WO2021036306A1 - 电容感测装置 - Google Patents

电容感测装置 Download PDF

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Publication number
WO2021036306A1
WO2021036306A1 PCT/CN2020/086636 CN2020086636W WO2021036306A1 WO 2021036306 A1 WO2021036306 A1 WO 2021036306A1 CN 2020086636 W CN2020086636 W CN 2020086636W WO 2021036306 A1 WO2021036306 A1 WO 2021036306A1
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Prior art keywords
switch
sensing
capacitance
coupled
circuit
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English (en)
French (fr)
Inventor
刘学欣
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Egis Technology Inc
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Egis Technology Inc
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Priority to US17/638,177 priority Critical patent/US20220311441A1/en
Priority to KR1020227008807A priority patent/KR20220048019A/ko
Publication of WO2021036306A1 publication Critical patent/WO2021036306A1/zh
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
    • H03K17/96—Touch switches
    • H03K17/962—Capacitive touch switches
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
    • G01R27/2605—Measuring capacitance
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K2217/00—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00
    • H03K2217/94—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated
    • H03K2217/96—Touch switches
    • H03K2217/9607—Capacitive touch switches
    • H03K2217/960705—Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K2217/00—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00
    • H03K2217/94—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated
    • H03K2217/96—Touch switches
    • H03K2217/9607—Capacitive touch switches
    • H03K2217/96071—Capacitive touch switches characterised by the detection principle
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K2217/00—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00
    • H03K2217/94—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated
    • H03K2217/96—Touch switches
    • H03K2217/9607—Capacitive touch switches
    • H03K2217/960735—Capacitive touch switches characterised by circuit details
    • H03K2217/96074—Switched capacitor

Definitions

  • the invention relates to a sensing device, in particular to a capacitance sensing device.
  • the invention provides a capacitance sensing device, which can improve the sensing quality of the capacitance sensing device, and avoid the situation that the sensing result of the capacitance sensing device is affected by the change of the electric field in the environment and the sensing error occurs.
  • the capacitance sensing device of the present invention includes a sensing electrode, a sensing circuit, an analog-digital converter, and a control circuit.
  • the sensing electrode accepts the touch operation of the touch tool.
  • the input terminal of the sensing circuit is coupled to the sensing electrode through the sensing signal line, and senses the change of the sensing capacitance between the touch tool and the sensing electrode to generate a sensing signal.
  • the sensing circuit includes a first switch, a second switch, a third switch, and an adjustable capacitor unit.
  • the first switch is coupled between the power supply voltage and the input terminal.
  • One end of the second switch is coupled to the input end, and the other end of the second switch is coupled to the output end of the sensing circuit.
  • the third switch is coupled between the other end of the second switch and the ground.
  • the first switch, the second switch, and the third switch periodically switch their conduction states. When the first switch and the third switch are in conduction In the state, the second switch is in the off state, and when the second switch is in the on state, the first switch and the third switch are in the off state.
  • the adjustable capacitor unit is coupled between the other end of the second switch and the ground.
  • the analog-digital converter is coupled to the sensing circuit and converts the sensing signal into a digital sensing signal.
  • the control circuit is coupled to the sensing circuit and the analog-to-digital converter, and adjusts the capacitance value of the adjustable capacitor unit according to the digital sensing signal, so that the capacitance value of the adjustable capacitor unit approaches the background parasitic capacitance.
  • the control circuit of the embodiment of the present invention can adjust the capacitance value of the adjustable capacitor unit according to the digital sensing signal obtained by converting the sensing signal by the analog-to-digital converter, so that the capacitance value of the adjustable capacitor unit approaches the background parasitic capacitance In this way, the sensing result of the capacitance sensing device can be prevented from being affected by the change of the electric field in the environment and the sensing error occurs, thereby improving the sensing quality of the capacitance sensing device.
  • Fig. 1 is a schematic diagram of a capacitance sensing device according to an embodiment of the present invention
  • FIG. 2 is a waveform diagram of a control signal of a capacitance sensing device according to the embodiment of FIG. 1 of the present invention
  • Fig. 3 is a schematic diagram of an adjustable capacitor unit according to an embodiment of the present invention.
  • FIG. 4 is a schematic diagram of a capacitance sensing device according to another embodiment of the present invention.
  • FIG. 5 is a schematic diagram of a capacitance sensing device according to another embodiment of the present invention.
