KR100699627B1 - Potential fixing device, potential fixing method, and capacitance measuring instrument - Google Patents

Abstract

Even when the potential of the connecting line between the first and second capacitances is fixed when the first and second capacitances are directly connected, the total amount of total charge of the connecting lines between the first and second capacitances is prevented from changing. It is possible to provide a potential fixing device that can be.

The potential holding device has a first high resistance 3 and a second high resistance 4, and also maintains the total amount of charge between the measured capacitance 14 and the fixed capacitance 15, And a voltage supply circuit 1 which maintains a constant in the signal line 17 connecting the 14 and the fixed capacitor 15 to each other. The output terminal 5 of the voltage supply circuit 1 is connected to the signal line 17.

Description

Potential fixation device, potential fixation method and capacity measuring device {POTENTIAL FIXING DEVICE, POTENTIAL FIXING METHOD, AND CAPACITANCE MEASURING INSTRUMENT}

The present invention relates to an electric potential fixing device, an electric potential fixing method, and a capacitance measuring device, and in particular, comprising an electric potential fixing device, an electric potential fixing method, and such an electric potential fixing device for fixing an electric potential of a connection line between a first capacitance and a second capacitance. It relates to a capacity measuring device.

Background Art Conventionally, a capacitance measuring device for measuring a capacitance when a value of capacitance changes at various frequencies such as a condenser microphone is known. 6 is a circuit diagram showing an example of a conventional capacitance measuring device. As shown in FIG. 6, the conventional capacitance measuring device includes an operational amplifier 112, an AC voltage generator 113, a measured capacitance 114, and a feedback resistor 116 as a feedback impedance. The feedback resistor 116 and the measured capacitance 114 are connected via the signal line 117. The signal line 117 is connected to one terminal of the operational amplifier 112. One end of the AC voltage generator 113 is connected to an electrode opposite to the side connected to the signal line 117 of the capacitor 114 to be measured. The other end of the AC voltage generator 113 is grounded.

Here, the capacitance 114 to be measured is to change the capacitance Cs thereof in accordance with the received physical quantity (acceleration, pressure, gas, light, sound waves, etc.). In addition, the AC voltage generator 113 is for generating an operation signal Vin applied to the capacitance 114 under measurement at the time of capacitance measurement.

In the capacitance measurement operation of the conventional capacitance measurement device shown in FIG. 6, when an operation signal (voltage: Vin) is generated from the AC voltage generator 113, the voltage Vin of the operation signal is applied to both ends of the measured capacitance 114. . As a result, current flows through the capacitance 114 to be measured. In this case, since the input impedance of the operational amplifier 112 is ideally infinite, all the current flowing through the capacitor 114 to be measured flows to the feedback resistor 116. Thereby, the output voltage Vout corresponding to the capacitance Cs of the measured capacitance 114 can be output from the signal output terminal 118. The capacitance Cs can be obtained by performing various signal processings based on the output voltage Vout of the detection signal.

In the conventional capacitance measuring device shown in Fig. 6, since the feedback resistor 116 is used as the feedback impedance, the output voltage Vout of the signal output terminal 118 has a frequency characteristic as expressed by the following expression (1). Throw it away.

Referring to Equation 1, Vi is the amplitude of the signal Vin from the AC power generator 113, and ωin is the angular velocity of the operation signal Vin. Cd is a standard dose value of the dose 114 to be measured, and ΔC and ωc are dose values and angular velocity of the dose change in the dose 144, respectively. In Equation 1, a term in which the angular velocity ωc of the capacitance change is proportional to the capacitance value ΔC of the capacitance change is included. For this reason, since the output voltage Vout becomes proportional to the frequency (ωc / 2π = fc) of the capacitance change, it has a frequency characteristic. Therefore, it is necessary to newly prepare a processing circuit so as not to have a frequency characteristic at a later stage. As a result, irrationality that a circuit scale becomes large arises.

Thus, a technique has been proposed in which the feedback impedance is constituted by a capacitor (capacitance) instead of a resistance. 7 is a circuit diagram showing such a capacitance measuring device. With reference to FIG. 7, in this capacitance measuring apparatus, the feedback impedance is comprised by the feedback capacitance 115. As shown in FIG. The output voltage Vout of this circuit is expressed by the following equation.

