Capacitive sensor and array

• US 6,452,514 B1
• Filed: 01/26/2000
• Issued: 09/17/2002
• Est. Priority Date: 01/26/1999
• Status: Expired due to Term

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Harald Philipp
• Inventors: Philipp, Harald
• Primary Examiner(s): Edwards, Jr., Timothy
• Application Number:
  US09/491,129
• Time in Patent Office: 965 Days
• Field of Search: 341/33, 341/22, 178/18.06, 178/18.07, 200/343, 345/168
• US Class Current: 341/33
• CPC Class Codes: G01D 5/2405 by varying dielectric
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2017/9604 characterised by the number of electrodes
• CPC Class Codes: H03K 2217/960725 Charge-transfer
• CPC Class Codes: H03K 2217/960775 Emitter-receiver or "fringe" type detection, i.e. one or more field emitting electrodes and corresponding one or more receiving electrodes

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..

Claims

1. 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.

2. The method of claim 1 wherein the second terminal of the charge integrator is connected directly to the reference potential, wherein the plurality of switching elements comprises a first switching element and a second switching element different from the first switching element and wherein

in step a) the first switching element connects the first terminal of the charge integrator to the reference potential and the second switching element disconnects the receiving plate from the charge integrator; and

in step b) the first switching element does not connect the first terminal of the charge integrator to the reference potential and the second switching element connects the receiving plate to the first terminal of the charge integrator.

3. The method of claim 1 wherein the receiving plate is directly electrically connected to the second terminal of the charge integrator, wherein the plurality of switching elements comprise a first switching element connected to the second terminal of the charge integrator and a second switching element connected to the first terminal of the charge integrator and wherein in step a) the first and the second switching elements both connect the respective terminal to the reference potential.

4. 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. The apparatus of claim 4 wherein

a first of the two terminals of the charge integrator is directly connected to the reference potential and the first predetermined one of the plurality of switching elements is connected between the second terminal of the charge integrator and the reference potential; and

the second one of the plurality of switching elements is electrically connected between the receiving plate and the second terminal of the charge integrator.

6. The apparatus of claim 4 wherein:

the receiving plate is directly electrically connected to the first terminal of the charge integrator,

the first of the switching elements is connected between the first terminal of the charge integrator and the reference potential;

the second of the two switching elements is connected between the second terminal of the charge integrator and the reference potential; and

wherein

the controller is adapted to initiate a measurement by closing the first and the second of the switching elements so as to connect both terminals of the charge integrator to the reference potential.

7. 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.

8. The key matrix of claim 7 wherein:

the first predetermined number of switching elements comprises a multiplexer;

the second of the two terminals of the charge integrator is directly electrically connected to the reference potential; and

the first of the predetermined number of switching elements comprises a switching element adapted to connect the first terminal of the charge integrator to the reference potential.

9. The key matrix of claim 7 wherein:

each of the M output lines is directly electrically connected to a respective first terminal of a respective charge integrator;

each of a first M respective ones of the switching elements is connected between the respective first terminal of the respective charge integrator and the reference potential; and

each of a second M respective ones, separate from the first M respective ones, of the switching elements is connected between the second terminal of the respective charge integrator and the reference potential.

10. The key matrix of claim 7 wherein:

each of the M output lines is electrically connected to a respective one of a first set of M switching elements, each of the first set of M switching elements connecting the respective output line to either a first terminal of a respective charge integrator or to the second terminal of the respective charge integrator;

each of a second set of M switching elements, the second set separate from the first set, is connected between the respective first terminal of the respective charge integrator and the reference potential; and

each of a third set of M switching elements, the third set separate from both the first and the second sets, is connected between the second terminal of the respective charge integrator and the reference potential.