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Researchers Submit Patent Application, "Capacitive Proximity Sensor as Well as Method for Capacitive Approximation Detection", for Approval

June 25, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventor Erkens, Holger (Dusseldorf, DE), filed on January 3, 2012, was made available online on June 12, 2014.

No assignee for this patent application has been made.

News editors obtained the following quote from the background information supplied by the inventors: "With capacitive proximity sensors, by generation and measurement of electric alternating fields, the approach of an object to the sensor electrodes of the proximity sensor is measured without contact. From the measuring signal functions can be derived, for example switching functions of an electric hand-held device. For the approximation detection without contact of an object to a capacitive proximity sensor different solutions are known from prior art, which distinguish in the way of the signal production and of measurement.

"A first principle known from prior art for capacitive approximation detection provides the use of a capacitive proximity sensor with only one electrode. In this measurement system the capacity of the electrode is detected and evaluated in relation to the ground potential of the measuring electronics of the capacitive proximity sensor. This measurement system is also called loading method. If an object, for example a user, approaches the sensor electrode, the capacity at the sensor electrode changes, which can be detected and evaluated accordingly.

"Another measurement system known from prior art provides a capacitive proximity sensor with two sensor electrodes. One sensor electrode operates as transmitting electrode and the other sensor electrode as reception electrode. The electric alternating field emitted at the transmitting electrode is coupled into the reception electrode and measured by means of an electrical signal tapped at the reception electrode. This method is also called transmission method, as it measures the transmission between a transmitter and a receiver. In case of approach of a user to the sensor electrodes the alternating electric field formed between the transmitting electrode and the reception electrode changes, which can be measured and evaluated accordingly.

"The loading method, which measures the capacitive load against a reference knot (preferably the ground of an electric device), is preferably used in grounded systems. The transmission method, which measures the transmission between a transmitter and a receiver, is preferably used for battery-operated i.e. free-of-ground systems.

"The disadvantage of the capacitive proximity sensors known from prior art is on the one hand the dependence of the capacitive proximity sensor on the parasitic capacitive loop over people, for example a user and ground. This means that the measuring signal depends on the grounding conditions of the capacitive sensor on the one hand and on the grounding conditions of the object which approaches the capacitive proximity sensor on the other hand. If the concrete grounding conditions of the capacitive proximity sensor or of the object are not known, a correct measurement of an approach of the object to the capacitive proximity sensor cannot be guaranteed.

"On the other hand interference, for example by interfering electric fields, from the environment of the capacitive sensor on the sensor electrodes of the capacitive proximity sensor is problematic, because such interference can have a negative impact on the result of the measurement. Such interference or interfering electric fields can be caused for example by neighbouring electronic components in complex systems, like mobile phones. In order to avoid such interference or interfering electric fields, additional measures must be taken which avoid the coupling of external interfering fields into the sensor electrodes of the capacitive proximity sensor as far as possible, ideally completely. Such measures however lead to an increased structural expenditure, which affects the material and production cost of the capacitive proximity sensor or the electric device in which the capacitive proximity sensor is integrated.

"A possibility known from prior art to prevent the coupling of external electric interfering fields into the sensor electrode of the capacitive proximity sensor consists in shielding the sensor electrodes of the proximity sensor against other electronic components in a complex system, which can take place for example with the help of a screen electrode. In this respect it is however disadvantageous that a screen electrode can occupy or must occupy a large amount of space in order to guarantee safe shielding. Especially when using capacitive proximity sensors in electric hand-held devices, for example mobile phones, it is desirable to do without such screen electrodes in order to reach a possibly compact design of the electric hand-held device."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "According to various embodiments a capacitive proximity sensor and a method for the capacitive approximation detection can be provided which avoid the disadvantages known from prior art at least partially and guarantee a reliable and robust detection of an approach of an object to the sensor electrodes of a capacitive proximity sensor. Especially according to various embodiments a capacitive proximity sensor and a method for the capacitive approximation detection can be provided which are to a great extent independent of influences of external interfering fields and of the grounding conditions of the sensor electronics on the one hand and of an object approaching to the sensor electrodes on the other hand.

"According to an embodiment a capacitive proximity sensor comprises a first sensor electrode and a second sensor electrode, a signal generator for providing a first electric alternating signal and a second electric alternating signal, a first load element, which comprises a first electric load and a second electric load, in which the first electric alternating signal by means of the first electric load can be fed to the first sensor electrode and the second electric alternating signal can be fed by means of the second electric load to the second sensor electrode, and wherein the electric loads each time together with the capacitive load to be measured at the respective sensor electrode form a lowpass filter,

"and a signal processing device, which is coupled with the first sensor electrode and with the second sensor electrode, and which is adapted in order to form a first measurement value from the push-pull portion of a first electric variable at the first sensor electrode and a second electric variable tapped at the second sensor electrode.

"The signal processing device may include a first amplifying circuit which is formed preferably as fully differential amplifier and which selects the push-pull portions of the first electric variable and the second electric variable.

"The signal processing device may be adapted to form the first measurement value from the difference between the first electric variable and the second electric variable.

"The first electric alternating signal preferably has the same amplitude as the second electric alternating signal. Preferably the first electric alternating signal has a phase shift of 180.degree. as to the second electric alternating signal.

