JP2014206844A - Detection circuit, semiconductor integrated circuit device, and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an instruction to return to a normal operation mode when a person approaches a touch panel by sensing the approach of the person even in a standby state in which almost all functions of an electronic apparatus are at rest.SOLUTION: A detection circuit includes: a driving circuit that applies a predetermined potential to a first electrode of a sensor; a differential amplifier that has an inverted input terminal which is connected to a second electrode of the sensor, and outputs a detection signal; a first switch that is connected between an output terminal and inverted input terminal of the differential amplifier; a second switch that switches a capacitance value of the capacitor between the output terminal and inverted input terminal of the differential amplifier; and a control unit that controls the first switch so as to periodically cause short-circuiting between the output terminal and inverted input terminal of the differential amplifier, also controls the second switch in a standby state so as to make the capacitance value of the capacitor smaller than that in a normal operation mode, and controls transition to a normal operation mode on the basis of the detection signal.

Description

  The present invention relates to a detection circuit that detects a change in capacitance value in a capacitive sensor formed on a capacitive touch panel. Furthermore, the present invention relates to a semiconductor integrated circuit device including such a detection circuit, an electronic device, and the like.

  In many electronic devices, various touch panels having two functions of image display and information input are used. Among them, capacitive touch panels are often used alongside resistive touch panels. In a capacitive touch panel, a position touched by a fingertip is detected based on a change in capacitance between transparent electrodes in a sensor portion touched by a human fingertip. In addition, it is possible to detect the position where the fingertip has approached before the fingertip touches the sensor portion by utilizing the property that electrostatic coupling occurs only when the fingertip approaches the sensor portion.

  As a related technique, Patent Document 1 removes the influence of the offset voltage of the amplifier constituting the circuit and the charge of the switching transistor, and can detect the capacitance ratio extremely stably without being affected by the ambient temperature. A detection circuit for a capacitive sensor is disclosed. The detection circuit includes a switched capacitor circuit that converts a capacitance ratio of a capacitive sensor to a reference capacitance into an electric signal, a plurality of sample and hold circuits that sample the output of the switched capacitor circuit at different sampling timings, and a sample thereof And a differential amplifier that amplifies the output difference of the hold circuit and outputs it as a detection signal.

  Patent Document 2 discloses a capacitance detection circuit that can be applied to various types of capacitive sensors. The capacitance detection circuit includes an operational amplifier in which a feedback capacitance component is connected between an inverting input terminal and an output terminal, a capacitive sensor whose capacitance is changed by an external force, and a capacitance at a first clock timing for discharging the feedback capacitance component. Charge / discharge control means for charging the charge by connecting the charge / discharge terminal of the capacitive component to the reference voltage source and transferring the charge by switching the charge / discharge terminal to the feedback capacitive component at the second clock timing Voltage conversion means for converting the transferred charge into a voltage and outputting the sensor output as a voltage conversion value.

JP-A-8-327777 (paragraphs 0013-0014, FIG. 1) Japanese Patent Laid-Open No. 11-326409 (paragraphs 0011-0012, FIG. 1)

  However, Patent Document 1 and Patent Document 2 do not disclose switching the detection sensitivity in the detection circuit in accordance with the detection purpose. Therefore, one of the objects of the present invention is to use the characteristics of the capacitive touch panel to detect the approach of a person in a standby mode in which almost all functions of an electronic device are stopped. It is to give an instruction to return to the normal operation mode when a person approaches.

  In order to solve the above problems, a detection circuit according to a first aspect of the present invention is a detection circuit connected to a capacitive sensor formed on a touch panel, and is a first circuit of the capacitive sensor. A drive circuit for applying a predetermined potential to the electrode and an inverting input terminal connected to the second electrode of the capacitive sensor, and applied to the reference potential applied to the non-inverting input terminal and the inverting input terminal A differential amplifier that amplifies a difference from the output potential and outputs a detection signal from the output terminal; a first switch circuit connected between the output terminal and the inverting input terminal of the differential amplifier; A second switch circuit that switches a capacitance value of a capacitor connected between the output terminal and the inverting input terminal, and a first switch that periodically short-circuits between the output terminal and the inverting input terminal of the differential amplifier. While controlling the switch circuit, In machine mode, and a control unit which controls the second switch circuit so as to be smaller than in the normal operation mode the capacitance value of the capacitor, to control the shift to the normal operation mode based on the detection signal.

