Dynamic Range Control

Abstract

An apparatus (601) for controlling the dynamic range of a force sensing device includes a plurality of drive lines (606) and a plurality of sense lines (607) arranged to provide a plurality of intersections defining a plurality of keys. Each key includes a sensing element (602) indicative of a variable resistance. Since the controller (603) is configured to convert the analog output from each sensing element into a digital output and the input amplification unit is configured to provide a signal gain, the range of the controller is adapted by the signal gain. The input amplification unit includes a trans-impedance amplification unit (604) connected to a gain resistor (605).

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims priority based on UK Patent Application No. 22 09 719.0 filed on July 1, 2022, the entire content of which is incorporated herein by reference. [Technical Field] The present invention relates to an apparatus for controlling the dynamic range of a force sensing device and a method for controlling the dynamic range of a force sensing device.

Background Art

[0002] Many modern electronic devices use a keyboard to provide an input device for the electronic device. In a conventional keyboard, the keys of the keyboard may use a switch - type mechanism that operates in a traditional on / off pattern. An alternative keyboard includes a membrane in a matrix structure with a plurality of keys, and keys are arranged at each intersection of the matrix.

Summary of the Invention

Problems to be Solved by the Invention

[0003] During use, when several keys of a matrix keyboard are pressed simultaneously, due to the flow of current through the matrix, keys that are not pressed may be activated. This is known as ghosting by non - pressed keys that provide and activate "ghost keys". In addition, a further problem in matrix keyboards is crosstalk. Here, several keys on the same row or the same column of the matrix can be activated when a single key is pressed.

[0004] A further problem with this type of keyboard is that it typically comprises a number of sensing elements configured to measure force. Often, the same number of sensing elements as there are keys on the keyboard are provided. In production and manufacturing, the sensing elements may exhibit manufacturing variations, and in use, when a sensing element corresponding to a particular key is activated, the output response will vary from key to key. Thus, it is difficult to have consistent characteristics and signal ranges for each sensing element. Additionally, force sensors with low sensitivity or resistance changes use a small part of the dynamic range, resulting in a lower sensitivity. Conventional systems utilize a voltage divider input with a force sensing resistor. However, these do not provide a suitable means or construction for optimizing both low and high force inputs. [Means for Solving the Problem]

[0005] [Brief Description of the Invention] According to a first aspect of the present invention, there is provided an apparatus for controlling the dynamic range of a force sensing device, comprising a plurality of drive lines and a plurality of sensing lines arranged to provide a plurality of intersections defining a plurality of keys; each of said keys including a sensing element exhibiting a variable resistance, the apparatus further comprising: a controller configured to convert an analog output from each of said sensing elements into a digital output; and an input amplification unit configured to provide a signal gain, the range of the controller being adapted by the signal gain, the input amplification unit including a transformer-impedance amplification unit connected to a gain resistor: an apparatus is provided. The apparatus may be arranged to form an electronic keyboard or may be incorporated into an electronic device.

[0006] According to a second aspect of the present invention, there is provided a method of controlling the dynamic range of a force sensing device, comprising: providing a device including a plurality of drive lines and a plurality of sense lines arranged to provide a plurality of intersections defining a plurality of keys, each key including a sensing element exhibiting a variable resistance; activating one of the sensing elements in response to a mechanical interaction; supplying a current from the sensing element to an input amplification unit including a transformer-impedance amplification unit connected to a gain resistor in response to the mechanical interaction from the sensing element; receiving a signal gain from a response to the input amplification unit; and adapting a range of a controller configured to convert an analog output from each sensing element into a digital output by the signal gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0007]

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[0008] Embodiments of the present invention will be described by way of example only with reference to the drawings. The detailed embodiments show the best mode known to the inventors and support the claimed invention. However, these are merely examples and should not be used to interpret or limit the claims. These aims are to provide teaching to those skilled in the art. Elements and processes distinguished by ordinal terms such as "first" and "second" do not necessarily define any kind of order or ranking.

