Device for improving pressure detection precision of capacitive pressure-sensitive touch panel

Abstract

The invention discloses a device for improving the pressure detection precision of a capacitive pressure-sensitive touch panel, and relates to the technical field of input equipment. The device comprises a capacitive pressure sensor, a touch control chip, a DC-DC booster circuit and a TX signal amplitude amplification circuit, the touch control chip is connected with the DC-DC booster circuit and the TX signal amplitude amplification circuit, the DC-DC booster circuit is connected with the TX signal amplitude amplification circuit, a TX bonding pad welded to a bonding pad ring is arranged on the back face of a pressure-sensitive touch pad, and the TX bonding pad is connected with the pressure-sensitive touch pad. The TX signal amplitude amplifying circuit is connected with the TX bonding pad and the bonding pad ring, and the RX bonding pad is arranged on the back face of the pressure-sensitive touch pad and connected with the touch control chip. Through the DC-DC booster circuit, the TX signal amplitude amplification circuit and the capacitive pressure sensor for improving the capacitance variation, the sensitivity, consistency and linearity of pressure detection of the capacitive pressure-sensitive touch panel are greatly improved. The device has the functions of pressure sensing detection and touch detection at the same time.

Description

Technical Field

[0001] This invention relates to the field of input device technology, and in particular to a device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad. Background Technology

[0002] In existing pressure-sensitive laptop touchpad technology applications, pressure detection typically employs resistive, inductive, and capacitive methods. These three pressure detection principles differ, as do their methods of amplifying, sampling, and detecting pressure signals. Resistive pressure detection chips require support for Wheatstone bridge circuits, differential input, multi-stage preprocessing signal amplification, and a high-precision ADC (16 bits or more); while pressure-sensitive chips need to output a PWM signal with a certain driving capability and a conventional ADC (12 bits); capacitive pressure detection uses the parallel-plate capacitor principle, converting the deformation of the touchpad when pressed into a change in capacitance, and then calculating the pressure magnitude by detecting this change in capacitance.

[0003] Regarding the requirements for pressure sensors, piezoresistive pressure sensors can use strain gauges or piezoresistive sensors, while pressure-sensitive pressure sensors can have the detection coil directly designed on the PCB board without requiring a dedicated sensor device. Capacitive pressure sensors can use stainless steel dome sensors. Although piezoresistive pressure detection offers high accuracy, it is costly and structurally complex. Inductive pressure detection, while low-cost, has very high structural requirements, complex calibration, and poor consistency.

[0004] Capacitive pressure sensing has the lowest cost, simple structure, and requires fewer calibration points. Most importantly, capacitive pressure sensing does not require additional chips. It only requires connecting the capacitive pressure sensor to the capacitance detection channel of the touch chip on the touchpad to detect the change in capacitance between the pressure cooker sensor and the PCB board.

[0005] However, existing capacitive pressure sensors use a stainless steel dome structure. The distance between the dome and the PCB board is generally between 0.1mm and 0.15mm. The deformation surface and the fixed surface of the dome structure are closed and connected. Its deformation stroke is extremely weak, resulting in very small capacitance changes. Therefore, there are problems with low capacitance detection accuracy, poor consistency and linearity. This is the main reason why there are not many mass-produced products of capacitive pressure detection solutions for touch panels.

[0006] Therefore, a new capacitive pressure-sensitive touchpad system solution is needed to improve the capacitance detection accuracy of the pressure sensor in the dome structure and solve the consistency and linearity problems. Summary of the Invention

[0007] The purpose of this invention is to provide a device for improving the pressure detection accuracy of capacitive pressure-sensitive touchpads, thereby achieving the goal of improving the capacitive detection accuracy of existing pressure sensors and solving the technical problems of poor consistency and linearity. The various technical effects of the preferred solutions among the many technical solutions provided by this invention are detailed below.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a capacitive pressure sensor, comprising a pad ring on the periphery, a dome switch disposed within the pad ring, and a connecting portion disposed between the pad ring and the dome switch. The connecting portion lifts the dome switch from the plane of the pad ring, forming a stroke with a set height. The connecting portion includes a hollow structure and connecting ribs arranged at intervals in sequence. The connecting ribs and the dome switch form a deformable structure, and the pad ring, the dome switch, and the connecting ribs together constitute a conductor. When the pad ring is soldered onto the TX pad of a pressure-sensitive touch panel, the dome switch and the corresponding RX pad of the pressure-sensitive touch panel form a parallel plate capacitor. The pad ring and the RX pad form a fixed plate, and the dome switch is a deformable plate.

