Electrostatic capacity detection device, electrostatic capacity detection method, and input device

Abstract

The calculating section (25) calculates a detected value of the electrostatic capacity of the capacitor (Crg) based on the detection signal (Dm). The correcting section (26) repeatedly shifts to a correction mode, and in the case of shifting to the correction mode, controls the alternating voltage output section (20) so that the difference between the amplitudes of the first alternating voltage (V1) and the second alternating voltage (V2) changes, and acquires a correction value corresponding to the change in the detected value of the calculating section (25) accompanying the change in the difference between the amplitudes. The correcting section (26) corrects the detected value calculated by the calculating section (25) in correspondence with the change in the correction value acquired in the correction mode.

Description

Technical Field

[0001] This disclosure relates to an electrostatic capacitance detection device, an electrostatic capacitance detection method, and an electrostatic capacitance-type input device. Background Technology

[0002] In self-capacitance type electrostatic capacitance detection devices that detect the electrostatic capacitance of the detection electrode relative to ground, there is a problem of reduced detection sensitivity and accuracy due to parasitic capacitance generated between the ground and the detection electrode. In the past, to mitigate the effects of such parasitic capacitance, a shielding electrode (also called an active shield) driven at the same potential as the detection electrode was sometimes placed close to the detection electrode. By setting up the shielding electrode, it is difficult for the detection electrode to generate electrostatic coupling with surrounding conductors, thus reducing the capacitance of the parasitic capacitor. Furthermore, since the shielding electrode and the detection electrode are at the same potential, the electrostatic capacitance between the active shield and the detection electrode does not affect the detection results.

[0003] On the other hand, in the electrostatic capacitance detection device described in Patent Document 1 below, the amplitude of the AC voltage driving the detection electrode is adjusted to be smaller than the AC voltage of the shielding electrode. That is, the amplitude of the AC voltage of the shielding electrode is adjusted so that the charge supplied to the parasitic capacitor between the detection electrode and ground is canceled out by the charge supplied to the capacitor between the detection electrode and the shielding electrode. As a result, the influence of the parasitic capacitor between the detection electrode and ground on the detection sensitivity and detection accuracy can be further reduced.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2018 / 1167606 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, in the electrostatic capacitance detection device described in Patent Document 1, since the capacitor between the detection electrode and the shielding electrode is charged by the voltage difference between the detection electrode and the shielding electrode, if the capacitance value of the capacitor between the detection electrode and the shielding electrode changes, an error will occur in the detection result of the electrostatic capacitance between the detection electrode and ground. The capacitance of the capacitor between the detection electrode and the shielding electrode is larger than the electrostatic capacitance between the detection electrode and ground, which is the object of detection, and sometimes exhibits temperature dependence due to factors such as the temperature characteristics of the dielectric constant of the circuit board forming the shielding electrode. Therefore, when the capacitance of the capacitor between the detection electrode and the shielding electrode changes due to temperature or other influences, an error in the detection result arises.

[0009] Therefore, the purpose of this disclosure is to provide an electrostatic capacitance detection device, an electrostatic capacitance detection method thereof, and an input device equipped with such an electrostatic capacitance detection device, which can reduce the error in the detection result caused by the change in capacitance of the capacitor formed between the detection electrode and the shielding electrode.

[0010] Methods for solving problems

[0011] One aspect of this disclosure relates to a capacitance detection device that detects the capacitance between an object approaching a detection electrode and the detection electrode, comprising: an AC voltage output unit that outputs a first AC voltage supplied to a shielding electrode disposed near the detection electrode, and a second AC voltage with the same frequency and phase as the first AC voltage but a smaller amplitude than the first AC voltage; a detection signal generation unit that supplies charge to the detection electrode from a node connected to the detection electrode, such that the voltage of the node is close to the second AC voltage, and generates an AC detection signal corresponding to the supplied charge; and a calculation unit that calculates the capacitance between the object and the detection electrode based on the first AC voltage. The detection signal is used to calculate the detection value of the electrostatic capacitance; and a correction unit corrects for changes in the detection value that occur when the parasitic capacitance between the shielding electrode and the detection electrode, i.e., the shielding capacitance, changes. The correction unit repeatedly switches to a correction mode. When switching to the correction mode, the AC voltage output unit is controlled to change the amplitude difference between the first AC voltage and the second AC voltage, and a correction value corresponding to the change in the detection value that occurs with the change in the amplitude difference is obtained. The detection value is corrected according to the change in the correction value obtained in the correction mode.

[0012] The effects of the invention

[0013] According to this disclosure, an electrostatic capacitance detection device, an electrostatic capacitance detection method thereof, and an input device equipped with such an electrostatic capacitance detection device are provided, which can reduce the error in the detection result caused by the change in capacitance of the capacitor formed between the detection electrode and the shielding electrode. Attached Figure Description

[0014] Figure 1 This is a diagram illustrating an example of the structure of the input device involved in this embodiment.

[0015] Figure 2 This is a diagram illustrating an example of the structure of the electrostatic capacitance detection device according to this embodiment.

[0016] Figure 3 This is a diagram illustrating an example of the structure of a subtraction circuit.

[0017] Figure 4 This is a diagram illustrating an example of the structure of the calculation unit.

[0018] Figure 5 This is a flowchart illustrating an example of the electrostatic capacitance detection method according to the first embodiment.

[0019] Figure 6 It is used for explanation Figure 5 The flowchart illustrates an example of the correction mode processing in the initial state of the electrostatic capacitance detection method.

[0020] Figure 7 It is used for explanation Figure 5 The flowchart illustrates an example of the processing of the correction mode after the initial state in the electrostatic capacitance detection method.

[0021] Figure 8 It is used to explain in Figure 5 The flowchart illustrates an example of the process for obtaining a corrected detection value in the electrostatic capacitance detection method.

[0022] Figure 9 It is used for explanation Figure 5 A flowchart of a variation of the correction mode processing after the initial state in the electrostatic capacitance detection method shown.

[0023] Figure 10 It is used to explain in Figure 5 The flowchart illustrates a variation of the process for obtaining a corrected detection value in the electrostatic capacitance detection method shown.

[0024] Figure 11 It is used for explanation Figure 5 A flowchart of a variation of the correction mode processing in the initial state of the electrostatic capacitance detection method shown.

[0025] Figure 12 It is used to explain Figure 5 A flowchart of a variation of the correction mode processing after the initial state in the electrostatic capacitance detection method shown.

[0026] Figure 13 This is a flowchart illustrating an example of the electrostatic capacitance detection method according to the second embodiment.

[0027] Figure 14 It is used for explanation Figure 13 The flowchart illustrates an example of the correction mode processing in the initial state of the electrostatic capacitance detection method.

[0028] Figure 15 It is used for explanation Figure 13 The flowchart illustrates an example of the processing of the correction mode after the initial state in the electrostatic capacitance detection method.

[0029] Figure 16A as well as Figure 16B It is used for explanation Figure 13 A flowchart of a variation of the correction mode processing in the electrostatic capacitance detection method shown. Detailed Implementation

[0030] <Summary>

[0031] First, a summary of the electrostatic capacitance detection device, electrostatic capacitance detection method, and input device involved in this disclosure will be provided.

[0032] The first aspect of this disclosure relates to a capacitance detection device for detecting the capacitance between an object approaching a detection electrode and the detection electrode. This capacitance detection device includes: an AC voltage output unit that outputs a first AC voltage supplied to a shielding electrode disposed near the detection electrode, and a second AC voltage with the same frequency and phase as the first AC voltage but a smaller amplitude than the first AC voltage; a detection signal generation unit that supplies charge from a node to the detection electrode such that the voltage of the node connected to the detection electrode is close to the second AC voltage, and generates an AC detection signal corresponding to the supplied charge; a calculation unit that calculates a detected value of the capacitance based on the detection signal; and a correction unit that corrects for changes in the detected value associated with changes in the parasitic capacitance between the shielding electrode and the detection electrode, i.e., the shielding capacitance. The correction unit repeatedly switches to a correction mode. When switching to the correction mode, it controls the AC voltage output unit to change the difference in amplitude between the first AC voltage and the second AC voltage, and obtains a correction value corresponding to the change in the detected value associated with the change in the difference in amplitude. The detected value is corrected according to the change in the correction value obtained in the correction mode.

[0033] In the electrostatic capacitance detection device according to the first aspect, a voltage corresponding to the difference between a first AC voltage and a second AC voltage is applied to a parasitic capacitor formed between a detection electrode and a shielding electrode (hereinafter sometimes referred to as the "detection electrode-shielding electrode inter-capacitor"). A charge corresponding to this voltage is supplied from the detection signal generation unit to the detection electrode-shielding electrode inter-capacitor. If the capacitance of the detection electrode-shielding electrode inter-capacitor, i.e., the shielding capacitance, changes due to temperature or other factors, the charge supplied from the detection signal generation unit to the detection electrode-shielding electrode inter-capacitor changes. Correspondingly, the detection signal changes, and therefore, an error occurs in the detected value of the electrostatic capacitance calculated based on the detection signal.

[0034] Therefore, in the correction unit, a process is performed to correct for changes in the detection value associated with changes in the shielding capacitance. Specifically, the transition to the correction mode is repeated. In the correction mode, the AC voltage output unit is controlled to change the amplitude difference between the first and second AC voltages (hereinafter sometimes referred to as "AC voltage amplitude difference"), and a correction value corresponding to the change in the detection value associated with the change in the AC voltage amplitude difference is obtained. Since the change in the detection value associated with the change in the AC voltage amplitude difference has a value corresponding to the shielding capacitance, the correction value obtained in the correction mode has a value corresponding to the shielding capacitance. By correcting the detection value corresponding to the change in this correction value, the detection value is corrected to correspond to the change in the shielding capacitance, thereby correcting for changes in the detection value associated with changes in the shielding capacitance. Therefore, the error in the detection value corresponding to changes in the shielding capacitance caused by influences such as temperature is reduced.

[0035] Preferably, the correction unit corrects the detected value so as to cancel out the correction target component, wherein the correction target component is proportional to the difference between the correction value obtained in the correction mode of the initial state, i.e., the first correction value, and the correction value obtained in the correction mode after the initial state, i.e., the second correction value, and corresponds to the change in the detected value that accompanies the change in the shielding capacitance.

[0036] According to this structure, the correction target component, which is proportional to the difference between the first correction value obtained in the correction mode of the initial state and the second correction value obtained in the correction mode after the initial state, has a value corresponding to the change in the detection value associated with the change in the shielding capacitance. The detection value is corrected so that this correction target component is canceled out. Thus, the change in the detection value associated with the change in the shielding capacitance since the initial state is corrected.

[0037] Preferably, the correction unit calculates the correction target component each time it switches to a correction mode. In normal operating mode, the detection value can be corrected based on the correction target component calculated in the most recent correction mode.

[0038] According to this structure, in the case of a normal operating mode that is not a correction mode, the detection value is corrected based on the correction object component calculated in the most recent correction mode. As a result, compared to calculating the correction object component every time a detection value is calculated, the frequency of processing for calculating the correction object component is reduced, thus making it easier to reduce the processing burden.

[0039] Preferably, the electrostatic capacitance detection device may include an analog-to-digital converter that converts the detection signal into a digital signal in sync with a clock signal. The AC voltage output unit may output a first AC voltage and a second AC voltage, both having a sine wave of a first frequency. The calculation unit may multiply a synchronization signal having a sine wave of the first frequency and the detection signal converted into a digital signal in sync with a clock signal to obtain a detection value corresponding to the demodulated signal obtained by removing harmonic components from the result of the multiplication operation.

[0040] According to this structure, a synchronization signal having the same frequency as the first AC voltage and a detection signal are multiplied together to obtain a detection value corresponding to the demodulated signal obtained by removing harmonic components from the result of the multiplication. Therefore, a high-precision detection value corresponding to the charge supplied to the detection electrode corresponding to the first AC voltage and the second AC voltage can be obtained.

