JP2020166656A - Touch detection circuit, input device and electronic device - Google Patents

Abstract

To provide a touch detection circuit that reduces power consumption.SOLUTION: In use, a self-capacitive touch detection circuit 200 is connected with a plurality of electrodes 112_1 to 112_N disposed side by side. A capacitance-detecting circuit 210 changes a voltage Vy of a detection electrode Ex which is one of the plurality of electrodes 112_1 to 112_N and generates a detection signal Vs indicating an electrostatic capacitance Cs of the detection electrode Ex based on the transfer of electrical charges generated on the detection electrode Ex. A driving circuit 240 drives an adjacent electrode Ey so that the voltage Vy which is generated on at least one adjacent electrode Ey which is adjacent to the detection electrode Ex among the plurality of electrodes 112_1 to 112_N follows a voltage Vx of the detection electrode Ex. In a first mode, the touch detection circuit 200 can detect both of a touch on the detection electrode Ex and a touch on the adjacent electrode Ey based on the detection signal Vs.SELECTED DRAWING: Figure 5

Description

The present invention relates to a capacitance detection circuit.

In recent years, electronic devices such as computers, smartphones, tablet terminals, and portable audio devices are equipped with a touch-type input device as a user interface. As a touch-type input device, a touch pad, a pointing device, and the like are known, and various inputs can be made by touching or approaching a finger or a stylus.

Touch-type input devices are broadly classified into resistive film type and capacitance type. The capacitance method detects the presence / absence of user input and coordinates by converting changes in capacitance (hereinafter, simply referred to as capacitance) formed by a plurality of sensor electrodes into electrical signals in response to user input. ..

Capacitance detection methods are broadly divided into self-capacitance (Self Capacitance) and mutual capacity (Mutual Capacitance) methods. The self-capacity method has very high sensitivity and can detect not only the touch but also the proximity of the finger, but there is a problem that the adhesion of water droplets cannot be distinguished from the touch and the two-point touch cannot be detected. On the other hand, the mutual capacitance method has an advantage that it can detect two-point touch (or more multi-touch) and is not easily affected by water droplets. Therefore, depending on the application, the self-capacity method and the mutual capacity method are selected, or both methods are used together.

FIG. 1 is a block diagram of a self-capacity touch type input device 100R. The touch input device 100R includes a touch panel (or touch switch) 110 and a touch detection circuit 200R. The touch panel 110 includes electrodes 112 and shield 114. The shield 114 is grounded and the electrode 112 is connected to the sense (SNS) terminal of the touch detection circuit 200R. When the user's finger or stylus comes close to or comes into contact with the electrode 112, the capacitance Cs formed by the electrode 112 increases. The touch detection circuit 200R detects the presence / absence of touch and the coordinates based on the change in capacitance Cs.

The touch detection circuit 200R includes a capacitance detection circuit 210 and an A / D converter 230. The capacitance detection circuit 210 changes the voltage of the SNS terminal to charge or discharge the capacitance Cs. At this time, charge transfer occurs according to the voltage change of the SNS terminal. Capacitance detection circuit 210 generates a detection signal V _S corresponding to the moved amount of charge. A / D converter 230 converts the detection signal _{V S} to the digital value. Digital values are input to a processor such as a microcomputer (not shown) and used to determine the presence / absence of touch and coordinates.

There is a parasitic capacitance Cp between the electrode 112 and the shield 114. The capacitance measured by the touch detection circuit 200R is the combined capacitance of the capacitance Cs and the parasitic capacitance Cp. Since the parasitic capacitance Cp narrows the dynamic range of the capacitance Cs that can be measured by the touch detection circuit 200R, it is required to reduce the influence of the parasitic capacitance Cp. Techniques for reducing the effect of parasitic capacitance Cp with the shield 114 have also been proposed.

FIG. 2 is a block diagram of a self-capacity touch type input device 100S. The touch detection circuit 200S further includes a terminal SLD connected to the shield 114, and links the potential of the SLD terminal with the potential of the SNS terminal. Specifically, the buffer 202 receives the potential of the SNS terminal at its input and generates the potential of the SNS terminal at its output. As a result, the potential difference between the electrode 112 and the shield 114 is kept constant, so that charge transfer from the parasitic capacitance Cp does not occur. Therefore, the influence of the parasitic capacitance Cp can be canceled, and only the capacitance Cs caused by the touch can be detected.

If the touch-type input device is always operated regardless of the presence or absence of operation, the power consumption increases. Intermittent drive (presensing) is introduced to reduce power consumption. FIG. 3 is a block diagram of a touch-type input device 100T provided with 5-channel electrodes. The panel 110 includes five electrodes 112_1 to 112_5 arranged in a cross. The touch input device 100T includes a capacitance detection circuit 210, a selector 220, and an A / D converter 230.

The selector 220 connects the capacitance detection circuit 210 to one of the plurality of electrodes 112_1 to 112_5. The capacitance detection circuit 210 detects the capacitance of the selected electrode 112_ # (# = 1 to 5).