[0009] In some embodiments, when the pad ring is soldered onto the TX pad of the pressure-sensitive touch panel, the RX pad of the pressure-sensitive touch panel that forms a parallel plate capacitor with the dome switch is coated with insulating green oil.

[0010] In some embodiments, the pressure surface of the dome switch is provided with a soft silicone pressure head.

[0011] As a shared inventive concept, this invention also provides a device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad, comprising a capacitive pressure sensor as described above, and further comprising a touch chip, a DC-DC boost circuit, and a TX signal amplitude amplification circuit; wherein, the touch chip and the DC-DC boost circuit are both connected to the TX signal amplitude amplification circuit, the touch chip is connected to both the DC-DC boost circuit and the TX signal amplitude amplification circuit, and the DC-DC boost circuit is connected to the TX signal amplitude amplification circuit; the TX pad, soldered to the pad ring, is disposed on the back of the pressure-sensitive touchpad, and the TX signal amplitude amplification circuit connects the TX pad to the pad ring; the RX pad is disposed on the back of the pressure-sensitive touchpad and connected to the touch chip.

[0012] In some embodiments, the DC-DC boost circuit boosts the input voltage to a set value and outputs it to the TX signal amplitude amplification circuit. The circuit includes a boost converter U1, a first resistor R1, a second resistor R2, a first capacitor C1, a second capacitor C2, a third capacitor C3, and an inductor L. The input voltage is connected to pin 6 of the boost converter U1. Pin 2 is connected to pins 6 and 4 via inductor L. Pins 2, 4, and 6 are grounded via the first capacitor C1. Pin 5 of the boost converter U1 is connected between the first resistor R1 and the second resistor R2 in series. One end of the first resistor R1 is connected to pin 3 of the boost converter U1, and one end of the second resistor R2 is grounded. One plate of the second capacitor C2 is connected between the first resistor R1 and the second resistor R2 in series, and the other plate is connected to pin 3 of the boost converter U1. One plate of the third capacitor C3 is connected to pin 3 of the boost converter U1, and the other plate is grounded. Pin 3 of the boost converter U1 is the output terminal of the boosted voltage from the DC-DC boost circuit.

[0013] In some embodiments, the TX signal amplitude amplification circuit amplifies the voltage amplitude of the input TX signal to a preset amplitude and then outputs it to the TX pad, including comparator U2, third resistor R3, fourth resistor R4, fifth resistor R5, sixth resistor R6, seventh resistor R7, eighth resistor R8, and fourth capacitor C4. Pins 1 and 7 of comparator U2 are the two output terminals of the TX signal amplitude amplifier circuit, respectively. Pin 1 is pulled up to 15V through the third resistor R3, and pin 7 is pulled up to 15V through the sixth resistor R6. Pin 2 of comparator U2 is connected to the comparison voltage VDD through the fourth resistor R4, and pin 6 of comparator U2 is connected to the comparison voltage VDD through the seventh resistor R7. Pins 3 and 5 of comparator U2 are connected to the input TX signal through the fifth resistor R5 and the eighth resistor R8, respectively. Pin 8 of comparator U2 is connected to the output terminal of the DC-DC boost circuit and grounded through the fourth capacitor C4. The TX signal is a 5V square wave signal, and the comparison voltage VDD is a 3.3V voltage signal.

[0014] In some embodiments, the frequency of the TX signal sent by the touch chip to the TX signal amplitude amplification circuit is 100K~200KHz, and the frequency of the TX signal amplified by the TX signal amplitude amplification circuit is 100K~200KHz.

[0015] In some embodiments, when the pad ring of the capacitive pressure sensor is connected to the TX signal amplitude amplification circuit, electrostatic protection is also enhanced by a TVS diode D.

[0016] In some embodiments, the device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad further includes a main control chip, which is connected to the touch chip and the DC-DC boost circuit.

