Integrated circuit

Abstract

To provide a technique for enhancing sensitivity of a touch sensor in an integrated circuit for a touch sensor.SOLUTION: There is provided an integrated circuit for detecting an approach of a human body by a touch sensor. The touch sensor and the integrated circuit are operated by a voltage source. In the touch sensor, a sensor voltage as an output voltage of the touch sensor is changed by the approach of a human body. The integrated circuit includes: a control section for controlling the integrated circuit; an AD converter to be connected to the touch sensor and the control section; and a first type switch for switching connection among the AD converter, the voltage source, and the touch sensor. The control section performs: measuring a reference voltage as the sensor voltage one or more times while switching the connection by the first type switch before the approach of the human body; and determining an upper limit voltage value and a lower limit voltage value based on a predetermined range of the one or more reference voltages as the range of an input voltage of the AD converter according to the number of times of measurement of the reference voltage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to integrated circuits. [Background technology]

[0002] Conventionally, as described in, for example, Patent Document 1, a capacitive touch sensor detects a change in capacitance caused by a human body approaching an electrode of the touch sensor. Hereinafter, the capacitive touch sensor is referred to as a touch sensor. More specifically, the touch sensor detects a change in capacitance by measuring a voltage based on the difference between the capacitance of the sensor portion and the capacitance of an integrated circuit serving as a control unit.

[0003] The change in capacitance caused by the approach of a human body is very small. Therefore, in order to increase the sensitivity of a touch sensor, it is necessary to increase the capacitance of the sensor part. The capacitance of the sensor part can be increased by expanding the area of ​​the electrodes in the sensor part. In other words, in order to increase the capacitance of the sensor part, it is necessary to make the touch sensor larger. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-531877 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in a product equipped with a touch sensor, the space in which the touch sensor can be installed is limited by the size and shape of the product. In other words, if the size and shape of the product cannot be changed, it is difficult to increase the sensitivity of the touch sensor. Therefore, there has been a demand for a technology that can increase the sensitivity of the touch sensor regardless of the size and shape of the touch sensor. [Means for solving the problem]

[0006] The present disclosure can be realized in the following forms.

[0007] (1) According to a first aspect of the present disclosure, there is provided an integrated circuit that detects the approach of a human body using a touch sensor. The touch sensor and the integrated circuit are operated by a voltage source. The touch sensor is configured such that a sensor voltage as an output voltage of the touch sensor varies with the approach of the human body. The integrated circuit includes a control unit that controls the integrated circuit, an AD converter connected to the touch sensor and the control unit, and a first type switch that switches a connection between the AD converter, the voltage source, and the touch sensor. Before the approach of the human body, the control unit measures a reference voltage as the sensor voltage one or more times while switching the connection using the first type switch, and determines an upper limit voltage value and a lower limit voltage value based on a predetermined range from one or more reference voltages according to the number of measurements of the reference voltage, as a range of an input voltage of the AD converter. In the integrated circuit of the present disclosure, the reference voltage as the sensor voltage before the approach of the human body is determined by the state of connection between the AD converter, the voltage source, and the touch sensor. For example, the integrated circuit can determine the reference voltage in a state in which the touch sensor and the voltage source are disconnected. In a state in which the voltage source is disconnected, the reference voltage is likely to depend on the specifications of the touch sensor. Therefore, the integrated circuit of the present disclosure can determine the input voltage range of the AD converter according to the specifications of the touch sensor. In other words, by improving the resolution of the AD converter, the sensitivity of the touch sensor is also improved without changing the specifications of the touch sensor. Therefore, the integrated circuit of the present disclosure can increase the sensitivity of the touch sensor regardless of the size or shape of the touch sensor. (2) In the above embodiment, the touch sensor further includes a first capacitor having a first capacitance as a parasitic element, the integrated circuit includes a second capacitor having a predetermined second capacitance, the second capacitor being connected in parallel to the voltage source together with the first capacitor and the AD converter, and the control unit may control the first type switch to charge the first capacitor or the second capacitor from the voltage source, and generate the sensor voltage by connecting the first capacitor and the second capacitor when the first capacitor and the second capacitor are disconnected from the voltage source. In such a configuration using a capacitive touch sensor, the sensor voltage becomes lower than the voltage of the voltage source by disconnecting the first capacitor and the second capacitor from the voltage source. That is, the fluctuation of the sensor voltage due to the approach of a human body occurs in a range lower than the voltage of the voltage source. In contrast to such a capacitive touch sensor, for example, in a resistive touch sensor, the output voltage of the touch sensor occurs in a state in which the touch sensor and the voltage source are connected. Therefore, the fluctuation of the sensor voltage in the resistive touch sensor occurs in a range including the voltage value of the voltage source. Therefore, the fluctuation of the sensor voltage in the capacitive touch sensor is smaller than that in the resistive touch sensor. Therefore, in the capacitive touch sensor, a high resolution is required for the AD converter to detect the fluctuation of the sensor voltage. Therefore, the integrated circuit of the present disclosure is more suitable for the capacitive touch sensor. (3) In the above embodiment, the control unit may measure a first reference voltage as the reference voltage by charging the first capacitor with charge from the voltage source during the charging prior to generation of the reference voltage, measure a second reference voltage as the reference voltage by charging the second capacitor with charge from the voltage source during the charging prior to generation of the reference voltage, determine the upper limit voltage value based on the first reference voltage, and determine the lower limit voltage value based on the second reference voltage. With this configuration, the range of input voltages of the AD converter before the human body approaches is determined by the first reference voltage, and the lower limit voltage is determined by the second reference voltage. The sensor voltage is measured in the same manner before and when the human body approaches. Therefore, when the first capacitor is charged when the human body approaches, the sensor voltage is generated based on the first reference voltage. Also, when the second capacitor is charged when the human body approaches, the sensor voltage is generated based on the second reference voltage. That is, the upper limit voltage value and the lower limit voltage value are determined based on the reference voltage that is the reference for the sensor voltage when the human body approaches. Therefore, the integrated circuit of the present disclosure can bring the upper limit voltage value and the lower limit voltage value closer to the sensor voltage when the human body approaches. That is, the integrated circuit of the present disclosure can improve the resolution of the AD converter. (4) In the above embodiment, the control unit may measure a first reference voltage as the reference voltage by charging the first capacitor with electric charge from the voltage source during the charging prior to generation of the reference voltage, and the upper limit voltage value and the lower limit voltage value may be determined to be within a predetermined range from the first reference voltage. With this configuration, the input voltage range of the AD converter is determined only by the first reference voltage. Therefore, the integrated circuit of the present disclosure does not need to measure the sensor voltage multiple times to determine the input voltage range of the AD converter. Therefore, the integrated circuit of the present disclosure can more easily determine the input voltage range of the AD converter compared to the case where the sensor voltage is measured multiple times. (5) In the above embodiment, the input / output device may further include two DA converters connected to the control unit and the AD converter, respectively, and the two DA converters may be configured as a first DA converter that inputs the upper limit voltage value to the AD converter in response to a signal from the control unit, and a second DA converter that inputs the lower limit voltage value to the AD converter in response to a signal from the control unit. With this configuration, the integrated circuit of the present disclosure determines the input voltage range of the AD converter by the DA converter, and can therefore determine the input voltage range of the AD converter with higher accuracy than when a digital signal is converted to an analog signal only by voltage division of resistors, such as a digital potentiometer. (6) In the above embodiment, the second capacitor may include an adjustment capacitor in which a plurality of sets of an adjustment switch and an additional capacitor having a predetermined capacitance are connected in parallel, and the adjustment capacitor may determine a second component of the second capacitance as a combination of the capacitances of the additional capacitors by changing a combination of connections of the plurality of adjustment switches in the adjustment capacitor in response to a command from the control unit. With this configuration, the second capacitance of the second capacitor can be adjusted by the adjustment capacitor that can vary the second component. The reference voltage of the sensor voltage varies depending on the relationship between the capacitances of the first capacitor and the second capacitor by being cut off from the voltage source. In other words, the integrated circuit of the present disclosure can improve the sensitivity of the touch sensor by adjusting the input voltage range of the AD converter by adjusting the second capacitance. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a circuit diagram showing a configuration of an integrated circuit according to a first embodiment. [Diagram 2] 6 is a flowchart showing a detection process by a touch sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A. First embodiment: A-1.Circuit configuration: 1 is a circuit diagram showing a configuration of an integrated circuit 120 according to a first embodiment. The integrated circuit 120 detects the approach of a human body by a touch sensor 110. More specifically, the integrated circuit 120 is a circuit that measures a sensor voltage Vd that changes in response to the approach of a human body. The integrated circuit 120 is used, for example, in a touch sensor 110 mounted on a product such as an instrument panel P or a room lamp in a vehicle V.