[0041] Preferably, when the correction unit switches to the correction mode, it can obtain a first detection value and a second detection value, and obtain a correction value corresponding to the difference between the first detection value and the second detection value. The first detection value is the detection value when the AC voltage output unit is controlled so that the amplitude difference (AC voltage amplitude difference) is a first amplitude difference, and the second detection value is the detection value when the AC voltage output unit is controlled so that the amplitude difference (AC voltage amplitude difference) is a second amplitude difference different from the first amplitude difference.

[0042] Based on this structure, a correction value is obtained corresponding to the difference between the two detection values ​​(first detection value and second detection value) obtained when the AC voltage amplitude difference is set to two amplitude differences (first amplitude difference and second amplitude difference).

[0043] Preferably, when the correction unit switches to the correction mode, it can control the AC voltage output unit to output a first AC voltage and a second AC voltage whose amplitude difference (AC voltage amplitude difference) is modulated by a modulation signal having a second frequency lower than the first frequency (synchronization signal), and obtain a correction value corresponding to the amplitude of the AC component of the second frequency contained in the demodulated signal.

[0044] According to this structure, by modulating the AC voltage amplitude difference with a modulation signal having a fixed amplitude and a second frequency, the demodulated signal contains an AC component of the second frequency corresponding to the modulation signal. The amplitude of this AC component has a magnitude corresponding to the change in the detected value associated with the change in the AC voltage amplitude difference. Therefore, a correction value corresponding to the change in the detected value associated with the change in the AC voltage amplitude difference is obtained based on the amplitude of the AC component of the second frequency contained in the demodulated signal.

[0045] Preferably, the electrostatic capacitance detection device may have an analog-to-digital converter that converts the detection signal into a digital signal in sync with a clock signal. The AC voltage output unit may output a first AC voltage and a second AC voltage, both having a first frequency and a sine wave, respectively. The calculation unit, in sync with the clock signal, multiplies a first synchronization signal having a first frequency and a phase approximately similar to the first AC voltage with the detection signal converted to a digital signal, and, in sync with the clock signal, multiplies a second synchronization signal having a first frequency and a phase deviating from the first synchronization signal by a quarter of a period with the detection signal converted to a digital signal with the detection signal, to obtain a detection complex number. This detection complex number has a real part consisting of a first demodulated signal obtained by removing harmonic components from the result of the multiplication of the first synchronization signal and the detection signal, and an imaginary part consisting of a second demodulated signal obtained by removing harmonic components from the result of the multiplication of the second synchronization signal and the detection signal. When the correction unit switches to correction mode, it controls the AC voltage output unit to change the amplitude difference (AC voltage amplitude difference) and obtains a complex number corresponding to the change in the detection complex number associated with the change in amplitude difference (AC voltage amplitude difference), which is used as a correction value. Furthermore, the correction unit performs a first phase correction on the correction value obtained in the initial state correction mode, i.e., the first correction value, where the phase is corrected so that the deflection angle of the first correction value is close to zero. It also performs a second phase correction on the correction value obtained in subsequent correction modes, i.e., the second correction value, where the phase is corrected so that the deflection angle of the second correction value is close to zero, and performs the second phase correction on the detection complex number. Then, the correction unit can obtain a value obtained by correcting the real part of the detection complex number that has undergone the second phase correction as a corrected detection value, so as to cancel the correction target component, wherein the correction target component is proportional to the difference between the real part of the first correction value that has undergone the first phase correction and the real part of the second correction value that has undergone the second phase correction, and corresponds to the change in the real part of the detection complex number that accompanies the change in the shielding capacitance.

[0046] According to this structure, two demodulated signals (first demodulated signal and second demodulated signal) are obtained by multiplying two orthogonal synchronization signals (first synchronization signal and second synchronization signal) with the detection signal, and then removing harmonic components from the multiplication result. A detection complex number is obtained by setting the real and imaginary parts of the two demodulated signals. The deflection angle of this detection complex number characterizes the deviation of the detection signal from the phase of the first synchronization signal, whose phase is approximately the same as the first AC voltage. When switching to correction mode, the AC voltage output section is controlled to change the AC voltage amplitude difference, and a complex number corresponding to the change in the detection complex number associated with this change in AC voltage amplitude difference is obtained as a correction value. Since the deflection angle of the detection complex number remains approximately constant even when the AC voltage amplitude difference changes, the deflection angle of the correction value, like the deflection angle of the detection complex number, characterizes the deviation of the detection signal from the phase of the first synchronization signal.

[0047] Here, if a phase / frequency variation (jitter) occurs in the clock signal, the frequencies of the two synchronization signals (first synchronization signal and second synchronization signal) generated synchronously with the clock signal will change. Therefore, the phases of the first AC voltage and the second AC voltage relative to the two synchronization signals will change, and consequently, the phase of the detection signal relative to the two synchronization signals will also change. On the other hand, since the two synchronization signals (first synchronization signal and second synchronization signal) are generated synchronously with the clock signal respectively, the relative phases of these synchronization signals will not change. Therefore, in the case of clock signal jitter, the phase deviation of the detection signal relative to the first synchronization signal changes, and the deviation angle of the detection complex number and the correction value will change respectively.

[0048] Therefore, in the correction unit, a first phase correction is applied to the first correction value obtained in the correction mode of the initial state, and a second phase correction is applied to the second correction value obtained in the correction mode after the initial state. As a result, the deflection angles of the first and second correction values ​​are close to zero. Furthermore, in the correction unit, the same second phase correction as for the second correction value is applied to the detection complex number. Since the deflection angle of the second correction value also characterizes the phase deviation of the detection signal relative to the first synchronization signal in the same way as the detection complex number, by applying the second phase correction to the detection complex number, the deflection angle of the detection complex number is approximately close to zero. As a result, since the deflection angles of the first, second, and detection complex numbers are aligned near zero, the real parts of these complex numbers become values ​​that have largely eliminated the effects of clock signal jitter.

[0049] Then, in the correction unit, a detection value that has been corrected for the change in shielding capacitance is obtained based on the first correction value, the second correction value (after removing the effect of clock signal jitter), and the real part of the detection complex number. That is, since the correction target component, which is proportional to the difference between the real part of the first correction value (after implementing the first phase correction) and the real part of the second correction value (after implementing the second phase correction), has a value corresponding to the change in the detection value associated with the change in shielding capacitance, the real part of the detection complex number that has implemented the second phase correction is corrected so that the correction target component is canceled out.

[0050] The obtained detection values ​​are thus corrected for errors associated with changes in the shielding capacitance from the initial state and errors associated with clock signal jitter, respectively.

[0051] Preferably, when the correction unit switches to the correction mode, it can obtain a first detection complex number and a second detection complex number, and obtain a correction value corresponding to the difference between the first detection complex number and the second detection complex number. The first detection complex number is the detection complex number used when the AC voltage output unit is controlled so that the amplitude difference (AC voltage amplitude difference) is a first amplitude difference, and the second detection complex number is the detection complex number used when the AC voltage output unit is controlled so that the amplitude difference (AC voltage amplitude difference) is a second amplitude difference different from the first amplitude difference.

[0052] Based on this structure, a correction value is obtained corresponding to the difference between the two detection complex numbers (first detection complex number and second detection complex number) obtained when the AC voltage amplitude difference is set to two amplitude differences (first amplitude difference and second amplitude difference).

[0053] Preferably, when the correction unit switches to the correction mode, it can control the AC voltage output unit to output a first AC voltage and a second AC voltage that have been modulated by a modulation signal having a fixed amplitude of a second frequency lower than the first frequency to modulate the difference in amplitude (AC voltage amplitude difference), and obtain the real part of the correction value corresponding to the amplitude of the AC component of the second frequency contained in the first demodulated signal, and the imaginary part of the correction value corresponding to the amplitude of the AC component of the second frequency contained in the second demodulated signal.

[0054] According to this structure, by modulating the AC voltage amplitude difference with a modulation signal having a fixed amplitude and a second frequency, the first demodulated signal and the second demodulated signal each contain an AC component of the second frequency corresponding to the modulation signal. Since the amplitudes of the AC components in the two demodulated signals (the first demodulated signal and the second demodulated signal) represent the changes in the detection complex number (real part and imaginary part) associated with the changes in the AC voltage amplitude difference, correction values ​​(real part and imaginary part) corresponding to the changes in the detection complex number associated with the changes in the AC voltage amplitude difference can be obtained based on the amplitudes of these AC components.

[0055] Preferably, the correction unit can multiply the difference between the real part of the first correction value after the first phase correction and the real part of the second correction value after the second phase correction by a scaling factor, and obtain the corrected detection value based on the sum of the result of the multiplication operation and the real part of the detection complex number after the second phase correction.

[0056] Preferably, the correction unit may perform a second phase correction on an intermediate correction value corresponding to the sum of the complex number obtained by multiplying the second correction value by a scaling factor and the detection complex number, so that the phase angle corresponding to the deflection angle of the second correction value is rotated. The corrected detection value is obtained by subtracting the value obtained by multiplying the real part of the first correction value, which is the first phase correction, by a scaling factor from the real part of the intermediate correction value on which the second phase correction has been performed.

[0057] Preferably, the correction unit can obtain a second correction value whenever it shifts to a correction mode. In the normal operating mode, the corrected detection value is obtained based on the first correction value after the first phase correction, the second correction value obtained in the most recent correction mode, and the detection complex number.

[0058] According to this structure, in the normal operating mode that is not a correction mode, the corrected detection value is obtained based on the first correction value after the first phase correction is implemented, the second correction value obtained in the most recent correction mode, and the detection complex number. Therefore, compared to the case where processing related to the acquisition of the second correction value is performed every time the detection complex number is acquired, the processing burden is easily reduced.

[0059] Preferably, in normal operating mode, when there is no object approaching the detection electrode, the AC voltage output unit can output a second AC voltage with an adjusted amplitude so that the charge supplied from the node to the detection electrode is close to zero, or a second AC voltage with the amplitude of the detection signal adjusted to be close to zero.

[0060] According to this structure, since the amplitude of the detection signal becomes small or close to zero when there is no object near the detection electrode in the normal operating mode, it becomes easy to ensure the dynamic range of the output of the detection signal generation unit.

[0061] The second aspect of this disclosure relates to a capacitance detection method performed in a capacitance detection apparatus for detecting the capacitance between an object near a detection electrode and a detection electrode. In this capacitance detection method, the capacitance detection apparatus includes: an AC voltage output unit that outputs a first AC voltage supplied to a shielding electrode disposed near the detection electrode, and a second AC voltage with the same frequency and phase as the first AC voltage but a smaller amplitude than the first AC voltage; and a detection signal generation unit that supplies charge from a node to the detection electrode such that the voltage of the node connected to the detection electrode approaches the second AC voltage, thereby generating an AC detection signal corresponding to the supplied charge. The electrostatic capacitance detection method includes: a calculation step, which calculates the detected value of electrostatic capacitance based on the detection signal; and a correction step, which corrects for changes in the detected value associated with changes in the parasitic capacitance between the shielding electrode and the detection electrode, i.e., the shielding capacitance. The correction step includes: repeatedly switching to a correction mode; when switching to the correction mode, controlling the AC voltage output unit to change the difference in amplitude between the first AC voltage and the second AC voltage, and obtaining a correction value corresponding to the change in the detected value associated with the change in the difference in amplitude; and correcting the detected value according to the change in the correction value obtained in the correction mode.

[0062] The input device according to the third aspect of this disclosure includes: a detection electrode that changes the electrostatic capacitance between itself and the object in response to the object's approach; a shielding electrode that is configured to detect the object upon approach; and the electrostatic capacitance detection device according to the first aspect described above, which detects the electrostatic capacitance between the object and the detection electrode.

[0063] <First Implementation>

[0064] Figure 1 This is a diagram illustrating an example of the structure of an input device according to an embodiment of the present invention. Figure 1 The input device shown has a sensor unit 1, a capacitance detection device 2, a processing unit 3, a storage unit 4, and an interface unit 5.