[0017] In some embodiments, the device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad further includes a motor driver chip and a linear motor connected to the motor driver chip. The motor driver chip is connected to both the touch chip and the main control chip.

[0018] Implementing one of the above-described technical solutions of the present invention has the following advantages or beneficial effects: This invention utilizes a DC-DC boost circuit and a TX signal amplitude amplification circuit to increase the TX coding voltage of the touch chip's normal voltage process to over 15V, reaching a maximum of 20V. This high coding voltage allows for the detection of minute pressure deformations in a capacitive pressure-sensitive touchpad. Simultaneously, a capacitive pressure sensor is incorporated to significantly enhance the capacitance change, greatly improving the sensitivity, consistency, and linearity of pressure detection in the capacitive pressure-sensitive touchpad, effectively overcoming the shortcomings of existing capacitive pressure sensing methods. Furthermore, this invention's capacitive pressure-sensitive touchpad pressure detection device, in addition to pressure sensing functionality, also possesses touch detection capabilities. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of a capacitive pressure sensor structure according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the cross-section AA of a capacitive pressure sensor according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the dimensions of a capacitive pressure sensor according to an embodiment of the present invention; Figure 4 These are front, side, and rear views of a capacitive pressure sensor used for comparison according to an embodiment of the present invention. Figure 5 This is a structural diagram of a device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad according to an embodiment of the present invention; Figure 6 This is a schematic diagram of a mutual capacitance touch chip circuit structure according to an embodiment of the present invention; Figure 7 This is a schematic diagram of a DC-DC boost circuit structure according to an embodiment of the present invention; Figure 8 This is a schematic diagram of a TX signal amplitude amplifier circuit according to an embodiment of the present invention; Figure 9This is an exploded view of a capacitive pressure-sensitive touchpad with four capacitive pressure sensors according to an embodiment of the present invention. Figure 10 This is a schematic diagram of the driving and sensing interface of four capacitive pressure sensors of a capacitive pressure-sensitive touchpad according to an embodiment of the present invention. Figure 11 This is a schematic diagram of a touch chip structure according to an embodiment of the present invention.

[0020] In the diagram: 1. Pad ring; 2. Dome switch; 3. Connector; 31. Hollowed-out structure; 32. Connecting rib; 4. Pressure-sensitive touchpad; 41. Front of pressure-sensitive touchpad; 5. Soft silicone pressure head; 51. Back cover contact surface; 6. RX pad; 7. TX pad; 8. Insulating green solder mask; 9. Solder paste. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, various exemplary embodiments described below will be referenced to the accompanying drawings, which form part of the exemplary embodiments, illustrating various exemplary embodiments that may be used to implement the present invention. Unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. It should be understood that they are merely examples of processes, methods, and apparatuses consistent with some aspects of the present invention disclosed as detailed in the appended claims, and other embodiments may be used, or structural and functional modifications may be made to the embodiments listed herein without departing from the scope and spirit of the present invention.

[0022] In the description of this invention, the term "multiple" means two or more. The terms "connected" and "linked" should be interpreted broadly, for example, they can refer to fixed connections, detachable connections, integral connections, mechanical connections, electrical connections, communication connections, direct connections, indirect connections via an intermediate medium, or connections within two components or interactions between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0023] To illustrate the technical solution described in this invention, specific embodiments are described below, showing only the parts related to the embodiments of this invention.

[0024] Example 1: As Figure 1-2 As shown, a capacitive pressure sensor of this embodiment includes a pad ring 1 disposed on the periphery, a dome switch 2 disposed inside the pad ring 1, and a connecting part 3 disposed between the pad ring 1 and the dome switch 2. The connecting part 3 lifts the dome switch 2 from the plane where the pad ring 1 is located, forming a stroke with a set height.

[0025] In one or more embodiments, the connecting part 3 lifts the dome switch 2 from the plane where the pad ring 1 is located, forming a stroke height of 0.15mm.

[0026] Based on the above embodiments, the connecting part 3 includes a hollow structure 31 and a connecting rib 32 arranged at intervals. The connecting rib 32 and the dome switch 2 form a deformable structure, and the pad ring 1, the dome switch 2, and the connecting rib 32 together constitute a conductor. When the pad ring 1 is soldered onto the TX pad 7 of the pressure-sensitive touch panel 4, the dome switch 2 and the corresponding RX pad 6 on the pressure-sensitive touch panel 4 form a parallel plate capacitor. The pad ring 1 and the RX pad 6 form a fixed plate, and the dome switch 2 is a deformable plate.

