Touch-sensitive interface and method using orthogonal signaling

• US 8,605,054 B2
• Filed: 09/02/2010
• Issued: 12/10/2013
• Est. Priority Date: 09/02/2010
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Texas Instruments, Inc.
• Inventors: Krenik, William R., Dabak, Anand
• Primary Examiner(s): Chang, Kent
• Assistant Examiner(s): PHAM LU, NGAN T
• Application Number:
  US12/807,333
• Publication Number:
  US 20120056841A1
• Time in Patent Office: 1,195 Days
• Field of Search: 345156-184, 178 1801- 1811
• US Class Current: 345/174
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/04184 Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

A touch screen system includes a capacitive touch screen (1) including a plurality of row conductors (7-1,2 . . . n) and a column conductor (5-1). A plurality of cotemporaneous orthogonal excitation signals (S₁(t), S₂(t) . . . S_n(t)) are simultaneously driven onto the row conductors, respectively. The capacitively coupled signals on the column conductor may be influenced by a touch (10) on the capacitive touch screen. Receiver circuitry (50) includes a sense amplifier (21-1) coupled to generate an amplifier output signal (r₁(t)) in response to signals capacitively coupled onto the column conductor. WHT-based circuitry (35) determines amounts of signal contribution capacitively coupled by each of the excitation signals, respectively, to the amplifier output signal.

Claims

1. A touch screen system comprising:

(a) a capacitive touch screen including a plurality of row conductors and a column conductor;

(b) orthogonal drive circuitry coupled to simultaneously drive a plurality of cotemporaneous orthogonal excitation signals onto the row conductors, wherein the cotemporaneous orthogonal excitation signals occur over a plurality of successive time intervals each having a predetermined duration; and

(c) receiver circuitry including

(1) a sense amplifier coupled to generate an amplifier output signal in response to signals capacitively coupled onto the column conductor in response to the cotemporaneous orthogonal excitation signals on the row conductors, wherein one or more of the capacitively coupled signals on the column conductor may be influenced by a touch on the capacitive touch screen, and

(2) logic circuitry for determining amounts of contribution of the cotemporaneous excitation signals to the amplifier output signal due to capacitive coupling from each row conductor, respectively, to the column conductor,

wherein each of the cotemporaneous orthogonal excitation signals is generated by multiplying a plurality of segments of a carrier signal by a plurality of elements, respectively, of a corresponding Walsh-Hadamard sequence,

wherein the capacitive touch screen includes a plurality of the column conductors and a plurality of the sense amplifiers each coupled to generate a corresponding amplifier output signal in response to signals capacitively coupled onto the plurality of column conductors in response to the cotemporaneous orthogonal excitation signals on the row conductors, wherein one or more of the capacitively coupled signals on the plurality of column conductors may be influenced by the touch on the capacitive touch screen, wherein the receiver circuitry includes

a plurality of multiplier circuits for correlating the amplifier output signals by multiplying them by cotemporaneous orthogonal correlation signals,

a plurality of summation circuits for accumulating correlated signal information from the multiplier circuits, respectively, over time intervals equal to the predetermined duration, and

a plurality of sampling circuits for sampling outputs of the summation circuits, respectively, at ends of the successive time intervals, and wherein the logic circuitry determines amounts of signal contribution of the cotemporaneous excitation signals capacitively coupled from each row conductor, respectively, to each of the plurality of column conductors.

2. The touch screen system of claim 1 wherein each of the amplifier output signals is multiplied by a first cotemporaneous orthogonal correlation signal and then is input to a corresponding first summation circuit and is also multiplied by a second cotemporaneous orthogonal correlation signal and then is input to a corresponding second summation circuit.

3. The touch screen system of claim 2 wherein the second cotemporaneous orthogonal correlation signal is shifted 90°

in phase relative to the first cotemporaneous orthogonal correlation signal.

4. The touch screen system of claim 1 wherein the receiver circuitry includes a plurality of analog to digital converters (ADCs) coupled between the sense amplifiers and the multiplier circuits for converting the amplifier output signals to digital representations thereof.

5. The touch screen system of claim 1 wherein the plurality of sampling circuits include a plurality of switches, respectively, coupled between outputs of the summation circuits and inputs of the logic circuitry.

6. The touch screen system of claim 5 wherein each of the plurality of switches is controlled to generate information samples sampled at the ends of the successive time intervals.

7. The touch screen system of claim 6 wherein the logic circuitry includes Walsh-Hadamard Transform based logic circuitry which executes an inverse Walsh-Hadamard Transform on the information samples sampled at the ends of the successive time intervals to generate a coupling coefficient matrix.