[0065] The input device according to this embodiment detects the electrostatic capacitance between the electrodes of the sensor unit 1 and the object when an object 6, such as a finger or pen, approaches the sensor unit 1. Based on this detection result, it inputs information corresponding to the proximity of the object 6. For example, the input device obtains information such as whether the object 6 is close to the sensor unit 1 and the distance between the sensor unit 1 and the object 6 based on the electrostatic capacitance detection result. The input device is used, for example, in user interface devices such as touch sensors and touchpads. In addition, the term "proximity" in this specification means being nearby and does not limit whether the approaching objects are in contact with each other.

[0066] The sensor unit 1 includes: a detection electrode Es for detecting the proximity of an object 6 such as a finger or pen; and a shielding electrode Ea disposed on the proximity detection electrode Es. The detection electrode Es is disposed in the sensor unit 1 in the area where the object approaches. For example, the surface of the detection area of ​​the object 6 is covered by an insulating layer, and the detection electrode Es is disposed on a layer lower than the insulating layer. The shielding electrode Ea is an electrostatic shield used to prevent electrostatic coupling between a conductor other than the object 6 and the detection electrode Es. The shielding electrode Ea is disposed, for example, on a layer lower than the detection electrode Es in the detection area of ​​the object 6.

[0067] like Figure 1 As shown, a capacitor Crg, which forms a static capacitance between the detection electrode Es and the object 6, is formed. A capacitor Crs is formed between the shielding electrode Ea and the detection electrode Es. Furthermore, a capacitor Crgl is formed between the detection electrode Es and ground, and a capacitor Csg is formed between the shielding electrode Ea and ground.

[0068] The electrostatic capacitance detection device 2 detects the electrostatic capacitance of the capacitor Crg formed between the object 6 and the detection electrode Es, and outputs a detection value Ds representing the detection result.

[0069] The processing unit 3 is a circuit that controls the overall operation of the input device. For example, it may be a computer that executes processing according to command codes that follow a program stored in the storage unit 4, or hardware configured to perform a specific function (e.g., logic circuits such as ASICs or FPGAs). The processing in the processing unit 3 can be implemented in a computer based on a program, or at least part of it can be implemented using dedicated hardware.

[0070] The processing unit 3 determines whether the object 6 is close to the sensor unit 1 and calculates the distance between the object 6 and the sensor unit 1 based on the detected capacitance value Ds output from the capacitance detection device 2. Furthermore, the sensor unit 1 may include multiple detection electrodes Es, and the capacitance detection device 2 can detect the capacitance of the capacitor Clg of each of the multiple detection electrodes Es. The processing unit 3 can calculate the proximity position of the object 6 in the sensor unit 1, the size of the object 6, etc., based on the detected capacitance value Ds obtained from each detection electrode Es.

[0071] Storage unit 4 stores the computer program constituting processing unit 3, data used in processing within processing unit 3, and data temporarily held during processing. Storage unit 4 can be configured using any storage device such as DRAM, SRAM, flash memory, or hard disk.

[0072] Interface unit 5 is a circuit used to exchange data between the input device and other devices (such as the main controller of an electronic device equipped with the input device). Processing unit 3 outputs information obtained based on the detection results of electrostatic capacitance detection device 2 (the presence or absence of object 6, the proximity position of object 6, the distance to object 6, the size of object 6, etc.) to a host device (not shown) through interface unit 5. In the host device, this information is used to construct a user interface, such as recognizing pointing operations and gesture operations.

[0073] Next, the structure of the electrostatic capacitance detection device 2 will be explained. Figure 2 This is a diagram illustrating an example of the structure of the electrostatic capacitance detection device 2 according to this embodiment. Figure 2 The electrostatic capacitance detection device 2 shown includes an AC voltage output unit 20, a detection signal generation unit 23 for generating a detection signal Vm, an analog-to-digital conversion unit 24, a calculation unit 25, and a correction unit 26. Furthermore, in the following description, "analog-to-digital conversion" will sometimes be abbreviated as "A / D conversion," and "digital-to-analog conversion" will sometimes be abbreviated as "D / A conversion."

[0074] The AC voltage output unit 20 outputs a first AC voltage V1 and a second AC voltage V2 with a smaller amplitude than the first AC voltage V1 to the shielding electrode Ea. The first AC voltage V1 and the second AC voltage V2 each have the same frequency f1 and are approximately in phase with each other. For example, the first AC voltage V1 and the second AC voltage V2 are sinusoidal AC voltages, plus a fixed DC bias voltage (e.g., a DC voltage that is half the power supply voltage).

[0075] exist Figure 2 In the example, the AC voltage output unit 20 includes a first voltage output unit 21 and a second voltage output unit 22.

[0076] The first voltage output section 21 is a circuit that generates a first AC voltage V1 with a sine wave. For example, Figure 2 As shown, the first voltage output unit 21 includes a sine wave signal generation unit 211, a D / A converter 212, a low-pass filter 213, and an amplifier 214. The sine wave signal generation unit 211 generates a digital signal (a data string of the numerical data of the sine wave) of a sine wave synchronized with the clock signal CK, and inputs it to the D / A converter 212. The D / A converter 212 outputs an analog signal corresponding to the digital sine wave signal. The low-pass filter 213 removes high-frequency components from the analog signal output from the D / A converter 212, outputting a sine wave signal with frequency f1. The amplifier 214 is a buffer amplifier that outputs a first AC voltage V1 corresponding to the sine wave signal output from the low-pass filter 213.

[0077] The second voltage output section 22 is a circuit that outputs a second AC voltage V2 with the same frequency and phase as the first AC voltage V1 and with a smaller amplitude than the first AC voltage V1. For example, it is composed of an attenuation circuit that attenuates the amplitude of the first AC voltage V1.

[0078] exist Figure 2 In the example, the second voltage output unit 22 includes a series circuit of capacitors Ca and Cb. The first voltage output unit 21 applies a first AC voltage V1 to the two ends of this series circuit. The first AC voltage V1 is divided by capacitors Ca and Cb, generating a second AC voltage V2 in capacitor Cb. One terminal of capacitor Ca is connected to the output of the first voltage output unit 21, and the other terminal of capacitor Ca is connected to one terminal of capacitor Cb, which is connected to ground.

[0079] In one example, capacitor Ca has a fixed capacitance, and the capacitance of capacitor Cb can be adjusted. The amplitude of the second AC voltage V2 is adjusted according to the capacitance of capacitor Cb. In this case, capacitor Cb can be a discrete component of a variable capacitor, or it can be a component formed in a semiconductor chip or the like inside an IC. In the latter case, for example, capacitor Cb is composed of multiple capacitors connected in parallel, and the capacitance is adjusted by changing the number of capacitors connected in parallel using a switch or the like.

[0080] For example, in the normal operating mode (not the correction mode, as described later), when there is no object 6 approaching the detection electrode Es (the electrostatic capacitance of capacitor Crg is close to zero), the amplitude of the second AC voltage V2 is adjusted so that the charge Qs supplied from the detection signal generation unit 23 to the detection electrode Es is approximately zero. Figure 2 In the second voltage output section 22 shown, the electrostatic capacitance ratio of capacitor Ca to capacitor Cb is adjusted so that the charge Qs supplied from the detection signal generation section 23 to the detection electrode Es is approximately zero. If the charge Qs is zero when capacitor Crg is zero, the charge supplied to capacitor Crs and the charge supplied to parasitic capacitor Crgl cancel each other out. Therefore, since the amplitude of the second AC voltage V2 is adjusted so that the charge Qs is approximately zero, the component of parasitic capacitor Crgl contained in the detection signal Vm of the detection signal generation section 23 (described later) becomes small, thus making it easier to suppress the decrease in detection sensitivity and detection accuracy caused by parasitic capacitor Crgl.

[0081] Alternatively, the amplitude of the second AC voltage V2 can be adjusted so that the amplitude of the detection signal Vm is close to zero. Since the amplitude of the detection signal Vm is close to zero when there is no object 6 near the detection electrode Es, the dynamic range of the detection signal Vm relative to the static capacitance of the detected object (the static capacitance of capacitor Crg) is expanded, thus making it easier to improve the detection sensitivity.

[0082] The detection signal generation unit 23 supplies a charge Qs from node N1 to the detection electrode Es, so that the voltage of node N1 connected to the detection electrode Es is close to the second AC voltage V2, and generates an AC detection signal Vm corresponding to the supplied charge Qs.

[0083] exist Figure 2 In the example, the detection signal generation unit 23 includes a charge amplifier 231 and a subtraction operation unit 232. The charge amplifier 231 supplies a charge Qs from node N1 to the detection electrode Es, such that the voltage of node N1 is close to the second AC voltage V2 applied to node N2, and outputs a signal Vo corresponding to the supplied charge Qs. For example, Figure 2 As shown, charge amplifier 231 includes operational amplifier OP1, feedback capacitor Cag, and feedback resistor Rag. Operational amplifier OP1 amplifies the voltage difference between the inverting input terminal connected to node N1 and the non-inverting input terminal connected to node N2, and outputs the amplified result as signal Vo. Feedback capacitor Cag is located in the path between the output terminal of signal Vo and the inverting input terminal of operational amplifier OP1. Feedback resistor Rag is connected in parallel with feedback capacitor Cag.

[0084] exist Figure 2 In the example, the capacitance value of the feedback capacitor Cag and the resistance value of the feedback resistor Rag can be adjusted separately. By adjusting the values ​​of these components, the phase difference between the first AC voltage V1 and the second AC voltage V2 and the signal Vo, and the gain of the signal Vo's amplitude relative to the capacitance of the capacitor Cag, can be adjusted. The feedback capacitor Cag and the feedback resistor Rag can be, for example, discrete components whose values ​​can be adjusted, or components inside an IC whose values ​​can be adjusted by means of laser trimming, etc.

[0085] In addition, Figure 2In the example, charge amplifier 231 has a resistor Rs located in the path connecting node N1 and detection electrode Es. Charge amplifier 231, with its resistor R, forms a low-pass filter for the signal input from object 6 via capacitor CRG. Therefore, even if an AC noise voltage overlaps between the grounding point of object 6 and the grounding point of electrostatic capacitance detection device 2, the noise voltage can be attenuated by the low-pass filter formed by charge amplifier 231. The resistor Rs is, for example, a variable resistor, adjusted corresponding to the frequency f1 of the first AC voltage V1 and the second AC voltage V2.

[0086] The subtraction unit 232 subtracts a given reference signal from the signal Vo. The reference signal is equivalent to the signal Vo output from the operational amplifier OP1 in the normal operating mode (not in the correction mode) when there is no object 6 approaching the detection electrode Es. By subtracting the reference signal from the signal Vo, an AC detection signal Vm with an amplitude approximately proportional to the electrostatic capacitance of the capacitor Crg can be obtained. The subtraction unit 232 includes, for example, a fully differential amplifier, which outputs the differential signal obtained by subtracting the reference signal from the signal Vo as the detection signal Vm.

[0087] Figure 3 This is a diagram illustrating an example of the structure of the subtraction unit 232. Figure 3 In the example, the subtraction unit 232 includes a fully differential amplifier 233, resistors R1 to R7, and capacitors C1 to C3. Capacitor C1 is connected between the inverting input terminal and the non-inverting output terminal of the fully differential amplifier 233. Capacitor C2 is connected between the non-inverting input terminal and the inverting output terminal of the fully differential amplifier 233. The signal Vo of the charge amplifier 231 is input to the inverting input terminal of the fully differential amplifier 233 via resistors R3 and R4 connected in series. The signal Vo is input to one end of resistor R3, and one end of resistor R4 is connected to the inverting input terminal of the fully differential amplifier 233. The midpoint of the connection between resistors R3 and R4 is connected to the non-inverting output terminal of the fully differential amplifier 233 via resistor R1. A first AC voltage V1 is input to the non-inverting input terminal of the fully differential amplifier 233 via resistors R5 and R6 connected in series. The first AC voltage V1 is input to one end of resistor R5, and one end of resistor R6 is connected to the non-inverting input terminal of the fully differential amplifier 233. The midpoint of the connection between resistors R5 and R6 is connected to the inverting output terminal of the fully differential amplifier 233 via resistor R2. Capacitor C3 is connected between the midpoint of the connection between resistors R3 and R4 and the midpoint of the connection between resistors R5 and R6. Furthermore, a DC bias voltage Vr1 is input to the midpoint of the connection between resistors R5 and R6 via resistor R7.

