Capacitive-based touch apparatus and method therefor, with reduced interference

• US 8,890,841 B2
• Filed: 03/13/2013
• Issued: 11/18/2014
• Est. Priority Date: 03/13/2013
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Rebeschi, Thomas J., Cordeiro, Craig A., Farlow, William
• Primary Examiner(s): Edun, Muhammad N
• Application Number:
  US13/798,736
• Publication Number:
  US 20140267129A1
• Time in Patent Office: 615 Days
• Field of Search: None
• US Class Current: 345/174
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• 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
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe

Abstract

A touch-sensitive device that includes a touch surface circuit that facilitates a change in a coupling capacitance in response to a capacitance-altering touches occurring at the touch surface. The device includes a sense circuit that provides a signal, in response thereto, having transient portions for characterizing positive-going transitions towards an upper signal level and negative-going transitions towards a lower signal level. An amplification circuit is then used for amplifying and processing the signals, in response to the time-varying input parameters. The amplification circuit adjusts the gain for the transient portions relative to gain for portions of the response signals between the transient portions, and thereby suppresses RF interference, such as in the form of signal odd and/or even harmonics, to provide a noise filtered output for determining positions of capacitance-altering touches on the touch surface.

Claims

1. A touch-sensitive apparatus, comprising:

a touch surface circuit including a touch surface and a plurality of electrodes, each of the plurality of electrodes being configured and arranged to be associated with a coupling capacitance that changes in response to a capacitance-altering touch at the touch surface;

a sense circuit configured to generate response signals for the plurality of electrodes;

each of the response signals having an amplitude responsive to the coupling capacitance at the touch surface and including a differentiated signal representation with transient portions characterizing positive-going transitions towards an upper signal level and negative-going transitions towards a lower signal level; and

an amplification circuit configured and arranged to provide time-varying parameters for characterizing the transient portions, the amplification circuit including a variable-gain amplifier configured and arranged for processing the differentiated signal representation of the response signals to provide variable gain thereto, in response to the time-varying parameters, the gain being adjusted for the transient portions relative to gain for portions of the response signals between the transient portions, and therein suppressing harmonics in the response signals for providing a noise filtered output that characterizes the associated coupling capacitance for determining positions of touches on the touch surface.

2. The touch-sensitive apparatus of claim 1, wherein the variable-gain amplifier is further configured and arranged for processing the response signals to provide variable gain thereto by increasing gain for the transient portions and decreasing gain for portions of the response signals between the transient portions.

3. The touch-sensitive apparatus of claim 2, wherein the variable-gain amplifier is further configured and arranged to suppress harmonics, including the 3^rd and 5^th harmonics, in the response signals, to filter noise interference in the response signals as part of the processing by the variable-gain amplifier.

4. The touch-sensitive apparatus of claim 1, wherein the variable-gain amplifier includes an integration circuit that uses the time-varying parameters to provide an integration-and-dump filter operation at the transient portions with decimation to a multiple of a clock rate used for sampling the response signals, and further including a measurement circuit configured for responding to the response signals processed via the variable-gain amplifier by performing measurements on characterizations of the associated coupling capacitance and determining therefrom positions of touches on the touch surface.

5. The touch-sensitive apparatus of claim 1, wherein the variable-gain amplifier is further configured and arranged to perform an integration on the differentiated signal representation of the response signals using the time-varying parameters to facilitate decimation at the transient portions and creation of nulls in the frequency response of the integration for the 3^rd and 5^th harmonics of an RF signal in the differentiated signal representation.

6. The touch-sensitive apparatus of claim 1, wherein the plurality of electrodes includes drive electrodes and wherein the touch surface circuit further included a signal driver circuit configured and arranged for driving the drive electrodes with an RF signal for developing the response signal.

7. The touch-sensitive apparatus of claim 1, wherein the plurality of electrodes includes drive electrodes, wherein the touch surface circuit further includes a signal driver circuit configured and arranged for driving the drive electrodes with an RF signal for developing the response signal, and wherein the variable-gain amplifier is further configured and arranged to perform an integration on the differentiated signal representation of the response signals using the time-varying parameters to facilitate decimation at the transient portions and creation of nulls in a frequency response for the 3^rd and 5^th harmonics of the RF signal for filtering at the 3^rd and 5^th harmonics.

8. The touch-sensitive apparatus of claim 1, wherein the variable-gain amplifier is further configured and arranged to perform an integration on the differentiated signal representation of the response signals using the time-varying parameters to facilitate decimation at the transient portions and, in response thereto, facilitate suppression in the frequency response of the integration for both odd harmonics and of an RF signal in the differentiated signal representation.

9. The touch-sensitive apparatus of claim 1, wherein the variable-gain amplifier includes a first stage configured and arranged to perform an integration on the differentiated signal representation of the response signals using the time-varying parameters to facilitate decimation at the transient portions for creation of nulls for a set of odd and even harmonics of the RF signal, and a second stage, responsive to the first stage, configured and arranged to suppress in a frequency response of the integration for both odd and even harmonics of an RF signal in the differentiated signal representation, thereby filtering RF noise interference.