[0009] [Detailed Description of the Invention] (FIG. 1) A typical scenario showing an electronic device including a keyboard is shown. Electronic device 101 includes a personal computer having a display 102 and a keyboard 103. In this embodiment, keyboard 103 comprises a plurality of keys 104 arranged in the form of a keyboard membrane. When pressure is applied to each key, each key provides an input to electronic device 101, enabling control of the application being executed on electronic device 101.

[0010] In one embodiment, game applications can be controlled using any one of a plurality of keys 104. In one embodiment, for example, this includes character or similar controls, and it is necessary to press a plurality of keys 104 simultaneously, whereby a plurality of keys are activated simultaneously. In this way, the electronic device 101 is configured to be able to press a plurality of keys simultaneously, which may occur across the entire keyboard membrane on which the keys 104 are disposed.

[0011] (Figure 2) FIG. 2 shows a schematic diagram of an exemplary sensing array that forms a keyboard membrane as previously described with respect to FIG. 1. The sensing array 201 includes a plurality of conductive rows 202 and a plurality of conductive columns 203. In an embodiment, the drive control unit 204 is configured to sequentially supply a voltage to the plurality of conductive columns 203, or drive lines, so that a current can flow through the drive lines. The sensing array 201 further includes a sensing control unit 205 configured to receive outputs from the plurality of conductive rows 202 or sensing lines. In an embodiment, the outputs are received in analog form and are converted to digital outputs by an analog-to-digital converter or similar means as needed.

[0012] In an embodiment, the sensing array 201 includes a plurality of sensing elements disposed at each intersection between the drive lines 202 and the sensing lines 203. Each sensing element includes a material that exhibits a variable resistance in response to an applied force. Since each sensing element is arranged to correspond to one of the plurality of keys of the keyboard 103, when a force is applied to the key (or sensing element), the electrical resistance of the sensing element decreases and current flows through the sensing element and the intersection. In one embodiment, the sensing element includes a quantum tunneling material such as that sold under the name QTC (registered trademark) by the applicant Peratech Holdco Limited.

[0013] In one embodiment, the rows and columns are disposed in an upper conductive layer and a lower conductive layer having a sensing layer that defines sensing elements applied to either the row or the column. When pressure is applied, the sensing layer contacts the opposite conductive layer and is compressed, causing the resistance of the sensing layer to decrease. In this way, the resistance of each sensing element depends on the applied force or area, such as the level of force applied to a key on the keyboard 103. In an alternative embodiment, the sensing element comprises a single conductive layer including a variable resistance material and a conductive finger electrode including a first plurality of meshing first fingers and a second plurality of meshing second fingers on a second layer. In this way, the sensing array can provide a pressure output across two layers. It can be appreciated that in further embodiments, alternative arrangements may be utilized.

[0014] Accordingly, in use, for example, in an embodiment, when the drive line 206 is driven by the drive control unit 204 and the sensing element 207 is activated by the applied force, a current flows through the sensing line 208 to the sensing control unit 205. Although the keyboard with a keyboard membrane is used in the example described, it can be understood that the invention described herein is also applicable to alternative keyboard configurations using a plurality of sensing elements in the manner described with reference to FIG. 2.

[0015] (FIG. 3) FIG. 3 shows a simplified circuit of a keyboard membrane of a force sensing resistor corresponding keyboard in the form of a schematic circuit diagram. In an embodiment, the apparatus 301 comprises a keyboard membrane 302, an input amplification unit 303, and a controller 304.

[0016] The keyboard membrane 302 includes a plurality of drive lines arranged as a plurality of columns 304 and a plurality of sense lines arranged as a plurality of columns 305. At each intersection between the columns 304 and rows 305, there are keys such as keys 306, 307, 308, and 309. In an embodiment, each key exhibits a variable resistance and includes a sensing element represented by a variable resistor. Thus, when a force or pressure is applied to each key, the resistance decreases through the key. The measurement of this force can be performed in an analog manner by the construction described herein and can represent the pressure level applied to a particular key.

