WO2007140928A1 - Arrangement de circuit pour déterminer une capacité d'un élément de détection capacitif - Google Patents

Arrangement de circuit pour déterminer une capacité d'un élément de détection capacitif Download PDF

Info

Publication number
WO2007140928A1
WO2007140928A1 PCT/EP2007/004848 EP2007004848W WO2007140928A1 WO 2007140928 A1 WO2007140928 A1 WO 2007140928A1 EP 2007004848 W EP2007004848 W EP 2007004848W WO 2007140928 A1 WO2007140928 A1 WO 2007140928A1
Authority
WO
WIPO (PCT)
Prior art keywords
sensor element
charging
capacitive sensor
capacitance
voltage
Prior art date
Application number
PCT/EP2007/004848
Other languages
German (de)
English (en)
Inventor
Ralf Dorwarth
Original Assignee
E.G.O. Elektro-Gerätebau GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by E.G.O. Elektro-Gerätebau GmbH filed Critical E.G.O. Elektro-Gerätebau GmbH
Publication of WO2007140928A1 publication Critical patent/WO2007140928A1/fr

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
    • H03K17/96—Touch switches
    • H03K17/962—Capacitive touch switches
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K2217/00—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00
    • H03K2217/94—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated
    • H03K2217/96—Touch switches
    • H03K2217/9607—Capacitive touch switches
    • H03K2217/96071—Capacitive touch switches characterised by the detection principle
    • H03K2217/960725—Charge-transfer

