JP3061115B2 - Charge current detection circuit and coordinate input device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge current detecting circuit and a coordinate input device using the same, and more particularly, to a capacitive position sensor, a piezoelectric sensor, a capacitive humidity sensor, an electrostatic field sensor, and an electrostatic sensor. A circuit for detecting a small current (charge current) at the time of charge or discharge generated by a capacitive sensor or an electrostatic sensor such as a digitizer or a coordinate input device. The present invention relates to a charge current detection circuit for detecting a charge current.

[0002]

2. Description of the Related Art As a charge current detection circuit used in a capacitive sensor or an electrostatic sensor, a charge current detection circuit (an electrostatic sensor) for detecting a charge current generated by charging a capacitor as shown in FIG. Circuit). Reference numeral 9 denotes a charge current detection circuit, and reference numeral 1 denotes its electrostatic position sensor unit, which is provided with two capacitors Ca and Cb. One of the capacitors has a surface that can be touched from outside as a charge current detection sensor, a so-called touch sensor. This is, for example, a capacitor Ca.

[0003] 2 is the two capacitors Ca, C
b is a pulse drive circuit that applies a drive pulse to one terminal of b at a predetermined cycle. The other terminals of the capacitors Ca and Cb are connected to the (−) inputs of the operational amplifiers (OP) 3 and 4, respectively. The operational amplifiers 3 and 4 are inverting amplifiers, and their (+) inputs are grounded. The output voltages VA and VB are respectively connected to the feedback capacitors C3 and C3.
The signal is fed back to the (-) input side via C4. Switch circuits 5 and 6 for initial setting are provided in parallel with the capacitors C3 and C4. These switch circuits are turned on for a certain period by a control signal from a controller or the like before the detection operation.
To be.

The output voltage VB of the operational amplifier 4 is further input to the (−) input side of a buffer amplifier 7 of an inverting amplification type via a resistor R. This amplifier has a feedback resistor R
(A resistor having the same resistance value as the resistor R), whereby the amplifier is a buffer amplifier having an amplification factor of 1. Therefore, the output voltage VB of the operational amplifier 4 is inverted as it is, converted into a voltage signal of -VB, and
Outputs an output voltage −VB. The output voltage −VB of the buffer amplifier 7 and the output voltage VA of the operational amplifier 3 are input to the inverting amplification adder 8 and added. At this time, since the buffer amplifier 7 generates an output obtained by inverting the output of the operational amplifier 3, the output voltage VA of the operational amplifier 3 is substantially obtained.
Is subtracted from the output VB of the operational amplifier 4 to obtain − (VA−V
B) occurs as an output of the adder 8. As a result, when a difference occurs between the capacitances of the capacitors Ca and Cb, a difference occurs in the charge amount, and a difference occurs in the charging current flowing at this time. A detection signal corresponding to the difference is obtained by the adder 8.

[0005] This detection operation is described in the operational amplifier 3
4 and 4 operate in the same manner, and the operation of the operational amplifier 3 will be described below. First, the switch circuit 5 is turned on for a certain period in an initial state. The operational amplifier 3 has a (-) input and a (+) input.
Since the input is a virtual short, the output of the operational amplifier 3 falls to the ground level (GND) when the switch circuit 5 is turned on for a certain period. Thereby, the electric charge of the capacitor C3 is discharged and cleared. At this time, the electric charge of the capacitor Ca is discharged via the pulse drive circuit 2 and is similarly cleared. The pulse signal from the pulse drive circuit 2 is output to the capacitor Ca,
Output to Cb. This pulse signal is output from the capacitor Ca
, The current for charging the capacitor Ca flows through this path. Thereby, the capacitor Ca is charged. A current flows to the (-) input in accordance with the charge due to this charging. At this time, a voltage output that keeps the (−) input at the ground potential is generated on the output side of the operational amplifier 3. A current flows through the capacitor 3 according to the output voltage, and the capacitor 3 is charged. In this charging, since the operational amplifier 3 operates in a direction to make the output negative, as shown in FIG.
The terminal of a becomes + and the terminal of the output side capacitor Ca becomes-. Then, an output voltage VA is generated in the operational amplifier 3. Similarly, the output voltage VB is generated in the operational amplifier 4.