[0017] In an embodiment, the input amplification unit 307 is shown as one of a plurality of input amplification units corresponding to each sense row or column. Each input amplification unit is configured to apply a potential to any inactive drive line or inactive sense line. The input amplification unit 307 supplies an output voltage determined when each key is pressed to the controller 304. In an embodiment, each input amplification unit includes a trans-impedance amplification unit that provides a low impedance.

[0018] The controller 304 includes means for converting the analog output to a digital signal for further processing. In an embodiment, this includes an analog-to-digital converter 310, which is configured to convert the analog output from each key or sensing element to a digital output when a force is applied to the corresponding key for further processing. In an alternative embodiment, the analog-to-digital converter could be replaced by an alternative device such as a Schmitt trigger that converts the output from the input amplification unit 303 from analog to digital. In the illustrated embodiment, the keyboard membrane 302 has 3 rows and 3 columns. In reality, many keyboard membranes are much larger, but it can be understood that they operate on substantially the same principle.

[0019] (Figure 4) Figure 4 is again a schematic diagram of the apparatus 301. In Figure 4, forces are being applied simultaneously to keys 306, 307, 308, and 309. In an embodiment, when a force is applied to each of the keys, the resistance at each key decreases. This allows current to flow more freely from the input provided on the drive line to the output, through the input amplification unit 303 to the controller 304.

[0020] In an embodiment, when a voltage is applied to drive line 304B and key 309 is read, current is transmitted along 304B and then transmitted through amplification unit 403 across line 305B to analog-to-digital converter 310. Each of keys 306, 307, and 308 is depressed, but these are blocked by the high voltage of 401. Key 307 is activated in the same column as key 309, but the conductive path through key 307 is not read and interference is prevented by amplification unit 403, allowing for control of the voltage within the circuit.

[0021] In an alternative embodiment, the voltage amplification unit comprises a voltage buffer amplification unit configured to activate the voltage potential of each of the non-active drive lines and non-active sense lines, and a multiplexer configured to sequentially activate each drive line. This is an alternative to placing a trans-impedance amplification unit on each sense line. This can reduce the number of components required for the keys and is particularly beneficial in a large sense array matrix.

[0022] In an example including the illustrated sensing elements, since the full spectrum of forces for a given pressure is provided, it is advantageous to obtain the reading in analog form. During the scanning process, each key including the sensing element can be modeled as a variable resistor indicating the change in resistance due to the applied force. Each trans-impedance amplification unit supplies an input voltage controlled by a virtual ground that allows the absorption of current into the input node. Thus, the voltage can be controlled at the input node and, since current is absorbed, the flow of current through the trans-impedance amplification unit can be interrupted.

[0023] In this way, in the present invention, any number of keys can be pressed at a specific time, and there is no limitation on the size of the matrix array. Thus, in the application to a game, multiple keys can be pressed simultaneously, and by increasing the size of the matrix, it is possible to control this with respect to a keyboard of a larger size.

[0024] (FIG. 5) FIG. 5 is a graph showing the typical force detection characteristics of detection elements used in a typical detection array according to the present application. FIG. 5 shows a plot of a plurality of force-resistance curves 501, 502, and 503, each representing an individual detection element. Curve 502 represents the average force-resistance response of a typical detection element according to the present invention. However, in the case of a plurality of detection elements constituting an electronic keyboard such as the electronic keyboard 103 of FIG. 1, it can be understood that variations 504 in the force-resistance response shown in curves 501 and 503 occur from each detection element. Variation 504 is important and may affect the output from a plurality of keys 104. Therefore, this factor must be considered when optimizing the response of any of the keys 104.