FIG. 4 is a time chart illustrating the operation of the touch type input device 100T of FIG. Touch input device 100T is in the no-input state T ₁ is set to the intermittent mode, intermittently monitors the presence or absence of the operation of the user. Specifically, the detection period Ta and the stop period Tb are alternately generated, and during the detection period Ta, a plurality of electrodes 112_1 to 112_5 are selected in a time division manner, and the presence or absence of touch (including proximity) is determined. In the example of FIG. 4, it is assumed that the touch occurs in the third detection period Ta. When touch on any of the plurality of electrodes 112_1～112_5 is detected, it is determined that the operation start, subsequent period _{T 2,} the touch input device 100T is set to the continuous mode. In the continuous mode, the presence or absence of touch of the plurality of electrodes 112_1 to 112_5 is continuously detected in time division, and which electrode is touched (that is, touch coordinates) is detected.

Japanese Unexamined Patent Publication No. 2001-325858 Japanese Unexamined Patent Publication No. 2012-182781

As shown in FIG. 4, conventionally, in the detection period Ta, it was necessary to switch and drive a plurality of electrodes 112_1 to 112_5 in a time division manner in order to determine the presence or absence of an operation. If it is possible to detect the presence or absence of touching all the electrodes 112_1 to 112_5 with one drive, the power consumption can be further reduced.

The present invention has been made in such a situation, and one of the exemplary objects of the embodiment is to provide a touch detection circuit with reduced power consumption.

One aspect of the present invention relates to a self-capacitating touch detection circuit that is connected to a plurality of electrodes arranged side by side in use. The touch detection circuit is a capacitance detection circuit that changes the voltage of the detection electrode, which is one of a plurality of electrodes, and generates a detection signal indicating the capacitance of the detection electrode based on the movement of the charge generated in the detection electrode. A first drive circuit for driving the adjacent electrode so that the voltage generated in the adjacent electrode, which is at least one adjacent to the detection electrode, follows the voltage of the detection electrode. In the first mode, the touch detection circuit can detect both the touch on the detection electrode and the touch on the adjacent electrode based on the detection signal.

It should be noted that an arbitrary combination of the above components or a conversion of the expression of the present invention between methods, devices and the like is also effective as an aspect of the present invention.

According to the present invention, the power consumption of the touch detection circuit can be reduced.

It is a block diagram of the self-capacity type touch type input device. It is a block diagram of the self-capacity type touch type input device. It is a block diagram of the touch type input device including the electrode of 5 channels. It is a time chart explaining the operation of the touch type input device of FIG. It is a block diagram of the touch type input device provided with the touch detection circuit which concerns on embodiment. It is an equivalent circuit diagram of the touch type input device in the 1st mode. 7 (a) to 7 (c) are diagrams for explaining the capacitance formed in the no-input state and the input state. It is a time chart explaining the operation of the touch type input device of FIG. It is a circuit diagram of the touch detection circuit which concerns on Example 1. FIG. It is an operation waveform figure of the capacitance detection circuit of FIG. It is an operation waveform diagram of the touch detection circuit of FIG. 12 (a) and 12 (b) are waveform diagrams illustrating the operation of the first mode of the touch detection circuit of FIG. It is a circuit diagram of the touch detection circuit which concerns on Example 2. FIG. It is an operation waveform diagram of the capacitance detection circuit of FIG. It is an operation waveform diagram of the touch type input device of FIG. It is a block diagram of the touch type input device which concerns on modification 1. FIG. It is a block diagram of the touch type input device which concerns on modification 2. FIG. 18 (a) and 18 (b) are views showing the panel according to the modified example 3.

(Outline of Embodiment)
One embodiment disclosed herein relates to a self-capacitating touch detection circuit that, in use, is connected to a plurality of electrodes arranged side by side. The touch detection circuit is a capacitance detection circuit that changes the voltage of the detection electrode, which is one of the plurality of electrodes, and generates a detection signal indicating the capacitance of the detection electrode based on the movement of the charge generated in the detection electrode. A first drive circuit for driving the adjacent electrode so that the voltage generated in the adjacent electrode, which is at least one adjacent to the detection electrode, follows the voltage of the detection electrode. In the first mode, the touch detection circuit can detect both the touch on the detection electrode and the touch on the adjacent electrode based on the detection signal.

In the first mode, when the touch to the adjacent electrode occurs, the capacitance of the adjacent electrode increases, so that the change in the voltage of the adjacent electrode is delayed with respect to the change in the voltage of the detection electrode. Due to this effect, the parasitic capacitance between the detection electrode and the adjacent electrode becomes visible from the capacitance detection circuit, and the capacitance of the detection electrode appears to be slightly increased, and this slight capacitance change appears in the detection signal. Therefore, the touch to the adjacent electrode can be detected based on the detection signal. That is, since touches to a plurality of electrodes can be detected at the same time by one sensing, power consumption can be reduced.

In the second mode, it may be possible to detect only the touch on the detection electrode based on the detection signal. By ignoring the slight capacitance change caused by the touch on the adjacent electrode, that is, the change in the detection signal, only the touch on the detection electrode can be detected.