  According to the first aspect of the present invention, by utilizing the characteristics of a capacitive touch panel, even in a standby mode in which almost all functions of an electronic device are stopped, a touch of a person is detected by detecting the approach of a person. When a person approaches, an instruction to return to the normal operation mode can be given.

  Here, in the standby mode, the drive circuit may make the predetermined potential to be applied to the first electrode of the capacitive sensor smaller than in the normal operation mode. Further, the control unit may control the differential amplifier so as to perform an intermittent operation. In that case, power consumption in the standby mode can be reduced.

  The detection circuit according to the second aspect of the present invention further includes a comparator that determines whether the potential of the detection signal is higher or lower than the reference potential in the standby mode. According to the second aspect of the present invention, in the standby mode, the power supply to the A / D converter that A / D converts the detection signal can be stopped to reduce the power consumption.

  A detection circuit according to a third aspect of the present invention includes a first capacitor connected in series with a second switch circuit between an output terminal and an inverting input terminal of a differential amplifier, and an output of the differential amplifier. And a second capacitor connected between the terminal and the inverting input terminal and having a capacitance value smaller than the capacitance value of the first capacitor. According to the third aspect of the present invention, in the standby mode, the capacitance value of the capacitor can be made smaller than that in the normal operation mode to improve detection sensitivity.

  In the detection circuit according to the fourth aspect of the present invention, in the touch panel, a plurality of capacitive sensors are formed in a two-dimensional matrix, and one row of electrostatic sensors is formed from among the plurality of rows of capacitive sensors. The circuit further includes a selection circuit that selects the capacitive sensor and connects the inverting input terminal of the differential amplifier to the second electrode of the selected one row of the capacitive sensor. According to the fourth aspect of the present invention, signals from a plurality of rows of capacitive sensors can be sequentially amplified using one differential amplifier.

  Here, in the normal operation mode, the drive circuit starts applying a predetermined potential to the first electrodes of the plurality of columns of capacitive sensors every first interval time, and in the standby mode, the plurality of columns Application of a predetermined potential to the first electrode of the capacitive sensor may be started every second interval time longer than the first interval time.

  Further, in the standby mode, the selection circuit may connect the inverting input terminal of the differential amplifier to a part of the second electrode of the capacitive sensor formed in the touch panel region. Alternatively, the drive circuit may apply a predetermined potential to a part of the first electrodes of the capacitive sensor formed in the touch panel region. In that case, power consumption in the standby mode can be reduced.

  A semiconductor integrated circuit device according to one aspect of the present invention includes any one of the detection circuits described above. Thereby, a semiconductor integrated circuit device with a relatively small circuit scale and current consumption can be realized. An electronic apparatus according to one aspect of the present invention includes a touch panel on which a capacitive sensor is formed and any one of the detection circuits described above. Thereby, in an electronic device such as a vending machine such as a tablet PC (personal computer), a smartphone, or a ticket, an instruction to return to the normal operation mode can be given when a person approaches the touch panel.

FIG. 5 is a circuit diagram showing a part of an electronic apparatus including a detection circuit according to an embodiment of the invention. The figure for demonstrating operation | movement of the detection circuit which concerns on one Embodiment of this invention. The circuit diagram which shows the 1st modification of the detection circuit which concerns on one Embodiment of this invention. The circuit diagram which shows the 2nd modification of the detection circuit which concerns on one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same referential mark is attached | subjected to the same component and the overlapping description is abbreviate | omitted.
FIG. 1 is a circuit diagram illustrating a part of the configuration of an electronic apparatus including a detection circuit according to an embodiment of the present invention. This electronic device is an electronic device such as a tablet PC (personal computer), a smart phone, or a vending machine such as a ticket. In FIG. 1, only the detection circuit and its peripheral portion are shown.