[0010] The integrated circuit 120 includes a voltage source 124, an AD converter 121, a DA converter 123, a control unit 122, a second capacitor 127, a first type switch 125, and a fourth switch 126. First, the connection between each element in the integrated circuit 120 and the touch sensor 110 will be described. Note that ADC in FIG. 2 represents the AD converter 121. DAC represents the DA converter 123.

[0011] The control unit 122 is connected to the AD converter 121 and two DA converters 123, that is, a first DA converter 123a and a second DA converter 123b.

[0012] The AD converter 121 is connected to the control unit 122. The AD converter 121 includes an output terminal Tout for a digital signal, an input terminal Tin for an analog signal, and input terminals Tref1 and Tref2 that determine the range of the input voltage of the analog signal. More specifically, the output terminal Tout is connected to the control unit 122. Furthermore, the input terminal Tref1 is connected to the control unit 122 via a first DA converter 123a. The input terminal Tref2 is connected to the control unit 122 via a second DA converter 123b.

[0013] The AD converter 121 is further connected to the touch sensor 110. The touch sensor 110 functions as a first capacitor 110c having a first capacitance C1 as a parasitic element with respect to the integrated circuit 120. Therefore, the input terminal Tin is connected to the first capacitor 110c via the first type switch 125. More specifically, the AD converter 121 is connected in series from the input terminal Tin to the third switch SW3 as the first type switch 125, the second switch SW2 of the first type switch 125, and the first capacitor 110c in this order.

[0014] The first capacitor 110c is composed of a first parasitic capacitor 111 and a second parasitic capacitor 112 connected in parallel. The first parasitic capacitor 111 represents a parasitic capacitance that occurs between the terminals of the touch sensor 110 regardless of the approach of a human body. One polarity of the first parasitic capacitor 111 is connected to the second switch SW2 via one terminal 110ta of the touch sensor 110. The other polarity of the first parasitic capacitor 111 is connected to the ground via the other terminal 110tb of the touch sensor 110. The ground in FIG. 1 is also connected to the AD converter 121, the DA converter 123, and the control unit 122, but is omitted from the illustration in order to facilitate understanding of the technology.

[0015] The second parasitic capacitor 112 represents a parasitic capacitance that occurs between the human body and the touch sensor 110 due to the approach of the human body. One polarity of the second parasitic capacitor 112 is connected to the first parasitic capacitor 111 and the second switch SW2. The other polarity of the second parasitic capacitor 112 is connected to the ground via the human body. The second parasitic capacitor 112 is illustrated by a dashed line in FIG. 1 because it occurs due to the approach of the human body.

[0016] The second capacitor 127 is connected in parallel to the voltage source 124 together with the first capacitor 110c and the AD converter 121. The second capacitor 127 is composed of a hold capacitor 127ac and an adjustment capacitor 127b. More specifically, one terminal of the hold capacitor 127ac is connected to the third switch SW3 and the input terminal Tin of the AD converter 121. The other terminal of the hold capacitor 127ac is connected to the ground. One terminal of the adjustment capacitor 127b is connected to the third switch SW3 and the input terminal Tin of the AD converter 121. The other terminal of the adjustment capacitor 127b is connected to the ground.

