Capacitive sensing device, parasitic capacitance compensation method, electronic device and chip

Abstract

The application discloses a capacitive sensing device, a parasitic capacitance compensation method, an electronic device and a chip. The capacitive sensing device comprises a sensing capacitor, a sensing electrode of the sensing capacitor being connected to a first fixed potential end in an on-off mode; a capacitance detection module connected to the sensing electrode of the sensing capacitor through a conductive path, the capacitance detection module being used for detecting the sensing capacitor and outputting a detection signal corresponding to a variation of a capacitance value of the sensing capacitor; and a compensation module used for providing a parasitic compensation capacitor, the compensation module comprising a current compensation unit, the current compensation unit comprising a current source connected to the conductive path, the current compensation unit being used for controlling a charging and discharging process of the current source on the conductive path to provide an equivalent parasitic compensation capacitor. The capacitive sensing device has a high parasitic capacitance compensation capability.

Description

Technical Field

[0001] This application relates to the field of integrated circuit technology, specifically to a capacitance sensing device, a parasitic capacitance compensation method, an electronic device, and a chip. Background Technology

[0002] A capacitive sensor is a device that converts a measured physical or mechanical quantity into a change in capacitance. By using a capacitive sensor, the change in the sensing capacitance can be converted into an electrical signal output. By measuring the magnitude of the electrical signal, the magnitude of the change in the measured quantity can be determined.

[0003] The sensing capacitance Cx of a capacitive sensor consists of two parts: parasitic capacitance Cp and variable capacitance ΔC, where Cx = Cp + ΔC. Please refer to [reference needed]. Figure 1 This is a schematic diagram of a capacitive sensor with a self-capacitance structure. The capacitive sensor includes an electrode 11, which forms an inherent parasitic capacitance Cp with ground 10. When a finger approaches the sensor, a variable capacitance ΔC is formed between the finger and the electrode 11. Since the human body has a relatively large capacitance, its potential is equivalent to ground. Therefore, the variable capacitance ΔC is related to the distance between the finger and the electrode 11. By detecting the magnitude of the variable capacitance ΔC, it is possible to determine whether a finger is close or to calculate the distance between the finger and the electrode 11.

[0004] In practical applications, if the parasitic capacitance Cp is too large, it can easily lead to signal saturation in the capacitance detection circuit, making it impossible to detect changes in the variable capacitance ΔC. Existing capacitance sensors typically incorporate a capacitance compensation module, including a capacitor array, within the sensor chip to compensate for the inherent parasitic capacitance. By selecting a compensation capacitor Cb1 that is as close as possible to the size of the parasitic capacitance Cp, the change in the capacitance sensor's output signal is near zero when the variable capacitance ΔC = 0, ensuring that changes in the variable capacitance ΔC are effectively reflected in the output signal. However, due to the large capacitor area and limitations imposed by chip size and cost, the size of the compensation capacitor that can be implemented within the chip is limited, typically below 200pF. When the external parasitic capacitance exceeds the compensation range of the internal capacitance compensation module, the capacitance sensor will malfunction.

[0005] Improving the parasitic capacitance compensation capability of capacitive sensing devices is an urgent problem to be solved. Summary of the Invention

[0006] In view of this, this application provides a capacitance sensing device, a parasitic capacitance compensation method, an electronic device, and a chip to solve the problem of insufficient parasitic capacitance compensation capability in existing systems.

[0007] This application provides a capacitance sensing device, comprising: a sensing capacitor, the sensing electrode of which is connectable to a first fixed potential terminal; a capacitance detection module connected to the sensing electrode of the sensing capacitor via a conductive path, the capacitance detection module being used to detect the sensing capacitor and output a detection signal corresponding to the change in capacitance of the sensing capacitor; and a compensation module for providing parasitic compensation capacitance, the compensation module including a current compensation unit, the current compensation unit including a current source connected to the conductive path, the current compensation unit being used to control the charging and discharging process of the conductive path by the current source to provide an equivalent parasitic compensation capacitance.

[0008] Optionally, the capacitance detection module is further configured to receive a reference voltage, wherein the capacitance change corresponds to the offset between the detection signal and the reference voltage.

[0009] Optionally, the current compensation unit further includes a third switch, which is connected in series with the current source. One end of the series path of the third switch and the current source is connected to the first node of the conductive path, and the other end is connected to the second fixed potential terminal. A second switch is connected between the first node and the sensing electrode. A first switch is connected between the sensing electrode and the first fixed potential terminal.