  As shown in FIG. 1, this electronic device includes a capacitive touch panel 10 and a detection circuit 20 that detects a change in capacitance value in a capacitive sensor formed on the touch panel 10. It operates in the operation mode and the standby mode. In the normal operation mode, when a human fingertip touches the sensor portion of the touch panel 10, the detection circuit 20 detects the position of the sensor portion and causes the electronic device to perform an operation corresponding to the detected position. . When the electronic device is not operated for a certain period, the electronic device shifts to the standby mode. In the standby mode, almost all functions of the electronic device are stopped, and when the touch panel 10 senses the approach of a person, when the person approaches the touch panel 10, the detection circuit 20 issues an instruction to return to the normal operation mode. give.

  There are two types of capacitive touch panels, a surface type and a projection type. Hereinafter, a projection type touch panel will be described. In general, a projection-type touch panel has a plurality of mosaic electrode patterns of two layers, vertical and horizontal, formed by transparent electrodes such as ITO (indium tin oxide) on a glass or plastic substrate, and an insulator film is disposed thereon. Has a structured. When the fingertip touches the touch panel, the capacitance between the neighboring electrodes changes, so the position where the fingertip touches is accurately determined by detecting the capacitance between the electrodes via the two vertical and horizontal electrodes. be able to.

In FIG. 1, a plurality of columns of first electrodes extending in the vertical direction are represented by X ₀ , X ₁ ,..., X _M , and a plurality of rows of second electrodes extending in the horizontal direction. _{electrodes, Y 0, Y 1, ···} , are represented by _{Y N.} In addition, the capacitance formed between the first electrode and the second electrode is represented by C _0,0 , C _1,0 ,..., C _{M, N.} A plurality of capacitance-type sensors formed in a two-dimensional matrix on the touch panel 10 are configured by the capacitance, the plurality of rows of first electrodes, and the plurality of rows of second electrodes.

The detection circuit 20 is connected to a capacitive sensor formed on the touch panel 10 and operates by being supplied with power supply potentials V _DD and V _SS . For example, the power supply potential V _DD is 5V, and the power supply potential _VSS is 0V. The detection circuit 20 includes a drive circuit 21, a selection circuit 22, a differential amplifier 23, a first switch circuit 24, a second switch circuit 25, capacitors C1 and C2, and a sample hold circuit (S / H). ) 26, an A / D converter (ADC) 27, a comparator 28, and a control unit 29. At least some of the components of the detection circuit 20 may be built in the semiconductor integrated circuit device. Thereby, a semiconductor integrated circuit device with a relatively small circuit scale and current consumption can be realized.

The drive circuit 21 includes a plurality of voltage buffers and the like, and under the control of the control unit 29, a plurality of first electrodes X ₀ to X of a plurality of capacitive sensors formed in a two-dimensional matrix form. A predetermined potential V _S is applied to X _M.

The selection circuit 22 selects semiconductor switches SW _{0 to} SW _N such as transmission gates corresponding to the second electrodes Y _{0 to} Y _N in a plurality of rows of the plurality of capacitance sensors formed in a two-dimensional matrix. Contains. The selection circuit 22 sequentially turns on the semiconductor switches SW _{0 to} SW _N under the control of the control unit 29, so that one row of the capacitance type sensors is selected from among the plurality of rows of capacitance type sensors. Then, the inverting input terminal of the differential amplifier 23 is connected to the second electrode of the selected capacitive sensor in one row. As a result, signals from a plurality of rows of capacitive sensors can be sequentially amplified using one differential amplifier 23.

The differential amplifier 23 is configured by an operational amplifier or the like, and is applied with an inverting input terminal connected to the second electrode of the capacitive sensor via the selection circuit 22 and a reference potential V _AG (analog ground potential). A non-inverting input terminal and an output terminal for outputting a differentially amplified signal are provided. For example, the reference potential V _AG is set to (V _DD −V _SS ) / 2. The differential amplifier 23 amplifies the difference between the reference potential _VAG applied to the non-inverting input terminal and the potential applied to the inverting input terminal, and outputs a detection signal from the output terminal.

  The first switch circuit 24 is composed of a semiconductor switch such as a transmission gate, and is connected between the output terminal and the inverting input terminal of the differential amplifier 23. The second switch circuit 25 switches the capacitance value of the capacitor connected between the output terminal and the inverting input terminal of the differential amplifier 23.