The drive capability of the first drive circuit may be switchable between the first mode and the second mode. By lowering the drive capability of the first drive circuit in the first mode, the influence of the touch on the adjacent electrodes can be made larger. In the second mode, the influence of the touch on the adjacent electrodes can be reduced by increasing the driving ability of the first driving circuit.

The touch detection circuit is a second drive circuit that drives the peripheral electrodes so that the voltage generated in the peripheral electrode, which is at least one of the plurality of electrodes adjacent to the adjacent electrode, follows the voltage of the adjacent electrode in the first mode. May be further provided. As a result, the influence of parasitic capacitance between the adjacent electrode and the peripheral electrode can be reduced, and the sensitivity of touch to the adjacent electrode can be increased.

In the second mode, a selector for switching between the detection electrode and the adjacent electrode in a time division manner may be further provided. As a result, the circuit area can be reduced by sharing one capacitance detection circuit for a plurality of electrodes.

The first drive circuit may include a buffer.

The touch detection circuit may be integrally integrated on one semiconductor integrated circuit. "Integrated integration" includes cases where all the components of a circuit are formed on a semiconductor substrate or cases where the main components of a circuit are integrated integrally, and some of them are used for adjusting circuit constants. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate. By integrating the circuit on one chip, the circuit area can be reduced and the characteristics of the circuit element can be kept uniform.

(Embodiment)
Hereinafter, the present invention will be described with reference to the drawings based on preferred embodiments. The same or equivalent components, members, and processes shown in the drawings shall be designated by the same reference numerals, and redundant description will be omitted as appropriate. Further, the embodiment is not limited to the invention but is an example, and all the features and combinations thereof described in the embodiment are not necessarily essential to the invention.

In the present specification, the "state in which the member A is connected to the member B" means that the member A and the member B are physically directly connected, or the member A and the member B are electrically connected to each other. It also includes the case of being indirectly connected via other members, which does not substantially affect the connection state or does not impair the functions and effects performed by the combination thereof.

Similarly, "a state in which the member C is provided between the member A and the member B" means that the member A and the member C, or the member B and the member C are directly connected, and their electricity. It also includes the case of being indirectly connected via other members, which does not substantially affect the connection state, or does not impair the functions and effects performed by the combination thereof.

FIG. 5 is a block diagram of a touch type input device 100 including the touch detection circuit 200 according to the embodiment. The touch type input device 100 is a user interface that detects a touch operation by the user's finger 2 (or stylus).

The touch input device 100 includes a panel 110, a host processor 120, and a touch detection circuit 200. The panel 110 is a touch panel or a switch panel, and includes a plurality of N (N ≧ 2) electrodes 112_1 to 112_N. In this embodiment, N = 5, and the electrodes 112_1 to 112_5 are arranged in a cross shape. The touch input device 100 is a 5-channel electrostatic switch.

The host processor 120 integrally controls the device, the device, and the system on which the touch input device 100 is mounted. The touch detection circuit 200 is configured to be able to transmit the state of the panel 110, more specifically, the presence / absence of input (proximity) to the panel 110, and the touch position (or the ID of the touched button) to the host processor 120.

The touch detection circuit 200 can switch between two modes. The first mode is also referred to as a presensing mode. In the first mode, the touch detection circuit 200 operates intermittently to detect the presence or absence of an operation on the panel 110. The touch detection circuit 200 transitions to the second mode when the start of operation on the panel 110 is detected in the first mode.

In the second mode, the touch detection circuit 200 detects the capacitances Cs1 to Cs5 formed by each of the plurality of electrodes 112_1 to 112_5. Each capacitance Cs includes, in addition to the capacitance Cf between the finger 2 and the parasitic capacitance Cp formed between the two other than the finger 2 (for example, adjacent electrodes).

When the finger 2 contacts (including proximity) the electrode 112_i of the i-th channel, the capacitance Cfi increases, and the capacitance Csi is relative to the capacitance Csj (j ≠ i) of the other channel. Becomes larger. The touch detection circuit 200 monitors the capacitance Cs of each channel, and when the absolute value of the capacitance Csi of the i-th channel exceeds a predetermined threshold value (or the amount of change relative to other channels). When the threshold value is exceeded), it is determined that the i-th channel has a touch input.

The above is the configuration of the entire touch input device 100. Subsequently, the configuration of the touch detection circuit 200 will be described.

The touch detection circuit 200 includes N sense pins Ps1 to PsN, a capacitance detection circuit 210, a selector 220, an A / D converter 230, a drive circuit 240, a signal processing unit 250, and an interface circuit 260, and is integrated into one semiconductor chip. And housed in one package.

In use, the corresponding electrodes 112_ # are connected to N (N ≧ 1) sense pins Ps # (# = 1 to N).

The selector 220 is a switch matrix inserted between the capacitance detection circuit 210 and the drive circuit 240 and the plurality of sense pins Ps1 to PsN, and one of the plurality of sense pins Ps1 to PsN is connected to the capacitance detection circuit 210. The other of the plurality of sense pins Ps1 to PsN is connected to the drive circuit 240.