"The signal processing device moreover can be adapted, to form a second measurement value from the common mode portion of the first electric parameter and second electric parameter tapped at the sensor electrodes.

"The signal processing device can, for the formation of the second measurement value, include a second amplifying circuit, which is formed preferably as an impedance converter, in which the sum of the first electric parameter and the second electric parameter can be fed to the not inverting entry of the impedance converter.

"The proximity sensor may further include a field disturbing electrode, on which a third electric alternating signal can be applied.

"The proximity sensor may further include a third amplifying circuit, which comprises the first load element.

"The proximity sensor may further include a second load element, which is coupled with the signal generator, wherein the output signals of the second load element can be fed to the signal processing device.

"The proximity sensor may further include a fourth amplifying circuit, which comprises the second load element.

"The sensor electrodes and the exit of the second load element can be coupled in such a way with the entries of the first amplifying circuit that the first amplifying circuit at its exits provides the difference between the signals tapped at the sensor electrodes and the output signals of the second load element.

"It is advantageous if the first sensor electrode is coupled with the inverting exit of the third amplifying circuit, the second sensor electrode is coupled with the not inverting exit of the third amplifying circuit, the first electric alternating signal can be fed to the inverting entries of the third amplifying circuit and the fourth amplifying circuit, the second electric alternating signal can be fed to the not inverting entries of the third amplifying circuit and the fourth amplifying circuit, a first composite signal, which is formed from the electric signal tapped at the first sensor electrode and the signal applied at the not inverting exit of the fourth amplifying circuit, can be fed to the inverting entry of the first amplifying circuit, and a second composite signal, which is formed from the electric signal tapped at the second sensor electrode and the signal applied at the inverting exit of the fourth amplifying circuit, can be fed to the not inverting entry of the first amplifying circuit.

"The amplification of the fourth amplifying circuit can be adjustable.

"Also a method for the approximation detection is provided, wherein a first sensor electrode is fed with a first electric alternating signal and a second sensor electrode with a second electric alternating signal, wherein the electric alternating signals are applied to the sensor electrodes by means of a first load element, and from the push-pull portion of a first electric parameter, which is tapped at the first sensor electrode, and that of a second electric parameter, which is tapped at the second sensor electrode, a first measurement value is formed, wherein the first measurement value is indicative for the approach of the object to the sensor electrodes.

"The electric alternating signals are preferably selected in such a way that the first electric alternating signal preferably comprises the same amplitude as the second electric alternating signal and that the electric alternating signals are preferably dephased by 180.degree. to each other.

"From the common mode portion of the first electric parameter and of the second electric parameter a second measurement value is formed.

"A second load element can be fed with the first electric alternating signal and the second electric alternating signal, wherein the exits of the first load element and of the second load element are coupled with the entries of a first amplifying circuit in such a way that the first amplifying circuit at its exits provides the difference between the output signals of the first load element and the output signals of the second load element.

"Moreover a hand-held device is provided, especially an electrical hand-held device, which comprises at least one capacitive proximity sensor according to various embodiments.

"The electric hand-held device can be a smart phone, a two-way radio, a computer mouse, a remote control device, a digital camera, a game controller, a PDA, a tablet PC, a deaf-aid, a dictating machine, or similar.

BRIEF DESCRIPTION OF THE DRAWINGS

"Further details and characteristics of the invention as well as concrete embodiments of the invention result from the following description in connection with the drawing. The figures show:

"FIG. 1the electric flux lines of a capacitive proximity sensor according to an embodiment with the sensor idle;

"FIG. 2 a block scheme of a first embodiment of a capacitive proximity sensor;

"FIG. 3 the signal curves of the electric signals tapped at two sensor electrodes of the capacitive proximity sensor according to an embodiment as well as the differential signal resulting from this;

"FIG. 4a capacitive equivalent circuit of a person;

"FIG. 5the block diagram shown in FIG. 2 of a capacitive proximity sensor according to an embodiment together with the capacitive equivalent circuit from FIG. 4, in which the human being represents a part of a lowpass filter of the first order;

"FIG. 6 alternatives to the lowpass filter of the first order shown in FIG. 5 as a lowpass filter of the second order and a lowpass filter of the third order;

"FIG. 7a block diagram of a further embodiment of a capacitive proximity sensor, which in addition to the differential mode evaluation also provides a common mode evaluation;

"FIG. 8 the signal curves of a push-pull signal and a common mode signal, the way they are provided by a capacitive proximity sensor according to FIG. 7;

"FIG. 9 another embodiment of a capacitive proximity sensor, which allows a compensation of production tolerances;

"FIG. 10 two application cases using each time two capacitive proximity sensors according to an embodiment in an electric hand-held device; and

"FIG. 11 a capacitive proximity sensor according to an embodiment, which additionally provides a field disturbing electrode."

For additional information on this patent application, see: Erkens, Holger. Capacitive Proximity Sensor as Well as Method for Capacitive Approximation Detection. Filed January 3, 2012 and posted June 12, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=5145&p=103&f=G&l=50&d=PG01&S1=20140605.PD.&OS=PD/20140605&RS=PD/20140605

Keywords for this news article include: Patents, Signal Processing, Electronic Components.

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Source: Electronics Newsweekly