[0017] The adjustment capacitor 127b is configured by connecting multiple sets of an adjustment switch 127bs and an additional capacitor 127bc in series in parallel. In FIG. 1, in order to facilitate understanding of the technology, only one set of the configuration is shown. The additional capacitor 127bc is connected in parallel to the voltage source 124 together with the first capacitor 110c, the hold capacitor 127ac, and the AD converter 121. More specifically, one terminal of the additional capacitor 127bc is connected to the third switch SW3 and the input terminal Tin of the AD converter 121 via the adjustment switch 127bs. The other terminal of the additional capacitor 127bc is connected to the ground.

[0018] The voltage source 124 is connected to the touch sensor 110 and the second capacitor 127. More specifically, the voltage source 124 is connected to the ground in the order of the first switch SW1 as the first type switch 125, the third switch SW3, and the second capacitor 127. Furthermore, the voltage source 124 is connected to the ground in the order of the first switch SW1, the second switch SW2, and the first capacitor 110c.

[0019] That is, the first type switch 125 is connected between the AD converter 121, the voltage source 124, and the touch sensor 110. Furthermore, the first type switch 125 is connected to the ground via the fourth switch 126. That is, one terminal of the fourth switch 126 is connected to the first switch SW1, the second switch SW2, and the third switch SW3. The other terminal of the fourth switch 126 is connected to the ground.

[0020] A-2. Element Functions: The functions of each element in the integrated circuit 120 and the touch sensor 110 will be described.

[0021] The touch sensor 110 is configured such that the sensor voltage Vd varies with the approach of a human body. The touch sensor 110 has a structure in which electrodes and a dielectric such as glass or resin are laminated. Thus, as described above, the touch sensor 110 functions as a first capacitor 110c having a first capacitance C1 as a parasitic element with respect to the integrated circuit 120. That is, the touch sensor 110 varies the sensor voltage Vd by the first capacitance C1 varying with the approach of a human body. The sensor voltage Vd is a voltage between the terminal 110ta of the touch sensor 110 and the ground. However, in order to facilitate understanding of the technology, in FIG. 2, the sensor voltage Vd is illustrated at the position of the input voltage Vin of the AD converter 121. Thus, when the second switch SW2 and the third switch SW3 are in the ON state, the sensor voltage Vd is also the input voltage Vin of the AD converter 121. The variation of the sensor voltage Vd will be described in detail later.

[0022] The first capacitance C1 of the touch sensor 110 includes a first parasitic component C1p as the first capacitance C1 before the approach of the human body, and a second parasitic component C1h as the first capacitance C1 generated by the approach of the human body. That is, the touch sensor 110 is composed of a first parasitic capacitor 111 having the first parasitic component C1p, and a second parasitic capacitor 112 having the second parasitic component C1h. The second parasitic capacitor 112 is generated in a parallel connection relationship with the first parasitic capacitor 111. Therefore, the first capacitance C1 increases due to the approach of the human body.

[0023] The first parasitic capacitor 111 determines the sensor voltage Vd. More specifically, the first parasitic capacitor 111 determines the sensor voltage Vd that is generated by transferring charge to and from the second capacitor 127.

[0024] The second parasitic capacitor 112 determines the sensor voltage Vd when a human body approaches. More specifically, the second parasitic capacitor 112, together with the first parasitic capacitor 111, determines the sensor voltage Vd generated by transferring charge to and from the second capacitor 127 when a human body approaches.

[0025] The first capacitance C1 of the touch sensor 110 differs depending on the specifications of the touch sensor 110. For example, the first capacitance C1 changes when the specifications of the size of the electrodes constituting the touch sensor 110 and the thickness of the dielectric material change.

[0026] The second capacitor 127 determines the sensor voltage Vd. More specifically, the second capacitor 127 determines the sensor voltage Vd generated by transferring electric charge to and from the first capacitor 110c. The second capacitor 127 has a predetermined second capacitance C2. The second capacitance C2 includes a first component C2h due to the hold capacitor 127ac and a second component C2a due to the additional capacitor 127bc in the adjustment capacitor 127b.

[0027] The hold capacitor 127ac defines the second capacitance C2. The hold capacitor 127ac has a first component C2h as a constant capacitance, regardless of the first capacitance C1. That is, the first component C2h is determined when the integrated circuit 120 is manufactured.

[0028] The adjustment capacitor 127b defines the second capacitance C2 according to the first capacitance C1. The adjustment capacitor 127b is configured by connecting a plurality of sets of an adjustment switch 127bs and an additional capacitor 127bc having a predetermined capacitance in series in parallel, with each set being a series connection. In FIG. 1, in order to facilitate understanding of the technology, there is one set of the additional capacitor 127bc and the adjustment switch 127bs. However, in reality, as described above, a plurality of sets of the additional capacitor 127bc and the adjustment switch 127bs are provided. Each of the adjustment switches 127bs of the plurality of adjustment switches 127bs is controlled by the control unit 122. In FIG. 1, in order to facilitate understanding of the technology, the connection between the adjustment switch 127bs and the control unit 122 is omitted. Therefore, in response to a command from the control unit 122, the adjustment capacitor 127b determines the second component C2a of the second capacitance C2 as the combined capacitance of the additional capacitor 127bc by changing the combination of connections of the multiple adjustment switches 127bs in the adjustment capacitor 127b.

[0029] The second component C2a of the second capacitance C2 is determined based on the first capacitance C1. More specifically, when the first capacitance C1 includes only the first parasitic component C1p, the second component C2a is determined so that the second capacitance C2 matches the first capacitance C1. The second component C2a is determined in advance by the control unit 122 before detecting the approach of a human body. For example, the second component C2a is determined when the integrated circuit 120 and the touch sensor 110 are assembled.

[0030] The first type switch 125 switches the connection between the AD converter 121, the voltage source 124, and the touch sensor 110. The first type switch 125 includes a first switch SW1, a second switch SW2, and a third switch SW3. The function of the switches in this embodiment will be described in detail later.

