Multi-touch touch device with multiple drive frequencies and maximum likelihood estimation

• US 9,753,586 B2
• Filed: 10/08/2009
• Issued: 09/05/2017
• Est. Priority Date: 10/08/2009
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Marino, Rachael P., Peterson, Jr., Richard A.
• Primary Examiner(s): Lee, Nicholas
• Application Number:
  US12/575,860
• Publication Number:
  US 20110084857A1
• Time in Patent Office: 2,889 Days
• Field of Search: 345173, 341 5, 178 1801- 1806
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• 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-sensitive device includes a touch panel, drive unit, and measurement unit. A touch applied to a given node of the panel changes a capacitive coupling between a given drive and sense electrode of the touch panel. The drive unit delivers first and second drive signals, having different first and second frequencies, to first and second drive electrodes respectively at the same or overlapping times. The measurement unit receives a first response signal from a sense electrode, and analyzes the signal using maximum likelihood estimation to determine the coupling capacitance between the first drive electrode and the sense electrode, and between the second drive electrode and the sense electrode. More drive electrodes, including in some cases all the drive electrodes, can be driven with unique drive frequencies, and more sense electrodes, including in some cases all the sense electrodes, can be sensed by the measurement unit.

Claims

1. A touch-sensitive apparatus, comprising:

a panel comprising a touch surface, a plurality of drive electrodes, and a plurality of receive electrodes;

a drive unit configured to deliver a first drive signal having a first drive frequency to a first one of the drive electrodes while also delivering a second drive signal having a second drive frequency, different from the first drive frequency, to a second one of the plurality of drive electrodes; and

a measurement unit configured to receive a first response signal from a first one of the plurality of receive electrodes, and to analyze the first response signal to determine therefrom (a) a first coupling capacitance between the first receive electrode and the first drive electrode using a maximum likelihood estimation for a square of a first amplitude at a first frequency associated with the first drive frequency using a probability density function of the first amplitude and at least one amplitude of the first response signal, and (b) a second coupling capacitance between the first receive electrode and the second drive electrode using a maximum likelihood estimation for a square of a second amplitude at a second frequency associated with the second drive frequency using a probability density function of the second amplitude and the at least one amplitude of the first response signal.

2. The apparatus of claim 1, wherein the measurement unit is configured to evaluate the first response signal over a first sample time, the first sample time corresponding to a first integer number of periods of the first drive frequency and also corresponding to a second integer number of periods of the second drive frequency.

3. The apparatus of claim 2, wherein the first and second drive signals are a subset of a plurality of drive signals, each having a different drive frequency and each delivered to a different one of the drive electrodes respectively, and wherein the first sample time corresponds to different integer numbers of periods of each of the different drive frequencies.

4. The apparatus of claim 3, wherein the drive frequencies of the plurality of drive signals exhibit a uniform frequency spacing of Δ

f.

5. The apparatus of claim 3, wherein the drive frequencies of the plurality of drive signals have a greatest common factor of f_GCF, and wherein the first sample time is substantially the reciprocal of f_GCF or an integer multiple thereof.

6. The apparatus of claim 3, wherein the plurality of drive signals comprises at least four drive signals.

7. The apparatus of claim 1, wherein the measurement unit is further configured to filter, amplify, and/or digitize the first response signal.

8. The apparatus of claim 1, wherein the measurement unit is also configured to receive a second response signal from a second one of the plurality of receive electrodes, and to analyze the second response signal to determine therefrom (c) a third coupling capacitance between the second receive electrode and the first drive electrode using a maximum likelihood estimation for a square of a third amplitude at the first frequency using a probability density function of the third amplitude and at least one amplitude of the second response signal, and (d) a fourth coupling capacitance between the second receive electrode and the second drive electrode using a maximum likelihood estimation for a square of a fourth amplitude at the second frequency using a probability density function of the fourth amplitude and at least one amplitude of the second response signal.

