Source: http://www.patentsencyclopedia.com/app/20130113707
Timestamp: 2017-11-22 09:31:19
Document Index: 430558987

Matched Legal Cases: ['Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60']

Inventors: Haim Perski (Hod-Hasharon, IL) N-Trig Ltd. (Kfar-Saba, IL) Meir Morag (Savyon, IL)
Patent application number: 20130113707
1. A method for operating an on-screen keyboard, the method comprising: providing a transparent arrangement of sensing conductors located on an electronic display screen for detecting one or more finger touches when present, the transparent arrangement including a first and second set of conductor lines forming a grid across the electronic display screen with a plurality of junctions there between at which the conductor lines do not contact; providing a signal to a plurality of conductor lines of the first set of conductor lines; detecting output arising from one or more finger touches when present, wherein the output arising from each of the one or more finger touches is detected from at least one conductor line of the second set of conductor lines in response to the signal provided to the at least one conductor line of the first set of conductor lines; detecting positions of the one or more finger touches on the transparent arrangement responsive to the output detected; and associating the positions of the one or more finger touches on the transparent arrangement to positions of one or more keys of a keyboard displayed on the electronic display screen.
2. The method of claim 1, comprising detecting positions of simultaneous finger touches on the transparent arrangement responsive to the output detected.
3. The method of claim 1, comprising interpolating output detected over a plurality of conductor lines to increase accuracy of the position detection beyond the granularity of the transparent arrangement of sensing conductors.
4. The method of claim 1, comprising detecting output arising from an electromagnetic stylus when present, wherein the output arising from an electromagnetic stylus is detected from at least one conductor line of the first or second set of conductor lines.
5. The method of claim 4, wherein the output arising from the electromagnetic stylus and the one or more finger touches is detected from same conductor lines.
6. The method of claim 4, wherein position of the electromagnetic stylus and positions of the one or more finger touches are detected independently.
7. The method of claim 4, wherein position of the electromagnetic stylus and positions of the one or more finger touches are detected at different times.
8. The method of claim 4, comprising detecting output also from the first set of conductor lines.
9. The method of claim 4, comprising detecting output from first and second set of conductor lines simultaneously.
10. The method of claim 4, comprising providing a signal for exciting circuitry in the electromagnetic stylus.
11. The method of claim 4, wherein the signal for exciting circuitry in the electromagnetic stylus is applied to at least one conductor line of the first or second set of conductor lines.
12. The method of claim 1, comprising providing the signal to the plurality of conductor lines, one at a time.
13. The method of claim 1, comprising switching from providing the signal to the first set of conductor lines and detecting output from at least one conductor line of the second set of conductor lines to providing the signal to the second set of conductor lines and detecting output from at least one conductor line of the first set of conductor lines.
14. The method of claim 1, comprising detecting output in the second set of conductor lines, in response to each signal applied to the plurality of conductor lines in the first set of conductor lines.
15. The method of claim 1, wherein the signal provided is an oscillating signal.
16. The method of claim 15, wherein the signal is configured to oscillate with respect to a reference voltage level, thereby to permit a capacitive current flow between each of the one or more finger touches and at least one conductor line from the first and second set of conductor lines.
17. The method of claim 1, comprising detecting an oscillating signal transferred via the junctions to conductor lines in the second set of conductor lines, the transference being indicative of capacitive coupling change induced by positioning of the one or more finger touches over the transparent arrangement at the respective junctions.
18. The method of claim 1, comprising determining a tabulation of signal values detected at each junction while the one or more finger touches are removed from the sensor.
19. The method of claim 18, comprising correcting readings at each conductor responsive to the tabulation of signal values.
20. The method of claim 19, comprising updating the tabulation upon startup the position detection.
[0001] This application is a continuation of U.S. patent application Ser. No. 13/411,795 filed on Mar. 5, 2012, which is a continuation of U.S. patent application Ser. No. 12/153,343 filed on May 16, 2008, now U.S. Pat. No. 8,228,311, which is a continuation of U.S. patent application Ser. No. 11/727,301 filed on Mar. 26, 2007, now U.S. Pat. No. 7,843,439, which is a divisional of U.S. patent application Ser. No. 10/757,489 filed on Jan. 15, 2004, now U.S. Pat. No. 7,372,455, which claims the benefit of priority of U.S. Provisional Patent Application Nos. 60/446,808 filed on Feb. 10, 2003, and 60/501,484 filed on Sep. 5, 2003. The contents of all of the above applications are incorporated by reference as if fully set forth herein.