[0010] Optionally, the capacitance detection module includes an amplifier, a feedback capacitor, and a fourth switch. The negative input terminal of the amplifier is connected to the sensing electrode, and the positive input terminal is used to input a reference voltage. The two ends of the feedback capacitor are respectively connected to the output terminal and the negative input terminal of the amplifier. The fourth switch is connected in parallel across the two ends of the feedback capacitor.

[0011] Optionally, it may also include: a control module, which is connected to the first switch, the second switch, the third switch and the fourth switch, for controlling the on / off state of each switch.

[0012] Optionally, the control module is used to output control signals to the first switch, the second switch, the third switch, and the fourth switch, so that the detection module detects the sensing capacitance according to a detection cycle; the detection cycle includes a first stage and a second stage, and the control module is used to control the first switch and the fourth switch to be turned on and control the second switch and the third switch to be turned off in the first stage; in the second stage, the control module controls the first switch and the fourth switch to be turned off, controls the second switch to be turned on and the third switch to be turned on, and turns off the third switch after a preset time.

[0013] Optionally, within the configurable range, the current magnitude of the current source is configured as a preset compensation current, such that when the capacitance value of the sensing capacitor does not change, the offset between the detection signal output by the capacitance detection module and the reference voltage is less than a first threshold.

[0014] Optionally, the compensation module further includes a capacitor compensation unit, which is connected to a second node of the conductive path, and the second node is located between the second switch and the first node.

[0015] Optionally, the capacitor compensation unit includes a capacitor array consisting of several capacitors connected in parallel. One end of each capacitor is connected to the second node, and the other end is connected to a driving terminal. Each end of each capacitor is connected to the circuit through a corresponding control switch.

[0016] Optionally, the driving terminal is used to apply a periodic driving voltage, the high-level moment of the driving voltage corresponding to the on moment of the second switch.

[0017] Optionally, the effective capacitance value of the capacitance compensation unit is configured to a preset capacitance value, such that when the capacitance value of the sensing capacitor does not change, the offset between the detection signal output by the capacitance detection module and the reference voltage is less than a second threshold, and the second threshold is less than the first threshold.

[0018] Optionally, it also includes: a signal processing module, connected to the output terminal of the capacitance detection module, for processing the detection signal and outputting a digital signal.

[0019] This application also provides an electronic device, characterized in that it includes a capacitive sensing device as described in any of the preceding claims.

[0020] This application also provides a method for parasitic capacitance compensation of a capacitance sensing device as described in any of the preceding claims, comprising: acquiring a detection signal output by the capacitance detection module when the capacitance value of the sensing capacitor has not changed; and adjusting the current source according to the detection signal so that the offset between the detection signal output by the capacitance detection module and the reference voltage is less than a first threshold.

[0021] Optionally, when the compensation module of the capacitance sensing device includes a capacitance compensation unit, it further includes: after the current source is adjusted, configuring the effective capacitance value of the capacitance compensation unit so that the offset between the detection signal output by the capacitance detection module and the reference voltage is less than a second threshold, and the second threshold is less than a first threshold.

[0022] This application also provides a chip including the capacitive sensing device as described in any of the preceding claims.

[0023] The compensation module of the capacitance sensing device described in this application includes a current compensation unit. The current compensation unit includes a current source connected to a conductive path between the sensing capacitor and the capacitance detection module. Through the charging and discharging process of the conductive path by the current source, charge transfer is achieved, making the current compensation unit in the circuit equivalent to the charging / discharging effect of an equivalent capacitor. Therefore, parasitic capacitance compensation can be performed through the current compensation unit. Since the current source generating circuit includes structures such as transistors, the size of the circuit components is small, occupying a small chip area. With limited chip area, a larger parasitic compensation capacitance can be provided, thereby improving the parasitic capacitance compensation capability of the capacitance sensing device.

[0024] Furthermore, the compensation module also includes a capacitor compensation unit. Since the adjustment accuracy of the current source is limited, the accuracy of parasitic capacitance compensation solely through the current compensation unit is also limited. By further using a capacitor compensation unit, the higher capacitance accuracy of the capacitors within the unit can be achieved, thereby improving the accuracy of parasitic capacitance compensation and ultimately enhancing the detection accuracy of the capacitance sensing device. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of an existing self-capacitive capacitive sensor.