For example, the selector 220 connects the capacitance detection circuit 210 and the sense pin Ps1 in the first mode, and connects the remaining pins Ps2 to Ps5 to the drive circuit 240. Therefore, the electrode 112_1 becomes the detection electrode Ex, and the electrodes 112_2 to 112_5 adjacent thereto serve as the adjacent electrodes Ey.

In addition, "adjacent to the detection electrode Ex" means that the parasitic capacitance Cp that cannot be ignored exists between the detection electrode Ex and the detection electrode Ex. In one embodiment, the electrode vertically or horizontally adjacent to the detection electrode Ex may be the adjacent electrode Ey. In another embodiment, the electrode adjacent to the detection electrode Ex in the vertical, horizontal, and diagonal directions may be the adjacent electrode Ey. In yet another embodiment, the electrode whose distance from the detection electrode Ex is equal to or less than a predetermined value may be used as the adjacent electrode Ey. In yet another embodiment, all electrodes other than the detection electrode Ex may be adjacent electrodes Ey.

Further, in the second mode, the selector 220 connects the capacitance detection circuit 210 to one of the sense pins Ps1 to Ps5 in a time division manner, and switches the detection electrode Ex in a time division manner. Further, the pin connected to the adjacent electrode Ey is connected to the drive circuit 240 so that the electrode adjacent to the detection electrode Ex becomes the adjacent electrode Ey.

The capacitance detection circuit 210 changes the voltage of the detection electrode Ex, which is one of the plurality of electrodes 112_1 to 112_N connected via the selector 220, and static electricity of the detection electrode Ex based on the movement of the electric charge generated in the detection electrode Ex. A detection signal Vs indicating a capacitance Cs is generated. The capacitance detection circuit 210 can be grasped as a C / V converter.

The drive circuit 240 operates in synchronization with the capacitance detection circuit 210. Of the plurality of electrodes 112_1 to 112_N, at least one adjacent electrode Ey adjacent to the detection electrode Ex is connected to the drive circuit 240. The drive circuit 240 drives the adjacent electrode Ey so that the voltage Vy generated in the adjacent electrode Ey follows the voltage Vx of the detection electrode Ex. As will be described later, the drive capability of the drive circuit 240 is designed so that the voltage Vy is delayed with respect to Vx in the situation where the adjacent electrode Ey is touched in the first mode. Further, the drive capability of the drive circuit 240 is designed so that the voltage Vy follows Vx without delay in the second mode.

The A / D converter 230 converts the detection signal Vs into digital detection data Ds. By processing the detection data Ds, the signal processing unit 250 determines in the first mode whether or not the electrodes 112_1 to 112_N are touched. Further, in the second mode, the signal processing unit 250 determines which of the electrodes 112_1 to 112_N is touched. The interface circuit 260 transmits the determination result by the signal processing unit 250 to the host processor 120.

The above is the configuration of the touch detection circuit 200. Next, the operation will be described. The operation of the first mode will be described.

FIG. 6 is an equivalent circuit diagram of the touch type input device 100 in the first mode. Vx represents the voltage of the detection electrode Ex, and Vy represents the voltage of the adjacent electrode Ey. 7 (a) to 7 (c) are diagrams for explaining the capacitance formed in the no-input state and the input state. A parasitic capacitance Cp is formed between the central detection electrode Ex and the surrounding adjacent electrodes Ey. Further, let Cb be the parasitic capacitance between the adjacent electrodes Ey and the ground.

(I) No input state Refer to FIG. 7 (a). In the no-input state in which the finger 2 is not close to any of the electrodes, the drive circuit 240 causes the voltage Vy to follow the voltage Vx. At this time, since the potential difference of the parasitic capacitance Cp is zero, the influence of the parasitic capacitance Cp is canceled and becomes invisible from the capacitance detection circuit 210. Also, the parasitic capacitance Cb is not visible from the capacitance detection circuit 210. Therefore, the detection signal Vs generated by the capacitance detection circuit 210 indicates that Cs≈0.

(Ii-1) Input state (touch the detection electrode Ex)
See FIG. 7 (b). It is assumed that the finger 2 touches the detection electrode Ex. At this time, the capacitance Cs is greatly increased by the capacitance Cfx between the detection electrode Ex and the finger 2. Since the voltage Vy follows the voltage Vx by the drive circuit 240, the influence of the parasitic capacitance Cp is canceled and becomes invisible from the capacitance detection circuit 210. Also, the parasitic capacitance Cb is not visible from the capacitance detection circuit 210. Therefore, the detection signal Vs generated by the capacitance detection circuit 210 indicates that Cs≈Cfx, and the increase amount Cfx of the capacitance Cs by the finger 2 is directly detected.