[0088] exist Figure 3In the subtraction unit 232 shown, the gain is different with respect to the two inputs (signal Vo and the first AC voltage V1). That is, the gain with respect to the second AC voltage V2, which is input to the path connecting resistor R7, is smaller than the gain with respect to signal Vo. The subtraction unit 232 amplifies the difference between the AC voltage (reference signal) attenuated from the first AC voltage V1 and the signal Vo, and outputs the amplified result as a differential signal (detection signal Vm). Furthermore, the subtraction unit 232 constitutes a low-pass filter to remove high-frequency components input from the object 6 through capacitor Crg. Through this low-pass filter function, the foldback noise in the A / D conversion unit 24, described later, is reduced.

[0089] Back Figure 2 .

[0090] The A / D converter 24 converts the analog detection signal Vm output from the detection signal generation unit 23 into a digital detection signal Dm. When the detection signal Vm is a differential signal, the A / D converter 24 can, for example, be a Δ∑-type A / D converter with differential input.

[0091] The calculation unit 25 calculates the detected value of the electrostatic capacitance based on the detection signal Vm obtained by performing A / D conversion on the detection signal Vm.

[0092] For example, the calculation unit 25, synchronized with the clock signal CK, multiplies a first synchronization signal U1 having a frequency f1 and a phase approximately similar to the first AC voltage V1, and a detection signal Dm converted into a digital signal. Furthermore, synchronized with the clock signal CK, the calculation unit 25 multiplies a second synchronization signal U2 having a frequency f1 and a phase deviating from the first synchronization signal U1 by a quarter of a period, and the detection signal Dm converted into a digital signal. Then, the calculation unit 25 obtains a detection complex number Da, which has a real part obtained by removing harmonic components from the result of the multiplication of the first synchronization signal U1 and the detection signal Dm, and an imaginary part obtained by removing harmonic components from the result of the multiplication of the second synchronization signal U2 and the detection signal Dm.

[0093] Here, the first demodulated signal I (the real part of the complex number Da for detection), obtained by removing harmonic components from the result of multiplying the first synchronization signal U1 (whose phase is approximately the same as the first AC voltage V1) and the detection signal Dm, has a value corresponding to the amplitude of the detection signal Vm. Therefore, it is equivalent to the detected value of the electrostatic capacitance of the capacitor Crg, which is the object of detection. This detected value (the first demodulated signal I) includes errors associated with changes in the electrostatic capacitance of the capacitor Crs (hereinafter sometimes referred to as "shielding capacitance Crs") and errors associated with changes in the phase / frequency (jitter) of the clock signal CK. Therefore, these errors are corrected in the correction section 26 described later.

[0094] Since the two sine wave synchronization signals (U1, U2) are orthogonal with a phase deviation of one-quarter of a period, the two demodulated signals (I, Q), obtained by multiplying the detection signal Dm and the two synchronization signals (U1, U2) respectively and removing harmonic components, characterize the relative phase of the detection signal Dm with respect to the synchronization signals (U1, U2). That is, the detection complex number Da takes the first demodulated signal I (after removing harmonic components) from the result of multiplying the first sine wave synchronization signal U1 and the detection signal Dm as its real part, and the second demodulated signal Q (after removing harmonic components) from the result of multiplying the second sine wave synchronization signal U2 and the detection signal Dm as its imaginary part. The deflection angle of this detection complex number Da characterizes the phase deviation of the detection signal Dm relative to the first synchronization signal U1. Therefore, the detection complex number Da contains information about the amplitude of the detection signal Dm and information about the phase of the detection signal Dm relative to the first synchronization signal U1.

[0095] Figure 4 This is a diagram illustrating an example of the structure of the calculation unit 25. The calculation unit 25 is, for example, as shown below. Figure 1 As shown, it includes a first demodulation unit 251 and a second demodulation unit 254.

[0096] The first demodulation unit 251 multiplies the first synchronization signal U1 of the sine wave generated in the first synchronization signal generation unit 257 with the detection signal Dm to generate a first demodulated signal I from the result of the multiplication operation after removing harmonic components. Figure 4 In the example, the first demodulation unit 251 includes: a multiplication operation unit 252 that multiplies the detection signal Dm and the first synchronization signal U1; and a low-pass filter 253 that removes harmonic components from the multiplication result of the multiplication operation unit 252.

[0097] The second demodulation unit 254 multiplies the second synchronization signal U2, a sine wave generated in the second synchronization signal generation unit 258, with the detection signal Dm to generate a second demodulation signal Q, from which harmonic components are removed. Figure 4 In the example, the second demodulation unit 254 includes: a multiplication unit 255 that multiplies the detection signal Dm and the second synchronization signal U2; and a low-pass filter 256 that removes harmonic components from the multiplication result of the multiplication unit 255.

[0098] The first synchronization signal generation unit 257 and the second synchronization signal generation unit 72 generate a first synchronization signal U1 and a second synchronization signal U2, respectively, which are sine waves with a frequency f1 synchronized with the clock signal CK. In one example, the first synchronization signal generation unit 257 generates a COS wave with a frequency f1 as the first synchronization signal U1, and the second synchronization signal generation unit 258 generates a SIN wave that lags behind the first synchronization signal U1 by one-quarter of a period as the second synchronization signal U2.

[0099] Back Figure 2 .

[0100] The correction unit 26 corrects for changes in the detection value of the calculation unit 25 that occur when the electrostatic capacitance (shielding capacitance Crs) of the capacitor Crs formed between the shielding electrode Ea and the detection electrode Es changes. In this correction process, the correction unit 26 repeatedly switches to the correction mode. When switching to the correction mode, the correction unit 26 controls the AC voltage output unit 20 to change the difference in amplitude between the first AC voltage V1 and the second AC voltage V2 (V1-V2: AC voltage amplitude difference), and obtains a correction value corresponding to the change in the detection value of the calculation unit 25 associated with the change in the AC voltage amplitude difference (V1-V2). Then, the correction unit 26 corrects the detection value of the calculation unit 25 according to the change in the correction value obtained in the correction mode, obtaining a corrected detection value Ds.

[0101] Here, we explain the change in the amplitude of the signal Vo that accompanies the change in the shielding capacitance Crs. The voltage amplitude of the signal Vo output from the charge amplifier 231 is characterized by the following formula.

[0102] [Mathematical Expression 1]

[0103]

[0104] In equation (1), “Vo”, “V1” and “V2” represent the voltage amplitudes of signal Vo, the first AC voltage V1 and the second AC voltage V2, respectively, and “Crg”, “Crgl”, “Crs” and “Cag” represent the electrostatic capacitances of capacitors Crg, Crgl, Crs and Cag, respectively.

[0105] Here, the amplitude of the first AC voltage V1 is set to be fixed, and the amplitude of the second AC voltage V2 is changed by "ΔV". If the electrostatic capacitance of each capacitor (Crg, Crgl, Crs, Cag) is assumed to be unchanged, then the change in the amplitude of the signal Vo, ΔVo, is characterized by the following formula.

[0106] [Mathematical Expression 2]

[0107]

[0108] If the shielding capacitor Crs in the initial state is set as "Crs_ref", then the change in amplitude ΔVo_ref of the signal Vo when the amplitude of the second AC voltage V2 changes by "ΔV" in the initial state is characterized by the following formula.

[0109] [Mathematical Expression 3]

[0110]

[0111] The change ΔCrs of the shielding capacitance Crs from the initial state is characterized by the following formula, which is derived from equations (2) and (3).

[0112] [Mathematical Expression 4]

[0113]

[0114] In equation (4), it is assumed that the changes in the static capacitances of capacitors Crg, Crgl, and Cag are sufficiently small and negligible compared to the changes in the shielding capacitor Crs (ΔCrs).

[0115] On the other hand, the change in the amplitude of the signal Vo, ΔVo_crs, which is associated with the change in the shielding capacitance Crs, is characterized by the following formula.

[0116] [Mathematical Expression 5]

[0117]

[0118] In equation (5), it is also assumed that the changes in the static capacitance of capacitors Crg, Crgl, and Cag are sufficiently small and negligible compared to the changes in shielding capacitance Crs ΔCrs.

[0119] If we substitute equation (4) into equation (5), the change in the amplitude of signal Vo, ΔVo_crs, which is associated with the change in shielding capacitance Crs, is characterized by the following equation.

[0120] [Mathematical Expression 6]

[0121] ΔVo_crs=-α·(ΔVo-ΔVo_ref)…(6)

[0122] The proportionality coefficient α in equation (6) is characterized by the following formula.

[0123] [Mathematical Expression 7]

[0124]

[0125] When the shielding capacitance Crs changes by "ΔCrs" compared to the initial state, the amplitude of the signal Vo contains a change (error) equivalent to "ΔVo_crs" in equation (6) due to this change in shielding capacitance Crs. Therefore, the change (error) in the amplitude of the signal Vo associated with the change in shielding capacitance Crs ΔCrs is corrected by subtracting this "ΔVo_crs" from the amplitude "Vo". The corrected amplitude of the signal Vo is characterized by the following formula.

[0126] [Mathematical Expression 8]

[0127]

[0128] As can be seen from comparing equations (1) and (8-2), the amplitude calculated by correcting the amplitude of the signal Vo by equation (8-1) is equivalent to the amplitude of the signal Vo obtained when the shielding capacitance Crs, which changes from the initial state, is returned to the shielding capacitance Crs_ref of the initial state.

[0129] In order to perform corrections to Equation (8-1), the correction unit 26 obtains correction values ​​for "ΔVo_ref" and "ΔVo" corresponding to Equation (8-1) in each correction mode. These correction values ​​correspond to the changes in the detection value of the calculation unit 25 associated with the change in the AC voltage amplitude difference (V1-V2) ΔV. "ΔVo_ref" corresponds to the correction value obtained in the initial state correction mode (the first correction value), and "ΔVo" corresponds to the correction value obtained in the subsequent correction modes (the second correction value). If two correction values ​​corresponding to "ΔVo_ref" and "ΔVo" are obtained, the correction unit 26 corrects the detection value of the calculation unit 25 corresponding to "Vo" according to Equation (8-1). That is, the correction unit 26 calculates the detection value of the calculation unit 25 according to the change in the correction value obtained in the correction mode (the second correction value - the first correction value), so that "Vo" is corrected in equation (8-1) according to the change in "ΔVo" relative to "ΔVo_ref" (ΔVo - ΔVo_ref). Thus, the correction unit 26 corrects the change (error) in the detection value of the calculation unit 25 caused by the change in the shielding capacitor Crs.

[0130] In addition to correcting the error in the detection value caused by the change in the shielding capacitor Crs, the correction unit 26 also corrects the error in the detection value caused by the jitter of the clock signal CK.

[0131] If the relative phase of the first AC voltage V1 and the second AC voltage V2 with the first synchronization signal U1 and the second synchronization signal U2 changes due to the jitter of the clock signal CK, the deflection angle of the detection complex number Da obtained by the calculation unit 25 changes accordingly. If the deflection angle of the detection complex number Da changes, its real part (the first demodulation signal I) also changes. Therefore, the real part of the detection complex number Da (the first demodulation signal I), which corresponds to the detection value of the electrostatic capacitance calculated by the calculation unit 25, is affected by the jitter of the clock signal CK, resulting in an error.