[0027] Figure 2 This is a schematic diagram of the structure of the capacitive sensing device according to the first embodiment of this application;

[0028] Figure 3 This is a schematic diagram of the structure of the capacitive sensing device according to the second embodiment of this application;

[0029] Figure 4a This is a schematic diagram of the structure of the capacitive sensing device according to the third embodiment of this application;

[0030] Figure 4b This is a schematic diagram of the driving voltage of the driving terminal to which the capacitive sensing unit of the capacitive sensing device of the third embodiment of this application is connected.

[0031] Figure 5 This is a schematic diagram of the structure of the capacitive sensing device according to the fourth embodiment of this application;

[0032] Figure 6This is a schematic diagram of the structure of the capacitive sensing device according to the fifth embodiment of this application;

[0033] Figure 7 This is a timing diagram of the control signals of each switch during the operation of the capacitive sensing device according to the fifth embodiment of this application;

[0034] Figure 8 This is a schematic diagram of the structure of the capacitive sensing device according to the sixth embodiment of this application;

[0035] Figure 9 This is a timing diagram of the control signals of each switch during the operation of the capacitive sensing device according to the sixth embodiment of this application;

[0036] Figure 10 This is a schematic flowchart of a parasitic capacitance compensation method for a capacitance sensing device according to an embodiment of this application.

[0037] Figure 11 This is a schematic flowchart of a parasitic capacitance compensation method for a capacitance sensing device according to another embodiment of this application. Detailed Implementation

[0038] As described in the background section, existing capacitive sensing devices have limited parasitic capacitance compensation capabilities due to the limited area available within the chip for forming compensation capacitors. Even forming larger compensation capacitors to improve parasitic capacitance compensation capabilities would increase chip area and cost.

[0039] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In the absence of conflict, the following embodiments and their technical features can be combined with each other.

[0040] Please refer to Figure 2 This is a schematic diagram of the structure of the capacitive sensing device according to the first embodiment of this application.

[0041] In this embodiment, the capacitance sensing device includes a sensing capacitor 110, a capacitance detection module 120, and a compensation module 130.

[0042] The sensing electrode A of the sensing capacitor 110 can be switched on and off connected to the first fixed potential terminal D1.

[0043] The capacitance detection module 120 is connected to the sensing electrode A of the sensing capacitor 110 through a conductive path. The capacitance detection module 120 is used to detect the sensing capacitor 110 and output a detection signal VO corresponding to the change in capacitance of the sensing capacitor 110.

[0044] The compensation module 130 is used to provide parasitic compensation capacitance, and the compensation module 130 includes a current compensation unit 131. The current compensation unit 131 includes a current source Icomp connected to the conductive path, and the current compensation unit 131 is used to control the charging and discharging process of the current source Icomp on the conductive path to provide an equivalent parasitic compensation capacitance.

[0045] Since the current source Icomp is typically generated by transistors, and transistors are relatively small, the chip area occupied by the current source Icomp is small. In some embodiments, the current source Icomp can also utilize current source structures in other circuits within the chip, further reducing the chip size. To provide a larger parasitic compensation capacitance, larger transistors can be used so that the current source Icomp can provide a larger current, thereby providing a larger equivalent capacitance. Since the chip size occupied by the current source Icomp to provide the same equivalent capacitance is much smaller than that occupied by the actual capacitor, in the case of limited chip area, this embodiment can provide a larger parasitic compensation capacitance through the current compensation unit 131, exhibiting greater parasitic capacitance compensation capability, thus broadening the application scenarios of the capacitive sensing device.

[0046] In this embodiment, the capacitance value of the sensing capacitor 110 is Cx. The sensing capacitor 110 has a self-capacitance structure and includes a sensing plate as a sensing electrode A. The sensing electrode A is connected to the capacitance detection module 120, and a parasitic capacitance is formed between the sensing electrode A and ground.

[0047] In other embodiments, the sensing capacitor 110 may further include two electrode plates, one of which serves as sensing electrode A and is connected to the capacitance detection module 120, while the other electrode plate is grounded. The capacitance value of the sensing capacitor 110 is Cx = Cp + ΔC; where Cp is the parasitic capacitance, including the fixed capacitance between sensing electrode A and ground, as well as parasitic capacitance generated by other circuit structures, and ΔC is the capacitance change. When a finger approaches the sensing capacitor, ΔC changes, and ΔC is the quantity to be detected during the capacitance sensing detection process.

