Patent ID: 8395599

Claim:
A capacitive touchscreen system, comprising: a touchscreen comprising a first plurality of electrically conductive drive electrodes arranged in rows or columns, and a second plurality of electrically conductive sense electrodes arranged in rows or columns arranged at an angle with respect to the rows or columns of the first plurality of electrodes, mutual capacitances existing between the first and second pluralities of electrodes at locations where the first and second pluralities of electrodes intersect, the mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto; a plurality of drive circuits, each of the plurality of drive circuits being operably connected to a corresponding one of the first plurality of drive electrodes, each drive electrode being operably connected to a third switch and a fourth switch, the third switch being configured to operably connect the drive electrode to a drive voltage, the fourth switch being configured to operably connect the drive electrode to ground, each drive electrode having a drive stray capacitance associated therewith; a plurality of sense circuits, each of the plurality of sense circuits being operably connected to a corresponding one of the second plurality of sense electrodes, each sense circuit comprising a first switch, a second switch, and a charge acquisition circuit comprising a charge storage capacitor arranged in parallel with a fifth switch, the first switch being configured to operably connect the sense electrode to ground, the second switch being configured to operably connect the sense electrode to the charge acquisition circuit, each sense electrode having a sense stray capacitance associated therewith; wherein a mutual capacitance existing between a given drive electrode and a given sense electrode at a given intersection of the first and second pluralities of electrodes, the drive stray capacitance associated with the given drive electrode, and the sense stray capacitance associated with the given sense electrode together defining a capacitance touchscreen network, during a first phase the third switch is closed, the fourth switch is open, the first switch is closed, the second switch is open, a first potential of the given sense electrode corresponds to ground, and the mutual capacitance between the given drive electrode and the given sense electrode is charged up to a first charge value corresponding substantially to the drive voltage times the mutual capacitance, during a second phase the third switch is open, the fourth switch is closed, the first switch is open, the second switch is closed, a second potential of the given drive electrode corresponds to ground, and the charge storage capacitor is charged up to a value corresponding approximately to a difference in touchscreen capacitance network charges occurring during the first and second phases, the first and second phases not overlapping in time.