JP2009109205A - Charge quantity measuring circuit and charge quantity measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a fine charge quantity and a capacitance with high resolution by a simple constitution wherein a power source, a resister, a capacitor or the like is added to a digital circuit. <P>SOLUTION: An electricity accumulation means is controlled to have a constant voltage according to whether the voltage of the electricity accumulation means into which the charge of a measuring object flows is higher or lower than a threshold value, and the charge quantity of the measuring object is determined from the charge quantity required for control. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a circuit for measuring an amount of charge flowing in a specific voltage used for measuring capacitance, detecting electric field changes in human body communication, and the like, and a method thereof.

  A method using an operational amplifier is used to measure the amount of charge flowing through a predetermined voltage Vt when measuring capacitance or detecting voltage change of an approaching object.

  A charge amount measurement circuit using a conventional operational amplifier will be described with reference to FIG.

In FIG. 2, the capacitor Cs accumulates the charge Qx flowing into the voltage Vt and converts it into a voltage. The switch SW is for initializing the electric charge of the capacitor. The voltage of the capacitor Cs storing Qx is converted into a digital value by the AD conversion means 51. Further, the charge amount Qx is calculated by the calculation means 52 from the value of the capacitor Cs and the digital value converted by the AD conversion means 51.
Japanese translation of PCT publication No. 2002-530680

  As described above, the conventional charge amount measurement circuit has a problem that the circuit scale becomes large because an active analog circuit and a digital circuit are mixed and an operational amplifier, an AD conversion unit, and a calculation unit are required. .

  An object of the present invention is to realize a charge amount measurement circuit or a method thereof that enables high-resolution measurement with a simple configuration in which a power supply, a resistor, a capacitor, and the like are added to a digital circuit.

  The charge amount measurement circuit according to the present invention includes a power storage unit that inputs a charge to be measured and converts the stored charge amount into a voltage, a charge input / output unit that inputs and outputs a charge to the power storage unit, A voltage measuring means for measuring a voltage; a first control means for controlling the charge input / output means according to a measurement result of the voltage measuring means; and a charge amount to be measured is calculated from control information of the first control means. It comprised with the 1st calculating means.

  According to the present invention, it is possible to realize a charge amount measurement circuit or a method thereof that enables high-resolution measurement with a simple configuration in which a power supply, a resistor, a capacitor, and the like are added to a digital circuit.

  Generally, there are a positive charge and a negative charge. For convenience of explanation, unless otherwise specified, in the following description, a charge means a positive charge.

  A preferred embodiment of the present invention will be described with reference to FIG.

  The charge amount measurement circuit according to the present invention includes a power storage unit 1 that inputs a charge to be measured and converts a stored charge amount into a voltage, a charge input / output unit 2 that inputs and outputs a charge to and from the power storage unit 1, Voltage measuring means 3 for measuring the voltage of the storage means 1, first control means 4 for controlling the charge input / output means 2 based on the measurement result of the voltage measuring means 3, and control information of the first control means 4 To the first calculating means 5 for calculating the charge amount of the measurement object.

  Hereafter, each component means will be described in detail.

  The power storage means 1 converts the stored charge into a corresponding voltage Vs. Further, the charge Qx to be measured is input to the power storage unit 1. Here, the voltage Vs of the power storage unit 1 is controlled by the charge Qa from the charge input / output unit 2 so as to approach the threshold voltage Vt of the voltage measurement unit 3. Strictly speaking, the voltage Vs of the power storage means varies minutely depending on time, but in the following description, the influence of the variation is acceptable unless otherwise specified.

  Specifically, as shown in FIG. 3, the power storage unit 1 can be realized by a capacitor Cs. However, the capacitor 1 or the like can convert the stored charge amount into a corresponding voltage Vs. Any type may be used.

  The charge input / output unit 2 causes the charge Qa to flow through the power storage unit 1. Therefore, a specific configuration example of the charge input / output unit 2 is shown in FIG.

FIG. 4 a is an example in the case of comprising two constant current sources for passing constant currents Ip and Im and two switches SWp and SWm controlled by the first control means 4. Here, the constant current source Ip is for inputting charges to the power storage means 1, and the constant current source Im is for outputting charges from the power storage means 1. Therefore, the amount of charge Qa flowing through the power storage means can be obtained from Equation 1 from the constant current values Ip and Im, the time Tp when the switch SWp is on, and the time Tm when the switch SWm is on.
(Expression 1) Qa = Ip × Tp−Im × Tm
When the current values Ip and Im are functions of time, the charge amount Qa flowing through the power storage means can be obtained by replacing multiplication with integration or adding current values for each time. is there.