[0048] In this embodiment, the sensing electrode A is connected to the first fixed potential terminal D1 via a first switch K1. By controlling the on / off state of the first switch K1, the connection state between the sensing electrode A and the first fixed potential terminal D1 is controlled. In other embodiments, other structures, such as a selector, can also be used to achieve a switchable connection between the sensing electrode A and the first fixed potential terminal.

[0049] In this embodiment, the capacitance detection module 120 is also connected to the reference voltage terminal to receive the reference voltage VCM, and the capacitance change corresponds to the offset between the detection signal VO and the reference voltage VCM.

[0050] In this embodiment, the current compensation unit 131 is connected to the first node B on the conductive path. The current compensation unit 131 includes a current source Icomp and a third switch K3, which are connected in series. One end of the series path of the third switch K3 and the current source Icomp is connected to the first node B of the conductive path, and the other end is connected to a second fixed potential terminal. A second switch K2 is connected between the first node B and the sensing electrode A. The second switch K2 can control the on / off state between the compensation module 130, the capacitance detection module 120, and the sensing capacitor 110. When the second switch K2 is on, the compensation module 130 performs parasitic capacitance compensation, and the detection module 120 performs capacitance detection.

[0051] The third switch K3 is used to control the on / off state between the first node B and the second fixed potential terminal D2. When the third switch K3 is off, the current path between the first node B and the second fixed potential terminal D2 is broken; when the third switch K3 is on, the current path between the first node B and the second fixed potential terminal D2 is connected. By controlling the on / off state of the third switch K3, the charging and discharging process of the current source on the conductive path can be controlled, so that the current compensation unit 122 can function as an equivalent capacitor in the circuit: when the third switch K3 is on, the current path is connected, which is equivalent to charging / discharging the equivalent capacitor; when the third switch K3 is off, it is equivalent to the DC blocking effect of the equivalent capacitor. Thus, by controlling the on / off state of the third switch K3, the current compensation unit 122 can provide an equivalent capacitor for parasitic capacitance compensation. The larger the current of the current source Icomp and / or the longer the current conduction time (the conduction time of the third switch K3), the larger the capacitance value of the equivalent capacitor. Therefore, the parasitic capacitance compensation capability can be adjusted by setting the current magnitude of the current source Icomp and / or the conduction time of the third switch K3, thereby adjusting the equivalent capacitance provided by the current compensation unit 122.

[0052] Preferably, the sensing electrode A is located outside the chip containing the capacitance detection module 120 and the compensation module 130. In one embodiment, the chip containing the capacitance detection module 120 and the compensation module 130 is mounted on a PCB board, and the sensing capacitor 110 is also disposed on the PCB board. The sensing electrode A of the sensing capacitor 110 can be a conductive metal piece on the PCB board, connected to the capacitance detection module 120 and the compensation module 130 through the chip's external interface.

[0053] Please refer to Figure 3 This is a schematic diagram of the capacitive sensing device according to the second embodiment of the present invention.

[0054] exist Figure 2 Based on the illustrated embodiment, in this embodiment, the compensation module 130 of the capacitance sensing device further includes a capacitance compensation unit 132. The capacitance compensation unit 132 is connected to a second node C on the conductive path between the capacitance detection module 120 and the sensing capacitor 110. The second node C is located between the second switch K2 and the first node B.

[0055] The current compensation unit 131 and the capacitance compensation unit 132 are both connected to the conductive path of the capacitance detection module 120 and the sensing capacitor 110, jointly providing parasitic compensation capacitance. The capacitance compensation unit 132 includes a capacitor array, providing compensation capacitance in parallel with the current compensation unit 131. Since the adjustment accuracy of the current source Icomp is limited, the accuracy of parasitic capacitance compensation using only the current compensation unit 131 is limited. In this embodiment, parasitic capacitance compensation is further performed through the capacitance compensation unit 132. The capacitance value accuracy of the capacitor in the capacitance compensation unit 132 is relatively high, which can further improve the accuracy of parasitic capacitance compensation, thereby improving the detection accuracy of the capacitance sensing device.

[0056] Please refer to Figure 4a This is a schematic diagram of the capacitive sensing device according to the third embodiment of the present invention.