As shown in Equation 2 above, when the feedback impedance is constituted by the feedback capacitance 115 (capacity value: Cf), the charge accumulated at the capacitance Cs and the charge accumulated at the capacitance value Cf of the feedback capacitance 115 are Since it becomes equal, the charge amount of the signal line 117 can be made constant. As a result, the output voltage Vout does not include a term proportional to the angular velocity ωc. For this reason, since the circuit output does not depend on the capacitance change frequency, it is not necessary to newly prepare a processing circuit so as not to have a frequency characteristic at a later stage. As a result, the circuit scale can be prevented from increasing.

However, as shown in the technique shown in Fig. 7, when the feedback impedance is constituted by the feedback capacitance 115, no direct current flows through the signal line 117 located between the feedback capacitance 115 and the measured capacitance 114. Therefore, the signal line 117 is in an electrically floating state (floating state). For this reason, there is an absurdity that the potential of the signal line 117 becomes unstable and the circuit does not operate normally, such as when the circuit output is saturated with the power supply voltage.

In order to prevent the above-mentioned irrationality, as shown in FIG. 7, it is also possible to fix the potential of the signal line 117 by connecting the resistor 119 between the signal line 117 and the GND.

However, when the potential is fixed by the resistor 119 as described above, a current may flow in the resistor 119 at the time of capacitance measurement. In that case, since the charge amount of the signal line 117 changes, there is a problem that the sensitivity of the capacitance measuring device is lowered. For this reason, it was difficult to carry out capacity measurement correctly.

When Vin is applied to the measurement target 114, the signal line 117 is covered with a shield line (not shown), and after the shield line and the signal line 117 are coined by a virtual short circuit, Even if the shield line and the signal line 117 are dropped to GND, in the actual op amp (operational amplifier 112), the signal line 117 does not become GND, and the Vin signal is barely carried on the signal line 117. For this reason, since a parasitic capacitance generate | occur | produces between the shield line and the signal line 117, it was difficult to perform capacitance measurement correctly by the influence of the parasitic capacitance.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a first object of the present invention is to provide a potential fixing device capable of preventing a change in the amount of charge in a connection line between a first capacitance and a second capacitance. It is.

A second object of the present invention is to provide a capacitance measuring device capable of performing accurate capacitance measurement without lowering the sensitivity even when the potential of the connecting line between the first capacitance and the second capacitance is fixed.

It is a third object of the present invention to provide a potential fixing method capable of preventing the amount of charge at the connection line between the first capacitance and the second capacitance from changing.

Disclosure of the Invention

The potential fixing device in the first aspect of the present invention is a potential fixing device for fixing a potential of a connection line between two capacitances of a first capacitance and a second capacitance directly connected to the first capacitance, and is at least two. It has a high impedance and the voltage supply means which keeps the electric potential of the connection line between two capacitance | capacitances, maintaining the total total charge amount of a 1st capacitance | capacitance and a 2nd capacitance. The output terminal of the voltage supply means is connected to a connection line between two capacitors. In addition, the high impedance in the present invention can be realized by using the reverse bias characteristics of the diode and the off state of the transistor in addition to the high resistance.

In the potential fixing device in the first aspect, a voltage supply means for maintaining the potential of the connection line between the two capacitances while maintaining the total total charge amount between the first capacitance and the second capacitance is provided. By connecting the output terminal of the voltage supply means to the connection line between two capacitances, it is possible to prevent the amount of charge in the connection line between the first capacitance and the second capacitance from changing. In addition, by including at least two high impedances in the voltage supply means, it is possible to effectively prevent a part of the current flowing in the connection line between the two capacitances from flowing to the voltage supply means side by the high impedance. This also prevents the amount of charge in the connection line between the first capacitor and the second capacitor from changing. In this way, since the amount of charges at the connection line between the first capacitor and the second capacitor can be prevented from changing, for example, the capacitance measuring device fixes the potential at the connection line between the first capacitor and the second capacitor. Even in this case, the sensitivity of the capacitance measurement value does not decrease. As a result, accurate capacity measurement can be performed.