  In FIG. 1, the second switch circuit 25 includes semiconductor switches 25a and 25b such as transmission gates. The semiconductor switch 25a is connected in series with the capacitor C1 between the output terminal and the inverting input terminal of the differential amplifier 23. The semiconductor switch 25b is connected in series with the capacitor C2 between the output terminal and the inverting input terminal of the differential amplifier 23.

  The control unit 29 controls each unit of the detection circuit 20. For example, the control unit 29 periodically activates the control signal S0 to a high level at a predetermined cycle in the normal operation mode and the standby mode, thereby periodically between the output terminal and the inverting input terminal of the differential amplifier 23. The first switch circuit 24 is controlled so as to short-circuit.

When the output terminal and the inverting input terminal of the differential amplifier 23 are short-circuited, the charge accumulated in the capacitor C1 or C2 is discharged, and the potential of the inverting input terminal of the differential amplifier 23 is equal to the reference potential _VAG . Become. Next, when the short circuit between the output terminal and the inverting input terminal of the differential amplifier 23 is released, the differential amplifier 23 outputs a detection signal corresponding to the capacitance value of the capacitive sensor.

Here, when the capacitance value of the capacitive sensor changes by ΔC _S when a human fingertip touches the capacitive sensor to which the predetermined potential V _S is applied to the first electrode, the electrostatic capacitance is changed. The change amount ΔQ _S of charge in the type sensor is expressed by the following equation.
ΔQ _S = ΔC _S (V _S −V _AG ) (1)

Further, assuming that the capacitance value of the capacitor connected between the output terminal and the inverting input terminal of the differential amplifier 23 is C _C and the potential change of the detection signal is ΔV _OUT , the amount of change in charge ΔQ _C in the capacitor is Is expressed by the following equation.
ΔQ _C = C _C (V _AG −ΔV _OUT ) (2)

Here, if the input impedance and the open loop gain of the differential amplifier 23 are sufficiently large, the following equation is established.
ΔQ _S = ΔQ _C (3)

If V _AG = 0 for the sake of simplicity, the following equations are obtained from equations (1) to (3).
ΔC _S V _S = C _C (−ΔV _OUT )
∴ΔV _OUT = − (ΔC _S / C _C ) V _S (4)

  The detection signal output from the differential amplifier 23 is sampled and held by the sample and hold circuit 26 in synchronization with the timing set by the control unit 29, and is converted into a digital detection signal by the A / D converter 27. The detection signal output from the A / D converter 27 is supplied to the control unit 29. In the normal operation mode, the control unit 29 detects a position touched by a human fingertip based on the detection signal.

  In the standby mode, the control unit 29 also sets the second switch circuit 25 so that the capacitance value of the capacitor connected between the output terminal and the inverting input terminal of the differential amplifier 23 is smaller than that in the normal operation mode. And the transition to the normal operation mode is controlled based on the detection signal.

  In the normal operation mode, the control unit 29 activates the control signal S1 to high level to turn on the semiconductor switch 25a, and deactivates the control signal S2 to low level to turn off the semiconductor switch 25b. Thus, the capacitor C1 is connected between the output terminal and the inverting input terminal of the differential amplifier 23. The capacitance value of the capacitor C1 is set so that sufficient detection sensitivity is obtained when a human fingertip touches the capacitance type sensor.

  In the standby mode, the control unit 29 deactivates the control signal S1 to low level to turn off the semiconductor switch 25a, and activates the control signal S2 to high level to turn on the semiconductor switch 25b. As a result, the capacitor C2 is connected between the output terminal and the inverting input terminal of the differential amplifier 23.

  The capacitance value of the capacitor C2 is set so that sufficient detection sensitivity can be obtained when a person approaches the touch panel 10 by utilizing the property that electrostatic coupling occurs only when the person approaches the capacitive sensor. The Therefore, the capacitance value of the capacitor C2 is set sufficiently smaller than the capacitance value of the capacitor C1.

The capacitance value of the capacitor C2 is sufficiently smaller than the capacitance value of the capacitor C1, in the standby mode, the potential change [Delta] V _OUT of the detection signal relative to the change [Delta] C _S of the capacitance value of the capacitive sensor in equation (4) becomes large, The sensitivity of the detection circuit 20 increases. Therefore, the detection circuit 20 can sense that a person has approached the touch panel 10, and the control unit 29 can detect that a person has approached the touch panel 10 based on the detection signal. Gives an instruction to return to normal operation mode.

