Communication between a master active stylus and a slave touch-sensor device
In one embodiment, a system comprises a stylus and a touch sensor. The stylus is operable to transmit a first signal. The touch sensor comprises a first plurality of electrode lines and a controller. Each electrode line is operable to sense the first signal transmitted by a stylus. The stylus tip of the stylus is located at a position relative to the first plurality of electrode lines at the time of transmission of the first signal. The controller is operable to measure a voltage, charge, or capacitance of the sensed first signal on each electrode line of the first plurality of electrode lines and estimate the position of the stylus tip based on interpolation of the measured voltages on each electrode line of the first plurality of electrode lines.
1. An apparatus comprising:
one or more processors;
one or more memory units coupled to the one or more processors, the one or more memory units collectively storing logic, the logic configured to, when executed by the one or more processors, cause the one or more processors to perform operations comprising:
measuring, on each of a first plurality of electrode lines of a touch sensor, a respective value associated with a first signal transmitted by a stylus at a first time and sensed on each electrode line of the first plurality of electrode lines for determining a position of the stylus in a first direction, the first plurality of electrode lines oriented in a second direction that is different than the first direction, each of the first plurality of electrode lines being configured to sense the first signal transmitted by the stylus at the first time, the stylus having a stylus tip located at a position relative to the first plurality of electrode lines at the time of transmission of the first signal;
measuring, on each of a second plurality of electrode lines of the touch sensor, a respective value associated with a second signal transmitted by the stylus at a second time that is different than the first time and sensed on each electrode line of the second plurality of electrode lines for determining a position of the stylus in the second direction, the second plurality of electrode lines oriented in the first direction, each of the second plurality of electrode lines being configured, in a first mode of operation, to sense the second signal transmitted by the stylus at the second time, each of the second plurality of electrode lines configurable to operate at another time in a second mode of operation in which the second plurality of electrode lines carry a drive signal; and
estimating at least a two-dimensional position of the stylus tip based on interpolation of the respective values associated with the first signal sensed on each of the electrode lines of the first plurality of electrode lines oriented in the second direction and the respective values associated with the second signal sensed on each of the electrode lines of the second plurality of electrode lines oriented in the first direction;
a peak detector operable to measure a peak voltage of the sensed first signal on an electrode line of the first plurality of electrode lines;
a capacitor operable to store the measured peak voltage;
a current-to-voltage converter positioned between a connection pad associated with the electrode line of the first plurality of electrode lines and the peak detector, the current-to-voltage converter having at least one programmable gain setting; and
a current conveyor positioned between the connection pad and the current-to-voltage converter, the current conveyor operable to provide low-impedance input.
2. The apparatus of claim 1 , wherein the first and second signals are signal pulses.
3. The apparatus of claim 1 , wherein:
the first plurality of electrode lines are sense lines;
the second plurality of electrode lines are drive lines; and
the operations further comprise toggling the drive lines between the first mode of operation and the second mode of operation.
4. The apparatus of claim 3 , wherein:
the drive lines are arranged relative to the sense lines such that intersections of the drive lines and the sense lines form one or more capacitive nodes;
the sense lines are further operable to sense a third signal in response to the drive lines transmitting the signal in the driving mode; and
the operations further comprise measuring the change in capacitance of the one or more capacitive nodes due to sensing of the third signal.
5. The apparatus of claim 1 , wherein the first signal is a square or sine wave.
6. The apparatus of claim 1 , wherein estimating at least a two-dimensional position of the stylus tip based on interpolation of the respective values associated with the first signal sensed on each of the electrode lines of the first plurality of electrode lines oriented in the second direction and the respective values associated with the second signal sensed on each of the electrode lines of the second plurality of electrode lines oriented in the first direction comprises:
calculating a position in a first dimension by applying a parabolic equation to at least a subset of the respective values associated with the first signal sensed on each of the electrode lines of the first plurality of electrode lines oriented in the second direction; and
calculating a position in a second dimension by applying a parabolic equation to at least a subset of the respective values associated with the second signal sensed on each of the electrode lines of the second plurality of electrode lines oriented in the first direction.
7. The apparatus of claim 1 , wherein the operations further comprise:
detecting, when the second plurality of electrode lines are configured to operate in the second mode of operation and when a capacitance increases at a capacitive node of the touch sensor, a presence of a stylus; and
detecting, when the second plurality of electrodes are configured to operate in the second mode of operation and when a capacitance decreases at a capacitive node of the touch sensor, a presence of a finger.
