Patent Number: 6,297,811

Title: Projective capacitive touchscreen

Abstract: An improved touchscreen utilizing two sets of electrodes that arefabricated in a single plane is provided. The individual electrodes ofeach set of electrodes are formed from a continuous length of a conductivematerial. Suitable electrode materials include fine wire and depositedconductive coatings. The overall electrode pattern is such that there isno overlap of electrodes, thus eliminating the need for insulating layersand/or coatings between electrodes. Although a variety of electrodepatterns can be used, preferably the pattern is comprised of a pluralityof approximately triangularly shaped electrodes, the pattern such that thebase of one triangularly shaped electrode is adjacent to the apex of thenext triangularly shaped electrode. The preferred triangular shape of anindividual electrode can be achieved by forming a continuous loop of theelectrode material into the desired shape or by forming a series of teethof varying height, the envelope of the teeth approximating the desiredtriangular shape. A touchscreen sensor employing the disclosed sensingelectrodes can use any of a variety of readout systems. For example, afrequency-domain readout approach can be used in which the operatingfrequency is fixed. In this approach a touch capacitance is detected byobserving an impedance change at the operating frequency, typically bymeasuring a corresponding current change. Alternately changes in a RCdecay time .tau. can be measured, for example by observing frequencyshifts in a relaxation oscillator. This technique is typically referred toas a time-domain approach. In a third alternate approach, capacitancechanges are detected via frequency shifts of LC oscillators. Touchposition information is determined from the capacitance changes of theelectrodes using any number of different techniques. Preferably prior tocalculating position, a subset of electrodes localized around the touchposition is determined. Electrode localization reduces the effects ofbackground signals while increasing the efficiency of the positiondetermining algorithm. Once a set of localized electrodes has beendetermined the touch coordinates are calculated, one coordinate from thedistribution of the touch signal within each set of electrodes and theother coordinate from the distribution of the touch signal between the twosets of electrodes.

Inventors: Kent; Joel (Fremont, CA), Ravid; Arie (Newark, CA)


International Classification:

Expiration Date: 10/02/2013