Patent ID: 8674709
Filing Date: 2014-03-18
Classification: G06F

Abstract:
1. A circuit for measuring a capacitance value of a touch screen, comprising: a target capacitor unit having a target capacitor charged with a target charging voltage which increases from a ground voltage with a predetermined slope; a target voltage control unit configured to charge the target capacitor using a target current source; a reference capacitor unit having a reference capacitor charged with a charging reference voltage which increases from an initial reference voltage with a slope smaller than the target charging voltage; a reference voltage control unit configured to charge the reference capacitor using a reference current source and a reference voltage source; a comparator configured to compare the target charging voltage as an output of the target capacitor and the charging reference voltage as an output of the reference capacitor, and output a transition signal at a moment when the target charging voltage becomes higher than the charging reference voltage; and a controller configured to receive an output signal of the comparator and a clock signal, and generate a digital output signal and a control signal, wherein a capacitance value of the target capacitor is measured using a time elapsed from a time when the target capacitor is initialized to the ground voltage to a time when the transition signal is outputted from the comparator, wherein the reference capacitor is connected to an input terminal of the comparator, wherein the reference voltage source is configured to charge the reference capacitor with the initial reference voltage, and wherein the reference current source is configured to charge the reference capacitor with the charging reference voltage after the reference capacitor has been charged with the initial reference voltage.