Techniques for Locally Improving Signal to Noise in a Capacitive Touch Sensor

• US 20160004357A1
• Filed: 09/11/2015
• Published: 01/07/2016
• Est. Priority Date: 07/16/2010
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Perceptive Pixel Incorporated (Microsoft Corporation)
• Inventors: Westhues, Jonathan, Han, Jefferson Y.
• Granted Patent: US 10,126,889 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G02F 1/13338 Input devices, e.g. touch panels
• CPC Class Codes: G06F 2203/04108 Touchless 2D- digitiser, i.e. digitiser detecting the X/Y position of the input means, finger or stylus, also when it does not touch, but is proximate to the digitiser's interaction surface without distance measurement in the Z direction
• 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

Abstract

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for digital signal processing (DSP) techniques for generally improving a signal-to-noise ratio (SNR) of capacitive touch sensors.

Claims

1. A system comprising:

a data processing apparatus;

a capacitive touch sensor configured to interact with the data processing apparatus; and

a liquid crystal display,

the system is configured to;

determine a noise frequency in the capacitive touch sensor;

identify that the noise frequency is a function of a frequency of the liquid crystal display; and

determine an excitation frequency for the sensor as a function of the determined noise frequency, wherein when determining the excitation frequency the system is further configured to;

select an initial excitation frequency for the sensor;

compute a cross-correlation between the noise frequency and the initial excitation frequency over an integration period, wherein the computation of the cross-correlation is presentable in a sinc-like waveform with at least one peak and at least two nulls; and

select the excitation frequency for the sensor by selecting a frequency at one of the nulls in the sinc-like waveform and assigning the determined excitation frequency to be a same frequency as the frequency at the selected null.

2. The system of claim 1, wherein the noise frequency is within a range of about 4 kHz to about 19 kHz, the capacitive touch sensor comprises a maximum transmit voltage of about 200V, and the capacitive touch sensor is configured to provide a current to travel through a user that is on an order of about tens of microamps.

3. The system of claim 1, wherein the capacitive touch sensor comprises a front end interface, the system is configured to demodulate a waveform at an output of the front end interface of the capacitive touch sensor, wherein the waveform comprises the cross-correlation of the noise frequency against the initial excitation frequency.

4. The system of claim 1, the system is configured to:

measure a level of noise in the sensor; and

set an initial threshold for detecting a touch from a user of the sensor based on the level of measured noise.

5. The system of claim 4, the system is configured to:

continuously measure the level of noise in the sensor; and

continuously adjust a threshold for detecting the touch from the user of the sensor based on the level of continuously-measured noise.

6. The system of claim 4, wherein

the liquid crystal display and the touch sensor are frequency locked.

7. The system of claim 6, wherein

the touch sensor comprises rows and columns of trace lines arranged in a matrix configuration, and

the data processing apparatus is configured to identify highest-noise columns with the highest measured level of noise, and set a frame rate of the touch sensor so that the highest-noise columns appear stationary at a predetermined position on the liquid crystal display.

8. The system of claim 1, the system is configured to determine a plurality of orthogonal excitation waveforms for the sensor, wherein at least one of the orthogonal excitation waveforms comprises the selected excitation frequency,

wherein the sensor is configured for simultaneous transmission of the plurality of orthogonal excitation waveforms, and

wherein the plurality of orthogonal excitation waveforms are all orthogonal to the determined noise frequency.

9. A system comprising:

a data processing apparatus;

a capacitive touch sensor to interact with the data processing apparatus, the capacitive touch sensor comprising rows and columns of trace lines arranged in a matrix configuration; and

a liquid crystal display,

the system is configured to;

identify a noise frequency;

generate an excitation waveform to transmit across at least one of the trace lines in the sensor, wherein the excitation waveform is generated such that the excitation waveform is orthogonal to the identified noise frequency, wherein the excitation waveform is generated such that noise at the identified noise frequency is rejected in the excitation waveform, the system is configured to generate the excitation waveform by;

in a frequency domain, specifying an initial excitation waveform; and

converting the initial excitation waveform from the frequency domain into the excitation waveform in a time domain by using a Fourier transform in the conversion; and

transmit the generated excitation waveform across at least one of the trace lines.

10. The system of claim 9, the system is configured to:

measure a level of noise in the sensor; and

set an initial threshold for detecting a touch from a user of the sensor based on the level of measured noise.

11. The system of claim 10, the system is configured to:

continuously measure the level of noise in the sensor; and

continuously adjust a threshold for detecting the touch from the user of the sensor based on the level of continuously-measured noise.

12. The system of claim 10, wherein

the liquid crystal display and the touch sensor are frequency locked.

13. The system of claim 12, wherein

the data processing apparatus is configured to identify highest-noise columns with the highest measured level of noise, and set a frame rate of the touch sensor so that the highest-noise columns appear stationary at a predetermined position on the liquid crystal display.

14. The system of claim 9, the system is configured to determine a plurality of orthogonal excitation waveforms for the sensor,

wherein the sensor is configured for simultaneous transmission of the plurality of orthogonal excitation waveforms, and

wherein the plurality of orthogonal excitation waveforms are all orthogonal to the identified noise frequency.

15. A system comprising:

a data processing apparatus;

a capacitive touch sensor to interact with the data processing apparatus, the capacitive touch sensor comprising rows and columns of trace lines arranged in a matrix configuration; and

a liquid crystal display,

the system is configured to;

identify a noise frequency;

generate an excitation waveform to transmit across at least one of the trace lines in the sensor, wherein the excitation waveform is generated such that the excitation waveform is orthogonal to the identified noise frequency, wherein the excitation waveform is generated such that noise at the identified noise frequency is rejected in the excitation waveform, the system is configured to generate the excitation waveform by;

selecting an initial excitation waveform;

selecting an algorithm corresponding to a finite impulse response filter; and

generating the excitation waveform by applying the algorithm corresponding to the finite impulse response filter to the initial excitation waveform; and

transmit the generated excitation waveform across at least one of the trace lines.

16. The system of claim 15, the system is configured to:

measure a level of noise in the sensor; and

set an initial threshold for detecting a touch from a user of the sensor based on the level of measured noise.

17. The system of claim 16, the system is configured to:

continuously measure the level of noise in the sensor; and

continuously adjust a threshold for detecting the touch from the user of the sensor based on the level of continuously-measured noise.

18. The system of claim 16, wherein

the liquid crystal display and the touch sensor are frequency locked.

19. The system of claim 18, wherein

the data processing apparatus is configured to identify highest-noise columns with the highest measured level of noise, and set a frame rate of the touch sensor so that the highest-noise columns appear stationary at a predetermined position on the liquid crystal display.

20. The system of claim 15, where in the sensor is further configured to determine a plurality of orthogonal excitation waveforms for the sensor,

wherein the sensor is configured for simultaneous transmission of the plurality of orthogonal excitation waveforms, and

wherein the plurality of orthogonal excitation waveforms are all orthogonal to the identified noise frequency.