The potential fixing device in the second aspect of the present invention is a potential fixing device for fixing a potential of a connection line between a first capacitance and two capacitances of a second capacitance directly connected to the first capacitance, and includes at least two high voltages. It is provided with the voltage supply means which has an impedance and outputs the electric potential equivalent to the electric potential of the operation signal applied to a connection line. The output terminal of the voltage supply means is connected to a connection line between two capacitors.

In the potential holding device in the second aspect, a voltage supply means for outputting a potential equal to the potential of an operation signal applied to a connection line connecting the first capacitance and the second capacitance is provided, and the voltage supply means By connecting the output terminal to the connection line between the first capacitance and the second capacitance, the entry and exit of the connection line between the first capacitance and the second capacitance is eliminated, thereby preventing the total amount of total charge of the connection line from changing. can do. In addition, by including at least two high impedances in the voltage supply means, it is possible to effectively prevent a part of the current flowing through the connection line from flowing to the voltage supply means by the high impedance. By this, it is possible to prevent the total total charge of the connecting line from changing. In this way, since the charge amount of the connecting line between the first capacitor and the second capacitor can be prevented from changing, for example, even when the potential of the connecting line between the first capacitor and the second capacitor is fixed in the capacitance measuring device, The sensitivity of the capacitance measuring device does not decrease. As a result, accurate capacity measurement can be performed.

In the potential holding device in the first phase or the second phase, the voltage supply means preferably includes a first high resistance, a second high resistance directly connected to the first high resistance, and a first high resistance. And voltage divider means for outputting a potential divided by the resistor and the second high resistance. In addition, the "high resistance" in this invention is more than several Pa when the target capacitance is about 1pF and hundreds of MHz or more, and it is hundreds of Pa or more when the target capacitance is about 1pF and about several hundred Hz-1MHz. That is, "high resistance" means a resistor having a relatively high resistance value that is sufficiently large as compared to the impedance components of the first capacitance and the second capacitance. Thus, when the voltage supply means is configured to include voltage dividing means for outputting a potential divided by the first high resistance and the second high resistance, the resistance values of the first high resistance and the second high resistance are appropriately selected. By doing so, the output potential of the voltage supply means can be easily adjusted.

In the potential holding device in the first or second aspect, preferably, the voltage supply means comprises an amplifier, a predetermined voltage applying means, a first high resistance, a second high resistance, and an output terminal. One end of the first high resistance is connected to the amplifier, and one end of the second high resistance is connected to the other end of the first high resistance, and between the other end of the first high resistance and one end of the second high resistance. The output terminal is connected to the other end, and the other end of the second high resistance is connected to a predetermined voltage applying means. In such a configuration, the potential of the output terminal of the voltage supply means can be easily determined by determining the amplification degree of the amplifier, the resistance values of the first high resistance and the second high resistance, and the voltage values of the predetermined voltage application means. It is possible to control to a potential equal to the potential of the operation signal applied to the connection line between the first capacitor and the second capacitor.

In the capacitance measuring device including the potential holding device in the third aspect of the present invention, the potential holding device further includes a first operational amplifier, the first capacitance is a capacitance under test, and the connection line between the two capacitances is a signal line. And an input terminal of the first operational amplifier is connected to the signal line.

In the capacitance measuring device according to the third aspect, the potential fixing device having any one of the above-described configurations is configured, and the first capacitance of the potential fixing device is the measured capacity, and the two capacitances are measured. By using the connection line as a signal line, since a current does not flow in and out of a signal line, it can prevent that the total total charge amount of a signal line changes. Thereby, even when the potential of the signal line between the 1st capacitance | capacitance and the 2nd capacitance which comprise the capacitance | capacitance measured by a capacitance measuring apparatus is fixed, the sensitivity of a capacitance measuring apparatus does not fall. As a result, accurate capacity measurement can be performed.

