Multi-touch touch device using capacitive detection

Abstract

A multi-touch touch device (DIS) using capacitance detection, the multi-touch touch device comprising: a touch matrix array (7); and a voltage generating device (100), the voltage generating device being configured to generate a first input voltage having a first frequency for each row (2) and each column (4) of the matrix array (7), the first input voltage causing the generation of a first output voltage, characterized in that the device comprises a device for generating a second input voltage for each intersection between at least two rows (2) and at least two columns (4) of the matrix array, the second input voltage having a second frequency different from the first frequency and causing the generation of a second output voltage; and a processing device (11), the processing device being configured to determine whether the first output voltage and the second output voltage represent a press and the position thereof according to a first reference value and a second reference value.

Description

Technical Field

[0001] Embodiments and examples of the present invention relate to touch devices employing projected capacitive sensing (known as PCAP). More specifically, the present invention relates to touch surfaces known as "multitouch" that enable detection of multiple presses and their locations. Background Art

[0002] These touch devices include a sensor grid composed of very fine wires arranged in a way that forms a matrix array and detects local changes in capacitance introduced by the proximity of a user's finger or any other conductive object. In this way, when a finger touches the surface, a capacitance is formed between the finger and the sensor grid, making it possible to calculate the coordinates of the press.

[0003] A first alternative of PCAP technology consists in detecting mutual capacitance by reading each intersection between each row and column of a matrix array. The change in capacitance during a press is of the order of FemtoFarad.

[0004] According to a second alternative to projected capacitive sensing technology, self-capacitance sensing is implemented, which involves acquiring a press by reading the rows and then the columns of the matrix array. During a press, the self-capacitance variation is approximately picofarads, but when two simultaneous non-aligned presses occur, the matrix array does detect two real presses, but also two phantom presses in the case where the device cannot determine which press is the real press.

[0005] To solve this problem, French patent application No. 2 976 692 proposes a measurement method based on applying a transmission voltage at two different frequencies to a self-capacitance having values ​​representative of the presence of a press and its position on a row or column, depending on the frequency. However, this method can only eliminate phantom presses when there are two presses.

[0006] Therefore, there is a need to be able to detect the presence of more than two real presses while still eliminating the phantom presses that are created in order to best use the touch screen device. Summary of the invention

[0007] Therefore, the object of the present invention is a multi-touch touch device using capacitance detection, the multi-touch touch device comprising:

[0008] - Touch matrix array, and,

[0009] - a voltage generating device configured to generate, for each row and each column of the matrix array, a first input voltage having a first frequency, the first input voltage resulting in the generation of a first output voltage.

[0010] The apparatus comprises means for generating, for each intersection between at least two rows and at least two columns of the matrix array, a second input voltage having a second frequency different from the first frequency and resulting in the generation of a second output voltage, and

[0011] A processing device is configured to determine whether the first output voltage and the second output voltage represent a press and a position thereof based on a first reference value and a second reference value.

[0012] In other words, a first input voltage is sent to each self-capacitor of each row and column, which first input voltage represents the first output voltage after processing. In this way, if the first output voltage is different from the first reference value, a change in capacitance is detected, which means that there is a real press or a phantom press.

[0013] To distinguish between real presses and phantom presses, a second input voltage is sent to each mutual capacitance between at least two rows and at least two columns, the second input voltage representing the second output voltage after processing. If the second output voltage is different from the second reference value, then the press is real.

[0014] The first frequency is advantageously higher than the second frequency.

[0015] The first frequency is for example comprised between 1 MHz and 3 MHz. Ideally, it has a value of about 2 MHz.

[0016] The second frequency representing the identification frequency is for example comprised between 300 KHz and 500 KHz. Ideally, it has a value of about 400 KHz.

[0017] Preferably, the processing device comprises a first synchronous demodulator configured to operate at the first frequency, receive the first output voltage, so as to generate a first DC output voltage.

[0018] Synchronous demodulation can extract a DC component from the signal having the first output voltage, and thus can obtain a signal having the first DC output voltage. The DC output voltage is compared with the first reference value.

[0019] In addition, synchronous demodulation helps to resist electromagnetic interference "EMI".

[0020] Advantageously, the processing device comprises a second synchronous demodulator, said second synchronous demodulator being configured to operate at said second frequency, said second synchronous demodulator being configured to receive the second periodic output voltage in order to generate a second DC output voltage.

[0021] Preferably, the first reference value corresponds to the first DC output voltage when not pressed, and the second reference value corresponds to the second DC output voltage when not pressed.

[0022] The term "equivalent to" means that the first reference value is substantially equal to the first DC output voltage, and means that the second reference value is substantially equal to the second DC output voltage.