[0003] The popularity of computers has given rise to extensive research and development in the field of digitizers and touch screens. There are many inventions describing touch panels but very few describe a digitizer capable of detecting both an EM stylus and finger touch using the same sensing device. U.S. patent application Ser. No. 09/629,334, titled "Physical Object Location Apparatus and Method and a Platform using the same", filed Jul. 7, 2000 and assigned to N-trig Ltd., and U.S. patent application Ser. No. 09/628,334, titled "Transparent Digitizer", filed Aug. 28, 2003 and also assigned to N-trig Ltd., describe positioning devices capable of detecting multiple physical objects, preferably styluses, located on a flat screen display.
[0004] U.S. patent application Ser. No. 10/270,373, titled "Dual Function Input Device and Method", filed Oct. 15, 2002 and assigned to N-trig Ltd., describes a system capable of detecting electromagnetic objects and finger touch using the same transparent sensor. In the disclosure, the finger touch detection is implemented by a matrix of resistive stripes that are merged into the EM detection pattern. A special separation layer is placed between the conductor layers so as simultaneously to enable touch stripe contact and prevent contact between the EM lines. Additional electronics are required to drive and read the touch signals from the sensor. The major disadvantage of this method is the additional complexity to both sensor and electronics.
[0005] U.S. Pat. No. 3,944,740 employs an input pad mounted over the top of a plasma panel display. The input pad is a matrix of conductive rows and columns that are arranged so that a stylus having a conductive tip can short circuit a row electrode and a column electrode at its point of contact, with current conducted through the row and column electrodes representing the stylus location. U.S. Pat. No. 4,639,720 employs a similar idea using conductive pixels rather than a matrix of rows and columns
[0007] U.S. Pat. No. 4,550,221 describes a sensor array comprising of series of conductive plates/pixels connected by a conductive wire. A finger touch changes the pixel's capacitance with respect to ambient ground. The change is detected and translated to indicate a finger's position. The disclosure does not allow the detection of an EM stylus together with finger detection. The sensor's plates\pixels are not transparent and therefore cannot be mounted on a display screen.
[0008] U.S. Pat. No. 4,293,734 employs two current sources driving predetermined currents through each end of the antenna. The finger's position is calculated using Kirchoff's laws for current leakage through the finger to the ground. Disadvantages of the detection system disclosed therein are that it does not allow the detection of an EM stylus. Rather it requires current flows from both ends of the conductive surface which is in evidently power consuming. Furthermore, the detection is analog and involves relatively complicated circuitry.
[0010] U.S. Pat. No. 6,583,676 describes a method of detecting a finger's added capacitance upon application of a frequency change. A calibration circuit and method for a proximity/touch detector allow automatic calibration to the proximity/touch detector components, chassis affects, and ambient conditions such that initial factory calibration and periodic manual calibration are not needed. The calibration circuit switches a capacitance into the input capacitance of a Schmitt trigger free running oscillator to change the output frequency of the oscillator. A capacitive sensor forms part of the input capacitance. The change in frequency simulates the frequency shift associated with the difference in input capacitance generated when an object, such as a finger, is touching the capacitive sensor and when the capacitive sensor is free from contact with the object. The most evident disadvantages of this invention are the need for additional hardware and the inability to detect an EM stylus.
[0011] Other methods of finger detection can be found in U.S. Pat. Nos. 6,587,093, 6,633,280, 6,473,069, and 6,278,443. The above describe methods of finger detection all inherently different from the methods described hereinbelow, and none combine the ability to sense both an EM stylus and a finger touch.
[0015] a patterned arrangement of sensing conductors extending within the sensor, to and
[0028] Preferably, there is provided at least a second conductive element located within the sensor and having a junction with the one conductive element, wherein the to oscillator is applied to one of the conductive element and the junction is configured such that a touch by a capacitive body part causes an a.c short at the junction, the detector being configured to detect a resulting oscillating signal at the second conductive element and therefrom to infer the touch.
[0042] Preferably, there is provided at least a second conductor located within the sensor and having a junction with the at least one conductor, wherein the source of oscillating electrical energy is applied to one of the conductors and the junction is configured such that a touch by a conductive object causes an a.c short at the junction, the detector being configured to detect the oscillating signal at the second conductor as the capacitive effect and to infer the touch.