[0025] In an embodiment, the force-resistance response presents a dynamic range 505 of the force detection device. In a conventional system, the corresponding dynamic range 506 of an analog-to-digital converter (ADC) matches the dynamic range of the detection element 505 if there is no system in which further calibration is performed.

[0026] Therefore, in this way, any force detection device having a low sensitivity or resistance change can utilize only a small portion of the dynamic range 506, which leads to poor sensitivity, a poor signal-to-noise ratio (SNR), poor resolution, and potentially low yield. Thus, in some applications, it may be sufficient to utilize the dynamic range 505 of the force sensing element as the same as the ADC dynamic range 506, but there remains a need to apply the circuit so that the dynamic range 506 of the analog-to-digital converter can be adapted.

[0027] (Figure 6) FIG. 6 is a schematic diagram of a circuit that would be utilized to control the dynamic range of an analog-to-digital converter (ADC). The illustrated schematic circuit diagram shows an inverting amplification mode. However, it can be understood that the examples described herein can be further provided as a non-inverting version by following substantially the same principles as those described herein. However, for simplicity, in this application, the inverting amplification mode is focused on throughout, and a single sensing element that would further form part of the sensing array and the electronic keyboard described above.

[0028] In an embodiment, the apparatus 601 includes a sensing element 602 that provides a variable resistance force sensing resistor. The sensing element 602 is represented as a variable resistor and indicates a variable resistance. The controller 603 includes an analog-to-digital converter configured to convert an analog output from the force sensing resistor 602 to a digital output. The sensing element 602 is arranged with a gain resistor 605 and is electrically connected to the controller 603 via a trans-impedance amplification unit 604 configured to convert a signal from the sensing element 602 to a voltage for sampling by the controller 603.

[0029] Conventionally, the transformer-impedance amplification unit 604 provides a signal gain through the resistor 605, and this signal gain is utilized to adapt the minimum measurable resistance from the sensing element 602 to a lower range of the controller 603. In the inverting amplification mode as shown in FIG. 6, it can be understood that the resistance constituted by the sensing element 602 is low and is measured at the lower limit of the dynamic range of the analog-to-digital converter. In an embodiment where the amplification unit is provided in the non-inverting amplification mode, the upper limit of the dynamic range of the analog-to-digital converter is constituted by the corresponding circuit.

[0030] In an embodiment, a voltage V + is provided to activate the sensing element 602 along the drive line 606. When starting up, the voltage passing through the sensing element 602 passes through the sensing element 602 via the resistor 605 and the transformer-impedance amplification unit 604, and supplies a voltage output V OUT . In this mode, the controller 603 is configured in the single-ended mode and measures the output voltage V REF between zero and the reference voltage V OUT . Therefore, the output voltage can be calculated from the resistance values passing through the force sensing element 602, the gain resistor 605, and the transformer-impedance amplification unit 604.

[0031] The dynamic range of the analog-to-digital converter can thus be calculated to be in the range from infinity to the value obtained by multiplying the reference voltage (V REF ) by the gain resistance and dividing by the reference voltage (T REF ) from the transformer-impedance amplification unit 604. In a conventional system, the parameters are usually set such that the dynamic range of the ADC603 covers the entire dynamic range of the sensing element 602. As described above, in some cases, especially when there are large fluctuations in the sensing element, it may be difficult to achieve a good signal-to-noise ratio. Therefore, in some applications, since it is desirable to narrow the resistance range, not only the minimum resistance but also the maximum measurable resistance may be limited. Thus, the example shown in FIG. 6 would be adapted to use various combinations of reference voltages to enable adjustment of the dynamic range.

[0032] For example, if the reference voltage (V REF ) is lowered to a value below the voltage (T REF ) from the trans-impedance amplifier unit, this can provide a compensation effect similar to including an offset resistor. This method would be able to generate a more appropriate dynamic range according to the present invention.