[0057] In this embodiment, the capacitance detection module 120 further includes: an amplifier OP, a feedback capacitor CFB, and a fourth switch K4. The negative input terminal of the amplifier OP is connected to the sensing electrode A, and the positive input terminal is used to input a reference voltage VCM as the common-mode level of the amplifier OP. The two ends of the feedback capacitor CFB are respectively connected to the output terminal and the negative input terminal of the amplifier OP, and the fourth switch K4 is connected in parallel across the two ends of the feedback capacitor CFB. The feedback capacitor CFB is used to adjust the capacitance detection sensitivity of the capacitance detection module 120.

[0058] Furthermore, in this embodiment, the capacitance compensation unit 132 includes: n capacitors C0, C1, ... Cn-1 A capacitor array is formed in parallel, where n is an integer greater than or equal to 1. One end of each capacitor is connected to the second node C, and the other end is connected to a driving terminal. Each end of each capacitor is connected to a corresponding control switch S. i (i = 0, 1, ..., n-1) are connected in the circuit. In this embodiment, the control switch S i Connected in series with capacitor C i Between the drive end and the control switch S. In other embodiments, the control switch S i It can also be connected in series with capacitor C i Between the conductive path and the control circuit. This is achieved by controlling each control switch S. i The on / off state can adjust the effective capacitance value in the circuit connected to the capacitor array, that is, adjust the effective compensation capacitance value provided by the capacitor compensation unit 132.

[0059] The driving terminal is used to apply a periodic driving voltage VC, and the high level of the driving voltage VC corresponds to the conduction time of the second switch K2.

[0060] In this embodiment, the sensing electrode A is connected to a first fixed potential terminal D1 with a fixed potential VREF. Please refer to... Figure 4b The diagram illustrates the driving voltage VC. In this embodiment, the driving voltage VC is a rectangular wave signal with an amplitude of VREF. In other embodiments, the driving voltage VC may have other amplitudes.

[0061] In this embodiment, the current source Icomp of the current compensation unit 131 is connected to the second fixed potential terminal D2, which is the ground terminal. The current direction of the current source Icomp is to flow towards the second fixed potential terminal D2. When the third switch K3 is turned on, the current flows from the conductive path to the ground terminal, which is equivalent to charging the equivalent capacitor through the conductive path.

[0062] Please refer to Figure 5 This is a schematic diagram of the structure of the capacitive sensing device according to the fourth embodiment of the present invention.

[0063] In this embodiment, based on the aforementioned embodiments, the capacitance sensing device further includes a signal processing module 140. The signal processing module 140 is connected to the output terminal of the capacitance detection module 120 and is used to process the detection signal VO and output it as a digital signal for subsequent processing. The signal processing module 140 can be a digital-to-analog converter (ADC).

[0064] In other embodiments, it is also possible to... Figure 2 or Figure 3 Based on the embodiment shown, a signal processing module 140 is added to the capacitance detection module 120.

[0065] Please refer to Figure 6 This is a schematic diagram of the capacitive sensing device according to the fifth embodiment of the present invention.

[0066] In this embodiment, based on the aforementioned embodiment, the capacitance sensing device further includes a control module 150, which is connected to (shown in the figure) the first switch K1, the second switch K2, the third switch K3 and the fourth switch K4, and is used to control the on / off state of each switch.

[0067] In some embodiments, the control module 150 is used to output control signals to the first switch K1, the second switch K2, the third switch K3, and the fourth switch K4, so that the capacitance detection module 120 detects the sensing capacitance 110 according to a detection cycle. The detection cycle includes a first stage and a second stage. In the first stage, the control module 150 is used to control the first switch K1 and the fourth switch K4 to be turned on, and control the second switch K2 and the third switch K3 to be turned off. In the second stage, the control module 150 controls the first switch K1 and the fourth switch K4 to be turned off, and the second switch K2 and the third switch K3 to be turned on, and the third switch K3 is turned off after a preset time T.

[0068] The control module 150 is also connected to each control switch S in the capacitor compensation unit 132. i Used to control each of the control switches S i The on / off state is adjusted to adjust the effective capacitance value of the capacitor compensation unit 132.

[0069] Furthermore, the control module 150 is also connected to the output terminal of the signal processing module 140. The control module 150 may also include a processing unit for further processing of the digital signal output by the signal processing module 140 as needed, such as noise reduction and calculation.