[0079] a sensor comprising a grid array of conductors in a first sense and conductors in a second sense and having junctions there between,
[0090] FIG. 1A is a simplified block diagram showing a generalized embodiment of the present invention;
[0091] FIG. 1B is a simplified diagram illustrating an embodiment of the present invention in which oscillating energy is transmitted to a finger;
[0092] FIG. 3 is a simplified diagram illustrating an embodiment of the present invention in which the touching finger provides a capacitive link between sensing conductors on a grid;
[0093] FIG. 3 is a circuit diagram illustrating the electrical theory of the embodiment of FIG. 2;
[0094] FIG. 4 is a simplified schematic diagram illustrating an embodiment of the present invention in which the detection device is floated using a signal that oscillates with respect to a reference signal and wherein a finger incident upon a conductor provides a capacitive path to ground;
[0095] FIG. 5 is a circuit diagram illustrating one version of the embodiment of FIG. 4;
[0096] FIG. 6 is a circuit diagram illustrating a variation of the embodiment of FIG. 4;
[0097] FIG. 7 is a circuit diagram illustrating another variation of the embodiment of FIG. 4, in which the conductors are oscillated directly;
[0098] FIG. 8 is a circuit diagram illustrating a variation of the embodiment of FIG. 7 in which the conductors are oscillated from their far ends;
[0099] FIG. 9 is a block diagram of a variation of the embodiment of FIG. 4 in which isolation is provided by a DC to DC converter;
[0100] FIG. 10A is a block diagram illustrating another variation of the embodiment of FIG. 4 in which isolation by a DC to DC converter is provided between two parts of the detector;
[0101] FIG. 10B is a block diagram illustrating a modification to the embodiment of FIG. 10A to permit communication between the two parts of the detector;
[0102] FIG. 11 is a block diagram illustrating coil-based isolation of the detector according to an embodiment of the present invention;
[0103] FIG. 12 is a block diagram illustrating a variation of the embodiment of FIG. 11 in which the coil based isolation is used for a part of the detector;
[0104] FIG. 13 is a block diagram illustrating floating of the detector by placing tandem oscillators on the positive and ground power supply rails;
[0105] FIG. 14 is a simplified block diagram illustrating how the same excitation circuitry can be used for stylus and finger touch sensing according to a preferred embodiment of the present invention;
[0106] FIG. 15 is a theoretical circuit diagram illustrating sources of steady state noise that affect touch measurements in the present embodiments;
[0107] FIGS. 16A and 16B illustrate a grid of conductors and tabulation, both of magnitude and phase, of noise effects for the respective conductors;
[0108] FIG. 17 is a block diagram of touch detection apparatus able to use the tabulation of FIG. 16B in order to correct touch readings;
[0109] FIG. 18 is a simplified diagram illustrating signal patterns indicative of finger touches;
[0110] FIG. 19 is a simplified flow chart illustrating touch measuring procedures according to the present invention.
[0111] The present embodiments comprise a digitizer that allows finger clicks and movement detection on flat panel displays, in such a way that the same sensing infrastructure can be used for electromagnetic (EM) stylus detection. The digitizer is designed to work in conjunction with a patterned transparent conductive foil system, which allows for detecting the location of an electromagnetic stylus on top of an electronic display surface. Some of the presently preferred embodiments use finger induced capacitance connecting the sensor lines as a method of finger detection. The present embodiments include inter alia a method of identifying the presence and location of the finger by measuring the differential signal between two different sensor antennas. In the preferred embodiments the currents are driven from one end of the antenna, and the information is then sensed and digitized using the detector as will be described in greater detail hereinbelow.
[0112] Whilst the prior art teaches connection of a separate charge sensor or the like to each electrode, the present embodiments are able to utilize the differential signal generated between two electrodes.
[0113] One of the methods disclosed hereinbelow involves measuring voltage differences due to the finger's adding a capacitive short circuit to the ground.
[0114] The primary use of the preferred embodiments is to allow a natural and intuitive operation of an "on-screen-keyboard", in devices such as the tablet PC, separately, in addition and in parallel to the operation of an accurate electromagnetic stylus.
[0115] In the following description there are presented three methods of implementing touch sensors using the same detector unit and sensor grid used for the detection of an EM stylus. The sensing methods disclosed may require adjustments for given circumstances and devices, as will be apparent to the person skilled in the art. However, all methods are designed to enable the simultaneous and independent detection of an EM stylus in a manner similar to that disclosed in U.S. patent application Ser. No. 10/649,708 to the present assignee, filed 28 Aug. 2003, and claiming priority from U.S. Provisional Patent Application No. 60/406,662. Detection of finger touch and EM stylus is independent and can be performed simultaneously or at different times. It is left to the discretion of the user whether to use the presently disclosed embodiments in order to implement a detector for one kind of interaction alone (i.e. finger touch or EM stylus) or to allow the detection of both kinds of interactions.