Here, the time Tp during which the switch SWp was turned on and the time Tm during which the switch SWm was turned on are the total time during which the switch SWp was turned on during the measurement period Tt. For example, when the switch ON times of the switches SWp and SWm are fixed to tp and tm, respectively, and the number of times each switch is turned on during the measurement period Tt is Np [times] and Nm [times], the switches The time Tp during which the SWp is on and the time Tm during which the switch SWm is on can be obtained from Equation 2, respectively.
(Equation 2) Tp = tp × Np, Tm = tm × Nm
FIG. 4B shows an example in which charges are input to the power storage means 1 by a constant voltage power source Vp and a resistor Rp instead of the constant current source Ip of FIG. 4A. Since the voltage Vs of the power storage unit 1 is controlled so as to approach the threshold voltage Vt of the voltage measurement unit 3 as described above, when the switch SWp is turned on, a charge is input to the power storage unit 1 with the current value obtained by Equation 3. To do.
(Equation 3) Ip≈ (Vp−Vt) ÷ Rp
Similarly, the constant voltage power source Vm and the resistor Rm output electric charge from the power storage means 1 instead of the constant current source Im. When the switch SWm is turned on, electric charge is output from the power storage means 1 at the current value obtained by Equation 4.
(Equation 4) Im≈ (Vt−Vm) ÷ Rm
Here, the circuit for inputting electric charge to the electric storage means 1 and the circuit for outputting electric charge from the electric storage means 1 are not necessarily the same. For example, as shown in FIG. On the other hand, there are no restrictions on the combination, such as using a constant voltage source and a resistor.

  Further, since the switches SWp and SWm are connected in series with a constant current source and a resistor, it goes without saying that the switches SWp and SWm may be replaced with the power storage unit 1 as shown in FIG. 4d.

  Furthermore, as shown in FIG. 4e, the switch SWp and the switch SWm do not necessarily have to be in both, and may be in either one at least. For example, the case where the switch SWm is not present is the same as the case where the switch SWm is kept on. Therefore, the amount of charge Qa flowing through the power storage means 1 is calculated by setting the measurement time Tt to the time Tm when the SWm of Formula 1 is on. It can be obtained by substitution. Similarly, when there is no switch SWp, it can be obtained by substituting the measurement time Tt for the time Tp when the switch SWp was on.

  Further, it is not always necessary to have both a circuit for inputting charges to the power storage means 1 and a circuit for outputting charges from the power storage means 1. For example, when the charge Qx to be measured always flows out of the power storage means 1, if there is a circuit for inputting charge to the power storage means 1 as shown in FIG. It can be controlled to approach the threshold voltage Vt. Similarly, when the charge Qx to be measured always flows into the power storage unit 1, if there is a circuit for outputting the charge from the power storage unit 1, the voltage Vs of the power storage unit 1 is changed to the threshold voltage Vt of the voltage measurement unit 3. It can be controlled to approach.

  As another configuration, for example, as shown in FIG. 4g, if there are two switches SWp and SWm even with a single resistor R, a charge can be input to the power storage means 1 or a charge can be output from the power storage means 1. I can do it. As described above, the charge input / output unit 2 may have various configurations and combinations, but any means or method may be used as long as the charge amount Qa flowing to the power storage unit 1 can be controlled by the first control unit 4. May be used.

  The voltage measuring unit 3 measures the voltage of the power storage unit 1. For this reason, whether the voltage Vs of the power storage means 1 is higher or lower than the threshold voltage Vt is detected.

  The voltage measuring means 3 is not limited to this, and any voltage measuring means 3 can be used as long as it outputs information on the voltage necessary for controlling the voltage of the power storage means 1 to a certain range to the first control means 4. It may be used.

  The first control unit 4 controls the charge input / output unit 2 so that the voltage Vs of the power storage unit 1 falls within a constant voltage, and outputs control information to the first calculation unit 5.

  Therefore, the first control unit 4 turns on the switch SWp of the charge input / output unit 2 for a short time tp when the voltage measuring unit 3 detects that the voltage Vs of the power storage unit 1 is lower than the threshold voltage Vt. When it is detected that the voltage Vs of the power storage means 1 is higher than the threshold voltage Vt, the switch SWm is turned on for a short time tm, and this is repeated in small increments.

  The operation is the same when the charge input / output means has only one switch as in FIGS. For example, when the charge input / output unit 2 does not have the switch SWm, the switch SWp is turned on when the voltage measurement unit detects that the voltage Vs of the power storage unit 1 is lower than the threshold voltage Vt, and the voltage measurement unit 3 stores the voltage. When it is detected that the voltage Vs of the means is higher than the threshold voltage Vt, it is only necessary to wait for the detection result of the voltage measuring means 3 to change while the switch SWp is turned off.

  However, since the voltage Vs of the power storage means 1 may be greatly different from the threshold voltage Vt in the initial stage, the time until it is confirmed that the voltage Vs of the power storage means 1 has approached the threshold voltage Vt is being initialized. Do not use control information. Therefore, for example, in accordance with the flow shown in FIG. 14, the initialization is completed because the voltage measuring unit 3 has changed from the state where the voltage Vs of the power storage unit 1 is detected as being smaller than the threshold voltage Vt to the state where it is detected as being large. It is also good. Or the reverse may be the completion of initialization. Note that P in FIG. 14 is a state variable that can take a true value and a false value, and is used to detect a change in the measurement of the voltage measuring means. In addition to this, for example, a voltage source equivalent to the threshold voltage may be directly connected to the power storage means by switch connection. Any initialization method may be used as long as it can be confirmed that the voltage Vs of the power storage means 1 has approached the threshold voltage Vt.