Definitions

  • Circuit arrangement for determining a capacitance of a capacitive
  • the invention relates to a circuit arrangement for determining a capacitance of a capacitive sensor element whose capacitance changes in dependence on its operating state.
  • Circuit arrangements for evaluating capacitive proximity switches are known and, for example in WO 97/23738, have a capacitive sensor element whose capacitance changes as a function of its actuation state. This capacitance change is evaluated to determine the actuation state.
  • the sensor element is charged with a charging voltage, whereby a certain electrical charge is transferred to the sensor element as a function of its capacity and the charging voltage.
  • the sensor element is separated from the charging voltage and connected via a switching means with a collecting capacitor or a reference capacitor, whereby a charge transfer from the sensor element takes place on the collecting capacitor.
  • the process of charging and subsequent recharging is repeated for a predetermined number of cycles, whereby the charge of the collecting capacitor reaches a certain value, which is determined inter alia by the value of the capacitance of the sensor element.
  • the charge or the resulting voltage of the collecting capacitor is therefore a measure of the capacitance of the sensor element to be measured.
  • By evaluating the voltage of the collecting capacitor can be concluded that the operating state of the proximity switch. After voltage evaluation, the common capacitor is discharged in a defined manner and a new measuring cycle can follow.
  • Such circuit arrangements are also referred to as switched-capacitor circuits.
  • the switching operations are usually implemented by analog switches, which are relatively expensive and susceptible to interference.
  • the switched-capacitor circuit according to the invention for determining a capacitance of a capacitive sensor element, the capacitance of which changes as a function of its actuation state comprises a charging device, which is designed to supply the capacitive sensor element with a charging voltage during a charging cycle Charging current to apply and the capacitive sensor element during a Umladezyklus not to apply to the charging voltage or the charging current, a reference capacitor with a predetermined capacitance and coupled to the reference capacitor evaluation, which the at the reference pending voltage to determine the capacitance evaluates.
  • a charging device which is designed to supply the capacitive sensor element with a charging voltage during a charging cycle Charging current to apply and the capacitive sensor element during a Umladezyklus not to apply to the charging voltage or the charging current
  • a reference capacitor with a predetermined capacitance and coupled to the reference capacitor evaluation which the at the reference pending voltage to determine the capacitance evaluates.
  • only one ohmic resistance is connected between the capacitive
  • An ohmic resistance in the sense of the invention is a component which essentially has only ohmic components.
  • the ohmic resistance can of course also be formed by series connection and / or parallel connection of a plurality of resistors.
  • the core of the invention is consequently that, apart from the ohmic resistance, there are no further components between the capacitive sensor element and the reference capacitor, ie the ohmic resistance is in particular looped between the capacitive sensor element and the reference capacitor.
  • Switching means-free in the sense of the invention means that no switching means, such as analog switches, relays, diodes, etc. are looped or interposed between the capacitive sensor element and the reference capacitor in contrast to the conventional switched-capacitor circuits.
  • the resistor no switching means for example in the form of analog switches, relays, diodes, etc.
  • the circuit arrangement does not require any switches or analog switches which, as in the case of the conventional circuit arrangements, control the charge transfer from the capacitive sensor element to a collector or reference capacitor. This allows a reliable determination of the capacity or the operating state under all operating conditions, since a complex control of the switch can be omitted. Furthermore, costs can be saved due to the omission of the switch.
  • the charging device comprises a square-wave voltage source for generating the charging voltage as a rectangular voltage and a diode, wherein the diode in the flow direction between the square-wave voltage source and the capacitive sensor element - A -
  • the reference capacitor is charged via the diode. Since the capacitance of the sensor element is substantially smaller than the capacitance of the reference capacitor and due to the high-resistance between the capacitive sensor element and the reference capacitor, charged during the charging cycle of the reference capacitor compared to the capacitive sensor element only insignificantly. If the charging voltage during the recharging cycle, i. when the charging voltage is generated at a low level, due to the now blocking diode is not applied to the capacitive sensor element, a charge transfer from the capacitive sensor element to the reference capacitor via the intermediate resistor. The amount of charge transferred in this case is determined inter alia by the capacitance of the capacitive sensor element to be measured. Consequently, a capacitance measurement or a measurement of the capacitance change is possible via a voltage measurement carried out by the evaluation unit on the reference capacitor, which in turn enables the actuation state to be determined.
  • the charging device comprises a microprocessor, the microprocessor having a port which is configured to output the charging voltage at a high level during the charging cycle and which is configured in a high-resistance state during the recharging cycle.
  • the required charging voltage can be generated by means of a conventional microprocessor output port, wherein in the high-resistance state of the port no charge backflow into the port and thus the charge transfer from the capacitive sensor element to the reference capacitor is not affected by the charging voltage.
  • a resistance is looped in between the charging device and the capacitive sensor element. In this way, a charging current limit can be realized.
  • a resistor is connected in parallel with the reference capacitor.
  • the resistor leads to a defined, permanent discharge current from the reference capacitor. It then sets a mean voltage value at the reference capacitor, which depends on the capacitance of the capacitive sensor element.
  • the evaluation device comprises a microprocessor, wherein the microprocessor has a port coupled to the reference capacitor, which is configurable as an analog input for digitizing the pending at the reference capacitor voltage and the alternative to output a reference voltage for discharging the reference capacitor before determining the capacitance is configurable.