[0116] In the preferred embodiments of the present invention, the same detector can detect and process signals from an Electro Magnetic Stylus whether it is placed in contact with, or at a short distance from, the surface of a flat panel display. For example detection may be carried out in the manner described in U.S. patent application Ser. No. 09/628,334 "Physical Object Location Apparatus and Method and a Platform using the same" assigned to N-trig Ltd., and U.S. patent application Ser. No. 09/628,334 "Transparent Digitizer" again assigned to N-trig Ltd.). At the same time the detector can be used to detect a user's finger placed on the same display, as will be described hereinbelow. In other embodiments of the present invention the finger detection may function solely, or in combination with any other input device.
[0117] The principles and operation of a digitizer according to the present invention may be better understood with reference to the drawings and accompanying description.
[0118] Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.
[0119] Reference is now made to FIG. 1A, which is a schematic diagram illustrating a generalized embodiment of the present invention. In FIG. 1A a sensor 2 comprises at least one electrical conductor 4. In the typical case there is more than one conductor, and the conductors are set in an arrangement or pattern over the sensor, most often as a grid which extends over a surface such as an electronic screen for which touch sensing is required. A detector 6 picks up the output from the conductors. An oscillator 8 provides oscillations or a.c. energy to the system comprising the sensor and detector. In one embodiment, the system is not initially a.c. coupled. However a conductive object, including body parts such as fingers are capacitive and therefore touch by a finger or the like completes the a.c. coupling within the system and allows the touch to be sensed. Alternatively a touch by the finger may provide an a.c. short circuit to ground for a given conductor, again allowing the touch to be sensed.
[0120] A preferred embodiment detects touch as described above and additionally allows the location and identification of physical objects, such as styluses. The location of the physical objects is sensed by an electromagnetic transparent digitizer, preferably constructed on top of a display, and it is a feature of some of the preferred embodiments that the electromagnetic transparent digitizer makes use of the same components as the touch digitizer described herein, so that the two types of detection can be incorporated into a single digitizer, as will be explained hereinbelow. The construction of a suitable electromagnetic transparent digitizer is described in U.S. patent application Ser. No. 09/628,334. This application describes a sensing device that is to capable of detecting multiple physical objects located on top of a flat screen display.
[0121] The various components and functionality manner of the transparent digitizer are as follows:
[0123] As described in the above referred to applications and used in the presently preferred embodiments, the sensor comprises two transparent foils, one containing a set of vertical conductors and the other a set of horizontal conductors. The grid of conductive lines is made of conductive materials patterned on the transparent foils, which may for example be PET foils. In different embodiments, the present invention sensor could be implemented on other transparent conductive materials such as ITO. In a preferred embodiment, the resistance of the conductive lines is relatively high and it might exceed 100 KOhms for a line. Usually, higher resistance of transparent conductors results in a higher transparency of the material.
[0124] Further information regarding the construction of the sensor is available from U.S. provisional Patent Application No. 60/406,662 (sub-chapter 4.2 entitled: "Sensor") and corresponding U.S. patent application Ser. No. 10/649,708 filed Aug. 28, 2003, both assigned to N-Trig. Ltd. the contents of both of which are hereby incorporated by reference.
[0129] For further information see U.S. provisional Patent Application No. 60/406,662 (sub-chapter 4.3 entitled: "Front end") and corresponding U.S. patent application Ser. No. 10/649,708 filed Aug. 28, 2003, both assigned to N-Trig. Ltd. the contents of both of which are hereby incorporated by reference.
[0133] In one embodiment, all of the sensor inputs lines are sampled at the same time during one system cycle.
[0134] A digital signal processor (DSP) core, which performs the digital unit processing, reads the sampled data, processes it and determines the position of the physical objects, such as stylus or finger.
[0135] A calculated position is sent to the host computer via link.
[0136] For further information see U.S. provisional Patent Application No. 60/406,662 (sub-chapter 4.4 entitled: "Digital unit") and corresponding U.S. patent application Ser. No. 10/649,708 filed Aug. 28, 2003, both assigned to N-Trig. Ltd. the contents of both of which are hereby incorporated by reference. The above-mentioned applications discuss signal processing and position determination for signals emanating from an electromagnetic EM stylus, but do not provide any disclosure regarding finger detection. As will be explained below, in the present embodiments, finger touch may be detected using compatible signals on the same detection conductors which are processed in substantially the same way. It makes no substantial difference to the DSP core or to the intervening electronics whether the signals originate from a finger or from a stylus.
[0137] d. Detector
[0138] A detector consists of the digital unit and the Front end units, as described above.