In the capacitive measuring device comprising the potential holding device in the third aspect, preferably, the potential holding device further comprises a second operational amplifier, the output terminal of the second operational amplifier being connected to the second capacitance. have. If comprised in this way, a 2nd operational amplifier can be used as a current source.

A potential fixing method in the fourth aspect of the present invention is a potential fixing method for fixing a potential of a connection line between two capacitances of a first capacitance and a second capacitance directly connected to the first capacitance, wherein at least two The potential divided by the high impedance is used as the output potential, and the output potential is applied to the connection line between the two capacitances, and the output potential is fixed at the output potential without the entry and exit of the current.

In the potential fixing method in the fourth aspect, when fixing the potential of the connection line between the two capacitors, the output potential applied to the connection line between the two capacitors is fixed to the output potential with no current in and out of the connection line. As a result, it is possible to prevent the total amount of total charge at the connecting line between the first capacity and the second capacity from changing. In addition, it is effective by the high impedance that a part of the current flowing in the connection line between the first capacitance and the second capacitance flows toward the high impedance side by potential fixing by the output potential divided by using at least two high impedances. Can be prevented. By this, it is possible to prevent the total amount of total charge at the connecting line between the first capacity and the second capacity from changing. In this way, since the total amount of total charges at the connection line between the first capacitance and the second capacitance can be prevented from changing, for example, in the capacitance measuring device, the potential of the connection line between the first capacitance and the second capacitance is changed. Even when fixed, the sensitivity of the capacitance measuring device does not decrease. As a result, accurate capacity measurement can be performed.

The potential fixing method in the fifth aspect of the present invention is a potential fixing method for fixing a potential of a connection line between two capacitances of a first capacitance and a second capacitance directly connected to the first capacitance, and includes at least two The potential divided by the high impedance is used as the output potential, and the output potential is applied to the connection line between the two capacitances, and the output potential is equal to the potential of the operation signal applied to the connection line between the two capacitances. Set it to

In the potential fixing method in the fifth aspect, when the potential of the connecting line between the first capacitor and the second capacitor is fixed, an output potential applied to the connecting line is applied to the connection line between the two capacitors. By setting it to be equal to the potential, it is possible to prevent the total amount of total charge of the connection line between the two capacitances from changing. Further, by using the at least two high impedances, the potentials are fixed by the divided output potentials, whereby a part of the current flowing through the connection line can effectively be prevented by the high impedances. By this, it is possible to prevent the total total charge of the connecting line from changing. In this way, since the total amount of total charges of the connection lines between the two capacitances can be prevented from changing, for example, even when the potential of the connection line between the first capacitance and the second capacitance is fixed in the capacitance measuring apparatus, the capacitance measuring apparatus The sensitivity does not decrease. As a result, accurate capacity measurement can be performed.

In the potential fixation method in the fourth aspect or the fifth aspect, preferably, either one of the first dose and the second dose is used as the dose to be measured. In this way, capacity measurement can be easily performed.

1 is a circuit diagram showing a capacitance measuring device including a potential holding device according to Embodiment 1 of the present invention;

FIG. 2 is a circuit diagram showing an example of an internal configuration of an amplifier included in the potential holding device according to Embodiment 1 shown in FIG. 1;

3 is a circuit diagram showing a capacitance measuring device including a potential holding device according to Embodiment 2 of the present invention;

4 is a circuit diagram showing a capacitance measuring device including a potential holding device according to Embodiment 3 of the present invention;

5 is a circuit diagram showing a capacitance measuring device including a potential holding device according to Embodiment 4 of the present invention;

6 is a circuit diagram showing a capacitance measuring device in the case of using a resistor as a conventional feedback impedance;

FIG. 7 is a circuit diagram showing a capacitance measuring device when a capacitor (capacitance) is used as the feedback impedance in FIG.

Best Mode for Carrying Out the Invention

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described based on drawing.

(Example 1)

1 is a circuit diagram showing a capacitance measuring device including a potential holding device according to Embodiment 1 of the present invention. FIG. 2 is a circuit diagram showing an example of an internal configuration of an amplifier of the potential holding device of Embodiment 1 shown in FIG.