[0070] Please refer to Figure 7 ,for Figure 6 The diagram shows the timing sequence of the control signals for each switch in the operation of the capacitance detection module of the fifth embodiment shown.

[0071] Each detection cycle includes a first stage I and a second stage II. The control module 150 is used to control the first switch K1 and the fourth switch K4 to be turned on (corresponding to a high level) and control the second switch K2 and the third switch K3 to be turned off (corresponding to a low level) in the first stage I; in the second stage II, the first switch K1 and the fourth switch K4 are turned off, the second switch K2 is turned on and the third switch K3 is turned on, and the third switch K3 is turned off after a preset time T.

[0072] Please combine Figure 6 In the first stage I, K1 and K4 are turned on, K2 and K3 are turned off, and the sensing electrode A of the sensing capacitor 110 is connected to the first fixed potential terminal D1 to charge the sensing capacitor 110. The total charge on the sensing capacitor is Q = VREF * Cx. The output terminal of the amplifier OP is connected to the negative input terminal. Due to the virtual short effect of the amplifier OP, the voltage at the negative input terminal is the same as the voltage at the positive input terminal. Since the fourth switch K4 is turned on, the detection signal VO at the output terminal is VCM.

[0073] In the second stage, K1 and K4 are disconnected, K2 is turned on, and K3 is turned on simultaneously. At this time, the sensing electrode A of the sensing capacitor 110 is connected to the negative input terminal of the amplifier OP, and the feedback capacitor CFB is connected between the output terminal and the negative input terminal of the amplifier OP. The sensing capacitor 110 shares charge with the capacitor compensation unit 132, the current compensation unit 131, and the feedback capacitor CFB. During the conduction of K3, the charge on the sensing capacitor 110 is discharged in the form of current, and the amount of discharged charge is Icomp*T. When K3 is disconnected after a preset time T, and the circuit stabilizes, according to the law of charge conservation, we can obtain: ΔV is the change in the detection signal output by amplifier OP, i.e., the offset of the detection signal from the reference voltage VCM. Cb is the effective capacitance value of capacitor compensation unit 132, Cb=k0*C0+k1*C1+……+k n-1 *C1,k i =0 or 1, k i =0 corresponds to control switch S i Disconnect, k i =1 corresponds to control switch S i Conduction. By selecting appropriate circuit parameters, such as k... i The parameters Icomp, T, etc., can ensure that when the capacitance value Cx of the sensing capacitor 110 is equal to its inherent parasitic capacitance Cp, that is, when the capacitance value of the sensing capacitor 110 has not changed, ΔV is equal to or as close as possible to 0.

[0074] In order to achieve better parasitic capacitance compensation, in some embodiments, within a configurable range, the current magnitude of the current source of the current compensation unit 131 is configured to a preset compensation current, such that when the capacitance value of the sensing capacitor 110 does not change, the offset ΔV between the detection signal output by the capacitance detection module 120 and the reference voltage VCM is less than a first threshold.

[0075] When the compensation module 130 includes a capacitor compensation unit 132, the effective capacitance value Cb of the capacitor compensation unit 132 is configured to a preset capacitance value, such that the effective capacitance value Cb of the sensing capacitor Cb is ... XWhen the capacitance value remains unchanged, the offset between the detection signal VO output by the capacitance detection module 120 and the reference voltage VCM is less than the second threshold. Both the second threshold and the first threshold are close to 0, and the second threshold is less than the first threshold. Since the charging and discharging process of the capacitor takes time, the change in the detection signal is output after the circuit reaches a stable state after the third switch K3 is turned off.

[0076] In this embodiment, in order to establish a stable circuit state before the second switch K2 and the third switch K3 switch are switched on during the process, the first switch K1 and the fourth switch K4 are disconnected in advance before the second switch K2 and the third switch K3 are turned on; and the second switch K2 and the third switch K3 are turned on with a delay after they are disconnected.

[0077] Please refer to Figure 8 This is a schematic diagram of the capacitive sensing device according to the sixth embodiment of the present invention.

[0078] In this embodiment, the first fixed potential terminal D1 in the capacitance sensing device is a ground terminal, the second fixed potential terminal D2 is a high potential terminal, and the current direction of the current source Icomp is to flow to the conductive path between the capacitance detection module 120 and the sensing capacitor 110.