8. A non-transitory computer-readable medium comprising logic, the logic when executed by one or more processors configured to cause the one or more processors to perform operations comprising:
measuring, on each of a first plurality of electrode lines of a touch sensor, a respective value associated with a first signal transmitted by a stylus at a first time and sensed on each electrode line of the first plurality of electrode lines for determining a position of the stylus in a first direction, the first plurality of electrode lines oriented in a second direction that is different than the first direction, each of the first plurality of electrode lines being configured to sense the first signal transmitted by the stylus at the first time, the stylus having a stylus tip located at a position relative to the first plurality of electrode lines at the time of transmission of the first signal;
measuring, on each of a second plurality of electrode lines of the touch sensor, a respective value associated with a second signal transmitted by the stylus at a second time that is different than the first time and sensed on each electrode line of the second plurality of electrode lines for determining a position of the stylus in the second direction, the second plurality of electrode lines oriented in the first direction, each of the second plurality of electrode lines being configured, in a first mode of operation, to sense the second signal transmitted by the stylus at the second time, each of the second plurality of electrode lines configurable to operate at another time in a second mode of operation in which the second plurality of electrodes lines carry a drive signal;
estimating at least a two-dimensional position of the stylus tip based on interpolation of the respective values associated with the first signal sensed on each of the electrode lines of the first plurality of electrode lines oriented in the second direction and the respective values associated with the second signal sensed on each of the electrodes lines of the second plurality of electrode lines oriented in the first direction;
measuring, by a peak detector, a peak voltage of the sensed first signal on an electrode line of the first plurality of electrode lines, wherein a current-to-voltage converter is positioned between a connection pad associated with the electrode line of the first plurality of electrode lines and the peak detector, the current-to-voltage converter having at least one programmable gain setting;
storing, by a capacitor, the measured peak voltage; and
providing, by a current conveyor positioned between the connection pad and the current-to-voltage converter, low-impedance input.
9. The non-transitory computer-readable medium of claim 8 , wherein the first and second signals are signal pulses.
10. The non-transitory computer-readable medium of claim 8 , wherein:
the first plurality of electrode lines are sense lines;
the second plurality of electrode lines are drive lines; and
the operations further comprise toggling the drive lines between the first mode of operation and the second mode of operation.
11. The non-transitory computer-readable medium of claim 10 , wherein:
the drive lines are arranged relative to the sense lines such that intersections of the drive lines and the sense lines form one or more capacitive nodes;
the sense lines are further operable to sense a third signal in response to the drive lines transmitting the signal in the driving mode; and
the operations further comprise measuring the change in capacitance of the one or more capacitive nodes due to sensing of the third signal.
12. The non-transitory computer-readable medium of claim 8 , wherein the first signal is a square or sine wave.
13. A method comprising:
measuring, on each of a first plurality of electrode lines of a touch sensor, a respective value associated with a first signal transmitted by a stylus at a first time and sensed on each electrode line of the first plurality of electrode lines for determining a position of the stylus in a first direction, the first plurality of electrode lines oriented in a second direction that is different than the first direction, each of the first plurality of electrode lines being configured to sense the first signal transmitted by the stylus at the first time, the stylus having a stylus tip located at a position relative to the first plurality of electrode lines at the time of transmission of the first signal;
measuring, on each of a second plurality of electrode lines of the touch sensor, a respective value associated with a second signal transmitted by the stylus at a second time that is different than the first time and sensed on each electrode line of the second plurality of electrode lines for determining a position of the stylus in the second direction, the second plurality of electrode lines oriented in the first direction, each of the second plurality of electrode lines being configured, in a first mode of operation, to sense the second signal transmitted by the stylus at the second time, each of the second plurality of electrode lines configurable to operate at another time in a second mode of operation in which the second plurality of electrode lines carry a drive signal;
estimating at least a two-dimensional position of the stylus tip based on interpolation of the respective values associated with the first signal sensed on each of the electrode lines of the first plurality of electrode lines oriented in the second direction and the respective values associated with the second signal sensed on each of the electrodes lines of the second plurality of electrode lines oriented in the first direction;
measuring, by a peak detector, a peak voltage of the sensed first signal on an electrode line of the first plurality of electrode lines, wherein a current-to-voltage converter is positioned between a connection pad associated with the electrode line of the first plurality of electrode lines and the peak detector, the current-to-voltage converter having at least one programmable gain setting;
storing, by a capacitor, the measured peak voltage; and
providing, by a current conveyor positioned between the connection pad and the current-to-voltage converter, low-impedance input.
14. The method of claim 13 , wherein:
the first plurality of electrode lines are sense lines;
the second plurality of electrode lines are drive lines; and
the method further comprises toggling the drive lines from the first mode of operation to the second mode of operation.
15. The method of claim 14 , wherein the drive lines are arranged relative to the sense lines such that intersections of the drive lines and the sense lines form one or more capacitive nodes, the method further comprising:
sensing, by the sense lines, a third signal in response to the drive lines transmitting the signal in the driving mode; and
measuring the change in capacitance of the one or more capacitive nodes due to sensing of the third signal.