[0033] (FIG. 7) Thus, the embodiments described herein can provide an alternative approach that matches the example shown in FIG. 7. FIG. 7 shows an alternative force-resistance graph that replicates the curves 501, 502, and 503 previously shown in FIG. 5. Each of the curves 501, 502, and 503 is associated with each sensing element that would be present in an exemplary electronic keyboard.

[0034] The embodiment shows an application range 701 that preferably has a sensitivity related to the sensing element used for a particular application. Thus, in the embodiment, as shown in FIG. 7, the dynamic range 702 of the analog-to-digital converter can be reduced. Thus, the circuit described herein adjusts the performance of the sensing element to the more desirable application range 701 while adapting to the variations between each sensing element 504. This optimized range can be generated by the above-described apparatus with respect to FIG. 6, but can also be further provided by the embodiment described with respect to FIG. 8.

[0035] (Figure 8) Figure 8 shows a schematic circuit diagram for optimizing the dynamic range of an analog-to-digital converter along the graph shown in Figure 7. The embodiment of Figure 8 is substantially the same as the embodiment of Figure 6, except that it includes an offset resistor 801 that provides further control and conversion of the response from the sensing element 802 by limiting the highest measurable resistance. Thus, in the embodiment, the apparatus further comprises a trans-impedance amplification unit 803 and a gain resistor 804, which are also electrically connected between the sensing element 802 and a controller including an analog-to-digital converter 805.

[0036] Similarly, the voltage V + is applied along the drive line 806 and transmitted along the sense line 807, following which the sensing element 802 is activated. In the embodiment, the combination of resistors 801 and 804 enables both the upper and lower limits of the resistance range to be controlled, allowing the dynamic range of the analog-to-digital converter to be fully optimized to match the range of the force sensing element used in a particular application.

[0037] (Figure 9) In a further embodiment, a further reconfiguration of the apparatus is provided that includes dynamic switching to provide further flexibility with respect to yield and signal-to-noise ratio output. In the embodiment, the force-resistance curves 501, 502, and 503 corresponding to a plurality of sensing elements have variations 504 and an application range 701. However, in addition to this, the calibration of each sensing element may result in three separate dynamic ranges 901, 902, and 903 being generated for the analog-to-digital controller. The dynamic ranges 901, 902, and 903 correspond to the force-resistance curves 501, 502, and 903, respectively.

[0038] In this way, the apparatus could be configured to allow the selection of each of the dynamic ranges 901, 902, and 903 according to the requirements of the corresponding application. These narrow ranges can be utilized to improve the quality of the signal-to-noise ratio, particularly where the force-resistance response includes a substantially low gradient. As the range becomes wider, the yield will be further improved because a sensing element with a large resistance change can be operated within the measurement range of the analog-to-digital converter. Figure 10 shows an exemplary circuit that provides this.

[0039] (Figure 10) In an embodiment, the sensing element 1001 is electrically connected to an analog-to-digital converter 1002 via a transformer impedance amplification unit 1003 and a gain resistor 1004. An offset resistor 1005 is further included, and an electric switch 1006 is provided that is configured to activate and deactivate the offset resistor 1005 as needed. Thus, in this embodiment, the range can be further controlled by activating and deactivating the switch 1006 as needed. This is suitable for enabling control of both the upper and lower limits of the range. This provides a relatively low-cost solution since it only requires providing single switch control and multiple fixed resistors in addition to the existing circuit.

[0040] (Figure 11) Figure 11 is a further schematic diagram of a circuit in a further exemplary embodiment according to the present invention. In an embodiment, the circuit of Figure 11 is substantially similar to the circuit shown in Figure 8, and the circuit includes a sensing element 1101 and an analog-to-digital converter 1102 that are electrically connected via a transformer impedance amplification unit 1103 and a resistor 1104. The embodiment further includes an offset resistor 1105.

[0041] In an embodiment, the fixed resistors in Figures 8 and 10 are replaced by a high-resolution digital control resistor array (RDAC). This provides a more sophisticated solution incorporated into a variable resistor. However, it can be understood that its use depends on cost.