  When the charge Qx to be measured flows instantaneously once, for example, after the initialization, the switch SWp and the switch SWm are turned on and off Np and Nm and the on-times Tp and Tm are also set to 0, and the measurement charge Qx is caused to flow to the power storage unit 1. The first control means 4 may be operated for one cycle as shown in FIG. In this case, this one squill is the measurement period Tt.

  Further, when the charge Qx to be measured flows to the power storage unit 1 over a certain period of time, the charge Q to be measured is set so that the voltage Vs of the power storage unit 1 does not greatly deviate from the threshold voltage Vt of the voltage measurement unit 3. It is desirable to repeat the operation of multiple cycles so as to include the flowing time. In this case, a plurality of included cycles is the measurement period Tt.

  Nevertheless, the first control means does not necessarily have to operate so that the voltage of the power storage means always approaches Vt, the voltage change of the power storage means at the charge Qx by the measurement object is sufficiently small, and the charge amount measurement speed As long as it is within the allowable range, it may be operated intermittently. For example, even if the first control unit 4 is operated for one cycle every 10 [ms] and the operation is stopped thereafter, there is no problem as long as the voltage change of the power storage unit 1 during the stopped time is minute. However, when it is necessary to measure the time change of the charge to be measured, the measurement speed is governed by the cycle of the measurement cycle.

  The operation of the first control unit 4 is not limited to this. For example, when the voltage measurement unit 3 detects that the voltage Vs of the power storage unit 1 is lower than the threshold voltage Vt, the voltage measurement unit 3 uses the voltage Vs of the power storage unit 1. If the switch SWp of the charge input / output unit 2 is kept on until it is detected that the voltage Vs is higher than the threshold voltage Vt, and the voltage measuring unit 3 detects that the voltage Vs of the power storage unit 1 is higher than the threshold voltage Vt. This may be repeated by continuously turning on the switch SWm of the charge input / output means 2 until the voltage measuring means 3 detects that the voltage Vs of the power storage means 1 is lower than the threshold voltage Vt.

  In addition to this, the first control unit 4 detects, for example, that the voltage Vs of the power storage unit 1 is lower than the threshold voltage Vt by the voltage measurement unit 3 after the switch SWp of the charge input / output unit 2 is turned on for a predetermined time. Until the switch SWm is turned on for a short time, the power storage means 1 is managed while managing the values for understanding the amount of charge to and from the power storage means such as the times Tp and Tm for turning on the switches SWp and SWm of the charge input / output means 2. Any means or method may be used as long as it controls the charge input / output means 2 so that the voltage Vs is not greatly deviated from the target voltage Vt.

  The first calculation means 5 obtains the charge amount to be measured from the control information from the first control means 4.

The charge Qx flowing into the power storage unit 1 from the measurement target satisfies Equation 5 in order to preserve the charge amount.
(Formula 5) Qx + Qa = 0
This is because the voltage Vs of the power storage means 1 is kept substantially constant by the first control means and the amount of stored charge is also kept almost constant, so that the charge Qx flowing into the power storage means 1 and the charge input This is because the sum of the charges Qa from the output means 2 becomes zero.

  For this reason, the first calculation means 5 first calculates the total time during which the switch of the charge input / output means 2 is turned on during the measurement period Tt according to Equation 2. Needless to say, this calculation may be realized not only by addition and multiplication but also by a timer or a counter. Substituting the obtained Tp and Tm into Equation 1, Qa is obtained by calculation. After that, if a sign is required, it is reduced by 1 by Equation 5.

  As an example in the case of FIG. 4 a using a constant current source for the charge input / output means 2, a constant current value Ip = Im = 1 [mA], one on time ta of the switches SWp and SWm of the charge input / output means 2 = When tb = 1 [μs], the number of times the switch SWp of the charge input / output means 2 is turned on Na = 100 [times], and the number of times the switch SWm is turned on Nb = 50 [times], the switch SWp is turned on according to Equation 2. The time Tp = 100 [μs], the time Tm = 50 [μs] when the switch SWm was turned on, the input charge amount Qa = 50 [nC] of the charge input / output means 2 is obtained by Equation 1, and Qx = −50 [ In the calculation, 50 [nC] is extracted from nC]. Incidentally, in the case of the measurement period Tt = 10 [ms], the average current during that period is −5 [μA].

  Note that this calculation procedure is an example, and various methods are conceivable, such as calculating at once by a previously summarized formula or referring to a table calculated in advance for each value of Tp · Tm. Any calculation can be performed by the first calculation means 5 as long as the charge amount to be measured or a value corresponding to the charge amount is obtained from the control information of the first control means 4 and circuit constants. Means and methods may be used.

  Although the basic operation of the present invention has been described above, a method for improving accuracy and resolution will be described.

  In the charge amount measurement circuit according to the present invention, since there are variations in the current value of the constant current source, the voltage value and resistance value of the constant voltage source, etc., which are normally used for the charge input / output means, the charge amount measurement value is a considerable amount. Will cause an error. In order to solve this problem, as shown in the flow of FIG. 15, the charge amount measurement operation is performed when the charge to be measured is not input or output or when the charge to be measured is not input or output in a steady state. It is preferable to measure the charge amount of the measurement object after obtaining in advance a coefficient for correcting the charge calculation result in the first calculation means so that the result is close to zero.