[0027] It is understandable that the pad ring 1, the dome switch 2, and the connecting rib 32 together constitute a conductor. When the pad ring 1 is soldered to the TX pad 7 of the pressure-sensitive touchpad 4, the entire capacitive pressure sensor and the detection channel corresponding to the TX pad 7 form a complete capacitive detection channel. When force is applied to the touchpad or the dome switch 2, the dome switch 2 will move towards the RX pad 6, causing the deformable structure to deform, thereby reducing the distance between the parallel plates. Therefore, the change in capacitance can be calculated based on the deformation, and the pressure can be deduced by detecting the change in capacitance, thus realizing the capacitive pressure detection function. When the applied force disappears, the deformable structure returns to its original shape.

[0028] It is understandable that the pressure-sensitive touchpad 4 mentioned above can also be a PCB, FPC, etc. Furthermore, the connecting part 3 employs sequentially spaced perforated structures 31 and connecting ribs 32, such as four perforated structures 31 and four connecting ribs 32. The purpose is to reduce the resistance between the fixed surface (solder pad ring) and the deformable surface (dowel plate), resulting in a larger downward stroke. It is understandable that the number of perforated structures 31 and connecting ribs 32 is not limited to four; the number of perforated structures 31 can also be six, eight, or ten, and the number of connecting ribs 32 can also be six, eight, or ten.

[0029] In one or more embodiments, when the pad ring 1 is soldered onto the TX pad 7 of the pressure-sensitive touch panel 4, the RX pad 6 on the pressure-sensitive touch panel 4, which forms a parallel plate capacitor with the dome switch 2, is coated with insulating green solder mask 8. Therefore, when the dome switch 2 is pressed against the RX pad 6 by an external force, no short circuit occurs upon contact with the RX pad 6.

[0030] In one or more embodiments, the pressure-receiving surface of the dome switch 2 is provided with a soft silicone pressure head 5. In some specific embodiments, the diameter of the dome switch 2 is 8.5 mm, and the diameter of the soft silicone pressure head 5 is 5 mm, making the pressing area of ​​the dome switch 2 (deformation surface) larger and easier to have a larger stroke change. Furthermore, since the soft silicone pressure head 5 is elastic, when the pressure on the rear shell contact surface 51 of the soft silicone pressure head 5 (such as in the case of this capacitive pressure sensor applied to the pressure-sensitive touchpad of a laptop, where the rear shell is a structural component for mounting the pressure-sensitive touchpad, and this structural component is in direct contact with the soft silicone pressure head) is removed, the soft silicone pressure head 5 resets, thereby also causing the dome switch 2 to quickly reset.

[0031] It is understandable that the diameter of the dome switch 2 is 8.5mm, and the diameter of the soft silicone pressure head 5 is 5mm. The diameter of the soft silicone pressure head 5 is smaller than the diameter of the dome switch 2, thus the smaller force application surface acts like a "punch". If the soft silicone is compared to a user's finger, the dispersed pressing force is concentrated into a very small point and then transmitted to the dome switch 2. This can greatly improve the response speed of the dome switch 2's deformation.

[0032] Further, as shown in Figure 3, as a specific example, the outer ring of the capacitive pressure sensor is soldered to the TX pad 7 on the PCB, making the entire sensor a single TX channel. The dome switch 2 (deformation surface) has a φ=8.5mm diameter, and directly below it is the RX pad 6 on the PCB. The outer diameter of the pad ring is φ=13mm, and the inner diameter is φ=10.5mm. When a user presses anywhere on the touch surface of the PCB, the soft silicone pressure head 5 compresses the deformation surface of the dome switch sensor, changing its distance from the RX pad 6. This causes a change in the distance D between the two electrodes, resulting in a change in the capacitance value C. The touch chip detects this capacitance change and, based on the parallel plate capacitance formula, determines whether a press has occurred or the magnitude of the pressure applied.