[0031] The fourth switch 126 discharges the electric charges of the first capacitor 110c and the second capacitor 127. More specifically, the fourth switch 126 connects the first capacitor 110c and the second capacitor 127 to ground via the first type switch 125.

[0032] The first type switch 125 and the fourth switch 126 are connected to the control unit 122. That is, the switching of the connection by each switch is controlled by the control unit 122. The control of each switch will be described in detail later. In FIG. 1, in order to facilitate understanding of the technology, the connection between each switch and the control unit 122 is omitted.

[0033] The voltage source 124 applies a voltage to the touch sensor 110 and the integrated circuit 120. More specifically, the voltage source 124 charges the first capacitor 110c or the second capacitor 127. In the following description, the voltage of the voltage source 124 is referred to as a power supply voltage VDD. The ground voltage is referred to as a ground voltage Vg. In the following description, unless otherwise specified, Vg=0V.

[0034] The AD converter 121 converts an analog signal based on the sensor voltage Vd into a digital signal. Furthermore, the AD converter 121 sends the generated digital signal to the control unit 122. The AD converter 121 has an input terminal Tin for an analog signal, an output terminal Tout for a digital signal, and input terminals Tref1 and Tref2 for determining the range of the input voltage. The input voltage Vin of the input terminal Tin is also the sensor voltage Vd. That is, the AD converter 121 converts an analog signal based on the sensor voltage Vd input as the input voltage Vin into a digital signal.

[0035] The voltage range of the analog signal that can be converted by the AD converter 121 is called the input voltage range. In the input voltage range, the upper limit voltage value Vref1 is determined by the input voltage Vref1 of the input terminal Tref1. The lower limit voltage value Vref2 is determined by the input voltage Vref2 of the input terminal Tref2.

[0036] For example, if the resolution of the AD converter 121 is 10 bits, ie, 1023 LSB, the output value D of the digital signal of the AD converter 121 is calculated by the following equation (1). D={(Vin-Vref2) / (Vref1-Vref2)}×1023 …(1) The AD converter 121 outputs an output value D as a digital signal from an output terminal Tout.

[0037] The DA converter 123 converts the digital signal from the control unit 122 into an analog signal. The DA converter 123 is composed of a first DA converter 123a and a second DA converter 123b. The first DA converter 123a inputs an upper limit voltage value Vref1 to the AD converter 121 in response to a signal from the control unit 122. The second DA converter 123b inputs a lower limit voltage value Vref2 to the AD converter 121 in response to a signal from the control unit 122.

[0038] The control unit 122 controls the integrated circuit 120. The control unit 122 includes a CPU 122a, a ROM 122b, and a RAM 122c. The control unit 122 is realized, for example, by a microcomputer. The ROM 122b is a read-only semiconductor memory, and stores a control program for controlling the integrated circuit 120 in advance. The RAM 122c is a readable and writable semiconductor memory, and stores information required for controlling the integrated circuit 120. The CPU 122a loads the control program stored in the ROM 122b into the RAM 122c and executes it to realize various functions. The control unit 122 is also connected to a control unit of a product equipped with the touch sensor 110. For example, the control unit 122 transmits and receives information related to the control of the control unit 122 by being connected to a control unit of an instrument panel P. However, in FIG. 1, the control unit of the product equipped with the touch sensor 110 is omitted in order to facilitate understanding of the technology. The function of the control unit 122 will be described in detail later.

[0039] A-3. Measuring the sensor voltage: 2 is a flowchart showing a detection process by the touch sensor 110. The CPU 122a starts the process in response to the start-up of a product equipped with the touch sensor 110. More specifically, the process starts when the control unit 122 is started up in a state in which the AD converter 121 and the DA converter 123 are operable.

[0040] 2 are performed before a human body approaches. That is, in steps S110 to S200, the second parasitic capacitor 112 is not generated. The processes from step S210 onwards are performed when a human body may approach. That is, the processes from step S210 onwards are performed when the second parasitic capacitor 112 may be generated. In the following explanation, the processes from step S210 onwards are explained assuming that the second parasitic capacitor 112 is generated.

[0041] 2, the CPU 122a sets the range of the input voltage of the AD converter 121. More specifically, the CPU 122a applies the power supply voltage VDD as the upper limit voltage value Vref1 of the AD converter 121 through the first DA converter 123a. Furthermore, the CPU 122a applies the ground voltage Vg as the lower limit voltage value Vref2 of the AD converter 121 through the second DA converter 123b. Note that in step S110, the first type switch 125 and the fourth switch 126 are both off.

[0042] 2, the CPU 122a charges the second capacitor 127. More specifically, the CPU 122a turns on the first switch SW1 and the third switch SW3. Furthermore, the CPU 122a turns off the second switch SW2 and the fourth switch 126. Thus, the second capacitor 127 is charged with an electric charge based on the power supply voltage VDD.

[0043] 2, the CPU 122a discharges the second capacitor 127. More specifically, the CPU 122a turns on the third switch SW3 and the second switch SW2. Furthermore, the CPU 122a turns off the first switch SW1 and the fourth switch 126. Thus, the charge of the second capacitor 127 is discharged toward the first parasitic capacitor 111 in the first capacitor 110c.

[0044] As the sensor voltage Vd generated in step S130, the second sensor voltage Vd2 is calculated by equation (2) based on the relationship of charge Q=capacitance C×voltage V. Vd2={VDD×(C2h+C2a) / {(C2h+C2a)+C1p} …(2) For example, when the parameters of each element are C1=C1p=15pF, C2h=10pF, C2a=5pF, C2=C2h+C2a=15pF, and VDD=5V, the second sensor voltage Vd2 is 2.500V. In the following description, the second sensor voltage Vd2 is also referred to as the second reference voltage Vd2. The same parameters are used in the following processing examples.