In this case, it is assumed that the capacitor Ca is arranged at a predetermined detection position, and that the capacitance of the capacitor Ca changes when a person touches with a finger or when metal comes close to the capacitor Ca. Assuming that the capacitor does not change, the adder 8 can obtain an output signal of a voltage level corresponding to the change in capacitance due to the capacitor Ca. This makes it possible to detect a contact of a finger or a change in the position of a detection target. Generally, in an electrostatic digitizer, a coordinate input device, or the like, a plurality of capacitors C having contact electrodes arranged in a matrix are used as a basic circuit based on such a charge current detection circuit.
a. Then, each detection capacitor Ca is scanned by the multiplexer and sequentially selected. A change in the capacitance of the capacitor selected with respect to an adjacent capacitor due to a finger touch or the like is detected in the same manner as described above. as a result,
The input position by finger contact can be detected based on the selection timing of the multiplexer and the change in the capacitance of the selected detection capacitor. In this type of device,
The operational amplifiers 3 are provided for the respective detection capacitors Ca. Further, the multiplexer does not actually select the detection capacitor, but sequentially selects the output of the operational amplifier 3 at a predetermined timing.

[0007]

Generally, a detecting capacitor and a capacitor having a reference capacitance (or an adjacent capacitor) are used.
In the charge current detection circuit including the above, the wiring distance between this capacitor and the operational amplifier 3 is long because the capacitor Ca on the detection side is arranged at the detection position. As a result, the capacitance of the capacitor Ca (on the order of several pF to several tens of pF) is easily affected by noise, and its detection voltage is fluctuated, so that erroneous detection is likely to occur. Further, a change range of the detected voltage is small in order to detect a change in current generated in response to a change in capacitance due to an environmental change such as a person touching or approaching a metal. Then, when this is received by the operational amplifier, the offset amount in the operation of the operational amplifier becomes a problem with respect to the detection operation. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art, and to provide a charge current detection circuit which is hardly affected by noise when detecting a minute charge current. An object of the present invention is to provide a coordinate input device having a charge current detection circuit that is hardly affected by noise.

[0008]

SUMMARY OF THE INVENTION A charge current detecting circuit and a coordinate input device according to the present invention for achieving the above object are characterized in that first and second capacitors and one terminal of these capacitors are pulsed. A pulse driving circuit driven by a signal to charge and discharge the first and second capacitors in accordance with the rise and fall thereof to generate first and second detection signals at the other terminals of the capacitors; And first and second input terminals respectively receiving first and second detection signals, and first and second output terminals. First and second input terminals are provided in accordance with the rising timing of the pulse signal.
Are connected to the first and second output terminals, respectively, and the first input terminal is connected to the second output terminal, and the second input terminal is connected to the first output terminal according to the falling timing of the pulse signal. A connection circuit to be connected to each of them, a difference current generation circuit for receiving detection signals from the first and second output terminals and generating a current corresponding to a level difference between these signals, and integrating the output of the difference current generation circuit And at least one of the first and second capacitors is disposed in the detection unit.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, two capacitors are simultaneously driven by a pulse, and these two capacitors are charged and discharged according to the rise and fall of the pulse to generate a detection signal. The output is switched according to the rising and falling edges of the input signal, and one input is connected to the other output, and the other input is connected to one output. Can be generated as the same polarity (same phase). As a result, two difference current values are output for one pulse by the difference current generation circuit. By integrating the two difference current values with an integrating circuit to obtain a double difference current, a large detection current value can be obtained. As a result, the detected S / N ratio with respect to the detected value can be improved.

[0010]

FIG. 1 is an explanatory view mainly showing a charge current detection circuit of a coordinate input device according to an embodiment to which a charge current detection circuit of the present invention is applied, and FIG. 2 is a view explaining the structure of an electrostatic sensor unit. FIGS. 3 and 4 are explanatory diagrams of a detection state of a pair of capacitors selected by the multiplexer, and FIG. 4 is a timing chart of the detection operation. In FIG. 1, 10
Is a detecting unit, 11 is an electrostatic sensor unit, 12 is a multiplexer, 13 is a pulse drive circuit, and X
It comprises a side drive circuit 13a and a Y side drive circuit 13b. 14 is a connection switching circuit, 15 is a difference current generation circuit, 1
6 is a switch circuit, 17 is an integration circuit, and 18 is a control circuit. The integrating circuit 17 includes an integrating capacitor CS and a switch circuit SW connected in parallel with the integrating capacitor CS for resetting the electric charge charged in the capacitor. Reference numeral 20 denotes a detection signal determination unit, which includes an amplifier 21, a sample and hold circuit (S / H) 22,
An A / D conversion circuit (A / D) 23 and a data processing device 24 are provided.