  • FIG. 6 is a waveform diagram of a control signal of a capacitance sensing device according to the embodiment of FIG. 5 of the present invention.
  • FIG. 1 is a schematic diagram of a capacitance sensing device according to an embodiment of the present invention. Please refer to FIG. 1.
  • the capacitance sensing device includes a sensing electrode E1, a sensing circuit 102, an analog-to-digital converter 104, and a control circuit 106.
  • the sensing electrode E1 can be coupled to the input terminal of the sensing circuit 102 through a sensing signal line L1.
  • the converter 104 is coupled to the output terminal of the sensing circuit 102 and the control circuit 106.
  • the sensing electrode E1 can be used to receive a touch operation of the touch tool T1. For example, in this embodiment, it can receive a touch operation of a finger, but it is not limited to this.
  • the sensing circuit 102 can sense the change in capacitance value of the sensing capacitor Cf between the touch tool T1 and the sensing electrode E1 to generate a sensing signal to the analog-to-digital converter 104.
  • the analog-to-digital converter 104 can convert the sensing signal provided by the sensing circuit 102 into a digital sensing signal S1 and provide it to the subsequent circuit for analysis and processing.
  • the sensing circuit 102 may include switches SW1 to SW3 and an adjustable capacitor unit Cs, wherein the switch SW1 is coupled between the power supply voltage Vdd and the input terminal of the sensing circuit 102, and the switch SW1 is coupled to the sensing circuit 102 Between the input terminal and the output terminal of the switch SW3 is coupled between the output terminal of the sensing circuit 102 and the ground, and the adjustable capacitor unit Cs is coupled between the output terminal of the sensing circuit 102 and the ground.
  • the switches SW1 and SW3 can be controlled by the control signal CH to periodically switch between the on state and the off state, and the switch SW2 can be controlled by the control signal SH to periodically switch between the on state and the off state ,
  • the waveforms of the control signals CH and SH can be shown in Figure 2.
  • the switches SW1 and SW3 are in the conducting state (the control signal CH is at a high voltage level), the switch SW2 is in the off state (the control signal SH is at a low voltage level), and when the switch SW2 is in the conducting state (the control signal When SH is at a high voltage level), the switches SW1 and SW3 are in an off state (the control signal CH is at a low voltage level).
  • the power supply voltage Vdd can reset the voltage of the background parasitic capacitance Cp
  • the adjustable capacitor unit Cs can be discharged through the switch SW3 to reset the adjustable capacitor
  • the voltage of the cell Cs, where the background parasitic capacitance Cp may include, for example, the parasitic capacitance of the electrode E1 to the ground, the parasitic capacitance of the sensing signal line L1 to the ground, and the parasitic capacitance of the touch panel of the capacitance sensing device to the ground. Is limited.
  • the sensing voltage Vx (that is, a sensing signal) is generated on the adjustable capacitor unit Cs.
  • the sensing voltage Vx can be represented by the following formula (1):
  • the capacitance sensing device when the background parasitic capacitance Cp is much larger than the capacitance value of the sensing capacitor Cf, when Vx is equal to 1/2Vdd, that is, when the capacitance value of the capacitance unit Cs is equal to the capacitance value of the background parasitic capacitance Cp, the capacitance sensing device will Has the best sensing sensitivity.
  • the control circuit 106 can adjust the capacitance value of the adjustable capacitance unit Cs according to the digital sensing signal S1, so that the capacitance value of the adjustable capacitance unit Cs approaches the background parasitic capacitance Cp, thereby ensuring that the capacitance sensing device has the best sensing sensitivity ,
  • the capacitive sensing device will not be subject to sensing errors due to changes in environmental conditions or radio frequency signals. For example, when the sensing voltage Vx becomes larger due to changes in environmental conditions, the control circuit 106 can increase the capacitance value of the adjustable capacitor unit Cs according to the digital sensing signal S1 to resist the influence caused by the changes in environmental conditions.
  • the adjustable capacitor unit Cs can be implemented, for example, in the manner of the embodiment in FIG. 3.
  • the adjustable capacitor unit Cs can include a plurality of switches 201-20N and capacitors C1 ⁇ CN, and each switch is connected in series with a corresponding capacitor to the sensing circuit. Between the output terminal of 102 and the ground, the conduction state of the switches 301-30N can be controlled by the control circuit 106 to adjust the capacitance value of the adjustable capacitor unit Cs.