[0045] 2, the CPU 122a measures the second reference voltage Vd2. More specifically, the CPU 122a converts an analog signal based on the second reference voltage Vd2 into a digital signal by the AD converter 121. The CPU 122a receives a second output value D2 as the output value D from the output terminal Tout of the AD converter 121. The CPU 122a stores the second reference voltage Vd2 as the second output value D2 in the RAM 122c.

[0046] The second output value D2 is calculated by equation (1). In step S140, the AD converter 121 has Vref1=5 V and Vref2=0 V. Therefore, when Vin=Vd2=2.500 V, the second output value D2 is D2=551 [LSB].

[0047] 2, the CPU 122a discharges the charges stored in the first capacitor 110c and the second capacitor 127. More specifically, the CPU 122a turns on the second switch SW2, the third switch SW3, and the fourth switch 126. Furthermore, the CPU 122a turns off the first switch SW1. Thus, the charges stored in the first capacitor 110c and the second capacitor 127 are discharged to the ground via the fourth switch 126. Thus, the voltages of the first capacitor 110c and the second capacitor 127 become the ground voltage Vg.

[0048] 2, the CPU 122a charges the first capacitor 110c. More specifically, the CPU 122a turns on the first switch SW1 and the second switch SW2. Furthermore, the CPU 122a turns off the third switch SW3 and the fourth switch 126. Thus, the first parasitic component C1p of the first capacitor 110c is charged with an electric charge based on the power supply voltage VDD.

[0049] 2, the CPU 122a discharges the first capacitor 110c. More specifically, the CPU 122a turns on the third switch SW3 and the second switch SW2. Furthermore, the CPU 122a turns off the first switch SW1 and the fourth switch 126. Thus, the charge of the first capacitor 110c is discharged toward the second capacitor 127.

[0050] As the sensor voltage Vd generated in step S170, the first sensor voltage Vd1 is calculated by equation (3) based on the relationship of charge Q=capacitance C×voltage V. Vd1={VDD×C1p / {(C2h+C2a)+C1p} …(3) For example, when the parameters of each element are the same as those illustrated in step S130, the first sensor voltage Vd1 is 2.500 V. In the following description, the first sensor voltage Vd1 is also referred to as the first reference voltage Vd1. That is, the first reference voltage Vd1 generated in step S170 is equal to the second reference voltage Vd2 generated in step S130. The agreement between the second reference voltage Vd2 and the first reference voltage Vd1 occurs when the first capacitance C1 and the second capacitance C2 are equal in the example.

[0051] 2, the CPU 122a measures the first reference voltage Vd1. More specifically, the CPU 122a converts an analog signal based on the first reference voltage Vd1 into a digital signal by the AD converter 121. Furthermore, the CPU 122a receives a first output value D1 as the output value D from the output terminal Tout of the AD converter 121. The CPU 122a stores the first reference voltage Vd1 as the first output value D1 in the RAM 122c.

[0052] As described above, the CPU 122a controls the first type switch 125 to charge the first capacitor 110c or the second capacitor 127 with electric charge from the voltage source 124. Furthermore, the CPU 122a generates a sensor voltage Vd by connecting the first capacitor 110c and the second capacitor 127 in a state in which the first capacitor 110c and the second capacitor 127 are disconnected from the voltage source 124. That is, the CPU 122a generates a first reference voltage Vd1 and a second reference voltage Vd2, which are measured by measuring the sensor voltage Vd twice.

[0053] The process of step S190 in FIG. 2 is the same as step S150.

[0054] 2, the CPU 122a sets the range of the input voltage of the AD converter 121. More specifically, the CPU 122a applies a first correction voltage Vd1a obtained by correcting the first reference voltage Vd1 as the upper limit voltage value Vref1 of the AD converter 121 through the first DA converter 123a. Furthermore, the CPU 122a applies a second correction voltage Vd2a obtained by correcting the second reference voltage Vd2 as the lower limit voltage value Vref2 of the AD converter 121 through the second DA converter 123b. Note that in step S200, the first type switch 125 and the fourth switch 126 are both turned off.

[0055] The first correction voltage Vd1a and the second correction voltage Vd2a are determined by the CPU 122a within a predetermined range based on the respective reference voltages. More specifically, the first correction voltage Vd1a and the second correction voltage Vd2a are calculated by multiplying the respective reference voltages by predetermined correction coefficients. The correction coefficients are experimentally determined according to the relationship between the first capacitance C1 and the second capacitance C2 because the second capacitance C2 varies depending on the specifications and characteristics of the touch sensor 110. Each correction coefficient is stored in advance in the RAM 122c.

[0056] For example, the correction coefficient of the first reference voltage Vd1 is 1.06, and the correction coefficient of the second reference voltage Vd2 is 0.930. In this case, the first correction voltage Vd1a is Vd1a=Vd1×1.06=2.500×1.060=2.650. The second correction voltage Vd2a is Vd2a=Vd2×0.930=2.500×0.930=2.325. That is, in the example, the upper limit voltage value Vref1 is determined to be 2.650V. The lower limit voltage value Vref2 is determined to be 2.325V.

[0057] That is, before the human body approaches, the CPU 122a measures the first reference voltage Vd1 and the second reference voltage Vd2 as the sensor voltage Vd while switching the connection by the first type switch 125. The CPU 122a determines the upper limit voltage value Vref1 and the lower limit voltage value Vref2 based on a range determined in advance from each reference voltage in accordance with the number of times the reference voltage is measured, within the range of the input voltage of the AD converter 121. More specifically, the CPU 122a measures the first reference voltage Vd1 as the reference voltage by charging the first capacitor 110c with electric charge from the voltage source 124 in charging prior to the generation of the reference voltage. Furthermore, the CPU 122a measures the second reference voltage Vd2 as the reference voltage by charging the second capacitor 127 with electric charge from the voltage source 124 in charging prior to the generation of the reference voltage. Thus, the CPU 122a determines the upper limit voltage value Vref1 based on the first reference voltage Vd1. The CPU 122a determines the lower limit voltage value Vref2 based on the second reference voltage Vd2.