The electrostatic sensor section 11 is of a flat plate shape. As shown in FIG. 2, a plurality of stripe electrodes X1, X2,..., Xn arranged at predetermined intervals in the X direction and predetermined in the Y direction. , Stripe electrodes Y1, Y2,...
Ym, and these electrodes are stacked at predetermined intervals via a spacer (not shown) made of a dielectric resin. Each of the stripe electrodes X1, X2,..., Xn and the stripe electrodes Y1, Y
2,... Ym, one of two adjacent electrodes is sequentially selected as a pair and driven by the pulse driving circuit 13 through the other electrode . In this case, of selection
One electrode on the side to be supplied is supplied with a certain level of voltage. And all the other electrodes are driven simultaneously.
One of the two electrodes selected here, when selected, corresponds to the two capacitors Ca and Cb shown in FIG. 3 in relation to the other electrode. Then, a difference between the capacitance of one capacitor and the capacitance of the other capacitor is output as a current value by the difference current generating circuit 15. FIG. 3 shows the relationship.

Now, referring to FIG.
Here, first, two adjacent electrodes in the Y direction on the upper side in FIG. 2 are selected by shifting one by one, and when all two electrodes are completed, one adjacent electrode in the X direction is selected. Select one after another. This is because the electrodes Y1, Y2, electrode Y
2, Y3,..., Electrodes Yi-1, Yi,..., Electrodes Ym, Y1 are two adjacent electrodes in the Y direction. However, the last electrode Ym is two electrodes of the first electrode Y1. Next, electrodes X1, X2, electrodes X2, X3,.
The electrodes Xi-1, Xi,..., The electrodes Xn, X1 are two adjacent electrodes in the X direction. However, the last electrode Xn is also two electrodes of the first electrode X1. These are sequentially selected by the multiplexer 12 and a drive pulse is applied from the pulse drive circuit 13. When the Y-side electrode is selected , the X-side drive circuit 13a
Generates a drive pulse and applies it to the X electrode, and accordingly, Y
The pair of electrodes on the electrode side are sequentially scanned. This and
The Y-side drive circuit 13b applies a constant voltage to each Y electrode
ing. When the X-side electrode is selected,
Conversely, the Y-side drive circuit 13b generates a drive pulse.
A pair of electrodes on the X electrode side scan in addition to the Y electrode
Will be done. At this time, the X side drive circuit 13a is constant.
A voltage is applied to each X electrode. Which one is on the drive side and which is set to a constant voltage is determined by the selection signals S3 and S4 from the data processing device 24.

At first, the electrodes Y1, Y2,..., Ym are driven to the drive side by the selection signals S3, S4, and are driven by, for example, a pulse of a HIGH level, a voltage of Vcc or the like. At this time, the X-side electrodes X1, X2,.
It is set to a constant voltage such as W level, Vcc / 2, etc.
The electrodes are scanned sequentially. On the other hand, when the electrode on the X side is selected as the drive side and is driven by a pulse of a voltage such as a HIGH level or Vcc, on the other hand, the electrode on the Y side is set to a low level or a constant voltage such as Vcc / 2. Set
Then, each electrode on the Y side is sequentially scanned. Further, the selection of the electrodes of the multiplexer 12 and the generation of the drive pulses of the pulse drive circuit 13 are performed according to a control signal from the control circuit 18. FIG. 3 shows a circuit mainly showing a pair of adjacent two electrodes which are sequentially selected by the multiplexer 12. The pair of adjacent capacitors Ca and Cb selected by the multiplexer 12 under the control of the control circuit 18 are connected to the selected pair of Y electrodes , X electrodes, or a pair of X electrodes and Y electrodes. represents a capacitor formed by the same. FIG. 4 is a timing chart of the detection operation.

[0014] adjacent to the Y-direction Ri by the multiplexer 12
When the two electrodes are selected , a drive pulse P (see FIG. 4A) is applied to one end N (the first electrode on the X side) of the commonly connected capacitors Ca and Cb. The other ends Na and Nb (first electrodes on the Y side) of the selected capacitors Ca and Cb are input to the difference current generating circuit 15 via the multiplexer 12 and the connection switching circuit 14. Difference current generation circuit 1
Reference numeral 5 denotes a Gm amplifier (trans-conductance amplifier), whose positive and negative phase terminals receive voltage signals generated at the other ends Na and Nb of the capacitors Ca and Cb, respectively . The output has a current corresponding to the potential difference between these input signals as a difference current value, that is, 2
The current value generated from the capacitance difference between the two capacitors (each
(A current value corresponding to the difference between the charge currents) .
The switch circuit 16 is a switch that is turned on for a certain period, and receives a control signal from the control circuit 18. While the switch circuit 16 is ON, the output of the difference current generation circuit 15
It is sent to S and charged by its output current.