[0042] (Figure 12) Figure 12 is a schematic diagram of a circuit of a further embodiment including dynamic switching. In an embodiment, the sensing element 1201 is connected to the analog-to-digital converter 1202 by the transformer impedance amplifier unit 1203 and the gain resistor 1204 again. In an embodiment, the reference voltage V from the analog-to-digital converter 1202 REF and the reference voltage T from the transformer impedance amplifier unit 1203 REF are digitally controlled by a voltage analog-to-digital converter (DAC).

[0043] Accordingly, in the embodiment of Figure 12, the n-bit analog-to-digital converter 1205 is connected to the analog-to-digital converter 1202, and the further n-bit analog-to-digital converter 1206 is electrically connected to the transformer impedance amplifier unit 1203. Correspondingly, the further digital control and dynamic switching of the reference voltages V REF and T REF become possible respectively.

[0044] This combination of reference voltages would be able to provide a substantially similar range of optimization of the analog-to-digital converter shown above using corresponding resistors. However, this particular option would be more cost-effective than the example illustrated in Figure 11, specifically when one or more voltage DACs are already incorporated in the system.

Claims

1. An apparatus for controlling the dynamic range of a force sensing device, comprising: a plurality of drive lines and a plurality of sense lines arranged to provide a plurality of intersections defining a plurality of keys; each of the keys including a sensing element exhibiting a variable resistance, the apparatus further comprising: a controller configured to convert an analog output from each of the sensing elements into a digital output; and an input amplification unit configured to provide a signal gain, wherein the range of the controller is adapted by the signal gain, and the input amplification unit includes a transformer impedance amplification unit connected to a gain resistor: the apparatus.

2. The apparatus according to claim 1, wherein the signal gain is provided by the gain resistor.

3. The apparatus according to claim 1 or claim 2, wherein the gain resistor includes a high-resolution digital control resistor array.

4. The apparatus according to any one of claims 1 to 3, further comprising an offset resistor arranged to limit the upper limit of the resistance measured from the sensing element.

5. The apparatus according to claim 4, further comprising an electrical switch configured to activate and deactivate the offset resistor.

6. The apparatus according to claim 4 or claim 5, wherein the offset resistor includes a high-resolution digital control resistor array.

7. The apparatus according to any one of claims 1 to 6, wherein the input amplification unit is further configured to supply a voltage potential to each of the inactive drive lines and the inactive sense lines.

8. The apparatus according to any one of claims 1 to 7, wherein the plurality of drive lines are arranged as a plurality of columns and the plurality of sense lines are arranged as a plurality of columns to form a sensing array.

9. The apparatus according to any one of claims 1 to 8, wherein each of the sensing elements includes a quantum tunneling material.

10. The apparatus according to any one of claims 1 to 9, further comprising a voltage analog-to-digital converter configured to control a reference voltage.

11. The apparatus according to claim 10, wherein the reference voltage is a reference voltage from the controller.

12. The apparatus according to claim 10, wherein the reference voltage is a reference voltage from the input amplification unit.

13. The apparatus according to any one of claims 1 to 12, wherein the apparatus forms part of an electronic keyboard.

14. An electronic device including the apparatus according to any one of claims 1 to 13.

15. Providing a plurality of drive lines and a plurality of sense lines arranged to provide a plurality of intersections defining a plurality of keys, each key including a sensing element exhibiting a variable resistance; Activating one of the sensing elements in response to a mechanical interaction; Supplying current in response to the mechanical interaction from the sensing element to an input amplification unit including a transformer impedance amplification unit connected to a gain resistor; Receiving a signal gain from a response to the input amplification unit; and Adapting the range of a controller configured to convert an analog output from each sensing element to a digital output by the signal gain; A method of controlling a dynamic range of a force sensing device, comprising.

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