10. The touch-sensitive apparatus of claim 1, further including a measurement circuit configured for responding to the response signals processed via the variable-gain amplifier by performing measurements on characterizations of the associated coupling capacitance and determining therefrom positions of touches on the touch surface, wherein the variable-gain amplifier includes a first stage configured and arranged to perform an integration on the differentiated signal representation of the response signals using the time-varying parameters to facilitate decimation at the transient portions for creation of nulls for odd harmonics of the RF signal, and a second stage, responsive to the first stage, configured and arranged to suppress in a frequency response of the integration for both odd and even harmonics of an RF signal in the differentiated signal representation, thereby filtering RF noise interference.

11. The touch-sensitive apparatus of claim 10, wherein the first stage is configured and arranged to perform an integration on the differentiated signal representation of the response signals using the time-varying parameters to facilitate decimation at the transient portions and creation of nulls in the frequency response of the integration for the 3^rd and 5^th harmonics of an RF signal in the differentiated signal representation.

12. The touch-sensitive apparatus of claim 11, wherein the second stage is configured and arranged to perform an integration for combining the transient portions at the positive-going transitions and the negative-going transitions, for increasing signal strength.

13. The touch-sensitive apparatus of claim 1, wherein the plurality of electrodes includes drive and receive electrodes that are arranged to provide an electrode matrix in which each drive electrode is capacitively coupled to each receive electrode at a respective node of the matrix.

14. The touch-sensitive apparatus of claim 13, further including a drive unit configured to generate a drive signal and to deliver the drive signal to the drive electrodes, and wherein the sense unit is further configured to generate, for drive signals delivered to each drive electrode, response signals for the plurality of receive electrodes.

15. The touch-sensitive apparatus of claim 1, wherein the variable-gain amplifier and the measurement unit are further configured and arranged to reduce or eliminate common mode noise.

16. The touch-sensitive apparatus of claim 1, wherein the plurality of electrodes includes drive and receive electrodes that are arranged to provide an electrode matrix in which each drive electrode is capacitively coupled to each receive electrode at a respective node of the matrix, and further including

a drive unit configured and arranged to generate a drive signal and to deliver the drive signal to the drive electrodes, and wherein the sense unit is further configured to generate, for drive signals delivered to each drive electrode, response signals for the plurality of receive electrodes;

and

a measurement circuit configured and arranged to measure an amplitude of each of the response signals for each of the nodes, and to determine therefrom the positions of multiple temporally-overlapping touches, if present, on the touch surface, wherein the measurement unit includes an analog-to-digital converter (ADC) and a multiplexer, the ADC coupling to the sense unit through the multiplexer.

17. The touch-sensitive apparatus of claim 1, further including a drive unit configured to generate pulsed drive signals and to deliver the pulsed drive signals to the drive electrodes, wherein the sense unit is further configured to generate, for the pulsed drive signals delivered to each drive electrode, response signals for the plurality of receive electrodes, wherein the plurality of electrodes includes drive and receive electrodes that are arranged to provide an electrode matrix in which each drive electrode is capacitively coupled to each receive electrode at a respective node of the matrix, and wherein the sense unit includes, for each of the receive electrodes, a reset switch coupled to the respective capacitor and configured to discharge the respective capacitor in response to a reset signal.

18. The apparatus of claim 1, wherein the drive signal includes a plurality of sequential pulses, each in the form of a ramped pulse or a rectangular pulse, and each response signal includes a corresponding plurality of response pulses, and wherein the measurement unit is configured to measure for each response signal an amplitude representative of amplitudes of the plurality of response pulses.

19. A touch-sensitive apparatus, comprising:

touch surface means, including a touch surface and a plurality of electrodes, each of the plurality of electrodes being configured and arranged to be associated with a coupling capacitance that changes in response to a capacitance-altering touch at the touch surface, and the touch surface means for providing the response;

sensing means configured to generate response signals for the plurality of electrodes;

each of the response signals having an amplitude responsive to the coupling capacitance at the touch surface and including a differentiated signal representation with transient portions characterizing positive-going transitions towards an upper signal level and negative-going transitions towards a lower signal level; and

means for using time-varying parameters to process the response signals to provide variable gain thereto by adjusting gain for the transient portions relative to gain for portions of the response signals between the transient portions, and therein suppressing harmonics in the response signals; and

thereby facilitating measurement of the response signals to determine therefrom positions of touches on the touch surface in response to changes of the coupling capacitance.

20. A method for use of a touch surface circuit including a touch surface and a plurality of electrodes, each of the plurality of electrodes being configured and arranged to be associated with a coupling capacitance that changes in response to a capacitance-altering touch at the touch surface, the method comprising:

using a circuit to generate response signals for the plurality of electrodes, wherein each of the response signals has an amplitude responsive to the coupling capacitance at the touch surface and includes a differentiated signal representation with transient portions characterizing positive-going transitions towards an upper signal level and negative-going transitions towards a lower signal level;

operating another circuit that

uses time-varying parameters for processing the response signals to provide variable gain thereto by adjusting gain for the transient portions relative to gain for portions of the response signals between the transient portions, and therein suppressing harmonics in the response signals, and

measures the response signals and for determining therefrom positions of touches on the touch surface in response to changes of the coupling capacitance.