[0132] In order to correct the error in the detection value caused by the jitter of the clock signal CK, the correction unit 26, in the aforementioned correction mode, obtains a complex number containing phase information as a correction value. That is, when the correction unit 26 switches to the correction mode, it controls the AC voltage output unit 20 to change the AC voltage amplitude difference (V1-V2), and obtains a complex number corresponding to the change in the detection complex number Da that accompanies the change in the AC voltage amplitude difference (V1-V2) as a correction value.

[0133] The correction unit 26 performs a first phase correction on the correction value B1 obtained in the initial state correction mode, i.e., the first correction value B1. In this first phase correction, the phase is corrected so that the deflection angle θ1 of the first correction value B1 is close to zero. The first phase correction is a correction that rotates the phase angle by "-θ1".

[0134] Furthermore, the correction unit 26 performs a second phase correction on the correction value B2 obtained in the correction mode after the initial state. In this second phase correction, the phase is corrected so that the deflection angle θ2 of the second correction value B2 is close to zero. The second phase correction is a correction that rotates the phase angle by "-θ2".

[0135] Furthermore, the correction unit 26 applies a second phase correction to the detection complex number Da, which is the same as the second correction value B2. Since the deflection angle of the detection complex number Da remains approximately constant even when the AC voltage amplitude difference (V1-V2) changes, the deflection angle θ2 of the second correction value, which corresponds to the change in the detection complex number Da associated with the change in the AC voltage amplitude difference (V1-V2), has a value close to the deflection angle of the detection complex number Da. Therefore, if the second phase correction is applied to the detection complex number Da, the deflection angle of the detection complex number Da also approaches zero.

[0136] Therefore, the first correction value B1, the second correction value B2, and the bias angle of the detection complex number Da are all brought close to zero through phase correction, eliminating the change in the bias angle of the detection complex number Da caused by the jitter of the clock signal CK. If the bias angles of the first correction value B1, the second correction value B2, and the detection complex number Da are close to zero, their imaginary parts also become close to zero. The real parts of the first correction value B1, the second correction value B2, and the detection complex number Da have values ​​corresponding to “ΔVo_ref”, “ΔVo”, and “Vo” in equation (8-1), respectively.

[0137] The correction unit 26 corrects the real part of the detection complex number Da for which the second phase correction has been implemented, so as to cancel out the correction target component, wherein the correction target component is a correction target component (ΔVo_crs, Equation (6)) that is proportional to the difference (ΔVo-ΔVo_ref) between the real part (ΔVo) of the first correction value B1 for which the first phase correction has been implemented and the real part (ΔVo) of the second correction value B2 for which the second phase correction has been implemented, and corresponds to the change in the real part of the detection complex number Da that accompanies the change of the shielding capacitor Crs (Equation (8-1)). Thus, the correction unit 26 obtains a detection value Ds that corrects the error caused by the change ΔCrs of the shielding capacitor Crs and the error caused by the jitter of the clock signal CK, respectively.

[0138] After the initial state, the correction unit 26 acquires the second correction value B2 whenever it transitions to the correction mode. In the normal operating mode other than the correction mode, the correction unit 26 acquires the corrected detection value Ds based on the first correction value B1 after the first phase correction is implemented, the second correction value B2 acquired in the most recent correction mode, and the detection complex number Da.

[0139] Next, the electrostatic capacitance detection method in the electrostatic capacitance detection device 2 with the above-described input device structure will be explained with reference to the flowchart. Figure 5 This is a flowchart illustrating an example of the electrostatic capacitance detection method according to the first embodiment.

[0140] For example, when the power is turned on and an instruction to set to the initial state is input from the processing unit 3, the electrostatic capacitance detection device 2 switches to the correction mode (ST100) in the initial state.

[0141] Figure 6 It is used for explanation Figure 5 A flowchart illustrating an example of the processing of the correction mode (ST100) in the initial state of the electrostatic capacitance detection method.

[0142] First, the correction unit 26 controls the AC voltage output unit 20 (second voltage output unit 22) to make the amplitude of the second AC voltage V2 a normal value (ST200). Here, the normal amplitude of the second AC voltage V2 is defined as "V2". The difference between the amplitude of the first AC voltage V1 and the amplitude of the second AC voltage V2, i.e., the AC voltage amplitude difference, is called "V1-V2". Hereinafter, the AC voltage amplitude difference of "V1-V2" is sometimes referred to as "first amplitude difference". In this case, the correction unit 26 controls the AC voltage output unit 20 to make the AC voltage amplitude difference the first amplitude difference "V1-V2".

[0143] When the calculation unit 25 obtains the detection complex number Da in the correction mode of the initial state, where the second AC voltage V2 is the normal amplitude "V2" (when the AC voltage amplitude difference is the first amplitude difference "V1-V2"), it is designated as "the first detection complex number Da_ref(V2)" (ST205). The real part of the first detection complex number Da_ref(V2) is "I_ref(V2)", and the imaginary part of the first detection complex number Da_ref(V2) is "Q_ref(V2)".

[0144] Next, the correction unit 26 controls the AC voltage output unit 20 (second voltage output unit 22) to make the amplitude of the second AC voltage V2 higher than the normal value by "ΔV" (ST210). The AC voltage amplitude difference becomes "V1-(V2+ΔV)". Hereinafter, the AC voltage amplitude difference of "V1-(V2+ΔV)" is sometimes referred to as the "second amplitude difference". In this case, the correction unit 26 controls the AC voltage output unit 20 to make the AC voltage amplitude difference the second amplitude difference "V1-(V2+ΔV)".

[0145] When the amplitude of the second AC voltage V2 is "V2+ΔV" in the correction mode of the initial state obtained by the calculation unit 25 (when the AC voltage amplitude difference is the second amplitude difference "V1-(V2+ΔV)"), the detection complex number Da is taken as "the second detection complex number Da_ref(V2+ΔV)" (ST215). The real part of the second detection complex number Da_ref(V2+ΔV) is "I_ref(V2+ΔV)", and the imaginary part of the second detection complex number Da_ref(V2+ΔV) is "Q_ref(V2+ΔV)".

[0146] In the initial state correction mode, the correction unit 26 obtains a first correction value B1 (ST220) corresponding to the change in the detection complex number Da that accompanies the change in AC voltage amplitude difference ΔV. The correction unit 26 obtains a complex number obtained by subtracting the first detection complex number Da_ref(V2) from the second detection complex number Da_ref(V2) as the first correction value B1.

[0147] The correction unit 26 obtains the coefficients used in the first phase correction, in which the phase is corrected so that the deflection angle θ1 of the first correction value B1 is close to zero (ST250). The first phase correction is a rotation transformation that rotates the phase angle by "-θ1". When the real and imaginary parts of the first correction value B1 before the first phase correction are set to "Re{B1}" and "Im{B1}" respectively, and the real and imaginary parts of the first correction value B1_R after the first phase correction are set to "Re{B1_R}" and "Im{B1_R}" respectively, the rotation transformation of the first phase correction is characterized by the following formula.

[0148] [Mathematical Expression 9]

[0149]

[0150] In equation (9), “A1” represents the matrix of the rotational transformation for the first phase correction. The correction unit 26 obtains “COS(θ1)” and “SIN(θ1)” as elements of the matrix A1. “COS(θ1)” and “SIN(θ1)” are represented by the following formulas respectively.

[0151] [Mathematical Expression 10]

[0152]

[0153]

[0154] The correction unit 26 obtains the first correction value B1_R (ST255) obtained by performing a first phase transformation on the first correction value B1. The real part Re{B1_R} of the first correction value B1_R is characterized by the following formula.

[0155] [Mathematical Expression 11]

[0156] Re{B1_R}=COS(θ1)·Re{B1}+SIN(θ1)·Im{B1}…(11)

[0157] Back Figure 5 .

[0158] The electrostatic capacitance detection device 2 determines whether it is a timing for transitioning to the correction mode (ST105). For example, the electrostatic capacitance detection device 2 determines that it is a timing for transitioning to the correction mode at a predetermined period. Furthermore, the electrostatic capacitance detection device 2 can determine that it is a timing for transitioning when a transition instruction to the correction mode is input from the processing unit 3. If it is determined in step ST105 that it is a timing for transitioning and the device transitions to the correction mode (step ST110), the electrostatic capacitance detection device 2 executes... Figure 7 The processing shown.

[0159] Figure 7 It is used for explanation Figure 5 A flowchart illustrating an example of the processing of the correction mode (ST110) after the initial state in the electrostatic capacitance detection method shown.

[0160] First, the correction unit 26 controls the AC voltage output unit 20 (second voltage output unit 22) so that the second AC voltage V2 becomes the normal amplitude "V2" (ST300). That is, the correction unit 26 controls the AC voltage output unit 20 so that the AC voltage amplitude difference becomes the first amplitude difference "V1-V2".

[0161] The calculation unit 25 obtains the detection complex number Da when the second AC voltage V2 is the normal amplitude "V2" in the correction mode after the initial state (when the AC voltage amplitude difference is the first amplitude difference "V1-V2"), as "the first detection complex number Da(V2)" (ST305). The real part of the first detection complex number Da(V2) is "I(V2)" and the imaginary part of the first detection complex number Da(V2) is "Q(V2)".

[0162] Next, the correction unit 26 controls the AC voltage output unit 20 (second voltage output unit 22) to make the amplitude of the second AC voltage V2 higher than the normal value by "ΔV" (ST310). The AC voltage amplitude difference becomes "V1-(V2+ΔV)". That is, the correction unit 26 controls the AC voltage output unit 20 to make the AC voltage amplitude difference become the second amplitude difference "V1-(V2+ΔV)".

[0163] The complex number Da used for detection, when the amplitude of the second AC voltage V2 is "V2+ΔV" in the correction mode after the calculation unit 25 obtains the initial state (when the AC voltage amplitude difference is the second amplitude difference "V1-(V2+ΔV)"), is designated as "the second detection complex number Da(V2+ΔV)" (ST315). The real part of the second detection complex number Da(V2+ΔV) is "I(V2+ΔV)", and the imaginary part of the second detection complex number Da(V2+ΔV) is "Q(V2+ΔV)".

[0164] In the correction mode after the initial state, the correction unit 26 obtains a second correction value B2 (ST320) corresponding to the change in the detection complex number Da that accompanies the change in AC voltage amplitude difference ΔV. The correction unit 26 obtains the complex number obtained by subtracting the first detection complex number Da(V2) from the second detection complex number Da(V2+ΔV) as the second correction value B2.

[0165] The correction unit 26 acquires the coefficients used in the second phase correction, in which the phase is corrected so that the deflection angle θ2 of the second correction value B2 is close to zero (ST350). The second phase correction is a rotation transformation that rotates the phase angle by "-θ2". When the real and imaginary parts of the second correction value B2 before the second phase correction are set to "Re{B2}" and "Im{B2}" respectively, and the real and imaginary parts of the second correction value B2_R after the second phase correction are set to "Re{B2_R}" and "Im{B2_R}" respectively, the rotation transformation of the second phase correction is characterized by the following formula.

[0166] [Mathematical Expression 12]

[0167]

[0168] In equation (12), “A2” represents the matrix of the rotational transformation for the second phase correction. The correction unit 26 obtains “COS(θ2)” and “SIN(θ2)” as elements of this matrix A2. “COS(θ2)” and “SIN(θ2)” are represented by the following formulas respectively.

[0169] [Mathematical Expression 13]

[0170]

[0171]

[0172] The correction unit 26 obtains the second correction value B2_R (ST355) obtained by performing a second phase transformation on the second correction value B2. The real part Re{B2_R} of the second correction value B2_R is characterized by the following formula.

[0173] [Mathematical Expression 14]

[0174] Re{B2_R}=COS(θ2)·Re{B2}+SIN(θ2)·Im{B2]…(14)

[0175] Back Figure 5 .