  • the control circuit 106 can be implemented by, for example, a digital integration circuit, which can integrate the digital sensing signal S1 and generate a bit signal according to the integrated value to control the conduction state of the switches 301-30N, thereby adjusting The capacitance value of the capacitance unit Cs.
  • the digital integration circuit can generate an integrated value according to the digital sensing signal S1, and adjust the capacitance value of the adjustable capacitor unit Cs according to the integrated value and the target value. For example, when the integrated value is higher than the target value, it represents the sensing voltage Vx If it is too large, the control circuit 106 can increase the capacitance value of the adjustable capacitor unit Cs. When the integrated value is lower than the target value, it means that the sensing voltage Vx is too small, and the control circuit 106 can reduce the capacitance value of the adjustable capacitor unit Cs.
  • FIG. 4 is a schematic diagram of a capacitance sensing device according to another embodiment of the present invention. Please refer to FIG. 4.
  • the difference between the capacitance sensing device of this embodiment and the capacitance sensing device of the embodiment in FIG. 2 is that the capacitance sensing device of this embodiment further includes a digital low-pass filter circuit 402, and the digital low-pass filter circuit 402 is coupled to Between the analog-digital converter 104 and the control circuit 106, the digital low-pass filter circuit 402 can perform low-pass filtering to remove the high-frequency noise of the digital sensing signal S1, and further avoid the sensing result from being interfered by radio frequency signals.
  • FIG. 5 is a schematic diagram of a capacitance sensing device according to another embodiment of the present invention, please refer to FIG. 5.
  • the capacitance sensing device of this embodiment further includes an exchange capacitor low-pass filter circuit 502, and the exchange capacitor low-pass filter circuit 502 is coupled It is connected between the sensing circuit 102 and the analog-to-digital converter 104 to perform low-pass filtering on the sensing signal provided by the sensing circuit 102.
  • the switched capacitor low-pass filter circuit 502 may include switches SW5 and SW6 and capacitors CA and CB.
  • the switches SW5 and SW6 are connected in series between the output terminal of the sensing circuit 102 and the analog-to-digital converter 104, and the capacitor CA is coupled Between the common contact of the switches SW5 and SW6 and the ground, the capacitor CB is coupled between the common contact of the switch SW6 and the analog-to-digital converter 104 and the ground.
  • the capacitance value of the capacitor CB is greater than the capacitance value of the capacitor CA.
  • the capacitance value of the background parasitic capacitance Cp is 1 to 64 picofarads (pF)
  • the capacitance value of the capacitor CB may be, for example, 1 to 4 picofarads.
  • the capacitance value of the capacitor CA may be, for example, 50 femtofarads (fF), but it is not limited thereto.
  • the switches SW5 and SW6 are controlled by the control signals SC1 and SC2 to change their conduction states.
  • the waveforms of the control signals CH, SH, SC1 and SC2 can be as shown in FIG. 6.
  • the implementation of the sensing circuit 102 is the same as that of the embodiment in FIG. 1, so it will not be repeated here.
  • the switch SW5 is turned on, the switch SW6 is turned off.
  • the capacitor CA can be reset by discharging the switch SW3 to ground, and when the switch SW2 is turned on, it receives the sensing information stored in the background parasitic capacitance Cp, That is, the sensing signal provided by the sensing circuit 102 is received. After that, when the switch SW6 is turned on and the switch SW5 is turned off, the capacitor CA transmits the sensed information it stores to the capacitor CB to complete the low-pass filtering of the sensed signal.
  • the analog-to-digital converter 104 can perform analog-to-digital conversion on the voltage on the capacitor CB to generate a digital sensing signal.
  • the control circuit 106 can adjust the capacitance value of the adjustable capacitor unit Cs according to the digital sensing signal S1 as described in the embodiment of FIG. 2, so that the capacitance value of the adjustable capacitor unit Cs approaches the background parasitic capacitance Cp, thereby ensuring capacitance sensing
  • the device has the best sensing sensitivity and will not cause sensing errors in the capacitance sensing device due to changes in environmental conditions or radio frequency signals.
  • the operating frequency fa of the analog-to-digital converter 104 of this embodiment can be lower than the operating frequency fl of the sensing circuit 102 and the switching capacitor low-pass filter circuit 502, and the operating frequency fs of the control circuit 106 can be lower than the analog The operating frequency fa of the digitizer 104.
