Decoding touch data based on a code word portion

1 . A method comprising:

providing a capacitive touch sensing system comprising transmit electrodes and receive electrodes positioned to have mutual capacitances between transmit electrodes and receive electrodes at electrode intersections called nodes, wherein the capacitance at respective ones of nodes deviates when touched; and

performing a touch position estimate by:

identifying a first and a second subset of transmit electrodes based on a prior touch position estimate, wherein at least one of the first subset of transmit electrodes is identified as touched or identified as assumed touched based on the prior touch position estimate, wherein the transmit electrodes of the second subset of transmit electrodes have been identified as not touched or identified as assumed not touched based on the prior touch position estimate;

assigning code words from a first subset of code words to respective ones of transmit electrodes of the first subset of transmit electrodes, wherein respective ones of code words from the first subset of code words are a complete code word having a first code word portion and a second code word portion;

assigning code words from a second subset of code words to respective ones of transmit electrodes of the second subset of transmit electrodes, wherein respective ones of code words from the second subset of code words are a complete code word having a first code word portion and a second code word portion;

generating a transmit signal for respective ones of transmit electrodes according to its assigned code word;

transmitting the transmit signals;

receiving a first portion of a receive signal, for respective ones of receive electrodes, indicative of the respective capacitances between the receive electrode and respective ones of transmit electrodes;

decoding the first portion of the receive signal for respective ones of receive electrodes using the first portions of the first subset of code words before the second portion of the first subset of code words of the receive signal is received; and

computing a touch position estimate for the first subset of transmit electrodes based on the decoded first portions of the receive signals.

2 . The method as in claim 1 , comprising:

receiving a second portion of receive signal for respective ones of receive electrodes;

decoding a complete receive signal for respective ones of receive electrodes using the complete code words; and

computing a touch position estimate for a set of transmit electrodes based on decoded complete receive signals.

3 . The method as in claim 2 , comprises serially and alternatingly decoding the first portion of the first subset of code words of the receive signal and decoding the complete receive signal.

4 . The method as in claim 1 , comprising default assigning respective ones of code words from the first subset of code words to respective ones of the first subset of transmit electrodes and default assigning respective ones of code words from the second subset of code words to respective ones of the second subset of transmit electrodes.

5 . The method as in claim 4 , wherein code words comprise unique numbers, wherein transmit electrodes are numbered uniquely, and wherein the default assigning comprises assigning a code word with a lowest number to a lowest numbered transmit electrode, and assigning a code word with a second lowest number to a second lowest numbered transmit electrode.

6 . The method as in claim 1 , comprising repeating the performing a touch position estimate.

7 . The method as in claim 1 , wherein assigning respective ones of code words from the first subset of code words to respective ones of the first subset of transmit electrodes comprises: adaptive assigning respective ones of code words from the first subset of code words to transmit electrodes identified as having been touched or identified as assumed to have been touched based on the prior touch position estimate, and wherein assigning respective ones of code words from the second subset of code words to respective ones of the second subset of transmit electrodes comprises: adaptive assigning respective ones of code words from the second subset of code words to transmit electrodes identified as having not been touched or identified as assumed to have not been touched based on the prior touch position estimate.

8 . The method as in claim 1 , wherein assigning respective ones of code words from the second subset of code words to respective ones of the second subset of transmit electrodes comprises: adaptive assigning respective ones of code words from the second subset of code words to transmit electrodes identified as having not been touched or identified as assumed to have not been touched based on the prior touch position estimate, and wherein assigning respective ones of code words from the first subset of code words to respective ones of the first subset of transmit electrodes comprises: adaptive assigning respective ones of code words from the first subset of code words to remaining unassigned transmit electrodes.

9 . The method as in claim 1 , wherein respective ones of the code words comprise binary sequences having 2*K chips of a Hadamard matrix where K is an integer, wherein the code word portions of respective ones of the code words comprise K chips.

10 . The method as in claim 9 , wherein respective ones of the code words comprise sixteen chips, wherein the code word portions of respective ones of the code words comprise eight chips, and the Hadamard matrix is a 16×16 matrix comprising two code word portions.

11 . The method as in claim 9 , wherein decoding comprises despreading the receive signal using code words from rows of the Hadamard matrix.

12 . The method as in claim 9 , wherein the Hadamard matrix comprises four quadrants, wherein the respective ones of the four quadrants comprise a Hadamard matrix themselves.