  For example, in the charge amount measurement operation when the charge to be measured is 0, for example, the charge input / output unit calculates 110 [nC] charge to the power storage unit, and outputs 91 [nC] charge from the power storage unit. In the case where the calculation is performed, the charge input to the storage unit of the charge input / output unit is calculated as 0 when the charge amount of the actual measurement target is calculated using the value obtained by dividing these values and the inverse of the square root. The measurement accuracy can be improved by multiplying the charge output from the power storage means by 1.1. As a calculation method, any method or means may be used as long as the same effect can be obtained, such as addition and subtraction.

  In the charge amount measuring circuit according to the present invention, when the voltage measuring means has a hysteresis characteristic, the voltage control range of the power storage means becomes wide. For this reason, the charge amount Qx itself to be measured may be affected, or the charge amount Qa to be controlled may be affected by the voltage of the power storage means when a constant voltage source and a resistor are used for the charge input / output means. is there.

  In order to solve this problem, the voltage fluctuation of the power storage means due to one-time switch on of the charge input / output means is set to be sufficiently smaller than the voltage range of the hysteresis characteristic of the voltage measuring means for measurement. By making the voltage of the power storage means substantially the same at the start and end of the control cycle, the hysteresis voltage range can be used almost uniformly, so that the measurement accuracy and repeatability can be improved. Specifically, after initialization with an operation cycle as shown in FIG. 14, it may be repeated using the same operation cycle.

  Here, the cycle starting point of the control operation may be obtained by using the smaller value of the current flowing through the switches SWp and SWm of the charge input / output means. For example, when Ip = 2 [mA] and Im = 1 [mA], as shown in FIG. 14, the voltage measuring means causes the voltage Vs of the power storage means to be higher than the threshold voltage Vt by turning on the switch SWm. It is better to set the starting point of the control cycle at the time when it is detected that the size has become smaller.

  Furthermore, in order to improve the resolution of the charge amount measurement, the current values Ip and Im of the charge input / output means are made sufficiently small to reduce the charge input / output amount by one-time switch on of the charge input / output means. Needless to say, when setting or repeated measurement is possible, the resolution and accuracy can be improved by summing or averaging the results of repeated measurements.

  In addition, in the charge amount measurement circuit using the conventional operational amplifier, initialization is required every time measurement is performed, but in the charge measurement circuit according to the present invention, the next cycle is performed after one cycle of the control operation is completed. Since the measurement can be started, continuous measurement can be performed even when repeated measurement or the charge to be measured changes with time.

  In this case, for example, by averaging or filtering the current values obtained for each cycle, it is possible to further increase the measurement resolution while eliminating the influence of noise.

  Further, in the charge measurement circuit according to the present invention, as shown in FIG. 5 as a whole of the charge measurement circuit using the charge input / output means of FIG. 4b, the constant voltage source Vp is Vdd, the constant voltage source Vm is Vss, and Vt is the input threshold value. In terms of voltage, the voltage measuring means 3, the first control means 4, and the first computing means 5 are realized by a logic circuit 20 such as a general-purpose microcomputer, and only a resistor and a capacitor are added to the input / output port. A charge measurement circuit can be realized with a simple configuration.

  Here, in the example of FIG. 5, three general-purpose input / output ports are required. However, if the switch SWm is not provided in the charge input / output circuit as shown in FIG. 6B, even if voltage measurement means is connected between the switch SWp of the charge input / output means and the resistor Rp as shown in FIG. 6B and voltage measurement is performed when the switch SWp is off, one port can be reduced. Further, by using both of them, or by using the charge input / output means of FIG. 4g as shown in FIG. 6c, the charge measuring circuit can be configured using only one input / output port by reducing two ports.

  As described above, according to the conventional method, the voltage of the capacitor in which the charge is accumulated by the operational amplifier is AD converted to obtain the charge amount. However, in the charge amount measuring circuit according to the present invention, the capacitor voltage is kept constant. Since the amount of charge to be measured is calculated from the amount of charge in the storage, the voltage of the storage capacitor does not saturate, and high-resolution measurement is possible with a simple configuration that simply adds a power supply, resistor, capacitor, etc. to the digital circuit It is possible to realize a charge amount measuring circuit or a method thereof.

  In the first embodiment, the method for obtaining the amount of charge flowing into the voltage Vt is shown. In the second embodiment, as an application example, the charge amount measurement capable of measuring a minute capacitance used in an electrostatic touch panel or the like. The circuit will be described.

  When measuring minute capacitance or its change due to the approach of an object, it is difficult to obtain an accurate value from a single charge / discharge characteristic. Are also used, but these methods have a relatively large circuit scale.

  For this reason, for example, as shown in FIG. 8, the switch SW1 and the switch SW2 are alternately turned on after being initialized by the switch SW3 by switching the switch of a transistor or the like, and the charge repeatedly discharged to the measurement target Cx is electrostatic capacitance. Is accumulated in the known accumulation capacitor Cs, and a method of obtaining the capacitance of the measurement object from the number of times of charge / discharge to the measurement object until the voltage of the accumulation capacitor Cs becomes a predetermined voltage is disclosed (for example, patent Reference 1).