[0140] The preferred embodiment of the present invention utilizes a passive EM stylus that includes a resonance circuit. The resonance circuit is formed by an inductor and a capacitor which is excited to oscillate in a basic resonance frequency. In some exemplary embodiments, contact between the stylus tip to the surface closes a touch switch and connects an additional capacitor to the resonant circuit in parallel to the existing capacitor. This changes the effective capacity and thus changes the resonance frequency. The digital unit detects the change in frequency and interprets the touch based on the detected change, e.g. left click, right click or both.
[0141] An external excitation coil that surrounds the sensor excites the resonance circuit within the stylus. The resonance circuit emits radiation which can be detected by the conductors. The exact position and unique identity of the stylus can then be determined by the detector as a result of processing the signals sensed by the sensor. Alternatively, the stylus can be internally powered using a battery.
[0142] For further information see U.S. provisional Patent Application No. 60/406,662 (sub-chapter 4.5 entitled: "Stylus") and corresponding U.S. patent application Ser. No. 10/649,708 filed Aug. 28, 2003, both assigned to N-Trig. Ltd. the contents of both of which are hereby incorporated by reference.
[0143] Algorithms
[0144] In the preferred embodiments of the present invention the basic detection operation cycle consists of averaging, decay compensation, windowing, FFT/DFT, peak detection, interpolation, error compensation, filtering and smoothing. The cycle is substantially the same whether a finger touch or a stylus is being detected with the notable exception that, as disclosed hereinbelow, the sources of noise and thus the types of appropriate error compensation differ.
[0145] For further information see U.S. provisional Patent Application No. 60/406,662 (sub-chapter 4.6 entitled: "Algorithms") and corresponding U.S. patent application Ser. No. 10/649,708 filed Aug. 28, 2003, both assigned to N-Trig. Ltd. the contents of both of which are hereby incorporated by reference.
[0156] In a preferred embodiment, the energy transmission source is external to the sensor. In other embodiments, the energy is transmitted by one of the sensor components, for example the sensor excitation coil, the sensor matrix or any other conductor that is added to the sensor in order to specifically transmit the energy. In one embodiment it is possible to transmit the energy by alternating between a first transmitter that is orthogonal to one set of sensing conductors and a second transmitter that is orthogonal to the other set of conductors. Regarding the concept of a transmitter being orthogonal to a conductor, when transmitting from an antenna that is orthogonal to one conductor axis and parallel to the other conductor axis--signals received on the conductors that are in parallel are very strong, hence a signal induced by a finger is undetected. However, the conductors orthogonal to the transmitting antenna are hardly disturbed by it. Hence, a signal induced by a finger is detectable on the conductors that are orthogonal to the transmitting antenna. Now in all the preferred embodiments, electromagnetic (EM) stylus excitation is performed prior to sampling, whereas finger detection energy is transmitted during sampling. Consequently it is possible to produce both stylus excitation and finger excitation, that is to say transmission, signals using the same hardware, typically a signal generator. The two signals are simply transmitted by the same physical antennas at different time slots. Furthermore the stylus sampling procedure includes an excitation period and a separate sampling period which is subsequent to the excitation period. Thus, whilst the stylus is being sampled the antenna can already start to generate the signal for finger detection. Hence both objects can be sensed in the finger excitation phase. Alternatively, a stylus excitation signal generator may be provided as a separate unit from the finger detection signal generator.
[0159] A dramatically reduced signal provided by the finger when the power supply of the system is grounded. This disadvantage makes a digitizer based thereon suitable mainly for devices powered by battery or those powered by a source highly isolated from the ground.
[0160] The need to transmit and therefore potentially interfere with other equipment.
[0161] Dependency on the distance from the user to the transmitter; meaning the further away the user is from the transmitter the lower is the signal. The resulting variation can lead to reliability problems.
[0166] Reference is now made to FIG. 3, which is the theoretical electric equivalent of FIG. 2. Parts that are the same as in previous figures are given the same reference numerals and are not referred to again except as necessary for understanding the present embodiment. The transmitted signal 22 is applied to the Horizontal conductor to 24. The finger 26 that touches the sensor creates two capacitors, C1 40 and C2 42 that transfer the signal from the horizontal line to the finger and from the finger to the vertical conductor 28. An output signal 30 is detected on the edge of the vertical conductor in the case of finger touch.
