Mutual capacitance measurement in a multi-touch input device

A method for determining multiple touch events in a multi-touch sensor system having a capacitance measurement unit, a pulse drive unit, a timer and a touch sensor having a plurality of nodes and a plurality of electrodes comprising at least two sets of electrodes, wherein the capacitance measurement unit comprises a voltage or current source, the method comprising:

• connecting a first electrode in a first set of electrodes to the voltage or current source of the capacitance measurement unit;
• driving, with the pulse drive unit, a voltage or current pulse onto a second electrode in a second set of electrodes while the voltage or current source is connected to the first electrode;
• starting the timer and measuring the voltage of the first electrode as a measured voltage when the timer reaches a pre-determined time;
• comparing the measured voltage to a previously measured voltage corresponding to the node;
• and
• reporting that the node has been touched if the measured voltage deviates from the previously measured voltage.

A method for determining multiple touch events in a multi-touch sensor system having a capacitance measurement unit, a pulse drive unit, a timer and a touch sensor having a plurality of nodes and a plurality of electrodes comprising at least two sets of electrodes, wherein the capacitance measurement unit comprises a voltage or current source, the method comprising:

• connecting a first electrode in a first set of electrodes to the voltage or current source;
• driving, with the pulse drive unit, a voltage or current pulse onto a second electrode in a second set of electrodes while the voltage or current source is connected to the first electrode;
• starting the timer, measuring the voltage of the first electrode as a measured voltage, and storing the time value of the timer when the measured voltage reaches a pre-determined voltage level;
• comparing the stored time value to a previously stored value corresponding to the node;
• and
• reporting that a node corresponding to the first and second electrodes has been touched if the stored time value deviates from the previously stored value.

A system for detecting one or more touch events on a touch sensor, comprising:

• a touch sensor having a plurality of nodes and a plurality of electrodes comprising at least a first and second set of electrodes;
• a touch controller having a pulse drive circuit selectably coupled to the plurality of electrodes, a timer circuit, a capacitance measurement unit comprising a charge time measurement circuit selectably coupled to the plurality of electrodes and coupled with the timer circuit;
• and a storage element coupled to the charge time measurement, circuit;
• wherein the touch controller is operable to:
• measure the mutual capacitance at a node corresponding to a first electrode in the first set of electrodes and a second electrode in the second set of electrodes by:
• coupling a voltage or current source in the charge time measurement circuit to the first electrode;
• starting the timer circuit;
• coupling the second electrode to the pulse drive circuit;
• and
• measuring the voltage of the first electrode as a measured voltage when the timer circuit reaches a predetermined time;
• compare the mutual capacitance at the node with a previously measured mutual capacitance corresponding to the node by comparing the measured voltage to a previously measured voltage corresponding to the node;
• and
• report that the node has been touched if there has been a deviation from the previously measured voltage.

A system for detecting one or more touch events on a touch sensor, comprising:

• a touch sensor having a plurality of nodes and a plurality of electrodes comprising at least a first and second set of electrodes;
• a touch controller having a pulse drive circuit selectably coupled to the plurality of electrodes, a timer circuit, a capacitance measurement unit comprising a charge time measurement circuit selectably coupled to the plurality of electrodes and coupled with the timer circuit;
• and a storage element coupled to the charge time measurement circuit;
• wherein the touch controller is operable to measure the mutual capacitance at a node by:
• coupling a voltage or current source in the charge time measurement circuit to the first electrode;
• starting the timer circuit;
• coupling the second electrode to the pulse drive circuit;
• measuring the voltage of the first electrode as a measured voltage;
• and
• storing, in the storage element, the time value of the timer circuit when the measured voltage reaches a predetermined voltage level;
• wherein the touch controller compares the mutual capacitance at the node by comparing the stored time value to a previously stored time value corresponding to the node;
• and
• wherein the touch controller reports that the node corresponding has been touched if the stored time value deviates from the previously stored time value.

A system for detecting one or more touch events on a touch sensor, comprising:

• a touch sensor having a plurality of nodes and a plurality of electrodes comprising at least a first and second set of electrodes;
• a touch controller having a pulse drive circuit, and a relaxation oscillator-based measurement circuit;
• wherein the touch controller is operable to measure the mutual capacitance at a node by:
• coupling the relaxation oscillator-based measurement circuit to a first electrode in the first set of electrodes;
• coupling a second electrode in the second set of electrodes to the pulse drive circuit;
• and
• measuring the frequency of the relaxation oscillator-based measurement circuit;
• wherein the touch controller compares the mutual capacitance at the node by comparing the frequency to a previously measured frequency corresponding to the node and determines whether the frequency deviates from the previously measured frequency;
• and
• wherein the touch controller reports that the node has been touched if there has been a deviation from the previously measured frequency.