  • the operating frequency f1 of the sensing circuit 102 and the switching capacitor low-pass filter circuit 502 may be, for example, 1 MHz
  • the operating frequency fa of the analog-to-digital converter 104 is 500 Hz
  • the operating frequency fs of the control circuit 106 is 50 Hz.
  • the analog-to-digital converter 104 samples the voltage on the capacitor CB every time the exchange capacitor low-pass filter circuit 502 receives the sensing signal provided by the sensing circuit 102 for 20 times. Similarly, whenever the analog-digital converter 104 After the converter 104 performs 10 analog-to-digital conversions, the control circuit 106 samples the digital sensing signal S1 accumulated by the analog-to-digital converter 104. Since the power consumed by the operation of the switched capacitor low-pass filter circuit 502 is very low, it has little effect on the power consumption of the capacitance sensing device, and it can also effectively remove high frequency noise.
  • the capacitance sensing device of this embodiment may include the digital low-pass filter circuit 402 to perform low-pass filtering on the digital sensing signal S1.
  • control circuit of the embodiment of the present invention can adjust the capacitance value of the adjustable capacitor unit according to the digital sensing signal obtained by converting the sensing signal by the analog-to-digital converter, so that the capacitance value of the adjustable capacitor unit approaches the background
  • the parasitic capacitance can prevent the sensing result of the capacitance sensing device from being affected by the change of the electric field in the environment and causing sensing errors, thereby improving the sensing quality of the capacitance sensing device.
  • the capacitance sensing device may further include an exchange capacitor low-pass filter circuit, by making the operating frequency of the analog-to-digital converter lower than the operating frequency of the sensing circuit and the exchange capacitor low-pass filter circuit, and the control circuit The operating frequency can be lower than the operating frequency of the analog-to-digital converter, which can effectively reduce the power consumption of the capacitance sensing device.