  This method is widely used because, for example, a minute electrostatic capacity can be measured simply by adding a constant component to a port of a general-purpose maciro computer.

  However, in this conventional method, as the number of times of charging / discharging the measurement target Cx is increased in order to increase the measurement resolution, the change in the voltage of the cumulative capacitor in one charging / discharging becomes smaller. Therefore, if the number of times of charging / discharging is increased to increase the resolution of detection, the voltage change of the accumulated capacitor becomes smaller than the accuracy of voltage measurement and cannot be measured, and the change is small relative to the capacitance of the measurement target. In some cases, there has been a problem that the amount of change cannot be measured accurately.

  The charge amount measuring circuit according to the second embodiment having the configuration shown in FIG. 7 can solve such a conventional problem. Here, the capacitance Cx to be measured may be not only the capacitance between the two terminals but also the floating capacitance of an object such as a detection electrode of an electrostatic touch panel. Here, the power storage means 1, the charge input / output means 2, the voltage measurement means 3, the first control means 4, and the first calculation means 5 are the same as those in the first embodiment. Therefore, the charge amount measurement circuit according to the second embodiment controls the operation of the CQ conversion unit 6 that converts the capacitance Cx to be measured into the charge amount Qx, and the operation of the CQ conversion unit 6 in addition to the charge amount measurement circuit according to the first embodiment. The second control means 7 is added, and the second calculation means 8 for calculating the capacitance of the measurement object from the charge amount from the first calculation means 5 and the control information from the second control means 7 is added. The configuration. Therefore, the CQ conversion means 6, the second control means 7 and the second calculation means 8 which are added in the second embodiment will be described in detail.

  The CQ conversion unit 6 converts the capacitance Cx to be measured into a charge amount Qx. For this reason, as shown in FIG. 9, for example, the CQ conversion unit 6 connects the capacitance Cx to be measured and the power storage unit Cs with a resistor Rc, and a connection point between the capacitance Cx to be measured and the resistor Rc. A constant voltage power supply Vc can be connected to the switch via the switch SWc. Here, the switch SWc is turned on / off by the second control means 7.

By connecting in this way, during the time Tc when SWc is on, the charge Qr shown in Equation 6 flows through the resistor Rc to the power storage means.
(Formula 6) Qr≈Tc × (Vc−Vt) ÷ Rc
Immediately after the switch SWc is turned off, the charge flowing because the voltage of the capacitance Cx to be measured changes from the voltage Vc of the constant voltage power supply to the voltage Vs of the storage means is proportional to the number Nc of times the switch SWc is turned off. Then, the charge amount Qc shown in Equation 7 flows to the power storage means.
(Expression 7) Qc≈Cx × (Vc−Vt) × Nc
Therefore, the measured charge amount Qx is the sum of these charge amounts as shown in Equation 8.
(Formula 8) Qx = Qr + Qc
Although an example of the CQ conversion means 6 has been described above, any means or method can be used as long as it is controlled by the second control means 7 and can convert the capacitance of the measurement object into the charge amount. good.

  The second control means 7 turns on / off the switch SWc a plurality of times during the charge amount measurement period Tt. In this case, the ON time may be a time required for the voltage of the capacitance Cx to be measured to change from the voltage Vs of the power storage means to the voltage Vc of the constant voltage power source. However, if the switch is turned on longer than necessary, the charge Qr shown in Equation 6 increases. However, since the charge Qr is not related to the capacitance, it is desirable not to make it longer than necessary. In addition, during the time when SWc is turned off, the charge moves from the capacitance Cx to be measured via the resistor Rc. For this reason, it is necessary to turn off SWc for a time sufficiently longer than the time constant determined by the capacitance Cx and the resistance Rc. Further, as the number of ON / OFF times Nc of SWc increases, the measurement accuracy of the capacitance Cx is improved.

The second calculation means 8 calculates the measured value of the capacitance Cx to be measured from the charge amount calculated by the first calculation means 5 and the control information by the second control means 7 by calculation. Here, Equation 9 is solved for Cx by substituting Equation 6 and Equation 7 into Qr and Qc of Equation 8, respectively.
(Equation 9) Cx≈ {Qx ÷ (Vc−Vt) −Tc ÷ Rc} ÷ Nc
In the second calculation means 8, the amount of charge obtained by the first calculation means 5 in Qx of Equation 9 is added to Tc, and the total that the second control means has turned on the switch SWc during the charge amount measurement period Tt. The time was calculated by substituting Nc for the number of times the second control means 7 turned on / off the switch SWc during the charge amount measurement period Tt to obtain the capacitance Cx to be measured. However, this is an example of calculation, and a constant part is calculated in advance, or the ON time Tt and ON / OFF count Nc of the switch SWc by the second control means in the measurement period Tt are set to predetermined conditions. The calculation of the second calculation means 8 is performed using the operation result of the CV conversion means and the calculation result from the first calculation means 5 such as referring to the table only from the charge amount obtained by the first calculation means. Any means or method may be used as long as the value corresponding to the target capacitance is obtained.

