Application of weighing matrices to simultaneous driving technique for capacitive touch sensors

Park, Jong Kang; Lee, Chang-Ju; Kim, Do-Yeon; Chun, Jung-Hoon; Kim, Jong-Tae

doi:10.1109/tce.2015.7150602

Cited by 8 publications

(18 citation statements)

References 13 publications

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“…According to integration procedures, accumulated capacitive signal and compared the SNR under the same conditions. A SNR is defined as the average sensing value of the junction capacitance (= average signal level) divided by its standard deviation (= average noise level) [1,9].…”

Section: Simulation Resultsmentioning

confidence: 99%

“…where h it refers to the modulating signals, forming the matrix of driving patterns [1]. i refers to the driving line number, and becomes the row index of the matrix.…”

Section: Inverted Tx Driving Techniquementioning

confidence: 99%

“…Among the various types, the mutual capacitive type have rapidly increased mostly for mobile devices, for its advantages including high response time to input, high light transparency and multi-touch capability. However, it is difficult to obtain a high SNR (signal-to-noise ratio) in the mutual capacitive sensors because they should deal with very small signals in limited sensing time [1], making it sensitive to noise. Among the various noise sources that can occur in touch screens [2], display noise is the main cause that lowers touch screen SNR, and many researches has explored to solve this problem [3,4].…”

Section: Introductionmentioning

confidence: 99%

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Inverted driving technique for removing display noise in capacitive touch sensors

Park

Lee

et al. 2015

IEICE Electron. Express

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As the technological advances in mobile display is focusing on thinner and wider structures, capacitive touch recognition suffers from everincreasing display noise. Realizing reliable touch recognition in thin displays requires a way to remove display noise. We observed that display noise is evident in various patterns and amplitudes according to the display image. In order to remove noise, we applied non-inverse signals and inverse signals across two data frames, in accordance with the periodicity of the noise. With all other conditions remaining the same, the proposed method showed higher signal-to-noise ratio (SNR) for all display noise patterns compared to existing methods. The proposed method showed a SNR that was averagely 5.39 dB higher than the SNR of the existing method. The results shows that the display noise was removed effectively.

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Section: Simulation Resultsmentioning

confidence: 99%

“…where h it refers to the modulating signals, forming the matrix of driving patterns [1]. i refers to the driving line number, and becomes the row index of the matrix.…”

Section: Inverted Tx Driving Techniquementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Inverted driving technique for removing display noise in capacitive touch sensors

Park

Lee

et al. 2015

IEICE Electron. Express

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show abstract

“…Therefore, noise immunity is a primary metric for quantitatively evaluating sensor systems. In the case of capacitive touch sensors, for overcoming various types of environmental and dynamic noise including display noise, simultaneous driving techniques can achieve a high signal-to-noise ratio (SNR) with a limited response time [ 1 , 2 ]. Because technological advancements continue to yield thinner and more compact panel designs, display noise has become one of the most problematic types of noise that deteriorate the SNR [ 3 , 4 , 5 ].…”

Section: Introductionmentioning

confidence: 99%

“…High transmission (TX) signals of sensors that are strong to the increased display noise and other external noise sources generate flickers on the display and affect the display’s quality and reliability. TX signal levels can also be constrained in ultrathin panels because of increased parasitic capacitance and power consumption [ 1 , 3 ]. Thus, when placed in close proximity, the display panel and touch sensors compete for their own specifications and performance levels in newer technologies.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Multi-Level Simultaneous Driving Technique for Capacitive Touch Sensors

Park

Lee

Kim

2017

Sensors

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The signal-to-noise ratio (SNR) and driving levels of capacitive touch sensors determine the applicability of these sensors to thinner displays and sensor-integrated modules. The simultaneous driving technique has been widely applied to capacitive touch sensors to cope with various types of environmental noise. A Hadamard matrix has been used to determine the driving code and multiplex capacitive signals required to increase the SNR and responsivity of touch sensors. Using multi-level Hadamard matrices, a new driving technique for sensing concurrent capacitive elements across multiple rows of a touch panel was developed. The technique provides more effective design choices than the existing bipolar driving method by supporting a variety of orders of matrices and regular capacity. The required TX voltage can be reduced by applying the Kronecker product for higher orders of simultaneous driving. A system model is presented for multiplexing capacitive signals to extract the SNR of the existing Hadamard matrices as well as one of the proposed multi-level sequences. In addition, the corresponding multi-level drivers and receivers were implemented to verify the theoretical expectations and simulation results of the proposed technique.

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Frequency Hopping and Parallel Driving With Random Delay Especially Suitable for the Charger Noise Problem in Mutual-Capacitive Touch Applications

2019

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Charger noise can cause inaccurate touch points and fake touch points to appear; this can cause a device to behave incorrectly. The intensity of charger noise could be much larger than the intensities of the original touch signals. Furthermore, the frequency of charger noise varies for each different charger. Therefore, industry experts have identified charger noise as the most difficult problem in capacitive touch applications. The demand for a solution to this problem has become crucial for the mobile market. In this paper, we prove that a particular combination of frequency hopping and repeated integration is an effective method to handle this problem. In addition, we propose an efficient discrete Fourier transform-based algorithm to select an effective sensing frequency. We propose parallel driving with random delay to enhance the signal-to-noise ratio (SNR). We show an efficient hardware-software co-design that facilitates the application of our methods in touch ICs. The experimental results show that our methods can increase SNR by over 45 dB and can find an effective sensing frequency fast and dynamically.INDEX TERMS Charger noise, parallel driving, frequency hopping, repeated integration, mutual-capacitive touch.

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Application of weighing matrices to simultaneous driving technique for capacitive touch sensors

Cited by 8 publications

References 13 publications

Inverted driving technique for removing display noise in capacitive touch sensors

Inverted driving technique for removing display noise in capacitive touch sensors

Analysis of Multi-Level Simultaneous Driving Technique for Capacitive Touch Sensors

Frequency Hopping and Parallel Driving With Random Delay Especially Suitable for the Charger Noise Problem in Mutual-Capacitive Touch Applications

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