First, with reference to FIG. 1 and FIG. 2, the structure of the capacitance measuring apparatus containing the potential holding device which concerns on Example 1 is demonstrated. The capacitance measuring device of the first embodiment includes the operational amplifier circuit 12, the AC voltage generator 13, the measured capacitance 14 having the capacitance Cs, and the fixed capacitance 15 as the feedback impedance having the capacitance value Cf. ). The operational amplifier 12 is an example of the "first operational amplifier" of the present invention. In addition, the measured dose 14 is an example of the "first dose" or "second dose" of the present invention, and the fixed dose 15 is an example of the "first dose" or "second dose" of the present invention. .

The capacitance 14 and the fixed capacitance 15 are connected by a signal line 17. The signal line 17 is connected to one terminal of the operational amplifier circuit 12. In addition, this signal line 17 is an example of the "connection line" of this invention. One end of the AC voltage generator 13 is connected to an electrode opposite to the side of the capacitor 14 to be connected to the signal line 17. In addition, the signal output terminal 18 is connected to the electrode opposite to the side connected to the signal line 17 of the fixed capacitor 15. The other end of the AC voltage generator 13 is grounded in this embodiment, but may be connected to a DC component. In addition, the measured capacitance 14 changes the capacitance Cs of the capacitor 14 according to the received physical quantity (acceleration, pressure, gas, light, sound waves, etc.). In addition, the AC voltage generator 13 is for generating an operation signal Vin applied to the capacitor 14 to be measured at the time of capacitance measurement.

Here, in the capacitance measuring device of Example 1, the electric potential of the signal line 17 is fixed using the electric potential fixing device provided with the voltage supply circuit 1. In addition, the voltage supply circuit 1 is an example of the "voltage supply means" of this invention. The voltage supply circuit 1 includes an amplifier 2 having an amplification degree A, a first high resistance 3 having a resistance value of Ra1, and a second high resistance 4 having a resistance value of Ra2. . Ra1 of the first high resistance 3 and Ra2 of the second high resistance 4 both have a resistance value of 1 dB or more. In addition, this resistance value may be a resistance value which has a relatively high enough value compared with the approximate characteristic impedance value calculated | required from the frequency and detection capacitance used.

An AC voltage generator (separate power supply) 7 different from the AC voltage generator 13 is connected to the input side of the amplifier 2. One end of the first high resistance 3 is connected to the output side of the amplifier 2. The output terminal 5 is connected between the other end of the first high resistance 3 and one end of the second high resistance 4. The output terminal 5 of the voltage supply circuit 1 is connected to the signal line 17 at point P. FIG. The other end of the second high resistance 4 is provided with a terminal 6. A predetermined potential Vs is applied to the terminal 6. This terminal 6 is an example of the "predetermined voltage application means" of the present invention. In addition, the voltage Va divided by the resistance division by the first high resistance 3 and the second high resistance 4 is output from the output terminal 5.

In addition, the amplifier 2 has the structure shown in FIG. 2, for example. That is, the amplifier 2 includes an operational amplifier circuit 21, a resistor 22 having a resistance value of R1, and a resistor 23 having a resistance value of R2. An AC voltage generator 7 (see FIG. 1) is connected to the non-inverting input terminal of the operational amplifier circuit 21. In addition, a resistor 22 is connected between the output terminal of the operational amplifier circuit 21 and the inverting input terminal. In addition, a resistor 23 is connected between the inverting input terminal of the operational amplifier circuit 21 and GND. In this way, the amplifier 2 of the amplification degree A = (R1 + R2) / R2 can be obtained easily.

In the potential fixing method of the capacitance measuring device according to the first embodiment, the amplifier 2 such that the voltage Vin of the operation signal flowing through the signal line 17 and the voltage Va of the output terminal 5 of the voltage supply circuit 1 are equal. ), The resistance value Ra1 of the first high resistance 3, the resistance value Ra2 of the second high resistance 4, and the voltage Vs of the terminal 6 are determined. In addition, the amplification degree A of the amplifier 2 can be easily adjusted by suitably selecting the resistance values R1 and R2 of the resistors 22 and 23 shown in FIG.