(Ii-2) Input state (touch adjacent electrode Ey)
See FIG. 7 (c). It is assumed that the finger 2 touches the adjacent electrode Ey. At this time, a capacitance Cfy is generated between the adjacent electrode Ey and the finger 2. Due to this capacitance Cfy, the load impedance of the drive circuit 240 becomes heavy, so that the voltage Vy cannot follow the voltage Vx. As a result, the parasitic capacitance Cp cannot be completely canceled and remains. At this time, the detection signal Vs generated by the capacitance detection circuit 210 includes the parasitic capacitance Cp that cannot be canceled, and Cs≈Cp. That is, the touch of the finger 2 to the adjacent electrode Ey can be indirectly detected as an increase in the capacitance Cs. For example, in the first mode, the touch determination criterion in the signal processing unit 250 may be looser than that in the second mode.

According to the touch type input device 100, not only the touch to the detection electrode Ex but also the touch to the adjacent electrode Ey can be detected in the first mode.

In the second mode, a plurality of electrodes 112_1 to 112_5 are selected as detection electrodes Ex in a time division manner and connected to the capacitance detection circuit 210. Further, an electrode adjacent to the detection electrode Ex is connected to the drive circuit 240 as an adjacent electrode Ey.

In the second mode, the touch detection circuit 200 can detect only the touch on the detection electrode Ex based on the detection signal Vs. At this time, a slight change in capacitance due to touching the adjacent electrode Eye, that is, a slight change in the detection signal Vs is ignored.

FIG. 8 is a time chart illustrating the operation of the touch type input device 100 of FIG. The touch-type input device 100 is set to the first mode in which the detection period Ta and the stop period Tb are alternately generated in the no-input state T ₁ , and intermittently monitors the presence or absence of user operation. The channel numbers shown in FIG. 8 indicate the detection electrode Ex. During the detection period Ta, one of the plurality of electrodes 112_1 to 112_5, 112_1, is selected as the detection terminal Ex, and the electrodes 112_1 to 112_5 around it serve as the adjacent electrodes Ey. Then, the presence or absence of touch on all the electrodes 112_1 to 112_5 is determined all at once by one sensing.

When the touch is detected in the third detection period Ta, it is determined that the operation start, subsequent period T _2, the touch input device 100T is set to the second mode. In the second mode, the plurality of electrodes 112_1 to 112_5 become detection electrodes Ex in order by time division, and the presence or absence of touch on the plurality of electrodes 112_1 to 112_5 is determined by time division.

The above is the operation of the touch type input device 100. According to the touch type input device 100, in the first mode, touches to a plurality of electrodes 112_1 to 112_5 can be detected at the same time by one sensing, so that power consumption can be reduced.

The present invention extends to various devices and methods grasped as a block diagram or a circuit diagram of FIG. 5 or derived from the above description, and is not limited to a specific configuration. Hereinafter, more specific configuration examples and examples will be described not to narrow the scope of the present invention but to help understanding the essence and operation of the invention and to clarify them.

(Example 1)
FIG. 9 is a circuit diagram of the touch detection circuit 200A according to the first embodiment. Here, the selector 220 is omitted, and the sense pin Ps connected to the capacitance detection circuit 210 is shown as Px, and the sense pin Ps connected to the drive circuit 240 is shown as Py.

The capacitance detection circuit 210A includes a plurality of switches SW21 to SW26, an operational amplifier 212, a reference capacitance Clef, and a feedback capacitance Cfb. One end of the reference capacitance Clef is grounded. The other end of the reference capacitance Clef is connected to the sense pin Ps via the charge transfer switch SW25, and is connected to the inverting input terminal (−) of the operational amplifier 212 via the amplification switch SW26.

The switches SW25 and SW26, the reference capacitance Cref, the feedback capacitance Cfb, and the operational amplifier 212 form an integrator 218 using a switched capacitor. A reference voltage Vref is input to the non-inverting input terminal (+) of the operational amplifier 212, and a feedback capacitance Cfb is provided between the output of the operational amplifier 212 and the inverting input terminal.

The pair of the upper switch SW21 and the lower switch SW22 forms the first drive unit 214, and changes the voltage of the sense pin Ps by two values of the power supply voltage Vdd and the ground voltage 0V.

The pair of the upper switch SW23 and the lower switch SW24 forms the second drive unit 216, and changes the voltage Vi of the reference capacitance Clef with two values of the power supply voltage Vdd and the ground voltage 0V.

The switches SW21 to SW26 are controlled by the controller 252. The controller 252 may be a part of the signal processing unit 250. It is preferable that Vref = Vdd / 2. An initialization switch (not shown) may be provided in parallel with the feedback capacitance Cfb.

In the (i) drive period, the capacitance detection circuit 210 applies one of the power supply voltage Vdd and the ground voltage 0V to the sense pin Ps in a state where the charge transfer switch SW25 is turned off and the sense pin Ps and the reference capacitance Clef are separated to refer to the reference pin Ps. The other of the power supply voltage Vdd and the ground voltage 0V is applied to the capacitance Clef.

In the subsequent sense period, only the charge transfer switch SW25 is turned on in the capacitance detection circuit 210, and the sense pin Ps and the reference capacitance Clef are connected. As a result, charge transfer occurs between the capacitance Cs and the reference capacitance Clef. Assuming that the power supply voltage Vdd is applied to the sense pin Ps and the ground voltage 0V is applied to the reference capacitance Clef in the immediately preceding drive period, the following equation holds from the law of charge conservation.
Cs × Vdd = Vi × (Cs + Clef)… (1)
Vi = Vdd × Cs / (Cs + Clef)… (2)
Vi represents the voltage of the reference capacitance Clef after the charge transfer is completed. If Cs = Clef, then Vi = Vdd / 2.