[0058] 2 is in a state in which the first parasitic capacitor 111 is generated due to the approach of a human body. That is, the first capacitance C1 is increased by the addition of the second parasitic component C1h. Therefore, the first capacitor 110c is charged and discharged by the first parasitic capacitor 111 and the second parasitic capacitor 112.

[0059] The process of step S210 in FIG. 2 is the same as the process of step S120.

[0060] The process of step S220 in Fig. 2 is the same as the process of step S130, except that the charge discharged from the second capacitor 127 is discharged toward the first parasitic capacitor 111 and the second parasitic capacitor 112 in the first capacitor 110c.

[0061] 2, the CPU 122a measures a third sensor voltage Vd3 as the sensor voltage Vd generated in step S220. The measurement method is the same as that in step S140. However, the third sensor voltage Vd3 is calculated by combining the first capacitance C1 with the second parasitic component C1h using formula (4). Vd3={VDD×(C2h+C2a) / {(C2h+C2a)+C1p+C1h} …(4) For example, when the second parasitic component C1h is set to C1h=0.5 pF and the parameters of the other elements are set to the same as those exemplified in step S130, the third sensor voltage Vd3 becomes 2.459V.

[0062] The CPU 122a stores the third sensor voltage Vd3 in the RAM 122c as the output value D of the AD converter 121. The third output value D3 is calculated by equation (1). In step S230, the AD converter 121 has Vref1=Vd1a=2.650V and Vref2=Vd2a=2.325V. Therefore, when Vin=Vd3=2.459V, the third output value D3 is D3=421 [LSB].

[0063] The process of step S240 in FIG. 2 is the same as step S150.

[0064] The processes in steps S250 and S260 in FIG. 2 are the same as the processes in steps S160 and S170, respectively.

[0065] 2, the CPU 122a measures a fourth sensor voltage Vd4 as the sensor voltage Vd in step S260. The measurement method is the same as that in step S180. However, the fourth sensor voltage Vd4 is calculated by adding the second parasitic component C1h according to formula (5). Vd4={VDD×(C1p+C1h) / {(C2h+C2a)+C1p+C1h} …(5) For example, when the second parasitic component C1h is set to C1h=0.5 pF and the parameters of the other elements are set to the same as those exemplified in step S170, the fourth sensor voltage Vd4 becomes 2.541V.

[0066] The CPU 122a stores the fourth sensor voltage Vd4 in the RAM 122c as the output value D of the AD converter 121. The fourth output value D4 is calculated by the formula (1). In step S270, the AD converter 121 has Vref1=Vd1a=2.650V and Vref2=Vd2a=2.325V. Therefore, when Vin=Vd4=2.541V, the fourth output value D4 is D4=679 [LSB].

[0067] The process of step S280 in FIG. 2 is the same as step S150.

[0068] In step S290 of FIG. 2, the CPU 122a detects the approach of a human body. More specifically, the CPU 122a calculates the difference between the third output value D3 and the fourth output value D4. Furthermore, the CPU 122a sends information based on the difference between the third output value D3 and the fourth output value D4 to a control unit of a product equipped with the touch sensor 110, for example, a control unit of an instrument panel P. That is, the CPU 122a causes the control unit of the instrument panel P to detect the approach of a human body based on the difference between the third output value D3 and the fourth output value D4. For example, the control unit of the instrument panel P recognizes that a human body is approaching when the difference between the third output value D3 and the fourth output value D4 exceeds a threshold value. The control unit of the instrument panel P recognizes that a human body is approaching when the difference between the third output value D3 and the fourth output value D4 is less than a threshold value.

[0069] In step S300 of FIG. 2, the CPU 122a determines whether or not it is necessary to reset the upper limit voltage value Vref1 and the lower limit voltage value Vref2. More specifically, the CPU 122a returns the process to step S110 after a predetermined time has elapsed, thereby newly setting the upper limit voltage value Vref1 and the lower limit voltage value Vref2. For example, the CPU 122a executes the processes of steps S210 to S290 at a cycle of 100 μs. In this state, the CPU 122a returns the process to step S110 10 minutes after the first execution of step S210, which is the predetermined time. That is, the CPU 122a advances the process to step S110 after the predetermined time has elapsed. The CPU 122a advances the process to step S310 before the predetermined time has elapsed.

[0070] 2, the CPU 122a determines whether to stop detection by the touch sensor 110. When the CPU 122a receives a command to stop detection by the touch sensor 110, for example, due to a command to turn off the power to a product equipped with the touch sensor 110, the CPU 122a stops the detection. When the CPU 122a has not received a command to stop detection by the touch sensor 110, the CPU 122a advances the process to step S210. When the CPU 122a receives a command to stop detection by the touch sensor 110, the CPU 122a ends the process.

[0071] As described above, in the integrated circuit 120 of the present disclosure, the reference voltage as the sensor voltage Vd before the approach of the human body is determined by the state of connection between the AD converter 121, the voltage source 124, and the touch sensor 110. For example, the integrated circuit 120 can determine the reference voltage in a state in which the touch sensor 110 and the voltage source 124 are disconnected. In a state in which the voltage source 124 is disconnected, the reference voltage is likely to depend on the specifications of the touch sensor 110. For this reason, the integrated circuit 120 of the present disclosure can determine the range of the input voltage of the AD converter 121 according to the specifications of the touch sensor 110. In other words, by improving the resolution of the AD converter 121, the sensitivity of the touch sensor 110 is also improved without changing the specifications of the touch sensor 110. Therefore, the integrated circuit 120 of the present disclosure can increase the sensitivity of the touch sensor 110 regardless of the size or shape of the touch sensor 110.