9. The apparatus of claim 8, wherein the first and second response signals are a subset of a plurality of response signals associated respectively with a corresponding plurality of receive electrodes.

10. The apparatus of claim 1, wherein the plurality of drive electrodes and the plurality of receive electrodes define an electrode matrix, each drive electrode being capacitively coupled to each receive electrode at a respective node of the matrix, the panel being configured such that a touch on the touch surface proximate a given one of the nodes changes a coupling capacitance between the drive electrode and the receive electrode associated with the given node.

11. The apparatus of claim 1, wherein the drive unit is further configured to deliver a third drive signal, having a third drive frequency different from the first and second drive frequencies, to a third one of the drive electrodes while also delivering the first drive signal to the first drive electrode and the second drive signal to the second drive electrode.

12. The apparatus of claim 1, wherein the drive unit comprises a first multiplexer configured to couple the first drive signal sequentially to the first drive electrode and at least another one of the plurality of drive electrodes.

13. The apparatus of claim 1, wherein the drive unit has a first operating mode in which the first drive signal is delivered at overlapping times to the first drive electrode and at least another one of the plurality of drive electrodes, the drive unit also having a second operating mode in which the first drive signal is delivered individually to the first drive electrode and the another drive electrode in a timed sequence.

14. The apparatus of claim 1, wherein the first drive signal has a first phase, and wherein the measurement unit is configured to analyze the first response signal to determine therefrom the first coupling capacitance and the second coupling capacitance without regard to the first phase.

15. The apparatus of claim 1, wherein the measurement unit includes a first band-pass filter coupleable to the first response signal to isolate a signal component at the first drive frequency from the first response signal, the signal component at the first drive frequency being responsive to the first coupling capacitance.

16. The apparatus of claim 15, wherein the measurement unit also includes a second band-pass filter coupleable to the first response signal to isolate a signal component at the second drive frequency from the first response signal, the signal component at the second drive frequency being responsive to the second coupling capacitance.

17. The apparatus of claim 1, further comprising:

a control unit coupled to the drive unit and to the measurement unit, the control unit configured to control the first and second drive frequencies delivered by the drive unit, the control unit also configured to provide the first and second drive frequencies to the measurement unit such that the maximum likelihood estimation implemented by the measurement unit analyzes the first response signal based on the first and second drive frequencies.

18. A method of determining a plurality of touch locations for touches on a touch panel that are simultaneous or overlapping in time, the method comprising:

providing a panel comprising a touch surface, a plurality of drive electrodes, and a plurality of receive electrodes;

delivering a first drive signal having a first drive frequency to a first one of the drive electrodes while also delivering a second drive signal having a second drive frequency, different from the first drive frequency, to a second one of the plurality of drive electrodes;

receiving a first response signal from a first one of the plurality of receive electrodes;

analyzing the first response signal to determine therefrom (a) a first coupling capacitance between the first receive electrode and the first drive electrode using a maximum likelihood estimation of a square of a first amplitude at a first frequency associated with the first drive frequency using a probability density function of the first amplitude and at least one amplitude of the first response signal, and (b) a second coupling capacitance between the first receive electrode and the second drive electrode using a maximum likelihood estimation of a square of a second amplitude at a second frequency associated with the second drive frequency using a probability density function of the second amplitude and the at least one amplitude of the first response signal.

19. The method of claim 18, wherein the analyzing includes evaluating the first response signal over a first sample time, the first sample time corresponding to a first integer number of periods of the first drive frequency and also corresponding to a second integer number of periods of the second drive frequency.

20. The method of claim 18, wherein the first drive signal is controlled to oscillate at the first drive frequency based on a first control value, wherein the first response signal is initially in analog form, wherein the analyzing includes digitizing the first response signal at a sampling frequency, and wherein the analyzing includes determining the first coupling capacitance by calculating a first amplitude of a first component of the digitized first response signal using the first control value.