  Further, as shown in FIG. 9, the configuration obtained by removing the capacitance Cx to be measured from the CQ conversion unit is the same as that of a part of the charge input / output unit, and is connected via a resistor connected to the power storage unit. A constant voltage power source that is turned on and off by a switch controlled by the control means is connected. Therefore, as shown in FIG. 10, the charge input / output means 12 can be used instead of the CQ conversion means to convert the charge amount according to the capacitance Cx to be measured. Accordingly, the case of FIG. 10 will be described in detail. However, since the power storage means 1, voltage measurement means 3, and first calculation means 5 in FIG. 10 are the same as those shown in FIG. 7, the charge input / output means 12, the first control means 14, and the second calculation means. 18 will be described in detail.

The charge input / output unit 12 shown in FIG. 10 is substantially the same as the charge input / output unit 2 shown in FIGS. However, as shown in FIG. 11, since the capacitance Cx to be measured is connected, in addition to the charge amount Qa obtained by Equation 1, the capacitance from the capacitance Cx to be measured immediately after the switch SWp is turned off. The electric charge Qc calculated | required by 10 flows into an electrical storage means excessively. The charge measurement circuit is operated with the charge amount Qc as the charge amount Qx to be measured. Here, Np is the number of times the switch SWp of the charge input / output means is turned on / off.
(Expression 10) Qx = Qc≈Cx × (Vp−Vt) × Np
Also in this case, as shown in FIG. 12, the number of ports in the case of using general-purpose input / output ports can be reduced as in the case of the first embodiment.

  For example, as shown in FIG. 12a, if the voltage Vs of the storage means is measured by voltage measurement via the resistor Rp without using the switch SWm, the number of general-purpose ports can be reduced to one port. .

Further, even if the charge input / output means shown in FIG. 4g is applied, the number of general-purpose ports can be reduced to 1 as shown in FIG. 12b. However, in this case, immediately after the switch SWm is turned off, the capacitance Cx to be measured draws charges from the power storage means, so the amount of charge shown in Equation 11 is measured instead of Equation 10.
(Expression 11) Qx = Qc≈Cx × {(Vp−Vt) × Np− (Vt−Vm) × Nm}
However, in the configuration of FIG. 12b, for example, the threshold voltage Vt of the voltage measuring means is approximately halfway between the voltages Vp and Vm of the constant voltage power supply, and the time tp for turning on the switch SWp once and the time tm for turning on the switch SWm once are In the same case, the number Np of turning on / off the switch SWp and the number of turning Nm of turning on / off the switch SWm are almost the same, and the Qx in the equation 11 becomes almost zero. In order to avoid this problem, for example, the measurement is performed under the condition that Qx in Equation 11 does not become 0, such as setting the time tp for turning on the switch SWp once to several times the time tm for turning on the switch SWm once. You should do it.

  The first control means 14 shown in FIG. 10 is substantially the same as the first control means 4 shown in FIG. However, similar to the control timing of the switch SWc of the CQ conversion means 6 in FIG. 7, the charge moves from the capacitance Cx to be measured through the resistor Rp during the time when the switch SWp is turned off. SWp needs to be off for a time sufficiently longer than the time constant determined by Cx and resistance Rp.

The second calculation means 18 shown in FIG. 10 is substantially the same as the second calculation means shown in FIG. However, since there is no electric charge flowing to the power storage means via the time resistor Rc when the switch SWc in FIG. 9 is on, the equation becomes simpler, and the capacitance of the measurement target is obtained by Equation 12 obtained by solving Equation 10 for Cx. Is obtained by calculation. Here, the amount of charge calculated by the first calculating means 5 is substituted for Qx, and the number of times the first control means 14 turns on / off the switch SWp of the charge input / output means is substituted for Np. The same applies when Expression 11 is used.
(Equation 12) Cx≈Qx ÷ {(Vp−Vt) × Np}
However, this is an example of the calculation of the second calculation means 18, and the calculation of the second calculation means 18, such as calculating a constant part in advance or referring to a two-dimensional table by Qx and Np. If the value corresponding to the capacitance to be measured is obtained using the operation of the charge input / output unit 12 controlled by the first control unit 14 and the calculation result of the first calculation unit 5, Various means and methods may be used.

  Here, an example is shown in which the capacitance Cx to be measured is connected between the switch SWp and the resistor Rp, but it goes without saying that the same is true even if the capacitance is connected between the switch SWm and the resistor Rm.

  Further, for convenience of explanation of the second embodiment, the example in the case of performing the calculation for each of the first calculation means and the second calculation means has been described. For example, Qx obtained by substituting Qa of Formula 1 into Formula 5 is used. Needless to say, the calculations of the first calculation means and the second calculation means may be realized by substituting into Equation 11 and preliminarily gathered and realized by table reference, calculation, or the like.

  In the charge amount measurement circuit according to the second embodiment, the number of on / off times of the switch SWc for CQ conversion and the number of control cycles of the first control unit are set with a relatively simple configuration by simply adding a resistor or a capacitor to the logic circuit. It is possible to realize a charge amount measurement circuit capable of increasing the resolution of the capacitance to be measured as the number is increased.