[0023] The first reference value is measured by generating the first input voltage on each row and each column without pressing.For example, for a first input voltage of 14V peak to peak and 1MHz, the first reference value is 2.96V after demodulation.

[0024] The second reference value is measured by generating the second input voltage at each intersection between each row and each column without pressing. For example, for a second input voltage of 20V peak-to-peak and 400KHz, the second reference value is 0.45V after demodulation.

[0025] Advantageously, the processing device comprises a storage module configured to store the first reference value and the second reference value.

[0026] After demodulation, the first reference value and the second reference value are stored in order to compare them with the first DC output voltage and the second DC output voltage in order to determine whether there is a real compression and thus locate it.

[0027] Advantageously, the first input voltage and the second input voltage are sinusoidal.

[0028] The sinusoidal shape avoids interference and radiation.

[0029] Preferably, the first frequency and the second frequency are adjustable.

[0030] Preferably, the first reference value and the second reference value are continuously adjusted during scanning of the matrix array.

[0031] According to another aspect, a method for capacitance detection of a multi-touch touch device is provided, the multi-touch touch device comprising a touch matrix array, wherein:

[0032] - for each row and each column of the matrix array, generating a first input voltage, the first input voltage having a first frequency and resulting in the generation of a first output voltage, characterized in that:

[0033] - for each intersection between at least two rows and at least two columns of the matrix array, generating a second input voltage having a second frequency different from the first frequency and resulting in the generation of a second output voltage, and

[0034] - Determining whether the first output voltage and the second output voltage represent a press and its location based on a first reference value and a second reference value.

[0035] Preferably, a first synchronous demodulation of the first output voltage is performed at said first frequency in order to generate a first DC output voltage.

[0036] Preferably, a second synchronous demodulation of the second output voltage is performed at said second frequency in order to generate a second DC output voltage.

[0037] Preferably, the first reference value is equivalent to the first DC output voltage when not pressed, and the second reference value is equivalent to the second DC output voltage when not pressed.

[0038] Preferentially, the first reference value and the second reference value are stored.

[0039] Advantageously, the first input voltage and the second input voltage are sinusoidal.

[0040] Preferably, the first frequency and the second frequency are adjustable.

[0041] Preferably, the first reference value and the second reference value are continuously adjusted during scanning of the matrix array. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Other objects, advantages and features of the invention will appear when examining the following description, which is given by way of non-limiting example only and is given with reference to the accompanying drawings, in which:

[0043] - Figure 1 Shown is a cross section of a projected capacitive touch screen.

[0044] - Figure 2 A longitudinal cross-sectional view of a sensor grid according to a conventional embodiment is shown.

[0045] - Figure 3 Circuit diagram showing the capacitance around the intersections between rows and columns of a grid.

[0046] - Figure 4 An overview diagram showing a projected capacitive touch device according to the present invention. DETAILED DESCRIPTION

[0047] Figure 1A simplified conventional model of a projected capacitive touch screen E is shown.

[0048] The projected capacitive touch screen E comprises a glass plate 1, and the glass plate can project the touch screen.

[0049] The glass plate 1 rests on a first conductive plate 2 which is separated from a second conductive plate 4 by an adhesive and an insulating layer 3 .

[0050] The two conductive plates advantageously consist of a -4 It is made of indium tin oxide (ITO) with a resistivity of Ω.cm.

[0051] The second conductive plate 4 rests on a display screen of LCD (Liquid Crystal Display) type.

[0052] The first conductive plate 2 includes a plurality of conductive thin wires arranged horizontally. The second conductive plate 4 also includes a plurality of conductive thin wires arranged vertically. Figure 2 As shown, the two plates form a fine wire grid in the form of a matrix array 7 , wherein the rows represent the wires of the first conductive plate 2 and wherein the columns represent the wires of the second conductive plate 4 .

[0053] The matrix array is a detection matrix array arranged to detect local changes in capacitance introduced by the proximity of a user's finger or any other conductive designated object coupled to ground.

[0054] Figure 3 A detailed view of the electronic circuitry between rows 2 and columns 4 of the matrix array is shown which results in the local variation of capacitance during pressing.

[0055] Conductive row 2 is coupled to a first self-capacitance CS2. During a depression 80 symbolically represented by a circuit RC comprising a resistor R80 and a capacitor C80, the first self-capacitance CS2 changes by about pico-farads.

[0056] Conductive column 4 is coupled to a second self-capacitor CS1. During the pressing period, the second self-capacitor CS1 also changes by about pico-farad.

[0057] The conductive rows 2 and the conductive columns 4 are connected by a mutual capacitance Cm. The change in said capacitance Cm during the pressing 80 is approximately femtofarads.

