Touch Screen Element
A capacitive two-dimensional (2D) touch panel has three sets of interleaved electrodes. A first set of electrodes is spaced apart along the y-direction and these are galvanically connected to each other by a resistive strip connected at either end to a connection line. A second set of electrodes is also arrayed along the y-direction and these are galvanically connected to each other via a notionally non-resistive first connection. A third set of electrodes is also arrayed along the y-direction and these are galvanically connected to each other via a notionally non-resistive second connection. The second and third sets of electrodes are interleaved without galvanic cross-conduction to provide a gradient along the x-direction to resolve touch position in the x-direction. The first set of electrodes resolves touch position along the y-direction. Passive or active capacitive sensing techniques may be used to acquire the position information from the 2D touch panel.
1 . A pen-less two-dimensional capacitive transducer, for detecting touch or proximity, comprising:
a first electrode set composed of a plurality of electrodes arranged substantially in a parallel array along a first axis, the electrodes being connected to each other via a resistive path, and having a first connection on a first one of said electrodes and a second connection on a second one of said electrodes;
a second electrode set composed of a plurality of gradient field generating shaped electrodes arranged substantially in a parallel array along the first axis and each extending along a second axis transverse to the first axis, the electrodes of the second electrode set being galvanically connected to each other and having one connection;
a third electrode set composed of a plurality of gradient field generating shaped electrodes arranged substantially in a parallel array along the first axis and each extending along the second axis, the electrodes of the third electrode set being galvanically connected to each other and having one connection;
wherein the electrodes of the second and third electrode sets are arranged in co-extending pairs to provide ratiometric capacitive signals,
wherein the electrodes of the second and third electrode sets are shaped and dimensioned to provide respective capacitive signals that allow position of touch to be resolved along the second axis by ratiometric analysis of the respective capacitive signals, and
wherein the resistive path interconnecting the electrodes of the first electrode set is arranged to provide a capacitive signal that allows position of touch to be resolved along the first axis.
2 . A transducer according to claim 1 , wherein an additional connection is made to the first electrode set at an electrode between the first and second electrodes.
3 . A transducer according to claim 2 , wherein there are a plurality of said additional connections.
4 . A transducer according to claim 3 , wherein said connections are wired to channels of a capacitive sensing device, said capacitive sensing device being configured to operate all connections in a phase-synchronous manner.
5 . A transducer according to claim 4 , wherein the capacitive sensing device comprises charge-transfer sensing circuits which are configured to be switched substantially in unison.
6 . A transducer according to claim 1 , wherein the parallel arrays of electrodes forming the first, second and third electrode sets have repeat dimensions scaled to be equal to or smaller than a human finger touch.
7 . A transducer according to claim 1 , wherein the electrodes of the second and third electrode sets are arranged in co-extending pairs with complementary tapers over their distance of co-extension.
8 . A transducer according to claim 1 , wherein the electrodes of the second and third electrode sets are arranged in co-extending pairs with adjacent blocks of varying area over their distance of co-extension.
9 . A transducer according to claim 1 , wherein the first and second electrodes of the first electrode set are end electrodes of the first electrode set.
10 . A transducer according to claim 1 , wherein the resistive path comprises a resistive strip extending over the electrodes of the first electrode set.
11 . A transducer according to claim 1 , wherein the resistive path and the electrodes of the first electrode set are formed in a single layer of material, the resistive path comprising a plurality of portions that interconnect ends of adjacent electrodes of the first electrode set.
12 . A transducer according to claim 1 , wherein the resistive path comprises a plurality of portions that interconnect adjacent electrodes of the first electrode set at alternating ends so that the electrodes and interconnecting portions of the resistive path form a serpentine shape.
13 . A transducer according to claim 1 , further comprising:
a drive circuit having an output connected to the electrodes of the first electrode set and operable to supply a common drive signal comprising voltage pulses to the first electrode set, wherein the resistive path forms a voltage divider causing a stepwise progression in voltage of the voltage pulses from electrode to electrode; and
first and second sensing circuits having respective inputs connected to the electrodes of the second and third electrode sets respectively, each sensing circuit comprising a sampling capacitor for accumulation of charge transferred from the electrode sets and a measurement circuit arranged to detect charge accumulated on the sampling capacitor.