In the standby mode, the power supply to the A / D converter 27 may be stopped, and the potential change of the detection signal may be determined by the comparator 28. The power consumption of the comparator can be made smaller than the power consumption of the A / D converter. Thereby, power consumption in the standby mode can be reduced. The detection signal held in the sample hold circuit 26 is supplied to one input terminal of the comparator 28, and the detection signal in a state where no person is approaching the touch panel 10 is supplied to the other input terminal of the comparator 28. A reference potential V _REF lower than the potential is applied.

The comparator 28 determines whether the potential of the detection signal is higher or lower than the reference potential _VREF . When the potential of the detection signal falls below the reference potential V _REF due to the person approaching the touch panel 10, the output signal of the comparator 28 changes to high level, so the control unit 29 sets the electronic device to the normal operation mode. can do.

  Next, the operation of the detection circuit according to the embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a diagram for explaining the operation of the detection circuit according to the embodiment of the present invention.

The controller 29 shown in FIG. 1 scans the touch panel 10 in the vertical direction by sequentially turning on the semiconductor switches SW _{0 to} SW _N of the selection circuit 22. In Figure 2, the n-th semiconductor switch _{SW n-1 (1 ≦ n} ≦ (N + 1)) of the semiconductor switch _SW 0 to SW _N is shown the period that is on.

Control unit 29, together with the turns on the switch circuit 24 activates the control signal S0 to a high level at a predetermined period, to the first electrode X ₀ to X _M of the capacitive sensor of the plurality of rows, columns The drive circuit 21 is controlled so that application of the predetermined potential V _S is started at different timings. The timing at which the detection signal output from the differential amplifier 23 is sampled by the sample hold circuit 26 may be immediately before the rising timing of the control signal S0.

For example, as shown in FIG. 2, first, the control unit 29 once sets the control signal S0 to high level to turn on the switch circuit 24, whereby the charge accumulated in the capacitor C1 or C2 is discharged. Thereafter, at time t ₀ , the drive circuit 21 starts applying a predetermined potential V _S to the first electrode X ₀ . Furthermore, after the sample and hold circuit 26 samples the detection signal after a certain time, the control unit 29 turns on the switch circuit 24 by once setting the control signal S0 to the high level, whereby the charge accumulated in the capacitor C1 or C2 is stored. Is discharged.

Then, at time _{t 1} the interval time Δt has elapsed from time _{t 0,} the drive circuit 21 starts the application of the predetermined potential _{V S} to the first electrode _{X 1.} Furthermore, after the sample and hold circuit 26 samples the detection signal after a certain time, the control unit 29 turns on the switch circuit 24 by once setting the control signal S0 to the high level, whereby the charge accumulated in the capacitor C1 or C2 is stored. Is discharged.

Then, at time _{t 2} when _the interval time Δt has elapsed from time _{t 1,} the driving circuit 21 starts the application of the predetermined potential _{V S} to the first electrode _{X 2.} Furthermore, after the sample and hold circuit 26 samples the detection signal after a certain time, the control unit 29 turns on the switch circuit 24 by once setting the control signal S0 to the high level, whereby the charge accumulated in the capacitor C1 or C2 is stored. Is discharged.

As a result of repeating the (N + 1) × (M + 1) times of sampling in this way, for example, from the time t _{m −1} to the time t _m in a period in which the _nth semiconductor switch SW _n−1 is on. When the potential change of the detection signal sampled during the period exceeds a predetermined value or is the largest, the control unit 29 determines that a human fingertip touches the capacitive sensor in the nth row and mth column. You may do it.

The above is the determination method in the normal operation mode. However, in the standby mode, when the potential change of the detection signal sampled in any period exceeds a predetermined value, the control unit 29 causes the touch panel 10 to be You may determine that you are approaching. Alternatively, as described above, it may be determined whether or not a person has approached the touch panel 10 by comparing the potential of the detection signal with the reference potential V _REF using the comparator 28.