  • the microprocessor is used both for capacity determination and for the defined discharge of the reference capacitor at the beginning of a new measurement.
  • the charging device is designed such that the charging cycle is generated with a much shorter duration than the Umladezyklus. This takes into account the fact that the capacitive sensor element is charged much faster than the reference capacitor due to its lower capacitance during the charging cycle. The transshipment process, however, takes more time compared to the recharge process. By choosing a suitable duty cycle, this can be taken into account.
  • a ratio between the duration of the charging cycle and the duration of the transfer cycle is less than 1 to 4, preferably less than 1 to 8, particularly preferably less than 1 to 16.
  • the capacitive sensor element forms a capacitor, wherein a first capacitor plate is formed by a conductive layer, a second capacitor plate is formed by a user who actuates the sensor element, and the conductive layer is charged during the charging cycle with the charging voltage or the charging current ,
  • FIG. 1 is a schematic circuit diagram of a first embodiment of a circuit arrangement for determining a capacitance of a capacitive sensor element, the capacitance of which changes as a function of its operating state,
  • FIG 2 is a circuit diagram of the circuit arrangement of FIG. 1, in which the capacitive sensor element of FIG. 1 is represented by its electrical equivalent circuit diagram
  • FIG 3 shows a circuit diagram of a further embodiment of a circuit arrangement for determining a capacitance of a capacitive sensor element, the capacitance of which changes as a function of its actuation state.
  • the capacitive sensor element 1 forms a capacitor, wherein a first capacitor plate 1a is formed by a conductive, in particular flat and planar layer, which can be arranged, for example, under a glass ceramic plate 1b of a cooktop, not shown.
  • a second capacitor plate is formed, for example, by a user's finger 1c or by the user himself.
  • the glass ceramic plate 1 b forms a dielectric between the two capacitor plates 1 a and 1 c.
  • Fig. 2 shows a circuit diagram of the circuit arrangement of Fig. 1, in which the capacitive sensor element 1 of Fig. 1 by its electrical equivalent circuit diagram in the form of a capacitor C3 is shown.
  • the capacitance of the capacitor C3 varies depending on the operating state, i. depending on how far apart the finger 1c is from the conductive layer 1a.
  • the capacitance of the capacitor C3 increases as the distance becomes smaller. From the capacitance or the capacitance change of the capacitor C3 can thus be determined whether an actuation of the capacitive proximity switch or of the capacitive sensor element C3 or 1 takes place.
  • the circuit arrangement shown further comprises a charging device in the form of a square-wave voltage source 2 for generating a rectangular square-shaped charging voltage, a diode D1, and a charging resistor R1, wherein the diode D1 and the resistor R1 are connected in series between the square wave voltage source 2 and the capacitive sensor element 1, 1 a and C3.
  • the charging resistor R1 is not a mandatory component of the charging device and can optionally be omitted altogether.
  • the charging device is designed to be the capacitive sensor element
  • the decoupling is effected by the diode D1, since it blocks when the square-wave voltage source 2 during the recharging cycle, the lower of the two voltage levels, i. the reference or ground voltage outputs.
  • the circuit arrangement furthermore comprises a reference capacitor C2 with a predetermined or known capacitance, an evaluation device in the form of a microprocessor MC, which evaluates the voltage applied to the reference capacitor C2 for determining the capacitance, and a discharge resistor R3, which is parallel to the reference capacitor C2 is switched.
  • the charge-reversal resistor R2 effects charge transfer from the capacitive sensor element 1 or C3 to the reference capacitor during the transfer cycle.
  • capacitor C2 Since the transferred charge amount depends on the capacitance of the capacitive sensor element C3, which in turn depends on an actuation state, an actuation-dependent voltage arises at the reference capacitor C2. This is evaluated by the microprocessor MC for determining the actuation state.
  • FIG. 3 shows a circuit diagram of a further embodiment of a circuit arrangement for determining a capacitance of a capacitive sensor element whose capacitance changes as a function of its actuation state.
  • the embodiment shown in FIG. 3 differs from the embodiment shown in FIG. 2 on the one hand in that the charging device is completely integrated in the microprocessor MC.
  • the microprocessor MC has a port P1, which is configured to output the charging voltage with a high level during the charging cycle and which is configured in a high-resistance state during the Umladezyklus.
  • Conventional microprocessors usually have ports that can have three states. In a first state, a reference voltage or ground voltage of the microprocessor is output, in a second state, a supply voltage of the microprocessor is output and in a third state, the port is switched to high impedance. To implement the charging device, the second and third states are used. This allows the saving of components compared to the embodiment shown in Fig. 2.
  • the discharge resistor R3 is saved in FIG. This is made possible by the fact that the microprocessor MC has a port P2 coupled to the reference capacitor, which can be configured as an analog input for digitizing the voltage present at the reference capacitor C2 and further configurable to output a reference voltage for discharging the reference capacitor C2 before re-determining the capacitance. In this case, before each new measurement, first the reference capacitor C2 is discharged by outputting the ground voltage at the port P2. Port P2 is configured as output in this case.
  • the port P2 is configured as an analog input or as a "normal" digital input, and the processor MC executes consecutive charge and charge cycles, thereby successively increasing the voltage across the reference capacitor C2 The number of charge cycles until a predetermined threshold voltage If the port P2 is configured as a digital input, a tipping binary value read in via the port P2 can serve as the threshold criterion if port P2 is configured as an analogue input is a digitized value can serve as a threshold criterion.
  • the embodiments shown enable a reliable determination of its actuation state under all operating conditions, can be produced inexpensively and are insensitive to EMC and HF interference.
  • an expensive and sensitive analog switch between the capacitive sensor element and the reference capacitor can be dispensed with.