In the subsequent amplification period, the amplification switch SW26 is turned on. As a result, the feedback capacitance Cfb is charged so that the voltage of the inverting input terminal of the operational amplifier 212 becomes Vref, and the following detection voltage Vs is obtained.
Vs = Vref-Clef / Cfb × (Vi-Vref)… (3)

From the equations (2) and (3), it can be seen that the detected voltage Vs depends on the capacitance Cs.

The drive auxiliary circuit 244 of the drive circuit 240A includes a first switch SW11 and a second switch SW12. The first switch SW11 is provided between the second terminal Pc and the power supply line, and the second switch SW12 is provided between the second terminal Pc and the ground line. The first switch SW11 is turned on in conjunction with the upper switch SW21 of the first drive unit 214, and pulls up the voltage Vy of the second terminal Pc to the power supply voltage Vdd. Further, the second switch SW12 is turned on in conjunction with the lower switch SW22 of the first drive unit 214, and the voltage Vy of the second terminal Pc is pulled down to the ground voltage 0V.

FIG. 10 is an operation waveform diagram of the capacitance detection circuit 210A of FIG. In the drive period T1, the upper switch SW21 and the lower switch SW24 are turned on, the power supply voltage Vdd is applied to the sense pins Ps, and the ground voltage 0V is applied to the reference capacitance Clef. In the subsequent transfer period T2, the charge transfer switch SW25 is turned on, and the charges of the capacitance Cs and the reference capacitance Clef are averaged. The voltage Vi of the reference capacitance Cref is expressed by the following equation.
Vi = Vdd × Cs / (Cs + Clef)

In the subsequent amplification period T3, the charge transfer switch SW25 is turned off and the voltage Vi is held. When the amplification switch SW26 is turned on, the detection voltage Vs is generated.

In the subsequent drive period T4, the lower switch SW22 and the upper switch SW23 are turned on, the ground voltage 0V is applied to the sense pins Ps, and the power supply voltage Vdd is applied to the reference capacitance Clef. In the subsequent transfer period T5, the charge transfer switch SW25 is turned on, and the charges of the capacitance Cs and the reference capacitance Clef are averaged.
Vi = Vdd × Cref / (Cs + Cref)

In the subsequent amplification period T6, the charge transfer switch SW25 is turned off and the voltage Vi is held. When the amplification switch SW26 is turned on, the detection voltage Vs is generated.

FIG. 11 is an operation waveform diagram of the touch detection circuit 200A of FIG. In the drive period T1, the voltage Vx of the sense pin Ps rises to the power supply voltage Vdd. Along with this, when the first switch SW11 is turned on, the voltage Vy of the second terminal Pc rises to the power supply voltage Vdd following the voltage Vx.

During the transfer period T2 and the amplification period T3, the third switch SW13 is turned on, and the second terminal Pc is connected to the output of the buffer 242. As a result, the voltage Vy of the second terminal Pc is made equal to the voltage Vx of the sense pins Ps by the buffer 242.

In the drive period T4, the voltage Vx of the sense pins Ps drops to the ground voltage 0V. At the same time, when the second switch SW12 is turned on, the voltage Vy of the second terminal Pc is reduced to the ground voltage 0V following the voltage Vx.

During the transfer period T5 and the amplification period T6, the third switch SW13 is turned on, and the second terminal Pc is connected to the output of the buffer 242. As a result, the voltage Vy of the second terminal Pc is made equal to the voltage Vx of the sense pins Ps by the buffer 242.

The above is the operation of the touch detection circuit 200A. According to this touch detection circuit 200A, the voltage Vy of the second terminal Pc can be made to follow the voltage Vx of the sense pin Ps at high speed, and the influence of the parasitic capacitance Cp between the electrode Ex and the second electrode Ec can be canceled. ..

At the start timing of the drive period T1, the voltage Vy can be sharply increased by the drive auxiliary circuit 244 instead of the buffer 242. Further, at the start timing of the drive period T4, the voltage Vy can be sharply reduced by the drive auxiliary circuit 244 instead of the buffer 242. As a result, the drive capacity required for the buffer 242 can be reduced as compared with the case where the drive auxiliary circuit 244 is not provided, and the size of the buffer 242 can be reduced.

12 (a) and 12 (b) are waveform diagrams illustrating the operation of the first mode of the touch detection circuit 200A of FIG. FIG. 12A is a waveform diagram in a no-input state. It is assumed that the capacitance Cs when there is no touch is equal to the reference capacitance Clef. In the transfer period T2, the voltages Vx and Vi converge to Vdd / 2, and in the amplification period T3, the voltage Vi is sample-held and amplified. By the drive circuit 240, the voltage Vy of the adjacent electrode Ey follows the voltage Vx of the detection electrode Ex.