Here, the connection switching circuit 14 receives the control signal S1 (see FIG. 4B) from the control circuit 18 and makes a connection indicated by a solid line at the rise and a connection indicated by a dotted line at the fall. Do. In the connection shown by the solid line, the first input I1 is connected to the first output O1, and the second input I2 is connected to the second output O2. In the connection indicated by the dotted line, the first input I1 and the second output O2
And the second input I2 is connected to the first output O1. The relationship between the drive pulse P and the control signal S1 is the same for each pulse width, and the phase of the control signal S1 is ahead of the drive pulse P. Therefore, the control signal S1 rises before the drive pulse P rises, and the control signal S1 falls just before the drive pulse P falls. As a result, when the driving pulse P rises, the connection switching circuit 14 is connected in a solid line state, and when the driving pulse P falls, the connection switching circuit 14 is connected in a dotted line state. In addition,
The pulse width of the drive pulse P is set to a period t longer than the period during which the charging of the capacitors Ca and Cb is completed, and the cycle T is twice or more (2t <T).

At this time, the other ends N of the capacitors Ca and Cb
In a and Nb, a voltage signal as shown in FIG. 4C is generated as a transient phenomenon corresponding to the rise and fall of the drive pulse P. The voltage signal generated by this transient phenomenon is applied to the + phase terminal and the − phase terminal of the difference current generation circuit 15, respectively. At this time, the waveform as the differential voltage applied between the terminals has the same polarity (same phase) at the rising and falling of the drive pulse P by the connection switching circuit 14. Therefore, a current signal shown in FIG. 4D is output to the output of the difference current generating circuit 15. As a result, the capacitor CS of the integrating circuit 17 is charged twice per drive pulse by the current generated at the rise and fall of the drive pulse P, and the charge is accumulated. In addition, FIG.
a> Cb, but when Ca <Cb, FIG.
The current signal shown in (d) has the opposite polarity.

Here, the switch circuit 16 is turned on by the control circuit 18 for a period of 16 drive pulses P. Therefore, the capacitor C of the integrating circuit 17
A pulse current for approximately 32 times is applied to S, whereby charging is performed. The terminal voltage value of the capacitor CS due to this charging is amplified by the amplifier 21 of the detection signal determination unit 20 and is applied to the sample and hold circuit (S / H) 22. Here, the signal is sampled by the sampling signal SP from the control circuit 18, the sampled value is input to the (A / D) 23 and converted into a digital value, which is input from the A / D 23 to the data processing device 24. . Note that the number of the drive pulses corresponding to the ON period of the switch circuit 16 may be larger, for example, a period corresponding to an appropriate number from a range of about 30.

Here, the terminal of the capacitor CS is connected to a bias terminal of a predetermined voltage, for example, Vcc / 2, similarly to the (-) input of the amplifier 21. Therefore, when the switch SW is turned on, the capacitor CS
Are preset to the bias voltage Vcc / 2.
Then, the capacitance of the capacitors Ca and Cb on the detection side is Ca>
In the case of Cb, the current output of the difference current generating circuit 15 is discharged, so that the capacitor CS has the bias voltage Vcc /
It is charged to a voltage higher than 2. On the other hand, when the capacitance of the capacitor is Ca <Cb, the current output of the difference current generation circuit 15 serves as a sink, so that the charge of the capacitor CS is discharged to a voltage lower than the bias voltage Vcc / 2. When the capacitance of the capacitor is Ca = Cb, no current output is generated in the difference current generating circuit 15, so that
The charging voltage of the capacitor CS becomes equal to the bias voltage Vcc / 2.

Now, the data processing device 24 includes an MPU 24
a, a memory 24b storing various processing programs,
It comprises a buffer memory 24c, an I / O interface 24d and the like. The data collection program 25 and the touch position detection program 26 are stored in the memory 24b.
Etc. are provided. MPU 24 of data processing device 24
a receives the control signal S2 from the control circuit 18, executes the data collection program 24, sends out the sample and hold signal SH and the A / D conversion signal SA, and sets the output voltage value of the sampled and held amplifier 21 to A. / D conversion and stores the data in the buffer memory 24c. Then, a control signal SS for starting the measurement is transmitted to the control circuit 18 via the I / O interface 24d. Further, the sample-and-hold circuit 22 is controlled by the control signal SS.
Is also reset.