  In the third embodiment, a charge amount measuring circuit for detecting a voltage change of an approaching object used for human body communication or the like will be described as another application example of the circuit and method for obtaining the amount of charge flowing into the voltage Vt shown in the first embodiment. .

  In the charge amount measurement circuit according to the third embodiment, a reception electrode that receives an electric field is connected as the measurement target charge Qx in FIG.

  Therefore, since the power storage unit 1, the charge input / output unit 2, the voltage measurement unit 3, the first control unit 4, and the first calculation unit 5 are the same as those in the first embodiment, the reception electrode 9 will be described.

  The receiving electrode 9 is disposed so as to be coupled to the approaching object 10 that changes the voltage by the capacitance Ce.

  The approaching object 10 changes its voltage Ve, and charges and discharges the electrostatic capacitance between the approaching object 10 and the receiving electrode 9.

Since the voltage Vs itself of the receiving electrode 9 is controlled so as to approach the threshold voltage Vt of the voltage measuring means 3, the electrostatic capacity Ce between the approaching object 10 and the receiving electrode 9 has a charge Qe shown in Formula 13. Is accumulated.
(Formula 13) Qe≈Ce × (Ve−Vt)
Here, when the voltage of the approaching object 10 increases by ΔVt, the approaching object 10 and the receiving electrode 9
The charge Qe accumulated in the electrostatic capacitance Ce between and increases by the charge amount ΔQx shown in Equation 14.
(Formula 14) ΔQe≈Ce × (ΔVt)
Strictly speaking, the positive charge is increased by ΔQe on the approaching object 10 side, and the negative charge is increased by ΔQe on the receiving electrode 9 side. The positive charge ΔQe for that flow flows into the power storage means and is measured as Qx.

Here, ΔQe flows because the capacitance Ce also fluctuates due to the change in the positional relationship between the approaching object 10 and the receiving electrode 9, but this change is sufficiently slower than the change in the received signal. It can be easily separated.

  Therefore, as in the first embodiment, by measuring the charge amount Qx, it is possible to detect a voltage change of an approaching object with high resolution with a simple configuration by simply adding a power source, a resistor, a capacitor, and the like to the digital circuit.

1 is a block diagram showing a first embodiment of a charge measuring circuit according to the present invention. Block diagram showing a conventional charge measurement circuit The figure which shows the electrical storage means of 1st Example The figure which shows the electric charge input / output means of 1st Example The figure which shows the example of a connection of the charge input / output means of 1st Example The figure which shows the other example of a connection of the input / output means of 1st Example The block diagram which shows the 2nd Example of the electric charge measurement circuit based on this invention Block diagram showing a conventional charge measurement circuit The figure which shows the example of a connection of the CQ conversion means of 2nd Example. The block diagram which shows the 2nd Example of the electric charge measurement circuit based on this invention The figure which shows the example of a connection of the charge input / output means of 2nd Example The figure which shows the other example of a connection of the input-output means of 2nd Example The figure which shows the example of a connection of the charge input / output means of 3rd Example Flow chart for explaining an example of a control operation cycle Diagram showing an example of correction flow

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power storage means 2, 12 Charge input / output means 3 Voltage measurement means 4, 14 First control means 5 First calculation means 6 CQ conversion means 7 Second control means 8, 18 Second calculation means 9 Reception electrode 10 Approaching object 20 Logic circuit

Claims (19)

