Capacitive touchscreen signal acquisition without panel reset

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, stray capacitances being associated with each of the second plurality of electrodes;
• one or more drive circuits operably connected to the first plurality of drive electrodes, and
• 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 gain capacitor having first and second terminals, a first switch, a second switch, a third switch, a fourth, and an operational amplifier having positive and negative input terminals and an output terminal, the first terminal of the gain capacitor being connected to the corresponding sense electrode, the second terminal of the gain capacitor being operably connected to the first switch, the positive input terminal being connected to ground, the first switch being located between the gain capacitor and the negative input terminal of the operational amplifier, the second switch being located in a first feedback loop of the operational amplifier between the negative input and output terminals thereof, a feedback capacitor having a first terminal connected to the negative input of the amplifier and a first terminal of the second switch, a second terminal of the feedback capacitor being connected to the third switch and the fourth switch, the third switch being located between the second terminal of the feedback capacitor and ground, the fourth switch being located between the second terminal of the feedback capacitor and the output terminal of the operational amplifier;
• wherein during a first stage the gain capacitor accumulates a charge representative of mutual capacitances and stray capacitances in the sense electrode corresponding thereto when the first, second and third switches are closed, the fourth switch is open, and a drive signal provided to at least one of the drive electrodes is high, and the charge accumulated in the gain capacitor during the first stage is transferred to the feedback capacitor during a second stage when the second and third switches are open, the first and fourth switches are closed, and the drive signal is low, the first switch being open momentarily between the first and second stages.

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, stray capacitances being associated with each of the second plurality of electrodes;
• one or more drive circuits operably connected to the first plurality of drive electrodes, and
• 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 gain capacitor having first and second terminals, first, second, third, fourth, fifth and sixth switches, an operational amplifier having positive and negative input terminals and an output terminal, and first and second feedback capacitors, the first terminal of the gain capacitor being connected to the corresponding sense electrode, the second terminal of the gain capacitor being operably connected to the first switch, the positive input terminal being connected to ground, the first switch being located between the gain capacitor and the negative input terminal of the operational amplifier, the second switch being located in a feedback loop of the operational amplifier between the negative input and output terminals thereof, the first feedback capacitor having a first terminal connected to the negative input of the amplifier and a first terminal of the second feedback capacitor, the sixth switch being connected between a second terminal of the second feedback capacitor and the output of the operational amplifier, a second terminal of the first feedback capacitor being connected to the third and fourth switches, the third switch being located between the second terminal of the first feedback capacitor and ground, the fourth switch being located between the second terminal of the first feedback capacitor and the output terminal of the operational amplifier, the fifth switch being located between the second terminal of the second feedback capacitor and ground;
• wherein during a first stage the gain capacitor accumulates a charge representative of mutual capacitances and stray capacitances in the sense electrode corresponding thereto when the first, second and third switches are closed, the fourth, fifth and sixth switches are open, and a drive signal provided to at least one of the drive electrodes is high, and the charge accumulated in the gain capacitor during the first stage is transferred to the first feedback capacitor during a second stage when the second, third, fifth and sixth switches are open, the first and fourth switches are closed, and the drive signal is low, the first switch being open momentarily between the first and second stages, during a third stage the gain capacitor accumulates a charge representative of mutual capacitances and stray capacitances in the sense electrode corresponding thereto when the first, second and fifth switches are closed, the third, fourth and sixth switches are open, and a drive signal provided to at least one of the drive electrodes is high, and the charge accumulated in the gain capacitor during the third stage is transferred to the second feedback capacitor during a fourth stage when the second, third, fourth and fifth switches are open, the first and sixth switches are closed, and the drive signal is low, the first switch being open momentarily between the third and fourth stages.