[0033] The formula for parallel plate capacitance is based on: C = ε*S / (4*π*K*D); Where C represents capacitance, ε represents dielectric constant, S represents the area of ​​the two parallel plates facing each other, K represents electrostatic constant, and D represents the distance from the deformed surface to the RX pad. In specific calculations, the dielectric constant can be 1, and the electrostatic constant can be 8900000000N.

[0034] like Figure 4 As shown, in comparison with the capacitive pressure sensor of this embodiment, another capacitive pressure sensor structure is provided. The difference between this structure and the capacitive pressure sensor of this embodiment is that the fixed surface and the deformable surface are connected by a ring of connecting ribs, and there is no hollow structure. Otherwise, it is the same as the capacitive pressure sensor of this embodiment.

[0035] If a force of 100g is applied to the capacitive pressure sensor of this embodiment, the deformation surface travels approximately 0.04mm, and the distance between the deformed surface of the sensor and the RX pad remains 0.11mm. For ease of calculation, S is defined as a square with a length of 7.53mm and a width of 7.53mm. Substituting into the parallel plate capacitance formula above, we obtain a capacitance of 4.61pF. Subtracting this from the original capacitance of 3.38pF yields a change of 1.23pF.

[0036] Applying a 100g force to the pressure sensor structure under comparison using a 5mm diameter soft silicone indenter resulted in a deformation surface travel change of approximately 0.01mm. The distance between the deformed surface of the pressure sensor and the RX pad remained at 0.14mm. For ease of calculation, S is defined as a square with a length of 7.53mm and a width of 7.53mm. Substituting these values ​​into the parallel plate capacitance formula yields a capacitance of 3.62pF. Subtracting this from the original capacitance of 3.38pF, we obtain a change of 0.24pF.

[0037] Therefore, the capacitive pressure sensor of this embodiment can significantly improve the change in capacitance, and can better solve the problems of poor consistency and linearity of existing capacitive pressure sensors.

[0038] Example 2: Figure 5 As shown, following the same inventive concept, this embodiment provides a device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad. It includes a capacitive pressure sensor as described in Embodiment 1, and further includes a touch chip, a DC-DC boost circuit, and a TX signal amplitude amplification circuit. The touch chip is connected to both the DC-DC boost circuit and the TX signal amplitude amplification circuit; the DC-DC boost circuit is connected to the TX signal amplitude amplification circuit; the TX pad, soldered to the pad ring, is located on the back of the pressure-sensitive touchpad, and the TX signal amplitude amplification circuit connects the TX pad to the pad ring; the RX pad is located on the back of the pressure-sensitive touchpad and connected to the touch chip.

[0039] This invention uses a DC-DC boost circuit and a TX signal amplitude amplification circuit to increase the TX coding voltage of the touch chip's normal voltage process to over 15V, up to a maximum of 20V. The high coding voltage can detect minute pressure deformations of the capacitive pressure-sensitive touchpad. Combined with the capacitive pressure sensor described in Embodiment 1, which can significantly increase the amount of capacitance change, this invention can effectively improve the sensitivity, consistency, and linearity of pressure detection on the capacitive pressure-sensitive touchpad.

[0040] In one or more embodiments, the system further includes a main control chip, a motor drive chip, and a linear motor connected to the motor drive chip. Specifically, the main control chip is connected to both the touch chip and the DC-DC boost circuit, and the motor drive chip is connected to both the touch chip and the main control chip.

[0041] Understandably, motor design allows users to experience pressure sensations, enhancing their tactile experience with products such as laptops, smartphones, and wearable devices.

[0042] Based on the above embodiments, the main control chip can provide operating power VDD to the touch chip, DC-DC boost circuit, and motor drive chip. With operating power VDD provided, the touch chip sends a start signal to the DC-DC boost circuit and a TX signal to the TX signal amplitude amplification circuit. The DC-DC boost circuit, based on the received start signal, boosts the input voltage provided by the main control chip to a set value. Upon receiving the boosted voltage, the TX signal amplitude amplification circuit amplifies the voltage amplitude of the TX signal to a preset amplitude. The amplified TX signal serves as the drive signal for the capacitive pressure sensor. The touch chip acquires the RX signal sensed by the capacitive pressure sensor due to pressure on the front of the pressure-sensitive touchpad in real time, and calculates the magnitude and position of the pressure based on the acquired RX signal using an algorithm. Finally, the calculated magnitude and position of the pressure are transmitted to the main control chip for further processing.

