US 6,452,514 B1 · Capacitive sensor and array

Abstract

Proximity of a body, which may be a user's finger, to an electrode pair is sensed by a charge transfer capacitive measurement approach. The electrode pair thus acts as a key that can be arrayed with other electrode pairs to form a keypad, keyboard, linear slider control, or liquid level sensor. In one embodiment of the invention each key is associated with an alternating voltage source and a pair of electrodes mounted on or within a solid dielectric substrate or panel so as to be separated from each other by a gap. The voltage source is connected to a driven electrode, a sampling charge detector is connected to a second, receiving, electrode, and the output of the charge detector is, in turn, fed into a signal processor. Disturbances in coupling between the two electrodes are detected through the solid substrate or panel material when a substance or object approaches or contacts the panel. The receiving electrode is a low-impedance node during the sampling phase of the process, which aids in keeping the sensor from being affected by wiring length or by extraneous objects near an output lead..

Claims10

Dependent claims

A method of operating a key by sensing the presence of a body proximate a coupling capacitor and spaced apart therefrom by a dielectric layer, the coupling capacitor comprising a driven plate and a receiving plate, the driven plate electrically connected to a signal generator supplying a plurality of voltage cycles, the receiving plate connected to a reference potential whenever it is not connected to processing circuitry comprising a charge integrator having two terminals, the method comprising the steps of:

a) controlling one or more of a plurality of switching elements so as to set both terminals of the charge integrator to the reference potential;
b) controlling one or more of the plurality of switching elements during a predetermined portion of each of a predetermined number of the voltage cycles, to connect the receiving plate to the charge integrator, thereby transferring electric charge from the receiving plate to the charge integrator;
and;
c) measuring a voltage on one of the two terminals of the charge integrator.

1 more element

Apparatus for sensing the presence of a body proximate a coupling capacitor and separated therefrom by a dielectric, the coupling capacitor comprising a driven plate and a receiving plate adapted to be connected to a reference potential whenever it is not connected to a processing circuit, the apparatus comprising:

a voltage source connected to the driven plate, the voltage source adapted to supply a periodic plurality of voltage cycles, each of the cycles having a predetermined duration, to the driven plate;
a plurality of switching elements;
the processing circuit comprising a charge integrator having two terminals, the charge integrator adapted to be connected to the receiving plate, the charge integrator directly connected to at least a first of the plurality of switching elements;
the processing circuit further comprising a voltage measurement circuit adapted to measure a voltage on the charge integrator, the measured voltage indicative of the change of electrical capacitance between the driven plate and the receiving plate;
wherein
the controller is adapted to initiate a measurement by controlling a first predetermined one or more of the switching elements, the first predetermined one or more of the switching elements comprising at least the first switching element, so as to connect both terminals of the charge integrator to the reference potential;
and wherein
the controller is further adapted to transfer electric charge from the receiving plate to the sampling capacitor by controlling a second one or more of the switching elements in synchrony with the voltage source.

5 more elements

A key matrix comprising a first plurality, N, of input lines, a second plurality, M, of output lines and N times M keys, wherein each key comprises a respective capacitive sensor adapted to sense the presence of an object proximate thereto and wherein each key is disposed adjacent a respective intersection of an input line and an output line, the key matrix characterized in that:

each of the keys comprises a respective driven plate connected to one of the N input lines and a respective receiving plate connected to one of the M output lines;
each of the input lines is electrically connected to a respective signal generator, each signal generator adapted to supply a respective periodic plurality of voltage cycles to each of the driven plates connected thereto;
the key matrix further comprising:
a controller adapted to control each of a plurality of switching elements;
the controller adapted to control a first predetermined number of the plurality of switching elements so as to connect each of the receiving plates to a reference potential when that receiving plate is not connected to one of the two terminals of a charge integrator;
the charge integrator adapted to be connected to at least one of the receiving plates during a predetermined portion of the respective voltage cycle supplied to the driven plate associated with the at least one of the receiving plates, the charge integrator directly connected to at least a first of the plurality of switching elements;
and
a measurement circuit adapted to measure a voltage on the charge integrator as an indication of the proximate presence of the object.

5 more elements

Dependencies are inferred from the claim text.

Capacitive sensor and array

Life of this patent

Capacitive sensor and array

Life of this patent

Abstract

Claims10