Browse Prior Art Database

Improving Robustness and Accuracy of Capacitive touch systems

IP.com Disclosure Number: IPCOM000209995D
Original Publication Date: 2011-Aug-19
Included in the Prior Art Database: 2011-Aug-19
Document File: 2 page(s) / 43K

Publishing Venue

Microsoft

Related People

Mark Casebolt: INVENTOR [+2]

Abstract

Two concepts are described which improve robustness and accuracy of capacitive touch systems. Firstly, the concept of jamming when the Capacitive touch conversion IC utilizes a synchronous sampling technique and in band radiated or conducted jamming source operates at some harmonic of the conversion sample rate within the capture window of the capacitive signal. Typical here would be high energy horizontal sweep signals which dominate CRET displays. The concept here is to make use of typical digital sampling processes such as median filters to minimize spurious noise and sample using spread spectrum techniques to decorrelate the repetitive jamming signal and allow operation in the presence of the jamming signal. The second problem is the step functions in environmental dielectric materials properties such as humidity and temperature. In this example the situation is exacerbated by materials near the capacitive sensing surfaces which have hygroscopic properties. For example, a capacitive detector such as an XBOX 360S positioned adjacent to the output of a swamp cooler vent on a hot dry day. When the swamp cooler starts there is an abrupt transition in local humidity and temperature which can take several seconds to several minutes for the normal feedback, loop control, and dynamic equalization of the capacitive touch system to rebalance in order to react properly to capacitive actuation. Additionally, the capacitive system may inadvertently actuate without the presence of an operator. The concept here is to make use of a secondary capacitive sample channel which is physically isolated from the capacitive actuation area, but fully exposed to the same environment. The resulting detection of capacitive actuation, then, would be determined by the ratioetric difference between the reference channel and the detection channel. Hygroscopic elements of the capacitive detection areas would cancel – avoiding the loss of functionality and aberrant behavior due to external environmental effects

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Document Author (alias)

Mark Casebolt; John Clavin

Defensive Publication Title 

Improving Robustness and Accuracy of Capacitive touch systems

Name(s) of All Contributors

Mark Casebolt

 

 

 

 

Summary of the Defensive Publication/Abstract

Two concepts are described which improve robustness and accuracy of capacitive touch systems.

Firstly, the concept of jamming when the Capacitive touch conversion IC utilizes a synchronous sampling technique and in band radiated or conducted jamming source operates at some harmonic of the conversion sample rate within the capture window of the capacitive signal. Typical here would be high energy horizontal sweep signals which dominate CRET displays. The concept here is to make use of typical digital sampling processes such as median filters to minimize spurious noise and sample using spread spectrum techniques to decorrelate the repetitive jamming signal and allow operation in the presence of the jamming signal.

The second problem is the step functions in environmental dielectric materials properties such as humidity and temperature. In this example the situation is exacerbated by materials near the capacitive sensing surfaces which have hygroscopic properties. For example, a capacitive detector such as an XBOX 360S positioned adjacent to the output of a swamp cooler vent on a hot dry day. When the swamp cooler starts there is an abrupt transition in local humidity and temperature which can take several seconds to several minutes for the normal feedback, loop control, and dynamic equalization of the capacitive touch system to rebalance in order to react properly to capacitive actuation. Additionally, the capacitive system may inadvertently actuate without the presence of an operator. The concept here is to make use of a secondary capacitive sample channel which is physically isolated from the capacitive actuation area, but fully exposed to the same environment. The resulting detection of capacitive actuation, then, would be determined by the ratioetric difference between the reference channel and the detection channel. Hygroscopic elements of the capacitive detection areas would cancel – avoiding the loss of functionality and aberrant behavior due to external environmental effects

Description:  Include architectural diagrams and system level data flow diagrams if: 1) they have already been prepared or 2) they are needed to enable another developer to implement your defensive publication. Target 1-2 pages, and not more than 5 pages.  

A capacitive system, either single or dual plate,  is a function of an exposed (not closely adjacent to a grounded surface) plate(s) whose capac...