[0170] A number of procedures for detection are possible. The most simple and direct approach is to provide a signal to each one of the matrix lines in one of the matrix axes, one line at a time, and to read the signal in turn at each one of the matrix lines on the orthogonal axis. The signal, in such a case, can be a simple cosine pattern at any frequency within the range of the sampling hardware and detection algorithms. If a significant output signal is detected, it means that there is a finger touching a junction. The junction that is being touched is the one connecting the conductor that is currently being energized with an input signal and the conductor at which the output signal is detected. The disadvantage of such a direct detection method is that it requires an order of n*m steps, where n stands for the number of vertical lines and m for the number of horizontal lines. In fact, because it is typically necessary to repeat the procedure for the second axis so the number of steps is more typically 2*n*m steps. However, this method enables the detection of multiple finger touches. When an output signal is detected on more than one conductor that means more than one finger touch is present. The junctions that are being touched are the ones connecting the conductor that is currently being energized and the conductors which exhibit an output signal.
[0173] The third embodiment uses a potential difference between the user∝s finger and the system to determine the finger position.
[0180] In one embodiment of the present invention, as described above, the entire detector is oscillated in reference to the common ground. A disadvantage of this option is that any communication between the detector and the outside world, such as serial communication to the host computer, must be adapted to compensate for the potential difference between the detector and the outside world and cannot use a common ground. There are numerous ways of communicating between components that have to be isolated from each other, and one example for a way to provide isolated communication is by using an optical link. The optical link transforms the electrical signal into light and then back into an electrical signal, and the level of isolation is very high. However the need for isolation can also be overcome by applying the oscillation to only a portion of the detector.
[0185] Sensor device 88 also oscillates in reference to the common ground, by virtue of its being connected to the detector front end, which is part of unit 84. In the present figure, the sensor device refers to the transparent film carrying the matrix of to sensors.
[0191] 1. Using differential signals, so that data is output on two parallel lines, one a signal and one a reference. Both the signal and its reference oscillate but the data is in fact carried in the difference between the two. The embodiment is described in greater detail hereinbelow with reference to FIG. 10b, under the heading `floating the system`.
[0192] 2. Using electrically isolated communication within the detector, such as opto-isolators.
[0200] Reference is now made to FIG. 8, which is a simplified diagram illustrating a variation of the embodiment of FIG. 7. Parts that are the same as in FIG. 7 are given the same reference numerals and are not referred to again except as necessary for understanding the present embodiment. The embodiment of FIG. 8 differs from FIG. 7 in that two reference signals are used, an oscillation reference signal Va is applied to the conductors on the ends extending into the sensor opposite to where detection is carried out, that is away from the inputs to the differential amplifier. A DC reference signal is applied to the output side of the conductors and is used to create a high reference level for the conductive lines. Other embodiments may not include a separate DC reference signal Vref, and rely on Va alone. Vref as used in the present embodiment, creates a high reference level for the conductors. That is to say, since the input resistance to the amplifier is very high the conductors are susceptive to noise from the environment. Connecting the conductors to a higher reference level eliminates, or at least reduces, their tendency to pick up noise. In the embodiment of FIG. 7, the Vref signal is used both for oscillating the conductive lines and setting the DC level. In the embodiment of FIG. 8 it is both clarified that the oscillations can be applied opposite to the detecting end of the conductor and that the oscillation and DC reference signals can be separated. It is further noted that it is possible to apply Va--without use of a separate Vref signal.
[0206] The DC-to-DC floating method may be modified so that only a portion of the detector oscillates in reference to the ground. Two such modifications are illustrated in FIGS. 10A and 10B respectively. Referring first to FIG. 10a, the detector 130 comprises two units 132 and 134. Due to the isolated DC-to-DC component 136 the detector component 134 floats in reference to the ground and the oscillator 138 oscillates detector unit 134 in reference to the common ground 140.
[0208] Reference is now made to FIG. 10b, which illustrates a possible solution to overcome the above-described communication problem. Parts that are the same as in FIG. 10A are given the same reference numerals and are not referred to again except as necessary for an understanding the present embodiment. Detector unit 134 floats in reference to the ground and oscillates, due to oscillator 136. The output signals of detector unit 134 oscillate in relatively the same phase as oscillator 136. Output signal 142 from detection unit 134 and the oscillator output 144 are inserted to a differential amplifier 146. The potential difference between signals 142 and 144 is amplified by the differential amplifier 146. The output signal of differential amplifier 146 is a steady signal representation of signal 142. Thus, detecting units 132 and 134 can communicate through differential amplifier 146, which serves as a communication device or channel.
[0215] An additional embodiment utilizes the DSP itself for creating the oscillations. One advantage of this option is that the phase of the oscillations can be easily synchronized for sampling. In this case DSP digital values are provided to a D2A (Digital to Analog) component, or any equivalent arrangement, and then the analog values are filtered and amplified as required. An additional version of such an implementation may utilize for the production of oscillations the same components that are being used for the excitation of the stylus. For further details on the excitation of the stylus see FIG. 9 in U.S. Provisional Patent Application No. 60/406,662, and the corresponding description, entitled "Stylus". The figure and corresponding description are hereby incorporated herein by reference.