[0058] As will be seen below, the conductive row 2 is connected to a resistor through which the current is injected.

[0059] A conductive column 4 is also connected to the resistor.

[0060] Thus, rows 2 are continuously scanned by a first input voltage generated by a current injected into the resistor at a first frequency (eg 1 MHz), and columns 4 of the matrix array 7 are continuously scanned by a second input voltage at a second frequency (eg 400 kHz).

[0061] For example, in the absence of a press, for a first input voltage of 14V peak-to-peak, 1 MHz, the value of the capacitor CS1 is 100 pF. In the presence of a real press or a phantom press, the value of the capacitor CS1 changes by 10 pF.

[0062] In order to distinguish between real pressing and phantom pressing, the capacitance Cm changes only in the case of real pressing. For example, in the case of no pressing, for the second input voltage of 20V peak-to-peak and 400KHz, the value of the capacitance Cm is 80fF. If it is a real pressing, the value of the capacitance Cm changes by 20fF.

[0063] Figure 4 A view showing a touch device using the capacitance detection DIS according to the present invention.

[0064] The device DIS comprises: a touch matrix array 7, the touch matrix array is as follows Figure 3 The device shown includes conductive lines 2 and conductive columns 4 parallel to each other, and a voltage generating device 100, which includes a variable frequency digital voltage generator 8, a digital-to-analog converter 9 (DAC) and an amplifier 10. The generator 8 provides an AC voltage to the touch matrix array 7 through the analog-to-digital converter 9, the amplifier 10 and the resistor R.

[0065] The voltage generating device 100 is configured to generate a first input voltage having a first frequency for each row 2 and each column 4 of the matrix array 7 and to generate a second input voltage having the second frequency for each intersection between at least two rows and at least two columns.

[0066] The device DIS further comprises a processing device 11 configured to determine, based on a first reference value and a second reference value, whether the first output voltage and the second output voltage represent a press and the position thereof.

[0067] Furthermore, it comprises an electronic processing chain including a first 12 and a second 13 acquisition chain, a first analog-to-digital converter (ADC) 14 , a second 15 analog-to-digital converter, a first 16 and a second 17 synchronous demodulator.

[0068] The first synchronous demodulator 16 and the second synchronous demodulator 17 are connected to a filtering device 18 .

[0069] Furthermore, the device DIS comprises a transceiver device 19 (UART for “Universal Asynchronous Receiver Transmitter”) configured to transmit the signal processed by the processing device 11 to another device, such as an LCD screen. The transceiver device is also configured to transmit information / instructions to the processing device 11.

[0070] Finally, the network of multiplexers 20, 21 and 22 is configured to apply the first input voltage and then the second input voltage to the touch matrix array 7 and to route the first output voltage and the second output voltage to the electronic processing chain.

[0071] The operation of the device DIS is as follows.

[0072] The transceiver device 19 first sends the signal 23 to be processed to the processing device 11 .

[0073] After being processed by the processing device 11 , the control signal 24 is sent to the voltage generating device 100 and more precisely to the digital voltage generator 8 , in order to generate said first input signal 25 .

[0074] The digital-to-analog converter 9 then converts the signal 25 into a sinusoidal AC signal 26 having the first frequency. The signal 26 is then amplified by the amplifier 10.

[0075] Thereafter, the resulting signal is sent to the multiplexer 20 , which sends the first input signal 27 to the multiplexer 21 and subsequently sends the second input signal 28 to the multiplexer 22 .

[0076] The first input signal then supplies the network of the conductive rows 2 , and the second input signal then supplies the network of the conductive columns 4 .

[0077] Thereafter, the multiplexer 21 acquires the first output signal and sends it to the multiplexer 20 , and the multiplexer 22 acquires the second output signal and sends it to the multiplexer 20 .

[0078] The first output signal, represented by signal 29 , is sent to the first acquisition chain 12 .

[0079] The second output signal, also represented by the signal 30 , is then sent to the first acquisition chain 12 .

[0080] The first acquisition chain 12 generates a signal 31 which is sent to the first analog-to-digital converter 14 .

[0081] The first analog-to-digital converter 14 generates a digital signal 33 representing a first digital output signal.

[0082] The first output signal 33 is subsequently demodulated by a first synchronous demodulator 16 operating at said first frequency.

[0083] The first synchronous demodulator then generates a signal 35 .

[0084] The signal 35 is then sent to the filtering device 18 , which generates as output a signal 37 , which is then sent to the processing device 11 and the transceiver device 19 .