8. The touch screen system of claim 7 wherein the coupling coefficient matrix represents the equations

9. The touch screen system of claim 8 wherein the inverse Walsh-Hadamard Transform corresponding to a column i with respect to a sequence of the information samples included in a Walch Hadamard code corresponding to a row j is given by the expression

10. The touch screen system of claim 1 wherein the carrier signal is sinusoidal.

11. The touch screen system of claim 1 wherein the cotemporaneous orthogonal excitation signals are wavelets.

12. The touch screen system of claim 1 wherein each of the cotemporaneous orthogonal excitation signals is multiplied by a common randomized spreading code to avoid radio frequency interference.

13. The touch screen system of claim 1 wherein each of the cotemporaneous orthogonal excitation signals includes a relatively short dead time at the end of each of the segments to allow effects of excitation signal dispersion to settle.

15. The method of claim 13 wherein step (b) includes executing an inverse Walsh-Hadamard Transform on information samples of the correlated and accumulated and then sampled amplifier output signals to generate information representative of a coupling coefficient matrix.

16. The method of claim 13 wherein the correlating includes also multiplying the amplifier output signals by a second cotemporaneous orthogonal correlation signal, wherein the second cotemporaneous orthogonal correlation signal is the same as but shifted in phase relative to the first cotemporaneous orthogonal correlation signal.

17. The method of claim 13 wherein the carrier signal is sinusoidal.

14. A method for operating a touch screen system including

a capacitive touch screen including a plurality of row conductors and a column conductor, and

receiver circuitry including a sense amplifier coupled to generate an amplifier output signal in response to signals capacitively coupled onto the column conductor,

the method comprising:

(a) simultaneously driving a plurality of cotemporaneous orthogonal excitation signals onto the row conductors, respectively, wherein one or more of the capacitively coupled signals on the column conductor may be influenced by a touch on the capacitive touch screen, and wherein the cotemporaneous orthogonal excitation signals occur over a common plurality of successive time intervals, each of the successive time intervals having a predetermined duration; and

(b) determining amounts of contribution by each of the cotemporaneous excitation signals to the amplifier output signal due to capacitive coupling from each row conductor, respectively, to the column conductor,

wherein each of the cotemporaneous orthogonal excitation signals is generated by multiplying a plurality of segments of a carrier signal by a plurality of elements, respectively, of a corresponding Walsh-Hadamard sequence, and wherein the receiver circuitry receives a plurality of the column conductors and includes a plurality of the sense amplifiers each coupled to generate a corresponding amplifier output signal in response to signals capacitively coupled onto the plurality of column conductors, respectively, in response to the cotemporaneous orthogonal excitation signals,

wherein the method includes

correlating the amplifier output signals by multiplying them by a first cotemporaneous orthogonal correlation signal,

accumulating the correlated amplifier output signals, respectively, over a time interval equal to the predetermined duration, and

sampling the correlated and then accumulated amplifier output signals at ends of the successive time intervals.

18. A touch screen system comprising:

(a) a capacitive touch screen including a plurality of row conductors and a column conductor;

(b) receiver circuitry including a sense amplifier coupled to generate an amplifier output signal in response to signals capacitively coupled onto the column conductor;

(c) means for simultaneously driving a plurality of cotemporaneous orthogonal excitation signals onto the row conductors, respectively, wherein one or more of the capacitively coupled signals on the column conductor may be influenced by a touch on the capacitive touch screen, and wherein the cotemporaneous orthogonal excitation signals occur over a common plurality of successive time intervals, each of the time intervals having a predetermined duration; and

(d) means for determining amounts of signal contribution by each of the cotemporaneous excitation signals to the amplifier output signal due to capacitive coupling from each row conductor, respectively, to the column conductor,

wherein each of the cotemporaneous orthogonal excitation signals is generated by multiplying a plurality of segments of a carrier signal by a plurality of elements, respectively, of a corresponding Walsh-Hadamard sequence,

wherein the capacitive touch screen includes a plurality of the column conductors and a plurality of the sense amplifiers each coupled to generate a corresponding amplifier output signal in response to signals capacitively coupled onto the plurality of column conductors in response to the cotemporaneous orthogonal excitation signals on the row conductors, wherein one or more of the capacitively coupled signals on the plurality of column conductors may be influenced by the touch on the capacitive touch screen, wherein the receiver circuitry includes

a plurality of multiplier circuits for correlating the amplifier output signals by multiplying them by cotemporaneous orthogonal correlation signals,

a plurality of summation circuits for accumulating correlated signal information from the multiplier circuits, respectively, over time intervals equal to the predetermined duration, and

a plurality of sampling circuits for sampling outputs of the summation circuits, respectively, at ends of the successive time intervals, and wherein the logic circuitry determines amounts of signal contribution of the cotemporaneous excitation signals capacitively coupled from each row conductor, respectively, to each of the plurality of column conductors.