The data processor 24 first generates a selection signal S3 for setting the Y side to a drive circuit, causes the control circuit 18 to control the selection of electrodes in the Y direction, and then sets the X side to a drive circuit. A selection signal S4 is generated to cause the control circuit 18 to control the selection of electrodes in the X direction,
The control signal S is kept until all the electrode selections in the Y and X directions are completed
Each time 2 is received, similar data is received and collected from the A / D 23, stored in the buffer memory 24c, and sends a control signal SS for starting measurement. When the measurement of all the electrodes in the Y direction and the X direction is completed, a measurement end signal SE is sent to the control circuit 18 to stop the operation.

The control circuit 18 turns on the switch circuit SW each time the control signal SS for starting the measurement is received from the data processing device 24, and then presets the capacitor CS to a bias voltage (for example, Vcc / 2). Then, the multiplexer 12 is driven to transmit a control signal for selecting the next pair of electrodes, and the switch circuit 17 is turned on.
Then, a control signal S1 is sent to the connection switching circuit 14, and
The pulse driving circuit 13 is driven. Control circuit 18
Receives the drive pulse P from the pulse drive circuit 13 (see FIG. S3) and counts the number. When the number of the driving pulses P is counted by 16, the switch circuit 17 is turned off, and the control signal S2 indicating the end of the measurement to the data processing device 24.
Is sent.

Thus, the control circuit 18 receives the control signal SS for starting the first measurement, and every time it receives this signal, the electrodes Y1, Y2, the electrodes Y2, Y3,..., The electrodes Yi-1, Yi, ... select the electrodes Ym and Y1 and two adjacent electrodes in the Y direction, then move to the X direction, and select the electrodes X1, X2,
Electrodes X2, X3, ... Electrodes Xi-1, Xi, ... Electrodes Xn, X1
Is performed to sequentially select two adjacent electrodes in the X direction. Also, for each selected pair of electrodes, the control signal S2 is transmitted when the number of drive pulses P has been measured to 16 and the control signal S5 for switching to the next electrode is transmitted to the multiplexer 12.

Next, after sending the measurement end signal SE to the control circuit 18, the MPU 24a executes the touch position detection program 26 to determine the touched electrode. Note that when any electrode is touched with a finger, the finger acts as a conductor, and the lines of electric force are interrupted by the conductor (finger), so that the capacitance of the touched electrode is reduced. Therefore, assuming that the capacitor Ca in FIG. 3 is a certain electrode and the capacitor Cb is the next electrode adjacent thereto, a pair of electrodes (X or Y electrodes) near the touched electrode and the other electrode near the touched electrode. The capacitance of the capacitor constituted by the (Y or X electrode) is Ca> Cb, and the capacitance of the capacitor constituted by the pair of electrodes and the other electrode near the back is Ca <Cb. Therefore, a change point where Ca> Cb changes to Ca <Cb can be detected as a touched electrode. The touch position detection program 26 detects this change point from the measured data for each of the electrodes in the Y direction and the electrodes in the X direction. Thus, the position given by the electrode number in the Y direction and the electrode number in the X direction is detected as a touch position.

Here, the difference current generating circuit 15 is described as an example of a Gm amplifier, but this may be a current output amplifier. In particular, although the waveforms (detection signals) shown in FIGS. 4C and 4D have been described above as voltage waveforms, the current waveform also takes the same form. Therefore, if the detection signal is a current signal, a current amplification amplifier can be used as the difference current generation circuit 15. Also, S
Japanese Patent Application No. 7-289 as a minute current detection circuit using a current mirror as a current output amplifier with an improved / N ratio.
No. 218, "Microcurrent detection circuit and coordinate input device using the same" has been filed by the present applicant. By substituting the minute current detection circuit shown as the detection circuit 10 of this application for the difference current generation circuit 15 as it is, a detection operation with a high S / N ratio can be performed.

As described above, in the embodiment, a circuit for generating a plurality of driving pulses and obtaining a voltage value corresponding to the detected current value by integrating the driving pulses is described. It is not necessary to use a plurality of pulses to obtain an integrated value for the period. In the embodiment, Y
Although a coordinate input device in which a large number of electrodes are arranged in the direction and the X direction is mainly described, the present invention includes two capacitors, one of which is arranged as can be understood from the detection circuit shown in FIG. It is needless to say that the present invention can be applied to a charge current detection circuit such as a touch sensor arranged at a detection position.