[0217] The finger is detected only during dedicated sampling periods, and
[0218] No excitation is performed during the dedicated sampling periods.
[0224] In an ideal environment, (Sa)=(Sb), and therefore no signal differentiation is amplified, by differential amplifier 222 which is connected between the two sensors 210 and 212, unless a user's finger touches a conductor. However, in practice, there are slight differences in distance, overlapping area, screen structure, intermediate material, temperature, etc. (Sa)≠(Sb), and therefore, a "steady noise": (Sa)-(Sb) is produced. The steady noise is amplified by the differential amplifier 222. Such "steady noises" based on (Sa) and (Sb) exist on any two sensor conductors connected by a differential amplifier, and thus it may be said that similar differentials to (Sa)-(Sb) are being amplified by any of the differential amplifiers connecting sensor conductors in the system. The result is various amplified steady noises that, although steady over time, are detected by the detector. The presence of these steady noises reduces the level of accuracy possible in detecting the user's finger's location.
[0234] Once the differential map is stored in memory, it can be used to compensate for the display panel signal steady noise phenomenon. Reference is now made to FIG. 17 which is a simplified schematic diagram illustrating a two-conductor sensor arrangement exhibiting the steady noise phenomenon. The display panel creates "steady noises" (Sa) and (Sb) on sensor conductors 240 and 242 respectively. The user's finger creates an (Sf) signal, which is the signal it is desired to measure. The overall differential, as determined by differential amplifier 244, between the sums of signals on both sensor conductors is: {(Sa)+(Sf)}'-(Sb)} The overall differential is amplified by the diff amplifier 244 and sampled by the detector 246. The DSP component 248 reads the differentiation {(Sa)-(Sb)} stored within the differential map 250. The DSP 250 subtracts the differential from the sampled signal. As {(Sa)+(Sf)}-(Sb)}-{(Sa-Sb)}=(Sf) the DSP is able to isolate and identify the finger signal, and identify the finger's location.
[0239] For simplicity of explanation the opposite case is taken: a user's finger may be placed on the display panel during the actual mapping process. The finger inputs a signal (Hs) to a sensor conductor 242 as before. The sensor conductor also receives a steady noise signal (D1s) from the display panel. Another sensor conductor 240 receives a steady noise signal (D2s) from the display panel. These two sensor conductors are connected to the same diff amplifier 244. The differential received and amplified by the diff amplifier equals {(D1s)+(F1s)}-(D2s). Some time after the mapping process is over, the finger is removed. The new differential amplified is now equal to: (D1s)-(D2s). The DSP subtracts the value stored in the differential map from the new value. The result equals: {(D1s)-(D2s)}-[{(D1s)+(F1s)}-(D2s)]=-(F1s). Realistically, the (F1s) value represent the magnitude, and the (-) sign represents the phase. This result is exactly the differentiation expected when a finger is placed on the second sensor conductor and assuming that a finger had not been placed on the first sensor conductor during the mapping process. The DSP responds as if a finger was detected, although no finger is actually placed on the display panel.
[0240] One embodiment of the present invention utilizes the embodiment described above where the mapping process is performed once during the manufacturing process. As the expected signaling objects creating the detection of signaling objects through the mapping process problem explained above are mostly a user's finger, fingers, palm, first etc; and as the manufacturing environment is one where no user is present, the problem is solved.
[0241] The disadvantage of the above approach is the reliability of a single mapping to process. Due to system's mobility, temperature changes, mechanical changes, etc, the differentiation between the signals produced by the display panel on any two sensor conductors connected by a differential amplifier may change over time, rendering previously recorded differential map values obsolete. A strictly controlled manufacturing process may solve the disadvantage by ensuring that no such changes occur, but such a process increases costs. On the other hand it is reasonable to believe that extreme changes in environmental conditions will not occur during a single operation cycle of the system (i.e. from turning on the computer until shutting it down). Hence, initializing the mapping process upon system initialization should suffice in most cases.
[0242] One embodiment of the present invention comprises performing mapping during each system initialization. During the initialization the user may be warned, either by a caption on the display panel or in any other manner, not to touch the display panel. As the expected signaling objects are typically the user's finger, fingers, palm, first etc, this warning solves the problem. In a variation, not only is mapping carried out at each initialization but again at every time there is a doubt regarding the validity of the differential map. Methods designated to identify such doubts are described hereinbelow.
