements. A differential input sensing circuit can detect small changes in the mutual capacitance from the touch of a finger. The circuit is realized using discrete components, and for the evaluation of a large-sized LCD touch panel, a printed circuit board touch panel is used.