[0176] The electrostatic capacitance detection device 2 determines whether it is time to perform electrostatic capacitance detection (ST115). For example, the electrostatic capacitance detection device 2 determines that the timing for performing electrostatic capacitance detection is at a predetermined period. The timing for transitioning to the correction mode determined in step ST105 is set such that the period is longer than the timing for electrostatic capacitance detection determined in step ST115. As a result, the frequency of transitioning to the correction mode (ST110) is less than the frequency of performing electrostatic capacitance detection, thus reducing the processing burden.

[0177] If the timing for detecting electrostatic capacitance is determined in step ST115, the calculation unit 25 sets the second AC voltage V2 to the normal amplitude "V2" (and sets the AC voltage amplitude difference to the first amplitude difference "V1-V2"), and obtains the detection complex number Da(V2) (ST120) based on the detection signal Dm generated in this state. The correction unit 26, based on the obtained detection complex number Da(V2) and the first correction value B1_R (ST255) after performing the first phase correction, performs the first phase correction. Figure 6 ), and the second correction value B2_R(ST355) obtained in the most recent correction mode. Figure 7 ), to obtain the corrected detection value Ds(ST125).

[0178] Figure 8 It is used to explain in Figure 5The flowchart shows an example of the process (ST125) for obtaining a corrected detection value in the electrostatic capacitance detection method.

[0179] The correction unit 26 obtains the second phase correction coefficients "COS(θ2)" and "SIN(θ2)" (ST350) based on the second correction value B2 obtained according to the most recent correction mode. Figure 7 The second phase correction (ST400) is applied to the detection complex number Da(V2). The real part of the detection complex number Da_R(V2) after the second phase correction is applied is characterized by the following formula.

[0180] [Mathematical Expression 15]

[0181] Re[Da_R(V2)}=COS(θ2)·Re{Da(V2)}+SIN(θ2)·Im{Da(V2)}…(15)

[0182] The correction unit 26 multiplies the difference between the real part "Re{B1_R}" of the first correction value B1_R (after the first phase correction) and the real part "Re{B2_R}" of the second correction value B2R (after the second phase correction) by a scaling factor β. Based on the sum of the result of this multiplication and the real part "Re{Da_R(V2)}" of the detection complex number Da_R(V2) (after the second phase correction), the corrected detection value Ds is obtained. The corrected detection value Ds is represented by the following formula.

[0183] [Mathematical Expression 16]

[0184] Ds=Re{Da_R(V2)}+β×[Re{B2_R}-Re{B1_R}]…(16)

[0185] The electrostatic capacitance detection device 2 repeats the above-described steps ST105 to ST125 (ST135) until it receives an instruction to end from the processing unit 3. Furthermore, if the electrostatic capacitance detection device 2 receives an instruction from the processing unit 3 to return to the initial state, it returns to step ST100 and repeats the process after step ST100.

[0186] As explained above, according to this embodiment, the transition to the correction mode is repeated. When transitioning to the correction mode, the AC voltage output unit 20 is controlled to change the difference in amplitude (AC voltage amplitude difference) between the first AC voltage V1 and the second AC voltage V2, and correction values ​​(B1, B2) corresponding to the change in the detection value of the calculation unit 25 associated with the change in AC voltage amplitude difference are obtained. Since the change in the detection value of the calculation unit 25 associated with the change in AC voltage amplitude difference has a value corresponding to the shielding capacitor Crs (Equations (2) and (3)), the correction values ​​(B1, B2) obtained in the correction mode have a value corresponding to the shielding capacitor Crs. By correcting the detection value corresponding to the change in this correction value (B2-B1), the detection value of the calculation unit 25 is corrected corresponding to the change in the shielding capacitor Crs. Therefore, the change in the detection value of the calculation unit 25 associated with the change in the shielding capacitor Crs can be corrected, and the detection error of the electrostatic capacitance can be reduced.

[0187] Furthermore, according to this embodiment, the first correction value B1 obtained in the initial state correction mode, the second correction value B2 obtained in the subsequent initial state correction mode, and the deflection angle of the detection complex number Da(V2) are aligned near zero through phase correction. Therefore, the real parts of these complex numbers (Equations (11), (14), and (15)) become values ​​that substantially eliminate the influence caused by the jitter of the clock signal CK. Moreover, in the correction unit 26, the detection value Ds, which has been corrected for the change in the shielding capacitor Crs, is obtained based on the first correction value B1_R, the second correction value B2_R, and the real part of the detection complex number Da_R(V2) after eliminating the influence caused by the jitter of the clock signal CK. That is, since the correction target component, which is proportional to the difference between the real part of the first correction value B1_R with the first phase correction and the real part of the second correction value B2_R with the second phase correction, has a value corresponding to the change in the detection value associated with the change in the shielding capacitance Crs (Equation (6)), the real part of the detection complex number Da_R(V2) with the second phase correction is corrected to cancel out the correction target component (Equation (16)). The detection value Ds obtained in this way becomes a value that corrects the error associated with the change in the shielding capacitance Crs from the initial state and the error associated with the jitter of the clock signal CK, respectively, thus further reducing the detection error of the static capacitance.

[0188] Next, several variations of the electrostatic capacitance detection method involved in this embodiment will be described.

[0189] [Variation Example 1]

[0190] Figure 9 It is used for explanation Figure 5A flowchart of a variation of the correction mode processing (ST110) after the initial state in the electrostatic capacitance detection method shown.

[0191] In this variation 1, the second phase correction for the second correction value B2 (Equation (14)) and the second phase correction for the detection complex number Da(V2) (Equation (15)) are equivalently replaced by a second phase correction for the intermediate correction value M (Equation (17)) based on the second correction value B2 and the detection complex number Da(V2). Therefore, Figure 7 The processing of the second phase correction of the second correction value B in the flowchart shown (ST355) is in Figure 9 The following is omitted from the flowchart shown. Figure 9 Other processes in the flowchart shown are Figure 7 The flowchart shown is the same.

[0192] Figure 10 This is used to explain the process for obtaining corrected detection values ​​(ST125, Figure 5 A flowchart of a variant of )

[0193] The correction unit 26 processes the obtained corrected detection value Ds (ST125, Figure 5 First, the intermediate correction value M (ST450) is calculated. The intermediate correction value M is represented by the following formula.

[0194] [Mathematical Expression 17]

[0195] M=Da(V2)+β·B2…(17)

[0196] In equation (17), the complex number Da(V2) is detected in step ST120 ( Figure 5 The second correction value B2 is obtained in step ST320. Figure 9 ) obtained.

[0197] The correction unit 26 applies the calculated intermediate correction value M based on step ST350. Figure 9 The second phase correction (ST455) is obtained from the coefficients “COS(θ2)” and “SIN(θ2)”. That is, the correction unit 26 performs a second phase correction on the sum of the complex number obtained by multiplying the second correction value B2 by the scaling factor β and the detection complex number Da(V2), which rotates the phase angle corresponding to the deflection angle θ2 of the second correction value. The real part of the intermediate correction value M_R after the second phase correction is performed is characterized by the following formula.

[0198] [Mathematical Expression 18]

[0199] Re{M_R}=COS(θ2)·Re{M}+SIN(θ2)·Im{M}

[0200] =COS(θ2)·Re{Da(V2)}+SIN(θ2)·Im{Da(V2)}+β[COS(θ2)·Re{B2}+SIN(θ2)·Im{B2)]

[0201] =Re{Da_R(V2)}+β·Re{B2_R]…(18)

[0202] The correction unit 26 is based on the real part (ST455) of the intermediate correction value M_R after the first phase correction was applied, minus the real part (ST255) of the first correction value B1_R after the first phase correction was applied. Figure 6 The corrected detection value Ds(ST460) is obtained by multiplying the result by the scaling factor β. The detection value Ds obtained by this calculation is characterized by the following formula.

[0203] [Mathematical Expression 19]

[0204] Re{M_R]-β×Re{B1_R}=Re{Da_R(V2)]+β·Re{B2_R]-β×Re{B1_R}

[0205] =Re{Da_R(V2)}+β×[Re{B2_R}-Re{B1_R}]…(19)

[0206] As can be seen from equation (19), the detection value Ds calculated using the intermediate correction value M is equivalent to the detection value Ds calculated using equation (16).

[0207] [Variation Example 2]

[0208] In this modified example 2, when obtaining the correction values ​​(first correction value B1, second correction value B2) of the complex number corresponding to the change of the detection complex number Da that accompanies the change of the AC voltage amplitude difference (V1-V2), the AC voltage amplitude difference (V1-V2) is modulated by the modulation signal.

[0209] Figure 11 It is used for explanation Figure 5 The processing of the correction mode in the initial state of the electrostatic capacitance detection method shown (ST100, Figure 5 A flowchart of a variant of )

[0210] When the correction unit 26 shifts to the correction mode, it controls the AC voltage output unit 20 to modulate the AC voltage amplitude difference (V1-V2) by a modulation signal with a fixed amplitude having a frequency f2 (f2 < f1). For example, the correction unit 26 modulates the AC voltage amplitude difference (V1-V2) by making the sine wave signal generation unit 211 ( Figure 2A sinusoidal signal with an amplitude of frequency f1 is generated by a modulation signal with frequency f2, so that a first AC voltage V1 modulated by the modulation signal with frequency f2 is output from the first voltage output unit 21. Since the second AC voltage V2 output from the second voltage output unit 22 is a voltage that attenuates the amplitude of the first AC voltage V1, the modulation degree of the second AC voltage V2 is the same as that of the first AC voltage V1. Therefore, the AC voltage amplitude difference (V1-V2) becomes an AC voltage with frequency f1 modulated by the modulation signal with frequency f2.

[0211] When the AC voltage amplitude difference (V1-V2) is modulated as described above, the real part (first demodulation signal I) and imaginary part (second demodulation signal Q) of the detection complex number Da output from the calculation unit 25 respectively contain an AC component of frequency f2 caused by the modulation signal. The correction unit 26 detects the amplitude of the AC component of frequency f2 contained in the real part of the detection complex number Da, and obtains the detected amplitude as the real part "Re{B1}" (ST235) of the first correction value B1. In addition, the correction unit 26 detects the amplitude of the AC component of frequency f2 contained in the imaginary part of the detection complex number Da, and obtains the detected amplitude as the imaginary part "Im{B1}" (ST240) of the first correction value B1. For example, by detecting the upper and lower peak values ​​of the AC component and averaging their differences, the amplitude of the AC component can be detected. If the real part and imaginary part of the first correction value B1 are obtained respectively, the correction unit 26 can detect the amplitude of the AC component by... Figure 6 The same process is used in steps ST250 and ST255 of the flowchart to obtain the real part of the first correction value B1_R that has undergone the first phase correction.

[0212] Figure 12 It is used for explanation Figure 5 The processing of the correction mode after the initial state in the electrostatic capacitance detection method shown (ST110, Figure 5 A flowchart of a variant of )

[0213] In this case, the correction unit 26 also modulates the AC voltage amplitude difference (V1-V2) (ST330) using a modulation signal with a fixed amplitude of frequency f2. With the AC voltage amplitude difference (V1-V2) modulated, the correction unit 26 detects the amplitude of the AC component with frequency f2 contained in the real part of the detection complex number Da, and obtains the detected amplitude as the real part "Re{B2}" of the second correction value B2 (ST335). Furthermore, the correction unit 26 detects the amplitude of the AC component with frequency f2 contained in the imaginary part of the detection complex number Da, and obtains the detected amplitude as the imaginary part "Im{B2}" of the second correction value B2 (ST340). Moreover, the correction unit 26, through... Figure 7The flowchart steps ST350 and ST355 are the same to obtain the coefficients “COS(θ2)” and “SIN(θ2)” for the second phase correction, and to obtain the real part of the second correction value B2_R after the second phase correction is implemented.

[0214] In the electrostatic capacitance detection method of this modified example 2, since it is also possible to obtain the correction value (first correction value B1, second correction value B2) of the complex number Da corresponding to the change of the detection complex number Da that accompanies the change of the AC voltage amplitude difference (V1-V2), the corrected detection value Ds can be obtained in the same way as in the above-described embodiment.

