Finger touch sensing with a digitizer system
A method for multi-touch detection on a grid based capacitive sensor includes transmitting consecutively a first and then a second sequence of a Golay pair of sequences on a first driver line of a grid based capacitive sensor and transmitting the first and then the second sequence of a Golay pair of sequences on a second driver line, at a predefined delay with respect to transmission on the first driver line. Output on a receiver line of the grid based capacitive sensor is sampled and output originating from the first driver line is separated from output originating from the second driver line. The presence of an input object is detected responsive to the output as separated.
1. A method for multi-touch detection on a grid based capacitive sensor, the method comprising:
transmitting consecutively a first and then a second sequence of a Golay pair of sequences on a first driver line of a grid based capacitive sensor;
transmitting the first and then the second sequence of a Golay pair of sequences on a second driver line, at a predefined delay with respect to transmission on the first driver line;
sampling output on a receiver line of the grid based capacitive sensor;
separating output originating from the first driver line with output originating from the second driver line; and
detecting presence of an input object responsive to the output as separated.
2. The method of claim 1 , wherein the Golay pair of sequences is a pair of bipolar sequences.
3. The method of claim 1 , wherein the Golay pair of sequences transmitted on each of the first and second drive lines are encoded on a carrier signal.
4. The method of claim 3 , wherein the Golay pair of sequences is encoded as a sequence of phase inversions of the carrier signal.
5. The method of claim 1 , wherein the first sequence transmitted on the first driver line is encoded on a first carrier signal and wherein the second sequence transmitted on the second driver line is encoded on a second carrier signal that is orthogonal to the first carrier signal.
6. The method of claim 5 , wherein the first and second carrier signals are orthogonal in frequency.
7. The method of claim 1 , comprising using frequency domain multiplexing for transmitting the second sequence on the first driver line concurrently with transmitting the first sequence on the second driver line.
8. The method of claim 1 , comprising transmitting consecutively the first and then the second sequence of the Golay pair of sequences on a third driver line of the grid based capacitive sensor and in phase with transmission on the first driver line, wherein the Golay pair of sequences transmitted on the first driver line is encoded on a first carrier signal and wherein the Golay pair of sequences transmitted on the third driver line is encoded on a second carrier signal that is orthogonal to the first carrier signal.
9. The method of claim 1 , wherein the predefined delay is shorter than a transmission period for transmitting the first sequence on the first driver line.
10. The method of claim 1 , wherein the output originating from the first driver line is separated with output originating from the second driver line using a single correlator.
11. The method of claim 1 , comprising cross correlating the output on the receiver line with each of the first and second sequences of the Golay pair of sequences and summing results of the cross correlation with the first sequence with results of the cross correlation of the second sequence.
12. Circuitry for performing multi-touch detection on a grid based capacitive sensor comprising:
drive circuitry configured to transmit a Golay pair of sequences on a first and second driver lines of a grid based capacitive sensor, wherein the Golay pair of sequences transmitted on the second driver line is transmitted with a predefined delay with respect to transmission on the first driver line; and
receiver circuitry configured to sample output on a receiver line of the grid based capacitive sensor, separate output originating from the first driver line from output originating from the second driver line and detect presence of an input object responsive to the output as separated.
13. Circuitry according to claim 12 , wherein the pre-defined delay is shorter than duration for transmitting one sequence of the Golay pair of sequences.
14. The method according to claim 1 , wherein the predefined delay is an integer multiple of a period over which one coefficient of a sequence of the Golay pair is transmitted.
15. The method according to claim 1 , wherein the predefined delay is a period over which one coefficient of a sequence of the Golay pair is transmitted.
16. The circuit according to claim 12 , wherein the predefined delay is an integer multiple of a period over which one coefficient of a sequence of the Golay pair is transmitted.
17. The circuit according to claim 12 , wherein the predefined delay is a period over which one coefficient of a sequence of the Golay pair is transmitted.