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Abstract

一种电容感测装置，其中，控制电路（106）依据模拟数字转换器（104）转换感测信号所得到的数字感测信号调整可调电容单元（Cs）的电容值，而使可调电容单元（Cs）的电容值趋近背景寄生电容（Cp）。

Description

电容感测装置 技术领域
本发明涉及一种感测装置，尤其涉及一种电容感测装置。
背景技术
随着光电科技的发展，近接切换装置已被大量运用在不同的机器上，例如：智能手机、运输工具的购票系统、数字照像机、遥控器与液晶屏幕等。常见可达近接切换的感测装置包括近接传感器(Proximity sensor)与电容式触控开关(Capacitive touch switch)。其中电容式触控开关为通过感测其电极的寄生电容来确定开关的状态，然电极具有天线的特性，会反应环境中的电场变化(例如环境湿度变化或射频信号的影响)而影响到电容式触控开关的感测结果，进而出现感测错误的情形。
发明内容
本发明提供一种电容感测装置，可提高电容感测装置的感测质量，避免电容感测装置的感测结果受到环境中的电场变化的影响而出现感测错误的情形。
本发明的电容感测装置包括感测电极、感测电路、模拟数字转换器以及控制电路。感测电极接受触控工具的触控操作。感测电路的输入端透过感测信号线耦接感测电极，感测触控工具与感测电极间的感应电容变化量而产生感测信号。感测电路包括第一开关、第二开关、第三开关以及可调电容单元。第一开关耦接于电源电压与输入端之间。第二开关的一端耦接于输入端，第二开关的另一端耦接感测电路的输出端。第三开关耦接于第二开关的另一端与接地之间，第一开关、第二开关以及第三开关分别周期性地切换其导通状态，其中当第一开关与第三开关处于导通状态时，第二开关处于断开状态，当第二开关处于导通状态时，第一开关与第三开关处于断开状态。可调电容单元耦接于第二开关的另一端与接地之间。模拟数字转换器耦接感测电路，将感测信号转换为数字感测信号。控制电路耦接感测电路与模拟数字转换器， 依据数字感测信号调整可调电容单元的电容值，而使可调电容单元的电容值趋近背景寄生电容。
基于上述，本发明实施例的控制电路可依据模拟数字转换器转换感测信号所得到的数字感测信号调整可调电容单元的电容值，而使可调电容单元的电容值趋近背景寄生电容，如此可避免电容感测装置的感测结果受到环境中的电场变化的影响而出现感测错误的情形，进而提高电容感测装置的感测质量。
为让本发明的上述特征和优点能更明显易懂，下文特举实施例，并配合附图作详细说明如下。
附图说明
图1是依照本发明的实施例的一种电容感测装置的示意图；
图2是依照本发明图1实施例的一种电容感测装置控制信号的波形图；
图3是依照本发明的实施例的一种可调电容单元的示意图；
图4是依照本发明另一实施例的一种电容感测装置的示意图；
图5是依照本发明另一实施例的一种电容感测装置的示意图；
图6是依照本发明图5实施例的一种电容感测装置控制信号的波形图。
具体实施方式
图1是依照本发明的实施例的一种电容感测装置的示意图，请参照图1。电容感测装置包括感测电极E1、感测电路102、模拟数字转换器104以及控制电路106，其中感测电极E1可透过感测信号线L1耦接感测电路102的输入端，模拟数字转换器104耦接感测电路102的输出端与控制电路106。
感测电极E1可用以接收触控工具T1的触控操作，例如在本实施例中可接收手指的触控操作，然不以此为限。感测电路102可感测触控工具T1与感测电极E1间的感应电容Cf的电容值变化量而产生感测信号给模拟数字转换器104。模拟数字转换器104可将感测电路102提供的感测信号转换为数字感测信号S1而提供给后级电路进行分析处理。
进一步来说，感测电路102可包括开关SW1～SW3以及可调电容单元Cs，其中开关SW1耦接于电源电压Vdd与感测电路102的输入端之间，开关SW1 耦接于感测电路102的输入端与输出端之间，开关SW3耦接于感测电路102的输出端与接地之间，可调电容单元Cs耦接于感测电路102的输出端与接地之间。开关SW1与SW3可受控于控制信号CH而周期性地于导通状态与断开状态间切换，开关SW2则可受控于控制信号SH而周期性地于导通状态与断开状态间切换，控制信号CH与SH的波形可如图2所示。其中当开关SW1与SW3处于导通状态时(控制信号CH为高电压电平时)，开关SW2处于断开状态(控制信号SH为低电压电平)，当开关SW2处于导通状态时(控制信号SH为高电压电平时)，开关SW1与SW3处于断开状态(控制信号CH为低电压电平)。
