Self-sensing touch panel
AssigneeSTMicroelectronics Asia Pacific Pte Ltd
InventorsHugo GICQUEL, EngJye NG
Life of this patent
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Abstract
A method of differential self-capacitance measurement is used to enhance a signal-to-noise ratio of sense lines in a touch panel display, thereby improving touch sensor accuracy. The differential self-capacitance measurement is implemented for a touch panel using charge sharing between adjacent sense lines of the touch panel matrix. Sequential differential self-capacitance measurements can be compared with one another by computing the difference |CS1−CS2|−|CS2−CS1| to sense a change caused by an intervening event. By scanning the entire touch panel matrix, events can be tracked across the touch panel.
Claims20
A method comprising:
- discharging a first sense line capacitor of a touch panel;
- charging a second sense line capacitor of the touch panel;
- coupling the first and second sense line capacitors to one another to engage charge sharing;
- determining a differential self-capacitance;
- comparing a common voltage of the first and second sense line capacitors with a reference voltage;
- amplifying signals of the sense line capacitors;
- repeating the steps of discharging, charging, coupling, determining, comparing, and amplifying, for a plurality of first and second sense line capacitors of the touch panel, the plurality depending on a size of the touch panel;
- and
- determining, from changes in the differential self-capacitance measurements, a location on the touch panel where a finger is adjacent to the touch panel.
A circuit for use with a touch panel, the circuit comprising:
- a power supply;
- a first sense line capacitor coupled to the power supply by a first transistor switch;
- a second sense line capacitor coupled in parallel with the first capacitor, the second capacitor coupled to ground via a second transistor switch;
- a first charge sharing switch in line between the first and second sense line capacitors;
- an output buffer;
- and
- a second charge sharing switch coupling the first and second capacitors to the output buffer.
A method of operating a touch panel, comprising:
- charging a first capacitor of the touch panel to a supply voltage;
- measuring electric charge on the first capacitor;
- connecting the first capacitor to a second capacitor of the touch panel until charge on both capacitors reaches an equilibrium value;
- determining a first differential capacitance value from the measured charge and the supply voltage;
- charging the second capacitor to the supply voltage;
- measuring electric charge on the second capacitor;
- determining a second differential capacitance value from the measured charge and the supply voltage;
- and
- comparing the first and second differential capacitance values to detect a touch event associated with the touch panel.
Dependencies are inferred from the claim text.