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  • Electronic Switches (AREA)

Abstract

L'invention concerne un arrangement de circuit pour déterminer une capacité d'un élément de détection capacitif dont la capacité varie en fonction de sa situation d'actionnement. L'arrangement de circuit pour déterminer une capacité d'un élément (1) de détection capacitif, dont la capacité varie en fonction de sa situation d'actionnement, comprend un dispositif (2, D1) de charge qui est conçu pour soumettre l'élément (1) de détection capacitif à une tension de charge ou à un courant de charge pendant un cycle de charge et pour ne pas soumettre l'élément (1) de détection capacitif à une tension de charge ou à un courant de charge pendant un cycle de décharge, un condensateur (C2) de référence ayant une capacité prédéfinie et un dispositif (MC) d'interprétation couplé avec le condensateur (C2) de référence, lequel interprète la tension présente aux bornes du condensateur (C2) de référence afin de déterminer la capacité, seule une résistance (R2) ohmique étant branchée dans la branche entre l'élément (1) de détection capacitif et le condensateur (C2) de référence. Cette invention s'applique aux appareils ménagers, par exemple.
PCT/EP2007/004848 2006-06-02 2007-06-01 Arrangement de circuit pour déterminer une capacité d'un élément de détection capacitif WO2007140928A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102006026671 2006-06-02
DE102006026671.4 2006-06-02

Publications (1)

Publication Number Publication Date
WO2007140928A1 true WO2007140928A1 (fr) 2007-12-13

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102008009936A1 (de) * 2008-02-20 2009-09-03 Hypercom Gmbh Tastatur mit kapazitätssensitiven Tastenfeldern
WO2009151904A3 (fr) * 2008-05-27 2010-11-25 Microchip Technology Incorporated Capteur tactile de diviseur de tension capacitif
WO2014068008A1 (fr) * 2012-10-30 2014-05-08 Digades Gmbh Digitales Und Analoges Schaltungsdesign Système de détection pour la détection de l'approche de personnes et d'objets, procédé pour faire fonctionner le système de détection, et son utilisation
DE102021204005A1 (de) 2021-04-21 2022-10-27 E.G.O. Elektro-Gerätebau GmbH Kochfeld, Anordnung eines solchen Kochfelds und Verfahren zur Erfassung einer Gewichtsbelastung auf einem solchen Kochfeld

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4441034A (en) * 1981-11-26 1984-04-03 Inventio Ag Contact-controlled capacitive switching apparatus
US5973417A (en) * 1997-02-17 1999-10-26 E.G.O. Elektro-Geraetebau Gmbh Circuit arrangement for a sensor element
EP1341306A1 (fr) * 2002-02-27 2003-09-03 E.G.O. ELEKTRO-GERÄTEBAU GmbH Circuit pour un capteur à capacitance variable
EP1505734A2 (fr) * 2003-08-08 2005-02-09 i f m electronic gmbh Commutateur de proximité capacitif

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4441034A (en) * 1981-11-26 1984-04-03 Inventio Ag Contact-controlled capacitive switching apparatus
US5973417A (en) * 1997-02-17 1999-10-26 E.G.O. Elektro-Geraetebau Gmbh Circuit arrangement for a sensor element
EP1341306A1 (fr) * 2002-02-27 2003-09-03 E.G.O. ELEKTRO-GERÄTEBAU GmbH Circuit pour un capteur à capacitance variable
EP1505734A2 (fr) * 2003-08-08 2005-02-09 i f m electronic gmbh Commutateur de proximité capacitif

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102008009936A1 (de) * 2008-02-20 2009-09-03 Hypercom Gmbh Tastatur mit kapazitätssensitiven Tastenfeldern
WO2009151904A3 (fr) * 2008-05-27 2010-11-25 Microchip Technology Incorporated Capteur tactile de diviseur de tension capacitif
TWI498796B (zh) * 2008-05-27 2015-09-01 Microchip Tech Inc 量測電容的方法及系統，及計算電容的方法
US9367179B2 (en) 2008-05-27 2016-06-14 Microchip Technology Incorporated Capacitive voltage divider touch sensor
EP2279470B1 (fr) * 2008-05-27 2019-01-09 Microchip Technology Incorporated Capteur tactile à diviseur de tension capacitif
WO2014068008A1 (fr) * 2012-10-30 2014-05-08 Digades Gmbh Digitales Und Analoges Schaltungsdesign Système de détection pour la détection de l'approche de personnes et d'objets, procédé pour faire fonctionner le système de détection, et son utilisation
DE102021204005A1 (de) 2021-04-21 2022-10-27 E.G.O. Elektro-Gerätebau GmbH Kochfeld, Anordnung eines solchen Kochfelds und Verfahren zur Erfassung einer Gewichtsbelastung auf einem solchen Kochfeld
WO2022223340A1 (fr) 2021-04-21 2022-10-27 E.G.O. Elektro-Gerätebau GmbH Table de cuisson, agencement d'une telle table de cuisson et procédé de détection d'une charge de poids sur une telle table de cuisson

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