In the standby mode, the control unit 29 may set the interval time Δt longer than in the normal operation mode. Further, the control unit 29 may control the differential amplifier 23 so as to perform an intermittent operation. Furthermore, the drive circuit 21 may make the predetermined potential V _S to be applied to the first electrode of the capacitive sensor smaller than that in the normal operation mode. For example, the drive circuit 21 applies a potential of 3V to the first electrode of the capacitive sensor in the normal operation mode, and applies a potential of 1V to the first electrode of the capacitive sensor in the standby mode. You may do it. As a result, power consumption in the standby mode can be reduced.

  In the standby mode, the selection circuit 22 may connect the inverting input terminal of the differential amplifier 23 to the second electrode of a part of the capacitive sensor formed in the area of the touch panel 10. . For example, the selection circuit 22 continues to select only the capacitive sensor of the nth row (1 ≦ n ≦ (N + 1)) on the touch panel 10, and the differential amplifier 23 is added to the capacitive sensor of the nth row. An inverting input terminal may be connected.

Instead it, or in addition, the drive circuit 21, may be applied a predetermined potential V _S to the first electrode of the portion of the capacitive sensor formed in the region of the touch panel 10 . For example, the drive circuit 21 supplies a drive signal only to the first electrode of the capacitive sensor in the m-th column (1 ≦ m ≦ (M + 1)) in the touch panel 10. As a result, power consumption in the standby mode can be reduced.

  FIG. 3 is a circuit diagram showing a first modification of the detection circuit according to one embodiment of the present invention. In the first modification, instead of the capacitors C1 and C2 and the semiconductor switches 25a and 25b shown in FIG. 1, the capacitors C3 and C4 shown in FIG. 3 and the semiconductor switch 25c as the second switch circuit are used. . Other points are the same as those of the embodiment shown in FIG.

  In the normal operation mode, the control unit 29 shown in FIG. 1 activates the control signal S1 to a high level to turn on the semiconductor switch 25c. As a result, the capacitance value (C3 + C4) of the capacitor is connected between the output terminal and the inverting input terminal of the differential amplifier 23. Here, the capacitance value (C3 + C4) of the capacitor is set so that sufficient detection sensitivity can be obtained when a fingertip of a capacitive touch sensor formed on the touch panel is touched.

  In the standby mode, the control unit 29 deactivates the control signal S1 to a low level and turns off the semiconductor switch 25c. As a result, the capacitance value C4 is connected between the output terminal and the inverting input terminal of the differential amplifier 23. Therefore, in the standby mode, the capacitance value of the capacitor connected between the output terminal and the inverting input terminal of the differential amplifier 23 can be made smaller than in the normal operation mode. Specifically, the capacitance value C4 of the capacitor is set so that sufficient detection sensitivity is obtained when a person approaches the touch panel.

  FIG. 4 is a circuit diagram showing a second modification of the detection circuit according to one embodiment of the present invention. In the second modification, instead of the capacitors C1 and C2 and the semiconductor switches 25a and 25b shown in FIG. 1, capacitors C5 and C6 shown in FIG. 4 and a semiconductor switch 25d as a second switch circuit are used. . Other points are the same as those of the embodiment shown in FIG.

  In the normal operation mode, the control unit 29 shown in FIG. 1 activates the control signal S1 to a high level to turn on the semiconductor switch 25d. Thereby, the capacitance value C5 of the capacitor is connected between the output terminal and the inverting input terminal of the differential amplifier 23. Here, the capacitance value C5 of the capacitor is set so that sufficient detection sensitivity can be obtained when a fingertip of the person touches the capacitive sensor formed on the touch panel.

  In the standby mode, the control unit 29 deactivates the control signal S1 to a low level and turns off the semiconductor switch 25c of the second switch circuit. Accordingly, the capacitance value C5 · C6 / (C5 + C6) of the capacitor is connected between the output terminal and the inverting input terminal of the differential amplifier 23. Therefore, in the standby mode, the capacitance value of the capacitor connected between the output terminal and the inverting input terminal of the differential amplifier 23 can be made smaller than in the normal operation mode. Specifically, the capacitance value C5 · C6 / (C5 + C6) of the capacitor is set so that sufficient detection sensitivity is obtained when a person approaches the touch panel.

