Adaptive digital filtering method and apparatus in touch sensing system

• US 9,134,857 B2
• Filed: 05/09/2011
• Issued: 09/15/2015
• Est. Priority Date: 05/20/2010
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Park, Jong-kang, Ahn, Hae-yong, Choi, Yoon-kyung
• Primary Examiner(s): Wang, Quan-Zhen
• Assistant Examiner(s): DICKE, CHAD M
• Application Number:
  US13/103,257
• Publication Number:
  US 20110285654A1
• Time in Patent Office: 1,590 Days
• Field of Search: 345173-178, 178 1801- 1806
• US Class Current: 1/1
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• 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

An adaptive digital filtering method and apparatus for touch data in a touch system is described. Adaptive digital filtering involves estimating a signal-to-noise ratio (SNR) for stored touch data, and reducing a digital filter order if the SNR is high and increasing the digital filter order if the SNR is small.

Claims

1. An adaptive digital filtering method for touch data acquired in a touch display device including a plurality of sense channels in a touch system, the method comprising:

storing the touch data in a buffer;

prestoring signal-to-noise ratio (SNR) and coordinate jitter values according to digital filter order in a memory;

estimating a SNR for the stored touch data;

selecting a digital filter tap for a digital filter having a plurality of filter taps by comparing the prestored SNR with the estimated SNR and comparing the prestored coordinate jitter values with a preset standard jitter specified for the touch system;

filtering the touch data using the digital filter after selecting the digital filter tap;

after estimating of the SNR, determining a noise level reference value based on the estimated SNR; and

performing noise nulling on stored touch data having a value less than the noise level reference value,

wherein the noise level reference value is determined such that the estimated SNR satisfies a condition for the preset standard jitter, and

wherein the selecting a digital filter tap for a digital filter having a plurality of filter taps comprises selecting a smaller number of digital filter taps as the estimated SNR increases.

2. The method of claim 1, further comprising:

determining a noise level value for a preset sampling length using touch data continuously stored during a period of the preset sampling length, wherein the SNR is estimated in accordance with the determined noise level value.

3. The method of claim 2, further comprising:

defining estimation conditions for estimating of the SNR, such that a touch state during which a touch input is applied to the touch display device is maintained during the period of the preset sampling length during which the touch data is stored, and a state transition between the touch state and a non-touch state during which the touch input is not applied to the touch display device does not occur during the period of the preset sampling length.

4. The method of claim 3, wherein defining the estimation conditions for estimating the SNR further comprises:

defining that a maximum jitter from an average value for coordinates defined on the touch display device and associated with the touch data as collected during the period of the preset sampling length is to be less than a reference value.

5. The method of claim 3, wherein upon determining that the estimation conditions for estimating the SNR are not satisfied, estimating the SNR by reinitializing the buffer storing the touch data and restoring touch data in the buffer.

6. The method of claim 1, wherein the prestored SNR and coordinate jitter values are prestored in a pre-characterized lookup table within the memory.

7. A digital filtering touch controller device for a touch system comprising:

a touch data collection unit that stores touch data obtained from a sense channel of a touch display device; and

a signal-to-noise ratio (SNR) estimation unit that prestores SNR and coordinate jitter values according to digital filter order in a memory, estimates a SNR using the stored touch data, determines a noise level reference value based on the estimated SNR, performs noise nulling on stored touch data having a value less than the noise level reference value, and selects a digital filter tap of a digital filtering unit by comparing the prestored SNR with the estimated SNR and comparing the prestored coordinate jitter values with a preset standard jitter specified for the touch system,

wherein the digital filtering unit performing digital filtering on the touch data after selecting the digital filter tap, and the noise level reference value is determined such that the estimated SNR satisfies a condition for the preset standard jitter, and

wherein the SNR estimation unit selects a smaller number of digital filter taps for the digital filtering unit as the estimated SNR increases.

8. The digital filtering touch controller device of claim 7, wherein the SNR estimation unit determines a noise level value in a preset sampling length using touch data continuously stored during a period of the preset sampling length, and calculates the SNR from the determined noise level value.

9. The adaptive digital filtering touch controller device of claim 8, further comprising:

an SNR estimation condition check unit that determines whether a touch state during which a touch input is applied to the touch display device is maintained during the period of the preset sampling length during which the touch data is stored, and whether a state transition between the touch state and a non-touch state during which the touch input is not applied to the touch display device has occurred during the period of the preset sampling length.

10. The adaptive digital filtering touch controller device of claim 9, wherein the SNR estimation condition check unit further determines whether a maximum jitter derived from an average value for coordinates on the touch display device and associated with the touch data during the period of the preset sampling length is less than a reference value.

11. The adaptive digital filtering touch controller device of claim 9, further comprising:

a control unit that reinitializes a buffer in the touch data collection unit storing the touch data if at least one estimation condition used during the estimating of the SNR is not satisfied.

12. The adaptive digital filtering touch controller device of claim 7, wherein the prestored SNR and coordinate jitter values are prestored in a pre-characterized lookup table within the memory.

13. An adaptive digital filtering touch display system comprising:

a touch display that comprises a plurality of sensing channels for performing a touch sensing operation and is designed to sense changes in a plurality of sensing units disposed on the sensing channels and output a plurality of sensed touch signals;

a touch controller that prestores signal-to-noise (SNR) and coordinate jitter values according to digital filter order in a memory, receives the plurality of sensed touch signals, derives touch data from the plurality of sensed touch signal and stores the touch data in a buffer, estimates a SNR for the stored touched data, selects a digital filter tap for a digital filter having a plurality of filter taps by comparing the prestored SNR with the estimated SNR and comparing the prestored coordinate jitter values with a preset standard jitter specified for the touch display system, determines a noise level reference value such that the estimated SNR satisfies a condition for the preset standard jitter, performs noise nulling on stored touch data having a value less than the noise level reference value, and filters the stored touch data using the digital filter after selecting the digital tap filter to generate an adaptively digital-filtered touch signal; and

a display that displays the adaptively digital-filtered touch signal,

wherein the touch controller selects a smaller number of digital filter taps for the digital filter as the estimated SNR increases.