[0072] Moreover, in a configuration using a capacitive touch sensor, the sensor voltage Vd becomes lower than the voltage of the voltage source 124 by disconnecting the first capacitor 110c and the second capacitor 127 from the voltage source 124. That is, the fluctuation of the sensor voltage Vd due to the approach of a human body occurs in a range lower than the voltage of the voltage source 124. In contrast to such a capacitive touch sensor, for example, in a resistive touch sensor, the output voltage of the touch sensor occurs in a state in which the touch sensor and the voltage source are connected. Therefore, the fluctuation of the sensor voltage in the resistive touch sensor occurs in a range including the voltage value of the voltage source. Therefore, the fluctuation range of the sensor voltage Vd in the capacitive touch sensor is smaller than that in the resistive touch sensor. Therefore, in the capacitive touch sensor, a high resolution is required for the AD converter 121 to detect the fluctuation of the sensor voltage Vd. Therefore, the integrated circuit 120 of the present disclosure is more suitable for a capacitive touch sensor.

[0073] Furthermore, by adopting such a configuration, the range of the input voltage of the AD converter 121 before the approach of the human body is determined by the first reference voltage Vd1 as the upper limit voltage value Vref1, and the second reference voltage Vd2 as the lower limit voltage value Vref2. The sensor voltage Vd is measured in the same manner before and when the human body approaches. Therefore, when the first capacitor 110c is charged when the human body approaches, the sensor voltage Vd is generated based on the first reference voltage Vd1. Furthermore, when the second capacitor 127 is charged when the human body approaches, the sensor voltage Vd is generated based on the second reference voltage Vd2. That is, the upper limit voltage value Vref1 and the lower limit voltage value Vref2 are determined based on the reference voltage that is the reference for the sensor voltage Vd when the human body approaches. Therefore, the integrated circuit 120 of the present disclosure can bring the upper limit voltage value Vref1 and the lower limit voltage value Vref2 close to the sensor voltage Vd when the human body approaches. In other words, the integrated circuit 120 of the present disclosure can improve the resolution of the AD converter 121.

[0074] Moreover, by adopting such a configuration, the integrated circuit 120 of the present disclosure determines the input voltage range of the AD converter 121 by the DA converter 123. Therefore, the integrated circuit 120 of the present disclosure can determine the input voltage range of the AD converter 121 with higher accuracy than when a digital signal is converted into an analog signal only by voltage division of resistors, such as a digital potentiometer.

[0075] Furthermore, by adopting such a configuration, the second capacitor 127 can adjust the second capacitance C2 by the adjustment capacitor 127b that can vary the second component C2a. The reference voltage of the sensor voltage Vd varies depending on the relationship between the capacitances of the first capacitor 110c and the second capacitor 127 by being cut off from the voltage source 124. That is, the integrated circuit 120 of the present disclosure can improve the sensitivity of the touch sensor 110 by adjusting the range of the input voltage of the AD converter 121 by adjusting the second capacitance C2.

[0076] B. Second embodiment: The integrated circuit 120 of the second embodiment does not measure the second reference voltage Vd2 in the integrated circuit 120 of the first embodiment. The process of Fig. 2 in the second embodiment will be described below. The configuration of the integrated circuit 120 of the second embodiment is the same as that of the first embodiment.

[0077] The process of step S110 in FIG. 2 in the second embodiment is the same as the process of step S110 in FIG. 2 in the first embodiment.

[0078] In the second embodiment, the processes of steps S120 to S150 in Fig. 2 are not performed, so the CPU 122a does not measure the second reference voltage Vd2.

[0079] The processing in steps S160 to S190 in FIG. 2 in the second embodiment is the same as the processing in steps S160 to S190 in FIG. 2 in the first embodiment.

[0080] In the second embodiment, in step S200 of FIG. 2, the CPU 122a determines the upper limit voltage value Vref1 and the lower limit voltage value Vref2 based on the first reference voltage Vd1. That is, the CPU 122a calculates the first correction voltage Vd1a of the second embodiment and the second correction voltage Vd2a of the second embodiment by multiplying the first reference voltage Vd1 by two predetermined correction coefficients. For example, the first correction voltage Vd1a and the second correction voltage Vd2a of the second embodiment are the same as those of the first embodiment by setting the correction coefficient for calculating the first correction voltage Vd1a to 1.06 and the correction coefficient for calculating the second correction voltage Vd2a to 0.93. Therefore, the integrated circuit 120 of the second embodiment can determine the upper limit voltage value Vref1 and the lower limit voltage value Vref2 from one reference voltage.

[0081] That is, in charging prior to generation of the reference voltage, the CPU 122a measures a first reference voltage Vd1 as a reference voltage by charging the first capacitor 110c with electric charge from the voltage source 124. The CPU 122a determines the upper limit voltage value Vref1 and the lower limit voltage value Vref2 to be within a predetermined range from the first reference voltage Vd1.

[0082] In the second embodiment, the processes in steps S210 to S310 in FIG. 2 are the same as the processes in steps S210 to S310 in FIG. 2 in the first embodiment.

[0083] With this configuration, the input voltage range of the AD converter 121 is determined only by the first reference voltage Vd1. Therefore, the integrated circuit 120 of the present disclosure does not need to measure the sensor voltage Vd multiple times to determine the input voltage range of the AD converter 121. Therefore, the integrated circuit 120 of the present disclosure can determine the input voltage range of the AD converter 121 more easily than in the case of measuring the sensor voltage Vd multiple times.