[0215] <Second Implementation Method>

[0216] Next, the electrostatic capacitance detection device and its electrostatic capacitance detection method according to the second embodiment will be described. In the first embodiment described above, corrections were made for errors caused by changes in the shielding capacitance Crs and errors in the detection value caused by jitter in the clock signal CK. However, in the second embodiment, only the error in the detection value caused by changes in the shielding capacitance Crs is corrected. In this second embodiment, since no processing related to phase correction is performed, only the real part of the detection complex number Da (the first demodulation signal I) is used in the processing. Therefore, the calculation unit 25 of the electrostatic capacitance detection device 2 according to the second embodiment may not include the parts related to the generation of the second demodulation signal Q (the second demodulation unit 254 and the second synchronization signal generation unit 258). Other structures of the electrostatic capacitance detection device 2 according to the second embodiment are similar to those of the first embodiment. Figures 1-4 The electrostatic capacitance detection device 2 shown has a roughly the same structure.

[0217] Figure 13 This is a flowchart illustrating an example of the electrostatic capacitance detection method according to the second embodiment.

[0218] For example, when the power is turned on and an instruction to set to the initial state is input from the processing unit 3, the electrostatic capacitance detection device 2 switches to the correction mode (ST500) in the initial state.

[0219] Figure 14 It is used for explanation Figure 13 A flowchart of an example of the correction mode processing (ST500) in the initial state of the electrostatic capacitance detection method shown.

[0220] First, the correction unit 26 controls the AC voltage output unit 20 (second voltage output unit 22) so that the second AC voltage V2 has a normal amplitude "V2" (ST600). That is, the correction unit 26 controls the AC voltage output unit 20 so that the AC voltage amplitude difference becomes the first amplitude difference "V1-V2".

[0221] The calculation unit 25 obtains the detection value (first demodulation signal I) when the second AC voltage V2 is the normal amplitude "V2" in the correction mode of the initial state (when the AC voltage amplitude difference is the first amplitude difference "V1-V2"), and uses it as "first detection value Da_ref(V2)" (ST605).

[0222] Next, the correction unit 26 controls the AC voltage output unit 20 (second voltage output unit 22) so that the amplitude of the second AC voltage V2 becomes higher than the normal value by "ΔV" (ST610). That is, the correction unit 26 controls the AC voltage output unit 20 so that the AC voltage amplitude difference becomes the second amplitude difference "V1-(V2+ΔV)".

[0223] The calculation unit 25 obtains the detection value (first demodulation signal I) when the amplitude of the second AC voltage V2 in the correction mode of the initial state is "V2+ΔV" (when the AC voltage amplitude difference is the second amplitude difference "V1-(V2+ΔV)"), and uses it as "second detection value Da_ref(V2+ΔV)" (ST215).

[0224] In the initial state correction mode, the correction unit 26 obtains a first correction value B1 (ST620) corresponding to the change in the detection value (first demodulation signal I) associated with the change in AC voltage amplitude difference ΔV. The correction unit 26 obtains the value obtained by subtracting the first detection value Da_ref(V2) from the second detection value Da_ref(V2+ΔV) as the first correction value B1.

[0225] Back Figure 13 .

[0226] The electrostatic capacitance detection device 2 determines whether it is a timing for transitioning to the correction mode (ST505). For example, the electrostatic capacitance detection device 2 determines that it is a timing for transitioning to the correction mode at a predetermined period. Furthermore, the electrostatic capacitance detection device 2 can determine that it is a timing for transitioning when a transition instruction to the correction mode is input from the processing unit 3. If the timing for transitioning is determined in step ST505 and the device transitions to the correction mode (step ST510), the electrostatic capacitance detection device 2 executes... Figure 15 The processing shown.

[0227] Figure 15 It is used for explanation Figure 13 A flowchart of an example of the processing of the correction mode after the initial state in the electrostatic capacitance detection method shown (ST510).

[0228] First, the correction unit 26 controls the AC voltage output unit 20 (second voltage output unit 22) so that the second AC voltage V2 becomes the normal amplitude "V2" (ST700). That is, the correction unit 26 controls the AC voltage output unit 20 so that the AC voltage amplitude difference becomes the first amplitude difference "V1-V2".

[0229] The first detection value (first demodulation signal I) when the second AC voltage V2 is the normal amplitude "V2" (when the AC voltage amplitude difference is the first amplitude difference "V1-V2") in the correction mode after the calculation unit 25 obtains the initial state is used as "first detection value Da(V2)" (ST705).

[0230] Next, the correction unit 26 controls the AC voltage output unit 20 (second voltage output unit 22) to make the amplitude of the second AC voltage V2 higher than the normal value by "ΔV" (ST710). The AC voltage amplitude difference becomes "V1-(V2+ΔV)". That is, the correction unit 26 controls the AC voltage output unit 20 to make the AC voltage amplitude difference become the second amplitude difference "V1-(V2+ΔV)".

[0231] The detection value (first demodulation signal I) when the amplitude of the second AC voltage V2 is “V2+ΔV” (when the AC voltage amplitude difference is the second amplitude difference “V1-(V2+ΔV)”) in the correction mode after the calculation unit 25 obtains the initial state is used as “second detection value Da(V2+ΔV)” (ST715).

[0232] In the correction mode after the initial state, the correction unit 26 obtains a second correction value B2 (ST720) corresponding to the change in the detected value (first demodulated signal I) associated with the change in AC voltage amplitude difference ΔV. The correction unit 26 obtains the value obtained by subtracting the first detected value Da(V2) from the second detected value Da(V2+ΔV) as the second correction value B2.

[0233] The correction unit 26 calculates the first correction value B1 (ST620) obtained from the correction mode of the initial state. Figure 14 The correction target component P is proportional to the difference between the second correction value B2 (ST720) obtained in the correction mode after the initial state and the correction target component P = -β·(B2-B1)(ST750). The correction target component P corresponds to "ΔVo_crs" in equation (6) and has a value corresponding to the change in the detection value (first demodulation signal I) that accompanies the change in the shielding capacitance Crs.

[0234] Back Figure 13 .

[0235] The electrostatic capacitance detection device 2 determines whether it is time to perform electrostatic capacitance detection (ST515). For example, the electrostatic capacitance detection device 2 determines that the timing for performing electrostatic capacitance detection is at a predetermined period. The timing for transitioning to the correction mode determined in step ST505 is set such that the period is longer than the timing for electrostatic capacitance detection determined in step ST515. As a result, since the frequency of transitioning to the correction mode (ST510) is less than the frequency of electrostatic capacitance detection, the processing burden is reduced.

[0236] If step ST515 determines that the timing is for detecting electrostatic capacitance, the calculation unit 25 sets the second AC voltage V2 to the normal amplitude "V2" (and sets the AC voltage amplitude difference to the first amplitude difference "V1-V2"), and obtains the detection value Da(V2) based on the detection signal Dm generated in this state (ST520). The correction unit 26, based on step ST750 ( Figure 15 The correction unit 26 uses the correction target component P calculated in the original text to correct the obtained detection value Da(V2). That is, the correction unit 26 subtracts the correction target component P (Da(V2)-P) from the detection value Da(V2) so that the correction target component P corresponding to the change in the detection value (first demodulation signal I) that is associated with the change in the shielding capacitor Crs is canceled out, and the result of this subtraction operation is obtained as the corrected detection value Ds(ST525).

[0237] The electrostatic capacitance detection device 2 repeats the above-described steps ST505 to ST525 (ST535) until it receives an instruction from the processing unit 3 to end. Furthermore, if the electrostatic capacitance detection device 2 receives an instruction from the processing unit 3 to return to the initial state, it returns to step ST500 and repeats the processing after step ST500.

[0238] As explained above, in this embodiment, similar to the first embodiment already described, the error in the detection value caused by the change in the shielding capacitor Crs can be effectively reduced.

[0239] Furthermore, in the second embodiment, similar to the variation 2 of the first embodiment described above, the correction value (first correction value B1, second correction value B2) can be obtained when the AC voltage amplitude difference is modulated in the correction mode.

[0240] Figure 16A It is used for explanation Figure 13 A flowchart of a variation of the correction mode processing (ST500) in the initial state of the electrostatic capacitance detection method shown.

[0241] When the correction unit 26 shifts to the correction mode in the initial state, it controls the AC voltage output unit 20 so that the AC voltage amplitude difference (V1-V2) is modulated by a modulation signal with a fixed amplitude having a frequency f2 (f2 < f1) (ST630), the amplitude of the AC component with frequency f2 contained in the detection value (first demodulation signal I) is detected, and the detected amplitude is obtained as the first correction value B1 (ST635).

[0242] Figure 16B It is used for explanation Figure 13 A flowchart of a variation of the correction mode processing (ST510) after the initial state in the electrostatic capacitance detection method shown.

[0243] When the correction unit 26 transitions to a correction mode after the initial state, it controls the AC voltage output unit 20 to modulate the AC voltage amplitude difference (V1-V2) (ST730) using a modulation signal with a fixed amplitude having a frequency f2 (f2 < f1), and detects the amplitude of the AC component with frequency f2 contained in the detection value (first demodulation signal I), obtaining the detected amplitude as the second correction value B2 (ST735). Then, the correction unit 26 and... Figure 15 Similarly, in the steps of the flowchart ST750, the corrected object component P = -β·(B2-B1) is calculated.

[0244] In this modified electrostatic capacitance detection method, since it is possible to obtain correction values ​​(first correction value B1, second correction value B2) corresponding to the change in the detection value (first demodulation signal I) that is associated with the change in AC voltage amplitude difference (V1-V2), the corrected detection value Ds can be obtained in the same way as in the above-described embodiment.

[0245] Furthermore, the present invention is not limited to the embodiments described above, and includes various variations.

[0246] In the above embodiments, an example is given where the amplitude of the first AC voltage V1 is kept constant while the amplitude of the second AC voltage V2 is varied in order to change the AC voltage amplitude difference (V1-V2). However, in other examples of this embodiment, the AC voltage amplitude difference (V1-V2) can also be changed by keeping the amplitude of the second AC voltage V2 constant while changing the amplitude of the first AC voltage V1. Furthermore, in yet another embodiment of this embodiment, the AC voltage amplitude difference (V1-V2) can also be changed by changing the amplitudes of the first AC voltage V1 and the second AC voltage V2, respectively. In any case, it is assumed that the changes in the electrostatic capacitances of capacitors Crg, Crgl, and Cag are sufficiently small and negligible compared to the changes in the shielding capacitance Crs caused by temperature, etc., and thus equations (4) and (5) hold true. Therefore, the error in the detection value caused by the change in the shielding capacitance Crs can be corrected.

[0247] The input device described in this embodiment is not limited to user interface devices that input information about finger operations, etc. That is, the input device of the present invention can be widely used in devices that input information about the electrostatic capacitance of detection electrodes that changes upon approach to various objects, not limited to the human body.

[0248] Explanation of reference numerals in the attached figures

[0249] 1...Sensor section, 2...Electrostatic capacitance detection device, 3...Processing section, 4...Storage section, 5...Interface section, 6...Object, 20...AC voltage output section, 21...First voltage output section, 211...Sine wave signal generation section, 212...D / A conversion section, 213...Low-pass filter, 214...Amplifier, 22...Second voltage output section, 23...Detection signal generation section, 231...Charge amplifier, 232...Subtraction operation section, 233...Differential amplifier, 24...A / D conversion section, 25...Calculation section, 2 51... First demodulation unit, 252... Multiplication unit, 253... Low-pass filter, 254... Second demodulation unit, 255... Multiplication unit, 256... Low-pass filter, 257... First synchronization signal generation unit, 258... Second synchronization signal generation unit, 26... Correction unit, Rag... Feedback resistor, Rs... Resistor, Cag... Feedback capacitor, Ca, Cb, Crg, Crgl, Crs, Csg... Capacitors, OP1... Operational amplifier, Es... Detection electrode, Ea... Shielding electrode, N1, N2... Nodes.