13 . A system comprising:

a capacitive touch sensing system comprising transmit electrodes and receive electrodes positioned to have mutual capacitances between transmit electrodes and receive electrodes at electrode intersections called nodes, wherein the capacitance at respective ones of nodes deviates when touched;

a processor; and

a machine readable storage medium storing instructions, which when executed by the processor, cause the system to:

identify a first and a second subset of transmit electrodes based on a prior touch position estimate, wherein at least one of the first subset of transmit electrodes is identified as touched or identified as assumed touched based on the prior touch position estimate, wherein the transmit electrodes of the second subset of transmit electrodes have been identified as not touched or identified as assumed not touched based on the prior touch position estimate;

assign code words from a first subset of code words to respective ones of transmit electrodes of the first set of transmit electrodes, wherein respective ones of code words from the first subset of code words are a complete code word having a first code word portion and a second code word portion;

assign code words from a second subset of code words to respective ones of transmit electrodes of the second subset of transmit electrodes, wherein respective ones of code words from the second set of code words are a complete code word having a first code word portion and a second code word portion;

generate a transmit signal for respective ones of transmit electrodes according to its assigned code word;

transmit the transmit signals;

receive a first portion of a receive signal, for respective ones of receive electrodes, indicative of the respective capacitances between the receive electrode and respective ones of transmit electrodes;

decode the first portion of the receive signal for respective ones of receive electrodes using the first portions of the first subset of code words before the second portion of the first subset of code words of the receive signal is received; and

compute touch position estimates for the first subset of transmit electrodes based on decoded first portions of the receive signals,

whereby a touch estimate is performed.

14 . The system as in claim 13 , wherein the instructions, which when executed by the processor, cause the system to:

receive a second portion of receive signal for respective ones of receive electrodes;

decode a complete receive signal for respective ones of receive electrodes using the complete code words; and

compute touch position estimates for the subset of transmit electrodes based on decoded complete receive signals.

15 . The system as in claim 14 , wherein the instructions, which when executed by the processor, cause the system to serially and alternatingly decode the first portion of the first subset of code words of the receive signal and decode a complete receive signal.

16 . The system as in claim 13 , wherein the instructions, which when executed by the processor, cause the system to default assign respective ones of code words from the first subset of code words to respective ones of the first subset of transmit electrodes and default assign respective ones of code words from the second subset of code words to respective ones of the second subset of transmit electrodes.

17 . The system as in claim 16 , wherein code words comprise unique numbers, wherein transmit electrodes are numbered uniquely, and wherein the default assigning comprises assigning a code word with a lowest number to a lowest numbered transmit electrode, and assigning a code word with a second lowest number to a second lowest numbered transmit electrode.

18 . The system as in claim 13 , wherein the instructions, which when executed by the processor, cause the system to repeatedly perform a touch position estimate.

19 . The system as in claim 13 , wherein the instructions, which when executed by the processor, cause the system to:

adaptively assign respective ones of code words to transmit electrodes identified as having been touched or identified as assumed to have been touched based on the prior touch position estimate, and

adaptively assign respective ones of code words to transmit electrodes identified as having not been touched or identified as assumed to have not been touched based on the prior touch position estimate.

20 . The system as in claim 13 , wherein assign respective ones of code words from the second subset of code words to respective ones of the second subset of transmit electrodes comprises: adaptive assign respective ones of code words from the second subset of code words to transmit electrodes identified as having not been touched or identified as assumed to have not been touched based on the prior touch position estimate, and wherein assign respective ones of code words from the first subset of code words to respective ones of the first subset of transmit electrodes comprises: adaptive assign respective ones of code words from the first subset of code words to remaining unassigned transmit electrodes.

21 . The system as in claim 13 , wherein respective ones of the code words comprise binary sequences having 2*K chips of a Hadamard matrix where K is an integer, wherein the code word portions of respective ones of the code words comprise K chips.

22 . The system as in claim 21 , wherein respective ones of the code words comprise sixteen chips, wherein the code word portions of respective ones of the code words comprise eight chips, and the Hadamard matrix is an 16×16 matrix comprising two code word portions.

23 . The system as in claim 21 , wherein decoding comprises despreading a receive signal using code words from rows of the Hadamard matrix.

24 . The system as in claim 21 , wherein the Hadamard matrix comprises four quadrants, wherein the respective ones of the four quadrants comprise a Hadamard matrix.