[0079] use Figure 9 The timing sequence of the control signals for each switch in the operation of the capacitive sensing device of the sixth embodiment shown controls the on / off state of each switch. When VC = VREF, the change in the detection signal ΔV is obtained.

[0080]

[0081] Similarly, parameters within the control circuit, such as k, can be used. i Parasitic capacitance compensation is performed using Icomp, T, etc., so that when the capacitance value of sensing capacitor 110 does not change, ΔV is less than the second threshold, thus getting as close to 0 as possible.

[0082] Embodiments of the present invention also provide an electronic device including the capacitive sensing device described in any of the foregoing embodiments. The electronic device includes smart terminal devices such as mobile phones, tablet computers, wireless earphones, wristbands, and watches.

[0083] Embodiments of the present invention also provide a chip, including the capacitive sensing device described in any of the foregoing embodiments. All circuit elements and lines of the capacitive sensing device are integrated on the chip. The chip may include a single bare chip; the chip may also be packaged from at least one bare chip, with the lines and elements of the capacitive sensing device distributed on at least one of the bare chips. The chip can be applied in the electronic devices described in the foregoing embodiments.

[0084] Embodiments of this application also provide a method for compensating for parasitic capacitance in a capacitance sensing device.

[0085] Please refer to Figure 10 This is a schematic flowchart of a parasitic capacitance compensation method according to an embodiment of the present invention. The parasitic capacitance compensation method uses the capacitance sensing device described in the above embodiment.

[0086] The parasitic capacitance compensation method includes the following steps:

[0087] Step S101: When the capacitance value of the sensing capacitor has not changed, acquire the detection signal output by the capacitance detection module.

[0088] Step S102: Adjust the current source according to the detection signal so that the offset between the detection signal output by the capacitance detection module and the reference voltage is less than the first threshold.

[0089] When the variable portion (ΔC) of the capacitance of sensing capacitor 110 is equal to zero or nearly zero (e.g., for a proximity sensor, when no object is near the sensor electrode), parasitic capacitance compensation is performed only through current unit 131. By adjusting the magnitude of the current source Icomp and / or the preset conduction time T of the current source Icomp, the change in the detection signal ΔV is made less than a first threshold, which is greater than zero and close to zero.

[0090] for Figure 6 The embodiment shown uses only the current unit 131 for parasitic capacitance compensation, based on the calculation formula for the change in the detected signal ΔV at this time. Set the preset time T for the current source Icomp to be turned on.

[0091] for Figure 8 The embodiment shown only uses the current unit 131 for parasitic capacitance compensation, based on the formula for the change in the detected signal ΔV. Set the preset time T for the current source Icomp to be turned on.

[0092] When the compensation module only includes the current sensing unit 131, the compensation of parasitic capacitance is completed in step S102.

[0093] The above-mentioned capacitance compensation method can achieve parasitic capacitance compensation over a large area by adjusting the current source, using a relatively small area.

[0094] Please refer to Figure 11 This is a flowchart illustrating a parasitic capacitance compensation method according to another embodiment.

[0095] In this embodiment, the compensation module of the capacitance sensing device further includes a capacitance compensation unit. Steps S201 and S202 respectively correspond to... Figure 9 Steps S101 and S102 in the embodiment are included. Based on this, step S203 is further included: configuring the effective capacitance value of the capacitor compensation unit such that the offset between the detection signal output by the capacitor detection module and the reference voltage is less than a second threshold, and the second threshold is less than a first threshold.

[0096] for Figure 6 The illustrated embodiment is based on the formula for the change in the detection signal ΔV. Further setting k i The value of ΔV is adjusted to change the equivalent capacitance of the capacitive sensing unit, further reducing the value of ΔV to be less than the second threshold and even closer to 0.

[0097] for Figure 8 The illustrated embodiment is based on the formula for the change in the detection signal ΔV. Further setting k i The value of ΔV is adjusted to change the equivalent capacitance of the capacitive sensing unit, further reducing the value of ΔV to be less than the second threshold and even closer to 0.

[0098] The above-mentioned parasitic capacitance compensation method, based on current source compensation, further improves the accuracy of parasitic capacitance compensation by using capacitance compensation.