In the capacitance measuring operation of the capacitance measuring device of the first embodiment shown in FIG. 1, when an operating signal (voltage: Vin) is generated from the AC voltage generator 13, the voltage Vin of the operating signal is equal to both ends of the measured capacitance 14. Takes on As a result, current flows through the capacitance 14 to be measured. In this case, since the input impedance of the operational amplifier 12 is ideally infinite, all of the current flowing through the capacitor 14 to be measured flows into the fixed capacitor 15. As a result, the output voltage Vout corresponding to the capacitance Cs of the measured capacitance 14 is output from the signal output terminal 18. By performing various signal processings based on the output voltage Vout of this detection signal, the capacitance Cs of the measured capacitance 14 can be obtained.

In the first embodiment, as described above, the voltage supply circuit 1 for applying the alternating voltage for fixing the potential is provided to the signal line 17 connecting the capacitor 14 and the fixed capacitor 15, and Since the electric potential of the output terminal 5 of the voltage supply circuit 1 is set to be equal to the electric potential Vin of the operation signal applied to the signal line 17, the entry and exit of the current to the signal line 17 is lost. It is possible to prevent the charge amount of the signal line 17 from changing.

In addition, by including the high impedance of the first high resistance 3 and the second high resistance 4 in the voltage supply circuit 1, a part of the current flowing in the signal line 17 is directed to the voltage supply circuit 1 side. The flowing can be effectively prevented by the high impedance. This also prevents the charge amount of the signal line 17 from changing.

In the first embodiment, as described above, since there is no charge injection or discharge to the signal line 17, it is possible to prevent the total amount of total charge of the signal line 17 from changing.

Here, the total total charge amount between the measured capacitance 14 and the fixed capacitance 15 will be described. As shown in FIG. 1, since the operation signal (voltage Vin) from the AC voltage generator 13 is constant, the voltage Vs applied to the measurement target capacitor 14 is also constant. However, since the dose 14 to be measured is a dose detection unit, the dose value Cs of the dose 14 to be changed is changed. The change in the capacitance value Cs of the capacitance 14 under measurement is the change in the charge amount Qs of the capacitance 14 under measurement. In Embodiment 1, as described above, since there is no charge injection or discharge to the signal line 17, the sum of the charge amount Qf accumulated in the fixed capacitance 15 and the charge amount Qs accumulated in the measured capacitance 14 is It is constant. For this reason, the increase and decrease of the charge amount Qs of the capacitance 14 to be measured is represented by the increase and decrease of the charge amount Qf of the fixed capacitance 15.

The change (increase or decrease) in the charge amount Qf of the fixed capacitor 15 is represented as a change (increase or decrease) in the voltage value Vf applied to the fixed capacitor 15 because the capacitance value Cf of the fixed capacitor 15 is constant. The output of the voltage value Vf applied to the fixed capacitor 15 is output from the signal output terminal 18 as Vout.

That is, in the capacitance measuring device of Example 1, although there is a charge transfer between the capacitance value Cs of the measured capacitance 14 and the capacitance value Cf of the fixed capacitance 15, the signal line 17 as described above. Since there is no charge injection or discharge, the total total charge amount between the measured capacitance 14 and the fixed capacitance 15 is constant. Thereby, the electric potential fixed to the signal line 17 is applied by the voltage supply circuit 1, while the total total charge amount between the capacitance 14 and the fixed capacitance 15 is kept constant. For this reason, even when the potential of the signal line 17 which connects the measurement capacitor 14 and the fixed capacitor 15 is fixed, the sensitivity of the capacitance measuring device does not decrease. As a result, accurate capacity measurement can be performed.

(Example 2)

3 is a circuit diagram showing a capacitance measuring device having a potential holding device including a voltage divider circuit according to Embodiment 2 of the present invention. Referring to FIG. 3, in the voltage supply circuit 1 of the second embodiment, in the configuration of the above-described first embodiment, the signal line 17 is replaced on the input side of the amplifier 2 in place of the AC voltage generator 7. The example in which the AC voltage generator 13 for applying the operation signal Vin is connected to is shown. In addition, the other structure of Example 2 is the same as that of Example 1 mentioned above.