当开关SW1与SW3处于导通状态而开关SW2处于断开状态时，电源电压Vdd可重置背景寄生电容Cp的电压，此外可调电容单元Cs可经由开关SW3进行放电，而重置可调电容单元Cs的电压，其中背景寄生电容Cp可例如包括电极E1对地的寄生电容、感测信号线L1对地的寄生电容以及电容感测装置的触控面板对地的寄生电容，然不以此为限。之后，当开关SW1与SW3处于断开态而开关SW2处于导通状态时，背景寄生电容Cp将经由开关SW2与可调电容单元Cs进行电荷分享，而将背景寄生电容Cp所储存的感测信息传送给可调电容单元Cs，而于可调电容单元Cs上产生感测电压Vx(亦即感测信号)。进一步来说，感测电压Vx可如下式(1)所示：
Figure PCTCN2020086636-appb-000001
其中在背景寄生电容Cp远大于感应电容Cf的电容值的情形下，在Vx等于1/2Vdd，亦即可调电容单元Cs的电容值等于背景寄生电容Cp的电容值时，电容感测装置将具有最佳的感测灵敏度。控制电路106可依据数字感测信号S1调整可调电容单元Cs的电容值，而使可调电容单元Cs的电容值趋近背景寄生电容Cp，而确保电容感测装置具有最佳的感测灵敏度，不会因受到环境条件变化或射频信号的影响使电容感测装置出现感测错误的情形。举例来说，当感测电压Vx因受到环境条件变化而变大时，控制电路106可依据数字感测信号S1提高可调电容单元Cs的电容值，以抵抗环境条件变化所造成的影响。
其中，可调电容单元Cs可例如以图3实施例的方式实施，可调电容单元Cs可包括多个开关201～20N以及电容C1～CN，各个开关分别与对应的电容 串接于感测电路102的输出端与接地之间，开关301～30N的导通状态可受控于控制电路106，以调整可调电容单元Cs的电容值。在部份实施例中，控制电路106可例如以数字积分电路来实施，其可对数字感测信号S1进行积分，并依据积分值产生位信号来控制开关301～30N的导通状态，进而调整电容单元Cs的电容值。举例来说，数字积分电路可依据数字感测信号S1产生积分值，并依据积分值与目标值调整可调电容单元Cs的电容值，例如当积分值高于目标值时，代表感测电压Vx过大，控制电路106可提高可调电容单元Cs的电容值，当积分值低于目标值时，代表感测电压Vx过小，控制电路106可降低可调电容单元Cs的电容值。
图4是依照本发明另一实施例的一种电容感测装置的示意图，请参照图4。本实施例的电容感测装置与图2实施例的电容感测装置的不同之处在于，本实施例的电容感测装置还包括数字低通滤波电路402，数字低通滤波电路402耦接于模拟数字转换器104与控制电路106之间，数字低通滤波电路402可执行低通滤波，以去除数字感测信号S1的高频噪声，进一步避免感测结果受到射频信号的干扰。
图5是依照本发明另一实施例的一种电容感测装置的示意图，请参照图5。本实施例的电容感测装置与图2实施例的电容感测装置的不同之处在于，本实施例的电容感测装置还包括交换电容低通滤波电路502，交换电容低通滤波电路502耦接于感测电路102与模拟数字转换器104之间，以对感测电路102提供的感测信号进行低通滤波。详细来说，交换电容低通滤波电路502可包括开关SW5、SW6以及电容CA、CB，开关SW5、SW6串接于感测电路102的输出端与模拟数字转换器104之间，电容CA耦接于开关SW5、SW6的共同接点与接地之间，电容CB耦接于开关SW6与模拟数字转换器104的共同接点与接地之间。其中电容CB的电容值大于电容CA的电容值，举例来说，当背景寄生电容Cp的电容值为1～64皮法(pF)时，电容CB的电容值可例如为1～4皮法，电容CA的电容值可例如为50飞法(fF)，然不以此为限。
开关SW5、SW6受控于控制信号SC1、SC2而改变其导通状态，控制信号CH、SH、SC1与SC2的波形可如图6所示。其中有关感测电路102的实施方式与图1实施例相同，因此在此不再赘述，在交换电容低通滤波电路502中，当开关SW5导通时，开关SW6为断开状态。在开关SW5导通的期间， 当开关SW3导通时，电容CA可经由开关SW3对地放电而被重置，并在开关SW2导通时，接收来自背景寄生电容Cp所储存的感测信息，亦即接收感测电路102提供的感测信号。之后，当开关SW6导通而开关SW5断开时，电容CA将其储存的感测信息传送给电容CB，以完成感测信号的低通滤波。
模拟数字转换器104可对电容CB上的电压进行模拟数字转换，而产生数字感测信号。控制电路106可如图2实施例所述，依据数字感测信号S1调整可调电容单元Cs的电容值，以使可调电容单元Cs的电容值趋近背景寄生电容Cp，而确保电容感测装置具有最佳的感测灵敏度，不会因受到环境条件变化或射频信号的影响使电容感测装置出现感测错误的情形。