[0043] It is understandable that capacitive pressure-sensitive touchpads, in addition to pressure detection, also have touch detection capabilities, acquiring touch signals from the front of the touchpad through a touch sensor connected to the touch chip. This is existing technology and will not be elaborated upon here.

[0044] Furthermore, the aforementioned main control chip can be configured according to different products. When this device is used for pressure and touch detection in a laptop, the main control chip is the main control chip for the computer; when this device is used for pressure and touch detection in a wearable device, the main control chip is the main control chip for the wearable device.

[0045] It is understandable that the touch chip is a mutual capacitance touch chip. The mutual capacitance detection output data of this mutual capacitance touch chip is mainly related to the coding voltage of the TX signal, the internal operational amplification factor of the chip, and the magnitude of the change in the capacitance under test. ; Where V0 is the output voltage signal of the capacitor under test, V i C is the coding voltage for the TX signal. m The capacitor to be tested, C f This is the internal feedback capacitor of the chip.

[0046] like Figure 6 As shown in the figure, combined with the above formula, it can be seen that to improve the mutual capacitance detection output data of the touch chip, two directions can be considered: First, increase the coding voltage V of TX. iSecondly, increase the magnitude of the change in the measured capacitance Cm; Cf is the internal feedback capacitance of the chip, which determines the amplification factor of the operational amplifier. Once the chip is determined, the maximum value of this parameter is fixed. Currently, due to factors such as chip manufacturing process and cost, the maximum TX coding voltage of touchpad chips is generally around 12V, and some chips even have a maximum of only around 6V. Therefore, in order to increase the TX coding voltage, a boost circuit and a TX amplitude amplification circuit can be added to the external circuitry of the touch chip to increase the TX coding voltage to above 15V. It should be noted that... Figure 6 TXgen is a signal generator, used in this embodiment to generate a square wave of a specific frequency (such as 200KHz), i.e., the TX signal mentioned above.

[0047] like Figure 7 As shown, in one or more embodiments, the DC-DC boost circuit is used to boost the input voltage to a set value and then output it to the TX signal amplitude amplification circuit. The input voltage is provided by the main control chip mentioned above. The DC-DC boost circuit includes a boost converter U1, a first resistor R1, a second resistor R2, a first capacitor C1, a second capacitor C2, a third capacitor C3, and an inductor L. In this configuration, pin 6 of boost converter U1 is connected to the input voltage. Pin 2 is connected to pins 6 and 4 via inductor L. Pins 2, 4, and 6 are grounded via capacitor C1. Resistors R1 and R2 are connected in series. Pin 5 of boost converter U1 is connected between resistors R1 and R2. One end of resistor R1 is connected to pin 3 of boost converter U1, and one end of resistor R2 is grounded. One plate of capacitor C2 is connected between resistors R1 and R2, and the other plate is connected to pin 3 of boost converter U1. One plate of capacitor C3 is connected to pin 3 of boost converter U1, and the other plate is grounded. Pin 3 of boost converter U1 is the output terminal of the DC-DC boost circuit, which outputs a voltage boosted to the set value.

[0048] Based on the above embodiments, the boost converter U1 can be selected from SGM6602 of Sanbang Microelectronics, with a maximum voltage of 20V. That is, the range of the above-mentioned set value is not lower than 15V and not higher than 20V. The first resistor R1 and the second resistor R2 can be selected with different resistance values ​​to set the optimal output voltage value.

[0049] like Figure 8As shown, in one or more embodiments, the TX signal amplitude amplification circuit amplifies the voltage amplitude of the input TX signal to a preset amplitude and then outputs it to the TX pad. The input TX signal is provided by the touch chip. The TX signal amplitude amplification circuit includes a comparator U2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a fourth capacitor C4. In this circuit, pins 1 and 7 of comparator U2 are the two outputs of the TX signal amplitude amplifier circuit. Pin 1 is pulled up to 15V through resistor R3, and pin 7 is pulled up to 15V through resistor R6. Pin 2 of comparator U2 is connected to the comparison voltage VDD through resistor R4, and pin 6 of comparator U2 is connected to the comparison voltage VDD through resistor R7. Pins 3 and 5 of comparator U2 are connected to the input TX signal through resistors R5 and R8, respectively. Pin 8 of comparator U2 is connected to the output of the DC-DC boost circuit and grounded through capacitor C4. The TX signal is a 5V square wave signal, and the comparison voltage VDD is a 3.3V voltage signal. It should be noted that resistors R3 and R6 are pull-up resistors.