[0085] Thereafter, a new control signal 24 is sent to the voltage generating device 100 and more precisely to the digital voltage generator 8 in order to generate the first input signal 25 .

[0086] The digital-to-analog converter 9 then converts the signal 25 into a sinusoidal AC signal 26 having said second frequency. The signal 26 is then amplified by the amplifier 10.

[0087] Thereafter, the resulting signal is sent to the multiplexer 20 which sends the input signal 27 to the multiplexer 21 .

[0088] The input signal 27 is then provided at the intersection between the conductive row 2 and the conductive column 4 .

[0089] Advantageously, only intersection points are provided where a press has been detected.

[0090] Thereafter, the multiplexer 22 retrieves the output signal.

[0091] The output signal represented by signal 30 is sent to the second acquisition chain 13 .

[0092] The second acquisition chain 13 generates a signal 32 which is sent to the second analog-to-digital converter 15 .

[0093] The second analog-to-digital converter 15 generates a digital signal 34 representing the digital output signal.

[0094] The output signal 34 is then demodulated by a second synchronous demodulator 17 operating at a second frequency.

[0095] The second synchronous demodulator then generates a signal 36 .

[0096] The signal 36 is then sent to said filtering device 18 which generates as output a signal 37 which is then sent to the processing device 11 in order to distinguish between real and phantom presses.

Claims

1. A multi-touch touch device (DIS) using capacitance detection, the multi-touch touch device comprising: - Touch matrix array (7); - a voltage generating device (100) configured to generate a first input voltage having a first frequency for each row (2) and each column (4) of the matrix array (7), the first input voltage resulting in the generation of a first output voltage, characterized in that the multi-touch touch device comprises a device for generating a second input voltage having a second frequency different from the first frequency for each intersection between at least two rows (2) and at least two columns (4) of the matrix array, the second input voltage resulting in the generation of a second output voltage, and; - a processing device (11) configured to determine, based on a first reference value and a second reference value, whether the first output voltage and the second output voltage represent a press and a position thereof.

2. The multi-touch device (DIS) according to claim 1, wherein: The processing device (11) includes a first synchronous demodulator (16) configured to operate at the first frequency, receive the first output voltage to generate a first DC output voltage.

3. The multi-touch device (DIS) according to claim 2, wherein: The processing device (11) comprises a second synchronous demodulator (17) configured to operate at the second frequency, the second synchronous demodulator (17) configured to receive the second output voltage in order to generate a second DC output voltage.

4. The multi-touch device (DIS) according to claim 3, wherein: The first reference value is equivalent to the first DC output voltage when not pressed, and wherein the second reference value is equivalent to the second DC output voltage when not pressed.

5. The multi-touch device (DIS) according to any one of claims 1 to 4, wherein: The processing device (11) comprises a storage module configured to store the first reference value and the second reference value.

6. The multi-touch device (DIS) according to any one of claims 1 to 4, wherein: The first input voltage and the second input voltage are sinusoidal.

7. The multi-touch device (DIS) according to any one of claims 1 to 4, wherein: The first frequency and the second frequency are adjustable.

8. The multi-touch device (DIS) according to any one of claims 1 to 4, wherein: The first reference value and the second reference value are continuously adjusted during scanning of the matrix array (7).

9. A method for capacitance detection of a multi-touch touch device (DIS), the multi-touch touch device comprising a touch matrix array (7), wherein: - for each row (2) and each column (4) of the matrix array (7), a first input voltage is generated, the first input voltage having a first frequency and resulting in the generation of a first output voltage, characterized in that: - for each intersection between at least two rows (2) and at least two columns (4) of the matrix array (7), generating a second input voltage having a second frequency different from the first frequency and resulting in the generation of a second output voltage, and - determining whether the first output voltage and the second output voltage represent a press and its location based on a first reference value and a second reference value.

10. The method according to claim 9, wherein: A first synchronous demodulation of the first output voltage is performed at the first frequency to generate a first DC output voltage.

11. The method according to claim 10, wherein: A second synchronous demodulation of the second output voltage is performed at the second frequency to generate a second DC output voltage.

12. The method according to claim 11, wherein: The first reference value is equivalent to the first DC output voltage when not pressed, and wherein the second reference value is equivalent to the second DC output voltage when not pressed.

13. The method according to any one of claims 9 to 12, wherein: The first reference value and the second reference value are stored.

14. The method according to any one of claims 9 to 12, wherein: The first input voltage and the second input voltage are sinusoidal.

15. The method according to any one of claims 9 to 12, wherein: The first frequency and the second frequency are adjustable.

16. The method according to any one of claims 9 to 12, wherein: The first reference value and the second reference value are continuously adjusted during scanning of the matrix array (7).

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