Capacitive touch system using both self and mutual capacitance

Patent metadata

Field	Value
Publication number	US-8933907-B2
Application number	US-201113089701-A
Country	US
Kind code	B2
Filing date	Apr 19, 2011
Priority date	Apr 30, 2010
Publication date	Jan 13, 2015
Grant date	Jan 13, 2015

Abstract

Systems and methods for determining multiple touch events in a multi-touch sensor system are provided. The system may have a touch sensor including nodes defined by a plurality of electrodes, which may comprise a first and second set. The method may include measuring self capacitance for at least two electrodes, detecting a touched electrode, and measuring the mutual capacitance for only a subset of the nodes (e.g., fewer than all of the nodes and including at least the nodes corresponding to the touched electrodes) resulting in the detection of two or more touched nodes. The self capacitance measurements may be performed on each of the electrodes, and the touched electrodes may comprise electrodes from both the first and second sets. Alternatively, the self capacitance measurements may be performed only on electrodes in the first set, and the touched electrodes may comprise electrodes from only the first set.

First claim

What is claimed is:

1. A method for determining multiple touch events in a multi-touch sensor system having a touch sensor including a plurality of nodes defined by a plurality of electrodes, the method comprising:
performing self capacitance measurements for at least two of the plurality of electrodes;
detecting one or more touched electrodes as a result of the performed self capacitance measurements;
performing a plurality of mutual capacitance measurements for only a subset of the nodes, wherein the subset is fewer than all of the nodes and includes at least the nodes corresponding to the touched electrodes; and
detecting two or more touched nodes as a result of the plurality of mutual capacitance measurements,
wherein a mutual capacitance measurement comprises the steps of:
connecting a first selected electrode with a capacitance measurement circuit;
connecting a second selected electrode to a pulse drive circuit, and
measuring said mutual capacitance by a capacitance measurement unit comprising a charge time measurement circuit and a relaxation oscillator circuit, wherein a mutual capacitance measurement comprises a first measurement using the charge time measurement unit and a second measurement using the relaxation oscillator circuit.

2. The method of claim 1 wherein the one or more touched electrodes comprises only one touched electrode.

3. The method of claim 1 wherein:
the plurality of electrodes comprises a first set of electrodes and a second set of electrodes;
the self capacitance measurements are performed on each of the electrodes; and
the touched electrodes comprise electrodes from both the first set of electrodes and the second set of electrodes.

4. The method of claim 3 wherein the subset of nodes comprises only the nodes corresponding to the touched electrodes.

5. The method of claim 3 wherein the subset of nodes comprises nodes that are adjacent to the touched electrodes

6. The method of claim 3 wherein the touched nodes are detected by a process of elimination.

7. The method of claim 3 wherein the first set of electrodes corresponds to a first layer of the touch sensor.

8. The method of claim 7 wherein the second set of electrodes corresponds to a second layer of the touch sensor.

9. The method of claim 3 wherein the touched electrodes arc detected when an object is in proximity to, but not directly contacting, the touched electrodes.

10. A system according to claim 9 , wherein the touch controller is operable to:
perform, using the self capacitance measuring unit, self capacitance measurements for at least two of the plurality of electrodes;
detect one or more touched electrodes as a result of the performed self capacitance measurements;
perform, using the mutual capacitance measuring unit, a plurality of mutual capacitance measurements for only a subset of the nodes, wherein the subset is fewer than all of the nodes and includes at least the nodes corresponding to the touched electrodes, wherein each mutual capacitance measurement comprises a first measurement using the charge time measurement unit and a second measurement using the relaxation oscillator circuit; and
detect two or more touched nodes as a result of the plurality of mutual capacitance measurements.

11. The system of claim 10 wherein the one or more touched electrodes comprises only one touched electrode.

12. The system of claim 10 wherein:
the plurality of electrodes comprises a first set of electrodes and a second set of electrodes;
the touch controller performs the self capacitance measurements on each of the electrodes; and
the touched electrodes comprise electrodes from both the first set of electrodes and the second set of electrodes.

13. They system of claim 10 wherein:
the plurality of electrodes comprises a first set of electrodes and a second set of electrodes;
the touch controller performs the self capacitance measurements on each of the electrodes in the first set of electrodes and not on the electrodes in the second set of electrodes; and
the touched electrodes comprise electrodes from only the first set of electrodes.

14. The method of claim 3 wherein touched nodes are detected when an object is in proximity to, but not directly contacting, the touched nodes.

15. The method of claim 1 wherein the mutual capacitance measurement are performed with a series of first measurements using the charge time measurement unit for each of the nodes of said subset followed by a second series of measurements for each of the nodes using the relaxation oscillator circuit.

16. The method of claim 15 , comprising the step of synchronizing the pulse drive circuit with said relaxation oscillator circuit.

17. The method of claim 1 wherein detected touch is determined during the mutual capacitance measurement only if the first and second measurement indicate a touch condition.

18. The method of claim 1 wherein:
the plurality of electrodes comprises a first set of electrodes and a second set of electrodes;
the self capacitance measurements are performed on each of the electrodes in the first set of electrodes and not on the electrodes in the second set of electrodes; and
the touched electrodes comprise electrodes from only the first set of electrodes.

19. The method according to claim 1 , wherein the capacitance measurement circuit comprises a charge time measurement circuit.

20. The method according to claim 1 , wherein the mutual capacitance measurement are performed for each node of said subset first using the charge time measurement unit in a first measurement followed by a second measurement for each node using the relaxation oscillator circuit.

21. A system for detecting one or more touch events on a touch sensor, comprising:
a touch sensor having a plurality of nodes defined by a plurality of electrodes;
a touch controller comprising:
a self capacitance measuring unit for measuring the self capacitance of each of the plurality of electrodes;
a mutual capacitance measuring unit for measuring the mutual capacitance at only a subset of the nodes, wherein the subset is fewer than all of the nodes and is determined based on an output of the self capacitance measuring unit; and
a detection unit, which based on the output of the self capacitance measuring unit and an output of the mutual capacitance measuring unit, is operable to detect two or more touched nodes,

wherein the mutual capacitance measuring unit comprise a capacitance measurement circuit comprising a charge time measurement circuit and a relaxation oscillator circuit, each selectively operable to be connected to a first electrode associated with a node and a pulse drive circuit operable to be connected to a second electrode associated with said node.

22. The system of claim 21 , wherein the pulse drive circuit is synchronized with the capacitance measurement circuit.

23. The system according to claim 21 , wherein the capacitance measurement circuit detects a touch if either said first or said second measurement indicate a touch condition.

24. The system according to claim 21 , wherein the capacitance measurement circuit only detects a touch if said first and said second measurement indicate a touch condition.

25. The system of claim 21 , wherein the pulse drive circuit is synchronized with said charge time measurement circuit.

26. The system according to claim 21 , wherein the capacitance measuremen

Assignees

• Hanauer Jerry
• O'Connor Todd
• Microchip Tech Inc

Inventors

• Hanauer Jerry
• O'Connor Todd

Classifications

• G06F2203/04104

  Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger · CPC title

• G06F3/0416 Primary

  Control or interface arrangements specially adapted for digitisers · CPC title

• G06F3/044 Primary

  by capacitive means · CPC title

• G06F3/041662 Primary

  using alternate mutual and self-capacitive scanning · CPC title

• G06F3/0446

  using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes · CPC title