[0050] Based on the above embodiments, comparator U2 can be an RS8920 with high-speed and high-voltage performance, which amplifies the TX signal 5V coded square wave signal of the TX channel to 15V (preset amplitude), with a maximum amplitude of 20V.

[0051] Based on the above embodiments, the TX and RX signals used for pressure detection can be selected from the conventional touch channel pins of the touch chip according to the convenient wiring of the capacitive pressure-sensitive touchpad. The touch chip uses a conventional voltage process, which keeps the cost quite low. In addition, depending on the size of the touchpad, 4 or 6 capacitive pressure sensors can be selected. If there are 4, then 2 TX and 2 RX are used; if there are 6, then 3 TX and 3 RX are selected.

[0052] In one or more embodiments, the TX signal sent by the touch chip to the TX signal amplitude amplification circuit is a square wave signal with a voltage of 5V and a frequency of 100KHz~200KHz. The TX signal generated by the TX signal amplitude amplification circuit is a square wave signal with a voltage of 15V and a frequency of 100KHz~200KHz.

[0053] Based on the above embodiments, the TX signal frequency is set to 100KHz~200KHz. The signal delay generated by the comparator will not affect the reception of the RX signal of the touch chip, because one signal cycle of 200KHz is 5us (2.5us for high level and 2.5us for low level), while the delay time of the comparator RS8920 is within 100ns. With the load circuit delay, the total delay is less than 1us. The RX detection of the touch chip is generally set near the falling edge of the TX square wave signal, so the delay of the comparator will not affect the detection of the RX signal.

[0054] In one or more embodiments, the pad ring of the capacitive pressure sensor is further enhanced with electrostatic discharge protection via a TVS diode when connected to the TX signal amplitude amplification circuit.

[0055] like Figure 9-11 As shown, in one specific implementation, four capacitive pressure sensors, FS1-FS4, are set on the pressure-sensitive touchpad, and the four capacitive pressure sensors are respectively located at the four corners of the pressure-sensitive touchpad. The RX pads of sensors FS1 and FS3 correspond to the common port FRX1, and the RX pads of sensors FS2 and FS4 correspond to the common port FRX2; the TX pads of sensors FS1 and FS2 correspond to the common port FTX2, and the TX pads of sensors FS3 and FS4 correspond to the common port FTX1. Pins 19 and 20 of the touch chip are connected to the common ports FRX2 and FRX1 of the capacitive pressure sensors, respectively, and pins 37 and 38 are connected to the input terminals corresponding to pin 3 (pin 3 of comparator U2) and pin 5 (pin 5 of comparator U2), respectively, of the TX signal amplitude amplifier circuit. The output terminal corresponding to pin 1 of the TX signal amplitude amplifier circuit (pin 1 of comparator U2) is connected to the common port FTX1. The common port FTX1 is enhanced with electrostatic discharge protection through TVS diode D1. The output terminal corresponding to pin 7 (pin 7 of comparator U2) is connected to the common port FTX2. The common port FTX2 is enhanced with electrostatic discharge protection through TVS diode D2.

[0056] The above description is merely a preferred embodiment of the present invention. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A capacitive pressure sensor, characterized in that, It includes an outer pad ring, a dome switch inside the pad ring, and a connecting part between the pad ring and the dome switch. The connecting part lifts the dome switch from the plane of the pad ring to form a stroke with a set height. The connecting part includes a hollow structure and connecting ribs arranged at intervals. The connecting ribs and the dome switch form a deformable structure, and the pad ring, the dome switch, and the connecting ribs together constitute a conductor. When the pad ring is soldered to the TX pad of the pressure-sensitive touch panel, the dome switch and the corresponding RX pad on the pressure-sensitive touch panel form a parallel plate capacitor. The pad ring and the RX pad form a fixed plate, and the dome switch is a deformable plate.