[0099] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, such as the combination of technical features between embodiments, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A capacitive sensing device, characterized in that, include: A sensing capacitor, wherein the sensing electrode of the sensing capacitor is connectable to a first fixed potential terminal in a way that can be switched on or off. The capacitance detection module is connected to the sensing electrode of the sensing capacitor through a conductive path. The capacitance detection module is used to detect the sensing capacitor and output a detection signal corresponding to the change in capacitance of the sensing capacitor. A compensation module is used to provide parasitic compensation capacitance. The compensation module includes a current compensation unit, which includes a current source connected to the conductive path. The current compensation unit is used to control the charging and discharging process of the conductive path by the current source to provide an equivalent parasitic compensation capacitance. The current compensation unit also includes a third switch, which is connected in series with the current source. One end of the series path of the third switch and the current source is connected to a first node of the conductive path, and the other end is connected to a second fixed potential terminal. A second switch is connected between the first node and the sensing electrode. A first switch is connected between the sensing electrode and the first fixed potential terminal; The compensation module further includes a capacitor compensation unit, which is connected to a second node of the conductive path, and the second node is located between the second switch and the first node. The capacitor compensation unit includes a capacitor array consisting of several capacitors connected in parallel. One end of each capacitor is connected to the second node, and the other end is connected to a driving terminal. Each end of each capacitor is connected to the circuit through a corresponding control switch. The driving terminal is used to apply a periodic driving voltage, and the high-level moment of the driving voltage corresponds to the conduction moment of the second switch.

2. The capacitive sensing device according to claim 1, characterized in that, The capacitance detection module is also used to receive a reference voltage, and the change in capacitance corresponds to the offset between the detection signal and the reference voltage.

3. The capacitive sensing device according to claim 1, characterized in that, The capacitance detection module includes an amplifier, a feedback capacitor, and a fourth switch. The negative input terminal of the amplifier is connected to the sensing electrode, and the positive input terminal is used to input a reference voltage. The two ends of the feedback capacitor are respectively connected to the output terminal and the negative input terminal of the amplifier. The fourth switch is connected in parallel across the two ends of the feedback capacitor.

4. The capacitive sensing device according to claim 3, characterized in that, Also includes: A control module is connected to the first switch, the second switch, the third switch, and the fourth switch, and is used to control the on / off state of each switch.

5. The capacitive sensing device according to claim 4, characterized in that, The control module is used to output control signals to the first switch, the second switch, the third switch, and the fourth switch, so that the detection module detects the sensing capacitance according to the detection cycle; the detection cycle includes a first stage and a second stage, and the control module is used to control the first switch and the fourth switch to be turned on and control the second switch and the third switch to be turned off in the first stage; in the second stage, the control module controls the first switch and the fourth switch to be turned off, controls the second switch to be turned on and the third switch to be turned on, and turns off the third switch after a preset time.

6. The capacitive sensing device according to claim 2, characterized in that, Within the configurable range, the current magnitude of the current source is configured to a preset compensation current, such that when the capacitance value of the sensing capacitor does not change, the offset between the detection signal output by the capacitance detection module and the reference voltage is less than a first threshold.

7. The capacitive sensing device according to claim 6, characterized in that, The effective capacitance value of the capacitance compensation unit is configured to a preset capacitance value, such that when the capacitance value of the sensing capacitor does not change, the offset of the detection signal output by the capacitance detection module from the reference voltage is less than a second threshold, and the second threshold is less than the first threshold.

8. The capacitive sensing device according to claim 1, characterized in that, Also includes: A signal processing module is connected to the output terminal of the capacitance detection module and is used to process the detection signal and output a digital signal.

9. An electronic device, characterized in that, Includes the capacitive sensing device as described in any one of claims 1 to 8.

10. A method for compensating for parasitic capacitance in a capacitive sensing device as described in any one of claims 1 to 8, characterized in that, include: When the capacitance value of the sensing capacitor does not change, the detection signal output by the capacitance detection module is acquired; Based on the detection signal, the current source is adjusted so that the offset between the detection signal output by the capacitance detection module and the reference voltage is less than a first threshold.

11. The parasitic capacitance compensation method according to claim 10, characterized in that, When the compensation module of the capacitance sensing device includes a capacitance compensation unit, it further includes: after the current source is adjusted, the effective capacitance value of the capacitance compensation unit is further configured so that the offset between the detection signal output by the capacitance detection module and the reference voltage is less than a second threshold, and the second threshold is less than a first threshold.

12. A chip, characterized in that, Includes the capacitive sensing device as described in any one of claims 1 to 8.

Images