[0245] Thus, whenever the DSP simultaneously detects more than a single finger's signal pattern, a doubt in the validity of the differential map is inferred, and the DSP launches a new mapping process.
[0246] Reference is now made to FIG. 18 with which an example of such a procedure is described. Two groups of three lines are shown, a first group labeled Fs and a second group labeled PFs. Each line represents two sensor conductors connected to the same differential amplifier. The lines represent sensor conductor axial signal detection, preferably after subtracting the steady noise from whatever source, such as the display panel steady noise, as explained above. The height of each line represents to the signal's magnitude. (Fs) and (PFs) are finger signal patterns. If the user places a finger on the display panel during the mapping process, then a finger signal pattern (PFs) is detected only once the finger is removed, as explained above. Once the user actually places a finger, another finger signal pattern (Fs) is detected. Once two finger signal patters are detected on the same axis a doubt in the validity of the differential map occurs, and the DSP launches a new mapping sequence.
[0247] It is noted that the same method can be used to identify not only more than one finger but also one single object that is larger than a finger, such as a first or a palm. The detection of such an object's signal pattern immediately raises doubts regarding the validity of the differential map.
[0248] One disadvantage of the above described method of reinitializing in the face of a doubt is that it may enter an endless cycle of reinitializing. Thus, in the example explained in FIG. 18, the new mapping process is launched, but the finger that created signal pattern (Fs) in the first place is still in place on the display panel, damaging the validity of any reinitializing carried out at this point.
[0249] An additional disadvantage is that such a system may be used solely in systems capable of single finger detection. Once a system is designed to detect more than a single touch, then multiple touch is a totally legitimate input signal and cannot be taken as an indication that reinitializing is required.
[0251] Such a method is described in U.S. provisional Patent Application No. 60/406,662, in which the amplifier input (negative or positive) is determined using the magnitude of signals received by the neighbor conductors.
[0254] 1. A user's finger has been placed on the display panel through the mapping process. The finger has sent a signal through the sensor conductor connected to the positive input of the differential amplifier, and, as a result, a signal (F1s) is sent to the differential amplifier (N). The sensor conductor also receives a steady noise signal (D1s) from the display panel. The sensor conductor connected to the negative input of the differential amplifier receives a steady noise signal (D2s) from the display panel. The differential consequently received and amplified by the differential amplifier equals {(D1s)+(F1s)}-(D2s). The finger is now removed. The differential signal amplified upon removal of the finger now equals {(D1s)-(D2s)}. The DSP now subtracts the value stored in the differential map from the new value. The result equals {(D1s)-(D2s)}-[{(D1s)+(F1s)}-(D2s)]=-(F1s). Realistically, the (F1s) value represent the magnitude, and the (-) sign represents the phase shift.
[0255] 2. The pattern (magnitude and phase) is the result of a real finger currently sending a signal through the sensor conductor connected to the negative input of the differential amplifier.
[0256] By using the magnitude of signals received and the neighboring conductors method disclosed in subchapter 4.6 of U.S. provisional Patent Application No. 60/406,662, which subchapter is hereby incorporated by reference, the DSP detects whether the source is the negative input of the differential amplifier or the positive input thereof.
[0257] If the signal's source was the sensor conductor connected to the to positive input of the differential amplifier then scenario number 1 appears to be the case and the differential map is not valid. A new mapping process or initialization is launched.
[0258] If the signal's source was the sensor conductor connected to the negative input of the differential amplifier then scenario number 1 mentioned above did not happen and the mapping is valid. The DSP consequently detects a finger.
[0263] In one preferred embodiment of the present invention the signal induced by the finger is much larger than the steady noise signals. This ensures that a finger presence is always distinguished from the steady noise, hence enabling correct mapping process. For example, returning to FIG. 15, when capacitors 216 and 218 are of lower capacitances then the finger induced capacitance--a signal created by a finger touch is greater than the differential signal originating from capacitors 216 and 218. Hence, the steady noise originating from the coupling of the sensor array and the display screen cannot be mistaken for a finger touch. Any detected signals are translated into finger touch only when the received signal is considerably higher than the steady noise. Under these conditions, it is quite simple to identify a situation in which no fingers are present on the sensor plane to create a correct differential map.
[0264] One possibility for creating such conditions is ensuring an air gap between the conductive lines of the sensor and the display screen. The existence of an air gap in such a location reduces the coupling capacitance between the sensor lines and the display screen to such a level that finger signals are much greater than the steady noise. Another possibility comprises placing the sensor plane in close proximity to the user finger, thus ensuring that the finger induced signal is greater than the steady noise.
[0270] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, to which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.
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