Reduction of Common Mode Noise and Global Multivalued Offset in Touch Screen Systems by Correlated Double Sampling

Abstract

Touch based interactivity has become an important function in displays. This paper reports on the signal processing of touch signals in which touch interactivity is processed as an image and correlated double sampling (CDS) algorithm is applied for both common-mode noise reduction and global multi-valued offset cancellation. Based on experimental results, we achieved a boost in SNR of 7.6dB. The processed signal reduces detection errors and power consumption of the system.

Reduction of Noise Spikes in Touch Screen Systems by Low Pass Spatial Filtering

“…To reduce the noise spikes in the frame after CDS [11], a spatial LPF with an initial bandwidth is used. Since the touch and noise properties are dynamically changed, the bandwidth of the spatial LPF is required to be adjusted in order to optimize the performance.…”

“…Traditionally offset on a single electrode is not considered as this can be cancelled by deducting a dc value. However, in capacitance TSPs, the global multi-valued offset gives rise to potential errors [11], which ought to be accounted for as a noise component. In our previous work [11], the global multi-valued offset is removed along with the common-mode noise by correlated double sampling (CDS) [12]- [14].…”

“…However, in capacitance TSPs, the global multi-valued offset gives rise to potential errors [11], which ought to be accounted for as a noise component. In our previous work [11], the global multi-valued offset is removed along with the common-mode noise by correlated double sampling (CDS) [12]- [14]. However,when the correlation between the touch frames and the noise reference frame becomes weak, noise spikes still remain, giving rise to detection errors.…”

Development and Experimental Comparison of Low-Cost, Reliable Capacitive Touch Sensing Boards

“…Since QTouch succeeded in electromagnetic compatibility (EMC) tests without trouble in our study, we compared it experimentally with Atmel QMatrix (mutual-capacitance). Another successful method is the correlated double sampling (CDS) algorithm to cancel common-mode noise by saving a noise reference pattern for mutual-capacitance [10]. In addition, a numerically controlled oscillator (NCO), operational or charge amplifiers, and analog switches are usually used to reduce internal and external noise [11,12,13].…”

Ultrathin Multifunctional Graphene-PVDF Layers for Multidimensional Touch Interactivity for Flexible Displays

“…Two large pieces of CVD grown mono-layer graphene (5×5 cm ) were transferred onto the The two graphene layers constitute a capacitor for sensing capacitive based touch events, while the PVDF layer works to detect force touch events, expanding touch detection from 2D to 3D. A conventional projected capacitance technique 5,30 is used to measure the change of capacitance at the graphene electrodes to detect any capacitive touch event. When a conducting object (human finger or stylus) touches the screen, the electric field lines are disturbed, thus modulating the charge distribution and hence the capacitance 3 .…”