A charge amount measurement circuit for measuring the amount of charge flowing with respect to a certain voltage, the storage means for inputting the charge to be measured and converting the accumulated charge amount into a voltage, and the charge stored in the storage means Charge input / output means for increasing / decreasing the amount, voltage measuring means for measuring the voltage of the power storage means, and the voltage of the power storage means within a constant voltage using the charge input / output means according to the measurement result of the voltage measurement means A charge amount measuring circuit, comprising: first control means for controlling in such a manner; and calculation means for calculating the amount of charge of the measurement object using control information from the first control means. A charge amount measurement circuit for measuring capacitance, comprising: a CQ conversion means for converting a capacitance to be measured into a charge amount; a charge input from the CQ conversion means and a stored charge amount as a voltage Power storage means for converting the power storage means, charge input / output means for increasing or decreasing the amount of charge stored in the power storage means, voltage measurement means for measuring the voltage of the power storage means, and the charge input / output means based on the measurement result of the voltage measurement means Control information from the first control means, first control means for controlling the power storage means so that the voltage of the power storage means falls within a certain voltage, second control means for controlling the operation of the CQ means, and control information from the first control means And a calculation means for calculating the capacitance of the measurement object by using the control information from the second control means. A charge amount measurement circuit for measuring electrostatic capacity, wherein the storage means for converting the accumulated charge amount into a voltage and the amount of charge stored in the storage means connected to the capacitance to be measured are increased or decreased. Charge input / output means, voltage measuring means for measuring the voltage of the power storage means, and the charge input / output means are used to control the voltage of the power storage means to be within a constant voltage based on the measurement result of the voltage measurement means. A charge amount measurement circuit comprising: a first control unit; and a calculation unit that obtains the capacitance of the measurement object by calculation using control information from the first control unit. A charge amount measuring circuit for detecting a change in voltage of an approaching object, a receiving electrode for converting the change in voltage of the approaching object into a charge amount, and inputting and storing the charge from the receiving electrode Storage means for converting the amount of charge stored into voltage, charge input / output means for increasing or decreasing the amount of charge stored in the storage means, voltage measurement means for measuring the voltage of the storage means, and the measurement result of the voltage measurement means First control means for controlling the voltage of the power storage means to be kept at a constant voltage using the charge input / output means, and change in voltage of the approaching object using control information from the first control means A charge amount measuring circuit comprising: an arithmetic means for calculating 5. The charge amount measuring circuit according to claim 1, wherein the charge input / output means includes a constant current power source and a switch that is turned on / off by the control means. 5. The charge amount measuring circuit according to claim 1, wherein the charge input / output unit includes a constant voltage power source, an electric resistance, and a switch that is turned on / off by the control unit. 5. The method according to claim 1, wherein the first calculation unit corrects the calculation of the charge amount of the measurement target by the operation of the first control unit when the charge of the measurement target is not input. The charge amount measuring circuit according to claim 1. The first control means starts and ends the measurement of the capacitance of the measurement object under the same conditions in which the measurement result of the voltage measurement means changes in a specific manner. 5. The charge amount measuring circuit according to any one of 4 above. 5. The charge amount measurement circuit according to claim 1, wherein the voltage measurement unit, the first and second control units, and the calculation unit are realized by a programmable device. 6. 3. The charge amount measurement circuit according to claim 2, wherein the CQ conversion unit includes a constant voltage source, a switch that is turned on / off by the second control unit, and a resistor. 7. The charge amount measuring circuit according to claim 6, wherein the voltage measuring means is connected to a connection point of an electric resistance of the charge input / output means and a switch that is turned on / off by the control means. The same condition under which the measurement result of the voltage measuring means changes in particular is that the switch with the smallest voltage change of the power storage means when turned on among the plurality of switches constituting the charge input / output means is turned on. The charge amount measuring circuit according to claim 8, wherein the charge amount measuring circuit is caused by a change due to the above. A charge amount measuring method for measuring the amount of charge flowing with respect to a certain voltage, the storage means for inputting the charge to be measured and converting the accumulated charge amount into a voltage, and the charge stored in the storage means Charge input / output means for increasing / decreasing the amount, voltage measuring means for measuring the voltage of the power storage means, and the voltage of the power storage means within a constant voltage using the charge input / output means according to the measurement result of the voltage measurement means A charge amount measuring method comprising: a first control step for controlling in such a manner; and a calculation step for calculating the amount of charge to be measured by calculation using control information from the first control step. A charge amount measuring method for measuring a capacitance, comprising: a CQ conversion means for converting a capacitance to be measured into a charge amount; a charge from the CQ conversion means as input; Power storage means for converting the power storage means, charge input / output means for increasing or decreasing the amount of charge stored in the power storage means, voltage measurement means for measuring the voltage of the power storage means, and the charge input / output means based on the measurement result of the voltage measurement means A first control step for controlling the voltage of the power storage means so as to fall within a constant voltage, a second control step for controlling the operation of the CQ means, and control information from the first control step And a calculation step of calculating the measurement target capacitance by calculation using the control information from the second control step. A charge amount measuring method for measuring an electrostatic capacity, wherein a storage means for converting an accumulated charge amount into a voltage, and an amount of charge stored in the storage means connected to the capacitance to be measured are increased or decreased. Charge input / output means, voltage measurement means for measuring the voltage of the power storage means, and the charge input / output means are used to control the voltage of the power storage means to be within a constant voltage based on the measurement result of the voltage measurement means. A charge amount measuring method comprising: a first control step; and a calculation step for calculating the capacitance of the measurement object by using control information from the first control step. A charge amount measuring method for detecting a change in voltage of an approaching object, a receiving electrode that converts the change in voltage of the approaching object into a charge amount, and a charge from the receiving electrode is input and accumulated. Storage means for converting the amount of charge stored into voltage, charge input / output means for increasing or decreasing the amount of charge stored in the storage means, voltage measurement means for measuring the voltage of the storage means, and the measurement result of the voltage measurement means A first control step of controlling the voltage of the power storage means to be a constant voltage using the charge input / output means, and a change in the voltage of the approaching object using control information from the first control step A charge amount measuring method, comprising: a calculation step for calculating the charge amount by calculation. 17. The method according to claim 13, wherein the first calculation step adds correction to the calculation of the charge amount of the measurement target by the operation of the first control step when the charge of the measurement target is not input. 2. The method for measuring a charge amount according to item 1. 14. The first control step starts and ends the measurement of the capacitance of the measurement target under the same conditions in which the measurement result of the voltage measuring unit changes in a specific manner. 17. The charge amount measuring method according to any one of 16 above. The same condition under which the measurement result of the voltage measuring means changes in particular is that the switch with the smallest voltage change of the power storage means when turned on among the plurality of switches constituting the charge input / output means is turned on. The charge amount measuring method according to claim 18, wherein the charge amount measuring method is due to a change caused by the above.

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