FIG. 12B is a waveform diagram when there is a touch on the adjacent electrode Eye. In FIG. 12B, the waveform in the no-input state is shown by a broken line. The touch on the adjacent electrode Ey increases the load on the drive circuit 240 and slows down the change in the voltage Vy of the adjacent electrode Ey. As a result, the parasitic capacitance Cp between the detection electrode Ex and the adjacent electrode Ey cannot be canceled and remains. Due to this residual parasitic capacitance Cp, the voltage Vx (and the internal voltage Vi) becomes higher than the voltage Vx (internal voltage Vi) in FIG. 12 (a). Therefore, the touch to the adjacent electrode Eye can be detected.

(Example 2)
FIG. 13 is a circuit diagram of the touch detection circuit 200E according to the second embodiment. The circuit type of the capacitance detection circuit 210E is different from that of the capacitance detection circuit 210A of FIG. The capacitance detection circuit 210E includes a reset switch SW41, a current mirror circuit 274, and an integrator 276.

The reset switch SW41 is provided between the sense pin Ps and the ground line. In the current mirror circuit 274, the transistor M41 on the input side is connected to the sense pins Ps. The current mirror circuit 274 may include a sense switch SW42. The integrator 276 outputs a detection voltage Vs obtained by integrating the current Is flowing through the transistor M42 on the output side of the current mirror circuit 274.

FIG. 14 is an operation waveform diagram of the capacitance detection circuit 210E of FIG. In the reset section T11, the reset switch SW41 is turned on, 0V is applied to the sense pins Ps, and the capacitance Cs is discharged. Subsequently, when the sense switch SW42 is turned on in the sense interval T12, starts to flow the charging current _{I CHG} to the input side of the transistors of the current mirror circuit 274, the capacitance Cs is charged by the charging current _{I CHG.} When the voltage Vx rises to the vicinity of the power supply voltage Vdd, the transistor M41 on the input side of the current mirror circuit 274 cuts off and charging stops. The change width ΔV of the voltage Vx is almost equal to the power supply voltage Vdd, and the total charge Q flowing into the capacitance Cs at this time is
Q = Cs × ΔV = Cs × Vdd
Will be.

The charging current _ICHG is copied by the current mirror circuit 274, and the copied current Is is integrated by the integrator 276. The output voltage Vs undergoes a voltage change proportional to the amount of charge Q, in other words, proportional to the capacitance Cs.

Return to FIG. The drive circuit 240E changes the voltage Vy of the second terminal Pc following the voltage Vx shown in FIG. When the reset switch SW41 is turned on, the voltage Vx changes sharply. It is preferable that this steep change is generated by the drive auxiliary circuit 244E, and the gradual change of the voltage Vx after the sense switch SW42 is turned on is generated by the buffer 242. In this case, the drive auxiliary circuit 244E can include a second switch SW12 provided between the second terminal Pc and the ground.

FIG. 15 is an operation waveform diagram of the touch type input device 100E of FIG. In the reset section T11, the reset switch SW41 is turned on, and the voltage Vy of the second terminal Pc is pulled down to 0V. When shifting to the sense section T12, the third switch SW13 is turned on, and the buffer 242 drives the voltage Vy of the second terminal Pc to be equal to the voltage Vx.

The above is the operation of the touch detection circuit 200E. The same effect as in the first embodiment can be obtained by the touch detection circuit 200E.

The present invention has been described above based on the embodiments. This embodiment is an example, and it will be understood by those skilled in the art that various modifications are possible for each of these components and combinations of each processing process, and that such modifications are also within the scope of the present invention. is there. Hereinafter, such a modification will be described.

(Modification example 1)
As shown in FIGS. 7 (a) to 7 (c), the adjacent electrode Ey forms a parasitic capacitance Cb with the surrounding electrode Ey. In order to increase the touch detection sensitivity in the first mode, it is necessary to reduce the influence of the parasitic capacitance Cb.

FIG. 16 is a block diagram of the touch type input device 100F according to the first modification. Panel 110F further comprises electrodes 112_6. The electrode 112_6 is provided at a position adjacent to the electrodes 112_2 to 112_5, which are adjacent electrodes Eye in the first mode. This electrode 112_6 is referred to as a peripheral electrode Ez. The touch detection circuit 200F further includes a drive circuit 270 in addition to the touch type input device 100 of FIG.

In the first mode, the drive circuit 270 receives the output (voltage of the adjacent electrode Ey) Vy of the drive circuit 240 and drives the peripheral electrode Ez so that the voltage Vz of the peripheral electrode Ez follows the voltage Vy. The drive capability of the drive circuit 270 is designed to be sufficiently high so that the voltage Vz does not lag behind the voltage Vy. The drive circuit 270 may be configured in the same manner as the drive circuit 240.

According to this modification 1, the influence of the parasitic capacitance can be reduced by surrounding the adjacent electrode Ey with the peripheral electrode Ez and canceling the capacitance between the adjacent electrode Ey and the peripheral electrode Ez, and the touch detection sensitivity can be improved. Can be enhanced.