  As described above, according to the present embodiment, by utilizing the characteristics of the capacitive touch panel, even in the standby mode in which almost all functions of the electronic device are stopped, by detecting the approach of a person, An instruction to return to the normal operation mode can be given when a person approaches the touch panel.

  In the above embodiment, the case where the position of the capacitive sensor touched by a human fingertip is detected in the normal operation mode has been described. However, the fingertip approaches before the fingertip touches the capacitive sensor. Alternatively, the position of the capacitive sensor may be detected. The present invention is not limited to the embodiments described above, and many modifications can be made within the technical idea of the present invention by those having ordinary knowledge in the technical field.

DESCRIPTION OF SYMBOLS 10 ... Touch panel, 20 ... Detection circuit, 21 ... Drive circuit, 22 ... Selection circuit, 23 ... Differential amplifier, 24, 25 ... Switch circuit, 25a-25d ... Semiconductor switch, 26 ... Sample hold circuit, 27 ... A / D transducer, 28 ... comparator, 29 ... control _{unit, X} 0 to X M _... first _{electrode, Y} 0 to Y N _... second _{electrode, C} 0,0 -C _{M, N ...} capacitance, SW _{0 to} SW _N ... semiconductor switch, C1 to C6 ... capacitor

Claims (11)

A detection circuit connected to a capacitive sensor formed on a touch panel,
A drive circuit for applying a predetermined potential to the first electrode of the capacitive sensor;
An inverting input terminal connected to the second electrode of the capacitance type sensor, an output terminal for amplifying a difference between a reference potential applied to the non-inverting input terminal and a potential applied to the inverting input terminal A differential amplifier that outputs a detection signal from
A first switch circuit connected between an output terminal and an inverting input terminal of the differential amplifier;
A second switch circuit for switching a capacitance value of a capacitor connected between an output terminal and an inverting input terminal of the differential amplifier;
The first switch circuit is controlled to periodically short-circuit between the output terminal and the inverting input terminal of the differential amplifier, and the capacitance value of the capacitor is made smaller in the standby mode than in the normal operation mode. A controller that controls the second switch circuit to control the transition to the normal operation mode based on the detection signal;
Including a detection circuit.   2. The detection circuit according to claim 1, wherein the drive circuit makes a predetermined potential to be applied to the first electrode of the capacitive sensor in the standby mode smaller than that in the normal operation mode.   The detection circuit according to claim 1, wherein the control unit controls the differential amplifier to perform an intermittent operation in the standby mode.   The detection circuit according to claim 1, further comprising a comparator that determines whether the potential of the detection signal is higher or lower than a reference potential in the standby mode. A first capacitor connected in series with the second switch circuit between an output terminal and an inverting input terminal of the differential amplifier;
A second capacitor connected between an output terminal and an inverting input terminal of the differential amplifier and having a capacitance value smaller than a capacitance value of the first capacitor;
The detection circuit according to claim 1, further comprising: In the touch panel, a plurality of capacitive sensors are formed in a two-dimensional matrix,
A capacitance sensor of one row is selected from the plurality of capacitance sensors, and the inverting input terminal of the differential amplifier is connected to the second electrode of the capacitance sensor of the one row. The detection circuit according to claim 1, further comprising a selection circuit that performs the selection.   In the normal operation mode, the drive circuit starts applying a predetermined potential to the first electrodes of the plurality of columns of capacitive sensors every first interval time, and in the standby mode, 7. The detection circuit according to claim 6, wherein application of a predetermined potential to the first electrodes of the plurality of rows of capacitive sensors is started every second interval time longer than the first interval time.   The said selection circuit connects the inverting input terminal of the said differential amplifier to the 2nd electrode of a part of electrostatic capacitance type sensor formed in the area | region of the said touch panel in the said standby mode. Detection circuit.   9. The drive circuit according to claim 1, wherein the drive circuit applies a predetermined potential to first electrodes of a part of the capacitive sensors formed in the area of the touch panel in the standby mode. 10. Detection circuit.   A semiconductor integrated circuit device comprising the detection circuit according to claim 1. A touch panel on which a capacitive sensor is formed;
The detection circuit according to any one of claims 1 to 9,
Including electronic equipment.

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