[0026]

As described above, according to the present invention, 2
The two capacitors are driven simultaneously in pulses and the two capacitors are charged and discharged according to the rising and falling of the pulse to generate a detection signal, and the output is switched according to the rising and falling of the pulse, respectively. By connecting one input to the other output and connecting the other input to one output, a connection circuit generates the level difference between the charge-side detection signal and the discharge-side detection signal as the same polarity (same phase). Can be done. As a result, two difference current values are output for one pulse by the difference current generation circuit. By integrating the two difference current values with an integrating circuit to obtain a double difference current, a large detection current value can be obtained. As a result, the detected S / N ratio with respect to the detected value can be improved. Further, the change range of the detection voltage becomes large, and the circuit is hardly affected by the offset amount in the operation of the operational amplifier even when the voltage is received by the operational amplifier.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram centering on a detection circuit of a coordinate input device according to an embodiment to which a charge current detection circuit of the present invention is applied.

FIG. 2 is an explanatory diagram of a structure of an electrostatic sensor unit.

FIG. 3 is an explanatory diagram of a detection state of the pair of capacitors.

FIG. 4 is a timing chart of a detection operation.

FIG. 5 is a block diagram showing an example of a conventional charge current detection circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Detection part, 11 ... Electrostatic sensor part, 12 ... Multiplexer, 13 ... Pulse drive circuit, 14 ... Connection switching circuit, 1
5 ... Difference current generation circuit, 16 ... Switch circuit, 17 ... Integration circuit, 18 ... Control circuit, 20 ... Detection signal judgment section, 21 ... Amplifier, 22 ... Sample hold circuit, 23
... A / D conversion circuit (A / D), 24 ... Data processing device.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yasuhiro Niwa 21st Mizozakicho, Niinin, Ukyo-ku, Kyoto ROHM Co., Ltd. JP-A-8-106353 (JP, A) JP-A-7-200147 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G06F 3/03 335 G06F 3/03 380

Claims (4)

(57) [Claims] 1. A first and a second capacitor, and one terminal of the capacitor is driven by a pulse signal, and the first and the second capacitors are driven according to the rise and fall of the terminal.
A pulse drive circuit for charging / discharging the capacitors and generating first and second detection signals at the other terminals of the capacitors; and first and second input terminals for receiving the first and second detection signals, respectively. And first and second output terminals, wherein the first and second input terminals are connected to the first and second output terminals, respectively, in accordance with the rising timing of the pulse signal, and A connection circuit for connecting the first input terminal to the second output terminal and the second input terminal to the first output terminal, respectively, in response to a fall timing; and a first and second output terminal. A differential current generating circuit that receives the detection signals from the terminals and generates a current corresponding to the level difference between these signals; and an integrating circuit that integrates the output of the differential current generating circuit. A charge current detection circuit in which at least one of the second capacitor and the second capacitor is disposed in a detection unit. 2. The method according to claim 1, wherein the difference current generation circuit operates on both the positive phase side and the negative phase side of the detection signal, and the integration circuit performs the operation for a plurality of the pulse signals. 2. The charge current detection circuit according to claim 1, wherein the output of the difference current generation circuit is integrated. 3. A first and a second capacitor, and one terminal of the capacitor is driven by a pulse signal, and the first and the second capacitors are driven according to the rise and fall of the capacitor.
A pulse drive circuit for charging / discharging the capacitors and generating first and second detection signals at the other terminals of the capacitors; and first and second input terminals for receiving the first and second detection signals, respectively. And first and second output terminals, wherein the first and second input terminals are connected to the first and second output terminals, respectively, in accordance with the rising timing of the pulse signal, and A connection circuit for connecting the first input terminal to the second output terminal and the second input terminal to the first output terminal, respectively, in response to a fall timing; and a first and second output terminal. A differential current generating circuit that receives the detection signals from the terminals and generates a current corresponding to the level difference between these signals, and an integrating circuit that integrates an output of the differential current generating circuit, A coordinate input device in which a plurality of capacitors are continuously arranged in a detection unit. And a multiplexer for selecting two adjacent capacitors among the plurality of first capacitors, wherein the difference current generating circuit is configured to detect a difference between a positive phase side and a negative phase side of the detection signal. The first and second capacitors are selected by the multiplexer, and the remaining one is used as the second capacitor, and the integrating circuit is provided for the plurality of the pulse signals. 4. The coordinate input device according to claim 3, wherein the output of said difference current generating circuit is integrated.