(Modification 2)
FIG. 17 is a block diagram of the touch type input device 100G according to the second modification. In this modification, the panel 110G has a plurality of electrodes 112_1 to 112_N (N = 9 in this example) arranged in a matrix.

In the first mode, one of the plurality of electrodes 112_1 to 112_N (for example, one in the center 112_1) is designated as the detection electrode Ex, and the plurality of electrodes 112_1 to 112_5 vertically and horizontally adjacent thereto are designated as adjacent electrodes Ey, and the other electrodes 112_6. ~ 112_9 is a peripheral electrode Ez. In the first mode, the selector 220G connects the detection electrode Ex to the capacitance detection circuit 210, the adjacent electrode Ey to the drive circuit 240, and the peripheral electrode Ez to the drive circuit 270.

Further, in the second mode, a plurality of electrodes 112_1 to 112_N are designated as detection electrodes Ex in a time-division manner, and some adjacent electrodes are designated as peripheral electrodes Ey.

(Modification 3)
In the second modification, the panel 110 may include more electrodes 112. 18 (a) and 18 (b) are views showing the panel 110H according to the third modification. When the number of electrodes 112 is large, it is difficult to detect the touch of all the electrodes with only one detection electrode in the first mode. Therefore, in the third modification, in the first mode, the panel 110H is divided into areas, the detection electrode Ex is determined for each area, and the touch to the detection electrode Ex and the adjacent electrode Ey around it is individually monitored while switching the area. To do. The electrode adjacent to the adjacent electrode Ey may be driven as the peripheral electrode Ez. FIG. 18A shows a state in which the right half area is targeted for detection, and FIG. 18B shows a state in which the left half area is targeted for detection.

(Modification example 4)
In the first mode, in order to detect the touch on the adjacent electrode Ey, the voltage Vy of the adjacent electrode Ey must change later than the voltage Vx of the detection electrode Ex. Here, if the drive capability of the drive circuit 240 in the first mode is too high, the voltage Vy follows the voltage Vx, and a situation may occur in which the touch to the adjacent electrode Ey cannot be detected. Therefore, the drive capability of the drive circuit 240 may be made variable and switched between the first mode and the second mode. That is, in the first mode, the drive capability of the drive circuit 240 is lowered as compared with the second mode, so that the touch detection to the adjacent electrode Eye can be made more reliable.

The configuration for making the drive capability of the drive circuit 240 variable is not particularly limited. For example, in the first mode, an impedance element such as a resistor may be inserted into the output of the drive circuit 240. Alternatively, the size of the transistor in the output stage of the buffer 242 of the drive circuit 240 may be variable, or the bias current of the output stage of the buffer 242 of the drive circuit 240 may be changed.

(Modification 5)
In the embodiment, in the second mode, one capacitance detection circuit 210 is assigned to a plurality of electrodes in a time division manner, but this is not the case. One capacitance detection circuit 210 may be provided for each electrode.

2 fingers 100 touch type input device 110 panel 112 electrode 120 host processor 200 touch detection circuit 210 capacity detection circuit 220 selector 230 A / D converter 240 drive circuit 242 buffer 250 signal processing unit 260 interface circuit 270 drive circuit Ex detection electrode Ey adjacent electrode Ez peripheral electrode

Claims (9)

In use, it is a self-capacitating touch detection circuit that is connected to multiple electrodes arranged side by side.
A capacitance detection circuit that changes the voltage of a detection electrode, which is one of the plurality of electrodes, and generates a detection signal indicating the capacitance of the detection electrode based on the movement of charge generated in the detection electrode.
A first drive circuit that drives the adjacent electrode so that the voltage generated in the adjacent electrode, which is at least one adjacent to the detection electrode among the plurality of electrodes, follows the voltage of the detection electrode.
With
A touch detection circuit, characterized in that, in the first mode, both a touch on the detection electrode and a touch on an adjacent electrode can be detected based on the detection signal. The touch detection circuit according to claim 1, wherein in the second mode, only a touch to the detection electrode can be detected based on the detection signal. The touch detection circuit according to claim 2, wherein the drive capability of the first drive circuit can be switched between the first mode and the second mode. In the first mode, the second drive circuit that drives the peripheral electrode so that the voltage generated in the peripheral electrode that is at least one adjacent to the adjacent electrode among the plurality of electrodes follows the voltage of the adjacent electrode. The touch detection circuit according to any one of claims 1 to 3, further comprising. The touch detection circuit according to claim 2 or 3, further comprising a selector for switching between the detection electrode and the adjacent electrode in a time division manner in the second mode. The touch detection circuit according to any one of claims 1 to 5, wherein the first drive circuit includes a buffer. The touch detection circuit according to any one of claims 1 to 6, wherein the touch detection circuit is integrally integrated on one semiconductor integrated circuit. A panel that includes multiple sensor electrodes and changes the capacitance of the sensor electrodes near the coordinates that the user touches.
The touch detection circuit according to any one of claims 1 to 7, which is connected to the plurality of sensor electrodes.
An input device comprising. An electronic device comprising the input device according to claim 8.

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