Claims

1. A capacitance detection device for detecting the capacitance between an object approaching a detection electrode and the detection electrode, characterized in that, have: An AC voltage output section outputs a first AC voltage to a shielding electrode positioned close to the detection electrode, and a second AC voltage with the same frequency and phase as the first AC voltage but a smaller amplitude than the first AC voltage. The detection signal generation unit supplies charge to the detection electrode from a first node connected to the detection electrode, such that the voltage of the first node is close to the second AC voltage, and generates an AC detection signal corresponding to the supplied charge. The calculation unit calculates the detected value of the electrostatic capacitance based on the detected signal; and The correction unit corrects for changes in the detection value that occur when the parasitic capacitance between the shielding electrode and the detection electrode, i.e., the shielding capacitance, changes. The AC voltage output section includes: The first AC voltage output section is a circuit that generates the first AC voltage with a fixed amplitude; and The second AC voltage output section is composed of an attenuation circuit that outputs the second AC voltage after attenuating the amplitude of the first AC voltage. The detection signal generation unit includes: An operational amplifier amplifies the voltage difference between the inverting input terminal connected to the first node and the non-inverting input terminal connected to the second node to which the second AC voltage is applied, and outputs the amplified result as the first signal. A feedback capacitor is disposed in the path between the output terminal of the first signal of the operational amplifier and the inverting input terminal; and The subtraction unit subtracts a reference signal from the first signal and outputs the result of the subtraction as the detection signal. The reference signal is equivalent to the first signal output from the operational amplifier in normal operating mode when no object is near the detection electrode. The correction unit repeatedly switches from the normal operating mode to the correction mode. When switching to the correction mode, it controls the attenuation circuit of the second AC voltage output unit to change the difference in amplitude between the first AC voltage and the second AC voltage. It then obtains a correction value corresponding to the change in the detection value that accompanies the change in amplitude difference, and corrects the detection value according to the change in the correction value obtained in the correction mode.

2. The electrostatic capacitance detection device according to claim 1, characterized in that, The correction unit corrects the detection value to cancel out the correction target component, wherein the correction target component is proportional to the difference between the correction value obtained in the correction mode of the initial state (i.e., the first correction value) and the correction value obtained in the correction mode after the initial state (i.e., the second correction value), and corresponds to the change in the detection value that accompanies the change in the shielding capacitance.

3. The electrostatic capacitance detection device according to claim 2, characterized in that, Whenever the correction unit shifts to the correction mode, it calculates the correction target component and corrects the detection value based on the correction target component calculated in the most recent correction mode in the normal operation mode.

4. The electrostatic capacitance detection device according to any one of claims 1 to 3, characterized in that, The electrostatic capacitance detection device has the following features: The analog-to-digital converter converts the detected signal into a digital signal in sync with the clock signal. The AC voltage output section outputs a first AC voltage and a second AC voltage, both having a sine wave of a first frequency. The calculation unit, in sync with the clock signal, multiplies a synchronization signal having the first frequency of a sine wave and the detection signal converted into a digital signal, and calculates the detection value corresponding to the demodulated signal obtained by removing harmonic components from the result of the multiplication operation.

5. The electrostatic capacitance detection device according to claim 2 or 3, characterized in that, The electrostatic capacitance detection device has the following features: The analog-to-digital converter converts the detected signal into a digital signal in sync with the clock signal. The AC voltage output section outputs a first AC voltage and a second AC voltage, both having a sine wave of a first frequency. In the normal operating mode, the calculation unit controls the attenuation circuit of the second AC voltage output unit so that the amplitude difference becomes a first amplitude difference. Synchronously with the clock signal, it multiplies a synchronization signal having the first frequency (a sine wave) with the detection signal converted to a digital signal, and calculates the detection value corresponding to the demodulated signal obtained by removing harmonic components from the result of the multiplication operation. When the correction unit switches to the correction mode, it acquires a first detection value and a second detection value, and acquires a first correction value and a second correction value respectively, as the correction value corresponding to the difference between the first detection value and the second detection value. The first detection value is the detection value when the attenuation circuit of the second AC voltage output unit is controlled so that the amplitude difference becomes the first amplitude difference, and the second detection value is the detection value when the attenuation circuit of the second AC voltage output unit is controlled so that the amplitude difference becomes a second amplitude difference different from the first amplitude difference.

6. The electrostatic capacitance detection device according to claim 4, characterized in that, When the correction unit switches to the correction mode, it outputs the first AC voltage modulated by a modulation signal at a second frequency lower than the first frequency from the first AC voltage output unit, so that the output modulates the first AC voltage and the second AC voltage with the amplitude difference by the modulation signal having a fixed amplitude of the second frequency, and obtains the correction value corresponding to the amplitude of the AC component of the second frequency contained in the demodulated signal.

7. The electrostatic capacitance detection device according to claim 1, characterized in that, The electrostatic capacitance detection device has the following features: The analog-to-digital converter converts the detected signal into a digital signal in sync with the clock signal. The AC voltage output section outputs a first AC voltage and a second AC voltage, both having a first frequency sine wave. The calculation unit performs the following processing: Synchronously with the clock signal, a first synchronization signal having the first frequency and a phase approximately similar to the first AC voltage is multiplied by the detection signal converted into a digital signal. Synchronously with the clock signal, a second synchronization signal having the first frequency and whose phase is offset from the first synchronization signal by a quarter period is multiplied by the detection signal converted into a digital signal. A detection complex number is obtained, wherein the real part of the detection complex number is the first demodulated signal obtained by removing harmonic components from the result of multiplying the first synchronization signal and the detection signal, and the imaginary part is the second demodulated signal obtained by removing harmonic components from the result of multiplying the second synchronization signal and the detection signal. The correction unit performs the following processing: When switching to the correction mode, the attenuation circuit of the second AC voltage output section is controlled to change the amplitude difference, and a complex number corresponding to the change in the detection complex number accompanying the change in the amplitude difference is obtained as the correction value. A first phase correction is applied to the correction value obtained under the correction mode in the initial state, i.e., the first correction value. In this first phase correction, the phase is corrected so that the deflection angle of the first correction value is close to zero. A second phase correction is applied to the correction value obtained under the correction mode after the initial state, i.e., the second correction value. In this second phase correction, the phase is corrected so that the deflection angle of the second correction value is close to zero. Furthermore, the second phase correction is applied to the complex number used for detection. The value obtained by correcting the real part of the detection complex number for which the second phase correction has been applied is used as the corrected detection value, so as to cancel out the correction target component, wherein the correction target component is proportional to the difference between the real part of the first correction value for which the first phase correction has been applied and the real part of the second correction value for which the second phase correction has been applied, and corresponds to the change in the real part of the detection complex number that accompanies the change in the shielding capacitance.

8. The electrostatic capacitance detection device according to claim 7, characterized in that, The calculation unit controls the attenuation circuit of the second AC voltage output unit in the normal operating mode so that the amplitude difference becomes the first amplitude difference. When the correction unit switches to the correction mode, it obtains a first detection complex number and a second detection complex number, and obtains a correction value corresponding to the difference between the first detection complex number and the second detection complex number. The first detection complex number is the detection complex number used when the attenuation circuit of the second AC voltage output unit is controlled so that the amplitude difference becomes the first amplitude difference, and the second detection complex number is the detection complex number used when the attenuation circuit of the second AC voltage output unit is controlled so that the amplitude difference becomes a second amplitude difference different from the first amplitude difference.

9. The electrostatic capacitance detection device according to claim 7, characterized in that, When the correction unit switches to the correction mode, it outputs the first AC voltage modulated by a modulation signal at a second frequency lower than the first frequency from the first AC voltage output unit, such that the output modulates the first AC voltage and the second AC voltage with the amplitude difference by the modulation signal having a fixed amplitude of the second frequency, and obtains the real part of the correction value corresponding to the amplitude of the AC component of the second frequency contained in the first demodulated signal and the imaginary part of the correction value corresponding to the amplitude of the AC component of the second frequency contained in the second demodulated signal.

10. The electrostatic capacitance detection device according to any one of claims 7 to 9, characterized in that, The correction unit multiplies the difference between the real part of the first correction value after the first phase correction and the real part of the second correction value after the second phase correction by a scaling factor, and obtains the corrected detection value based on the sum of the result of this multiplication and the real part of the detection complex number after the second phase correction.

11. The electrostatic capacitance detection device according to any one of claims 7 to 9, characterized in that, The correction unit performs the following processing: The second phase correction is applied to an intermediate correction value corresponding to the sum of the complex number obtained by multiplying the second correction value by a scaling factor and the complex number used for detection, wherein the second phase correction rotates the phase angle corresponding to the deflection angle of the second correction value. The corrected detection value is obtained by subtracting the value obtained by multiplying the real part of the first correction value (after the first phase correction has been applied) by the scaling factor from the real part of the intermediate correction value after the second phase correction has been applied.

12. The electrostatic capacitance detection device according to any one of claims 7 to 9, characterized in that, Whenever the correction unit shifts to the correction mode, it obtains the second correction value. In the normal operating mode, it obtains the corrected detection value based on the first correction value after the first phase correction was implemented, the second correction value obtained in the most recent correction mode, and the detection complex number.

13. The electrostatic capacitance detection device according to any one of claims 1 to 3 and 7 to 9, characterized in that, When there is no object near the detection electrode in the normal operating mode, the AC voltage output unit outputs a second AC voltage with an adjusted amplitude so that the charge supplied from the first node to the detection electrode is close to zero, or the second AC voltage with the amplitude of the detection signal adjusted to be close to zero.

14. A method for detecting electrostatic capacitance, performed in an electrostatic capacitance detection device for detecting the electrostatic capacitance between an object near a detection electrode and the detection electrode, characterized in that... The electrostatic capacitance detection device has the following features: An AC voltage output section outputs a first AC voltage to a shielding electrode positioned close to the detection electrode, and a second AC voltage with the same frequency and phase as the first AC voltage but a smaller amplitude than the first AC voltage. and A detection signal generation unit supplies charge to the detection electrode from a first node connected to the detection electrode, such that the voltage of the first node is close to the second AC voltage, thereby generating an AC detection signal corresponding to the supplied charge. The AC voltage output section includes: A first AC voltage output section, which outputs the first AC voltage having a fixed amplitude; and The second AC voltage output section is composed of an attenuation circuit that outputs the second AC voltage after attenuating the amplitude of the first AC voltage. The detection signal generation unit includes: An operational amplifier amplifies the voltage difference between the inverting input terminal connected to the first node and the non-inverting input terminal connected to the second node to which the second AC voltage is applied, and outputs the amplified result as the first signal. A feedback capacitor is disposed in the path between the output terminal of the first signal of the operational amplifier and the inverting input terminal; and The subtraction unit subtracts a reference signal from the first signal and outputs the result of the subtraction as the detection signal. The reference signal is equivalent to the first signal output from the operational amplifier in normal operating mode when no object is near the detection electrode. The electrostatic capacitance detection method has the following characteristics: The calculation process involves calculating the detected value of the electrostatic capacitance based on the detection signal. and The correction process corrects for changes in the detection value that occur when the parasitic capacitance between the shielding electrode and the detection electrode, i.e., the shielding capacitance, changes. The correction process includes: The process repeatedly shifts from the usual action pattern to the correction pattern; When switching to the correction mode, the attenuation circuit of the second AC voltage output section is controlled to change the amplitude difference between the first AC voltage and the second AC voltage, and a correction value corresponding to the change in the detected value associated with the change in the amplitude difference is obtained; and The detection value is corrected according to the change in the correction value obtained in the correction mode.

15. An input device, characterized in that, have: The electrostatic capacitance between the detection electrode and the object changes as the object approaches. A shielding electrode is configured close to the detection electrode; and The electrostatic capacitance detection device according to any one of claims 1 to 13 for detecting the electrostatic capacitance between the object and the detection electrode.

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