2. A capacitive pressure sensor according to claim 1, characterized in that, When the pad ring is soldered onto the TX pad of the pressure-sensitive touchpad, the RX pad of the pressure-sensitive touchpad, which forms a parallel plate capacitor with the dome switch, is coated with insulating green solder mask.

3. A capacitive pressure sensor according to claim 1, characterized in that, The pressure surface of the dome switch is equipped with a soft silicone pressure head.

4. A device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad, characterized in that, The capacitive pressure sensor according to any one of claims 1-3 further includes a touch chip, a DC-DC boost circuit, and a TX signal amplitude amplification circuit; The touch chip is connected to both the DC-DC boost circuit and the TX signal amplitude amplification circuit. The DC-DC boost circuit is connected to the TX signal amplitude amplification circuit. The TX pad, which is soldered to the pad ring, is located on the back of the pressure-sensitive touch panel. The TX signal amplitude amplification circuit connects the TX pad to the pad ring. The RX pad is located on the back of the pressure-sensitive touch panel and is connected to the touch chip.

5. The device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad according to claim 4, characterized in that, The DC-DC boost circuit increases the input voltage to a set value and then outputs it to the TX signal amplitude amplifier circuit, which includes a boost converter U1, a first resistor R1, a second resistor R2, a first capacitor C1, a second capacitor C2, a third capacitor C3, and an inductor L. The input voltage is connected to pin 6 of boost converter U1. Pin 2 is connected to pins 6 and 4 through inductor L. Pins 2, 4, and 6 are grounded through the first capacitor C1. Pin 5 of boost converter U1 is connected between the first resistor R1 and the second resistor R2 in series. One end of the first resistor R1 is connected to pin 3 of boost converter U1, and one end of the second resistor R2 is grounded. One plate of the second capacitor C2 is connected between the first resistor R1 and the second resistor R2 in series, and the other plate is connected to pin 3 of boost converter U1. One plate of the third capacitor C3 is connected to pin 3 of boost converter U1, and the other plate is grounded. Pin 3 of boost converter U1 is the output terminal of the boosted voltage of the DC-DC boost circuit.

6. The device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad according to claim 5, characterized in that, The TX signal amplitude amplifier circuit amplifies the voltage amplitude of the input TX signal to a preset amplitude and outputs it to the TX pad. It includes comparator U2, third resistor R3, fourth resistor R4, fifth resistor R5, sixth resistor R6, seventh resistor R7, eighth resistor R8, and fourth capacitor C4. Pins 1 and 7 of comparator U2 are the two output terminals of the TX signal amplitude amplifier circuit, respectively. Pin 1 is pulled up to 15V through the third resistor R3, and pin 7 is pulled up to 15V through the sixth resistor R6. Pin 2 of comparator U2 is connected to the comparison voltage VDD through the fourth resistor R4, and pin 6 of comparator U2 is connected to the comparison voltage VDD through the seventh resistor R7. Pins 3 and 5 of comparator U2 are connected to the input TX signal through the fifth resistor R5 and the eighth resistor R8, respectively. Pin 8 of comparator U2 is connected to the output terminal of the DC-DC boost circuit and grounded through the fourth capacitor C4. The TX signal is a 5V square wave signal, and the comparison voltage VDD is a 3.3V voltage signal.

7. The device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad according to claim 4, characterized in that, The frequency of the TX signal sent by the touch chip to the TX signal amplitude amplifier circuit is 100K~200KHz, and the frequency of the TX signal amplified by the TX signal amplitude amplifier circuit is 100K~200KHz.

8. The device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad according to claim 4, characterized in that, When the pad ring of the capacitive pressure sensor is connected to the TX signal amplitude amplification circuit, electrostatic protection is also enhanced by a TVS diode D.

9. The device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad according to claim 4, characterized in that, It also includes a main control chip, which is connected to the touch chip and the DC-DC boost circuit.

10. The device for improving the pressure detection accuracy of a capacitive pressure-sensitive touchpad according to claim 9, characterized in that, It also includes a motor drive chip and a linear motor connected to the motor drive chip. The motor drive chip is connected to the touch chip and the main control chip.

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