Pen input apparatus and pen input method for detecting approach of pen to display integrated tablet by controlling lighting of back light

摘要

A pen input apparatus includes an inversion signal generation circuit (5) for generating an inversion signal to invert the direction of applied voltage to liquid crystal of a liquid crystal panel (1), a first conversion circuit (11) to detect a voltage induced at a detection pen (3) according to the inversion signal generated by the inversion signal generation circuit (5) for converting the induced voltage into a direct-current voltage, a comparator circuit (14) for comparing a voltage value of the direct-current voltage converted by the first conversion circuit (11) with a predetermined value to determine whether the detection pen (3) is close to the liquid crystal panel (1), and a detection period signal generation circuit (6) for turning on a back light (2) of the liquid crystal panel (1) when the first conversion circuit (11) is not detecting an induced voltage, and turning off the back light (2) when the first conversion circuit (11) is detecting an induced voltage. <IMAGE>