[0084] C. Other embodiments: (1) In the above embodiment, the integrated circuit is exemplified as a capacitive touch sensor as the touch sensor. However, the integrated circuit may use a resistive touch sensor in measuring the reference voltage. That is, the sensor voltage may be a voltage applied to a resistor, not a capacitor voltage. Thus, for example, in a resistive touch sensor, the integrated circuit may determine the input voltage range of the AD converter using the output voltage of the touch sensor as a reference voltage before the human body approaches. Even in a resistive touch sensor, the integrated circuit can increase the sensitivity of the touch sensor regardless of the size or shape of the touch sensor. (2) In the above embodiment, the range of the input voltage of the AD converter 121 is determined based on the reference voltage obtained by one or two measurements. However, the range of the input voltage of the AD converter 121 may be determined based on the reference voltage obtained by one or more measurements, such as three or four. For example, the third reference voltage may be measured as the voltage when the voltage source 124 and the first capacitor 110c are connected, and the third reference voltage may be used as the power supply voltage VDD in calculating the sensor voltage Vd. By adopting such a configuration, the CPU 122a can more accurately calculate the sensor voltage Vd without being affected by the voltage drop caused by the first type switch 125. (3) In the above embodiment, the integrated circuit includes the DA converter 123. However, the integrated circuit 120 may include a potentiometer instead of the DA converter 123. In other words, by using a potentiometer, the designer of the integrated circuit can configure the circuit more easily. (4) In the above embodiment, the integrated circuit includes the adjustment capacitor 127b. However, the integrated circuit does not have to include the adjustment capacitor 127b. That is, the first capacitor of the integrated circuit is composed of only the hold capacitor 127ac. By adopting this configuration, the integrated circuit can reduce costs compared to a configuration in which the integrated circuit includes the adjustment capacitor 127b. (5) In the process of Fig. 2 in the above embodiment, the second capacitor 127 is charged before the first capacitor 110c. However, the process may be performed in a different order, such that the first capacitor 110c is charged before the second capacitor 127. (6) In the above embodiment, the second component C2a of the adjustment capacitor 127b is adjusted when the integrated circuit 120 and the touch sensor 110 are assembled, that is, before the human body approaches. However, the second component C2a may be adjusted at the beginning of the process in FIG. 2. By adopting such a configuration, the integrated circuit 120 can more appropriately determine the second component C2a in response to the fluctuation of the first capacitance C1 due to the usage environment.

[0085] The present disclosure is not limited to the above-mentioned embodiment, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features of the embodiments corresponding to the technical features in each form described in the Summary of Disclosure can be appropriately replaced or combined to solve some or all of the above problems or to achieve some or all of the above effects. Furthermore, if the technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0086] 110...touch sensor, 110c...first capacitor, 110ta, 110tb...terminal, 111...first parasitic capacitor, 112...second parasitic capacitor, 120...integrated circuit, 121...AD converter, 122...control unit, 122a...CPU, 122b...ROM, 122c...RAM, 123...DA converter, 123a...first DA converter, 123b...second DA converter, 124...voltage source, 125...first type switch, 126...fourth switch, 127...second capacitor, 127ac...hold capacitor, 127b...adjustment capacitor, 127bc...additional capacitor, 127bs...adjustment switch, C1...second 1st capacitance, C1h...second parasitic component, C1p...first parasitic component, C2...second capacitance, C2a...second component, C2h...first component, D...output value, D1~D4...first~fourth output values, P...instrument panel, SW1~SW3...first~third switches, Tin, Tref1, Tref2...input terminal, Tout...output terminal, V...vehicle, VDD...power supply voltage, Vd...sensor voltage, Vd1...first sensor voltage, first reference voltage, Vd2...second sensor voltage, second reference voltage, Vd3, Vd4...third sensor voltage, fourth sensor voltage, Vg...ground voltage, Vin...input voltage, Vref1...upper limit voltage, Vref2...lower limit voltage

Claims

1. An integrated circuit that detects the approach of a human body by a touch sensor, the touch sensor and the integrated circuit are powered by a voltage source; the touch sensor is configured such that a sensor voltage as an output voltage of the touch sensor fluctuates in response to the approach of the human body; The integrated circuit comprises: A control unit that controls the integrated circuit; an AD converter connected to the touch sensor and the control unit; a first type switch that switches a connection between the AD converter, the voltage source, and the touch sensor; The control unit is measuring a reference voltage as the sensor voltage at least once while switching the connection by the first type switch before the human body approaches; an integrated circuit that determines, in accordance with the number of measurements of the reference voltage, upper limit voltage values ​​and lower limit voltage values ​​based on a predetermined range from one or more reference voltages, for a range of an input voltage of the AD converter;

2. 2. The integrated circuit of claim 1, The touch sensor further includes a first capacitor having a first capacitance as a parasitic element; The integrated circuit comprises: a second capacitor having a predetermined second capacitance, the second capacitor being connected in parallel with the first capacitor and the A / D converter to the voltage source; The control unit controls the first type switch, Charging the first capacitor or the second capacitor from the voltage source; an integrated circuit that generates the sensor voltage by connecting the first capacitor and the second capacitor in a state in which the first capacitor and the second capacitor are disconnected from the voltage source.

3. 3. An integrated circuit according to claim 2, comprising: The control unit is In the charging step prior to the generation of the reference voltage, a first reference voltage is measured as the reference voltage by charging the first capacitor with electric charge from the voltage source; In the charging step prior to the generation of the reference voltage, a second reference voltage is measured by charging the second capacitor with electric charge from the voltage source; determining the upper limit voltage value based on the first reference voltage; The lower limit voltage value is determined based on the second reference voltage.

4. 3. An integrated circuit according to claim 2, comprising: the control unit measures a first reference voltage as the reference voltage by charging the first capacitor with electric charge from the voltage source in the charging prior to generation of the reference voltage; The upper limit voltage value and the lower limit voltage value are determined to be within a predetermined range from the first reference voltage.

5. 4. The integrated circuit of claim 3, further comprising: two DA converters connected to the control unit and the AD converter, respectively; The two DA converters are a first DA converter that inputs the upper limit voltage value to the AD converter in response to a signal from the control unit; a second DA converter that inputs the lower limit voltage value to the AD converter in response to a signal from the control unit.

6. 6. An integrated circuit according to claim 4 or claim 5, the second capacitor includes an adjustment capacitor in which a plurality of sets of an adjustment switch and an additional capacitor having a predetermined capacitance are connected in parallel, each set being a series connection of the adjustment switch and an additional capacitor having a predetermined capacitance; The adjustment capacitor is an integrated circuit that determines a second component of the second capacitance as a combination of capacitances of the additional capacitors by changing a combination of connections of a plurality of adjustment switches in the adjustment capacitor in response to a command from the control unit.

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