值得注意的是，本实施例的模拟数字转换器104的工作频率fa可低于感测电路102与交换电容低通滤波电路502的工作频率fl，而控制电路106的工作频率fs可低于模拟数字转换器104的工作频率fa。举例来说，感测电路102与交换电容低通滤波电路502的工作频率fl可例如为1MHz，模拟数字转换器104的工作频率fa为500Hz，控制电路106的工作频率fs为50Hz。也就是说，每当交换电容低通滤波电路502累计接收20次感测电路102提供的感测信号后，模拟数字转换器104才对电容CB上的电压取样一次，类似地，每当模拟数字转换器104执行10次模拟数字转换后，控制电路106才取样模拟数字转换器104所累计的数字感测信号S1。由于交换电容低通滤波电路502的操作所消耗的功率很低，因此对于电容感测装置的功率消耗影响并不大，且也可有效去除高频噪声。而使模拟数字转换器104与控制电路106的工作频率低于感测电路102的工作频率可大幅地减低电容感测装置的功率消耗。此外，本实施例的电容感测装置可如图4实施例，包括数字低通滤波电路402，以对数字感测信号S1进行低通滤波。
综上所述，本发明实施例的控制电路可依据模拟数字转换器转换感测信号所得到的数字感测信号调整可调电容单元的电容值，而使可调电容单元的电容值趋近背景寄生电容，如此可避免电容感测装置的感测结果受到环境中的电场变化的影响而出现感测错误的情形，进而提高电容感测装置的感测质量。在部份实施例中，电容感测装置还可包括交换电容低通滤波电路，通过使模拟数字转换器的工作频率低于感测电路与交换电容低通滤波电路的工作频率，并使控制电路的工作频率可低于模拟数字转换器的工作频率，可有效 降低电容感测装置的功率消耗。
虽然本发明已以实施例揭示如上，然其并非用以限定本发明，任何所属技术领域中技术人员，在不脱离本发明的精神和范围内，当可作些许的更改与润饰，故本发明的保护范围当视权利要求所界定的为准。

Claims (10)

  1. 一种电容感测装置，其特征在于，包括：
    感测电极，接受触控工具的触控操作；以及
    感测电路，其输入端透过感测信号线耦接所述感测电极，感测所述触控工具与所述感测电极间的感应电容变化量而产生感测信号，所述感测电路包括：
    第一开关，耦接于电源电压与所述输入端之间；
    第二开关，其一端耦接于所述输入端，所述第二开关的另一端耦接所述感测电路的输出端；
    第三开关，耦接于所述第二开关的另一端与接地之间，所述第一开关、所述第二开关以及所述第三开关分别周期性地切换其导通状态，其中当所述第一开关与所述第三开关处于导通状态时，所述第二开关处于断开状态，当所述第二开关处于导通状态时，所述第一开关与所述第三开关处于断开状态；以及
    可调电容单元，耦接于所述第二开关的另一端与所述接地之间；
    模拟数字转换器，耦接所述感测电路，将所述感测信号转换为数字感测信号；以及
    控制电路，耦接所述感测电路与所述模拟数字转换器，依据所述数字感测信号调整所述可调电容单元的电容值，而使所述可调电容单元的电容值趋近背景寄生电容。
  2. 根据权利要求1所述的电容感测装置，其特征在于，还包括：
    交换电容低通滤波电路，耦接所述感测电路与所述模拟数字转换器，对所述感测信号进行低通滤波。
  3. 根据权利要求2所述的电容感测装置，其特征在于，所述交换电容低通滤波电路的工作频率大于所述模拟数字转换器的工作频率，所述模拟数字转换器的工作频率大于所述控制电路的工作频率。
  4. 根据权利要求3所述的电容感测装置，其特征在于，所述交换电容低通滤波电路的工作频率为1MHz，所述模拟数字转换器的工作频率为500Hz，所述控制电路的工作频率为50Hz。
  5. 根据权利要求2所述的电容感测装置，其特征在于，所述交换电容低 通滤波电路包括：
    第四开关，其一端耦接所述感测电路的输出端；
    第一电容，耦接于所述第四开关的另一端；
    第五开关，其一端耦接所述第四开关的另一端，所述第五开关的另一端耦接所述模拟数字转换器；以及
    第二电容，耦接所述第五开关的另一端与所述接地之间，所述第四开关与所述第五开关分别周期性地切换其导通状态，而使所述交换电容低通滤波电路对所述感测信号进行低通滤波，其中当所述第四开关处于导通状态时，所述第五开关处于断开状态，当所述第五开关处于导通状态时，所述第四开关处于断开状态。
  6. 根据权利要求5所述的电容感测装置，其特征在于，其中所述第二电容的电容值大于所述的第一电容的电容值。
  7. 根据权利要求1所述的电容感测装置，其特征在于，所述控制电路包括数字积分电路，依据所述数字感测信号产生积分值，依据所述积分值与目标值调整所述可调电容单元的电容值。
  8. 根据权利要求7所述的电容感测装置，其特征在于，当所述积分值高于所述目标值时，所述控制电路提高所述可调电容单元的电容值，当所述积分值低于所述目标值时，所述控制电路降低所述可调电容单元的电容值。
  9. 根据权利要求1所述的电容感测装置，其特征在于，还包括：
    数字低通率滤波电路，耦接于所述模拟数字转换器与所述控制电路之间，对所述数字感测信号进行低通滤波。
  10. 根据权利要求1所述的电容感测装置，其特征在于，所述可调电容单元包括：
    多个第四开关，各第四开关的一端耦接所述第二开关的另一端；以及
    多个电容，分别耦接对应的第四开关的另一端与接地之间，所述控制电路控制所述多个第四开关的导通状态而调整所述可调电容单元的电容值。
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