Patent ID: 8928622
Filing Date: 2015-01-06
Classification: G06F

Abstract:
1. A demodulation system for a differential sensing applied in capacitive touch panel with n first conductor lines of a first direction and m second conductor lines of a second direction, where n, m are each an integer greater than one, wherein a mutual capacitance is formed at each intersection between the first and the second conductor lines and the first direction is vertical to the second direction, the demodulation system comprising: a signal generator, having n voltage drivers connected to the n first conductor lines of the capacitive touch panel, for driving the n first conductor lines; a detection circuit, having m sensing circuits, for detecting the mutual capacitances and generating m detection signals correspondingly, wherein the detection circuit generates (n−1)×m detection signals when the capacitive touch panel is operated with (n−1) driving cycles; a programmable gain amplifier, connected to the detection circuit, for amplifying the (n−1)×m detection signals and generating (n−1)×m amplified detection signals; an analog to digital converter, connected to the programmable gain amplifier, for converting the (n−1)×m amplified detection signals into (n−1)×m digital detection signals; a demodulation device, connected to the analog to digital converter, for demodulating (n−1)×m digital detection signals into n×m digital signals; and an offset device, connected to the demodulation device, for performing an offset adjustment on the n×m digital signals to thereby generate n×m offset signals; wherein during a driving cycle, the signal generator drives two of the n first conductor lines by a pair of differential signals which are identical in amplitude but opposite in phase for eliminating common noises of the two first conductor lines, and an output voltage of the detection circuit is kept at a DC common voltage when there is no touch on the capacitive touch panel.