In the second embodiment, as described above, the AC voltage generator 13 of the first embodiment is connected to the input side of the amplifier 2 by connecting the AC voltage generator 13 for applying the operation signal Vin to the signal line 17. Since 7) can be omitted, the circuit configuration can be simplified as compared with the first embodiment.

In the second embodiment, similarly to the first embodiment, the amplification degree A of the amplifier 2, the resistance value Ra1 of the first high resistance 3, the resistance value Ra2 of the second high resistance 4, and the terminal 6 By adjusting the voltage Vs), the voltage Va at the output terminal 5 of the voltage supply circuit 1 can be easily set to be equal to the voltage Vin of the operation signal of the signal line 17. Specifically, by setting the resistance values of the resistors 22 and 23 of the amplifier 2 shown in FIG. 2 to R1 = R2, the amplification degree A of the amplifier 2 is set to A = 2, Vs = 0V, By setting Ra1 = Ra2, the voltage Va of the output terminal 5 of the voltage supply circuit 1 can be set to Va = Vin.

Thus, by setting the voltage Va at the output terminal 5 of the voltage supply circuit 1 to be equal to the voltage Vin of the operation signal of the signal line 17, the signal line 17 similarly to Example 1 mentioned above. Since no current flows in and out, it is possible to effectively prevent the charge amount of the signal line 17 from changing. As a result, even when the potential of the signal line 17 is fixed by the capacitance measuring device, since the sensitivity of the capacitance measuring device does not decrease, accurate capacitance measurement can be performed.

(Example 3)

4 is a circuit diagram showing a capacitance measuring device including a potential holding device according to Embodiment 3 of the present invention.

First, with reference to FIG. 4, the structure of the capacitance measuring apparatus containing the potential holding device which concerns on Example 3 is demonstrated. In the third embodiment, the operational amplifier circuit 11 serving as the current source, the operational amplifier circuit 12 in the state of imagery and short circuit, the AC voltage generator 13, the measurement target 14, and the fixed The capacity 15 is provided. The operational amplifier 11 is an example of the "second operational amplifier" of the present invention. The capacitance 14 to be measured and the fixed capacitance 15 are connected by a signal line 17. The signal line 17 is connected to one input terminal of the operational amplifier circuit 12. The AC voltage generator 13 is also connected to the other input terminal of the operational amplifier circuit 12.

Here, in the third embodiment, the potential of the signal line 17 is fixed by using the potential fixing device provided with the voltage supply circuit 1. In addition, the structure of the voltage supply circuit 1 and the structure of the amplifier 2 contained in it are the same as that of Example 1 mentioned above. In other words, the voltage supply circuit 1 includes an amplifier 2 having an amplification degree A, a first high resistance 3 and a second high resistance 4. An AC voltage generator 7 different from the AC voltage generator 13 is connected to the input side of the amplifier 2. One end of the first high resistance 3 is connected to the output side of the amplifier 2. The other end of the first high resistance 3 is provided with an output terminal 5 of the voltage supply circuit 1. The output terminal 5 of the voltage supply circuit 1 is connected to the signal line 17. The other end of the second high resistance 4 is provided with a terminal 6. A predetermined potential Vs is applied to the terminal 6. In addition, the voltage Va divided by the resistance division by the first high resistance 3 and the second high resistance 4 is output from the output terminal 5.

In the potential fixing method of the capacitance measuring device according to the third embodiment, the amplifier 2 such that the voltage Vin of the operation signal flowing through the signal line 17 and the voltage Va of the output terminal 5 of the voltage supply circuit 1 are equal. ), The resistance value Ra1 of the first high resistance 3, the resistance value Ra2 of the second high resistance 4, and the voltage Vs of the terminal 6 are determined.

In the capacitance measurement operation of the capacitance measuring device of the third embodiment shown in FIG. 4, since the operational amplifier 12 is in a state of imagery and short circuit, the voltage Vin (operation signal) from the AC voltage generator 13 is a signal line ( 17). As a result, a current flows through both ends of the capacitance 14 to be measured. Then, the output voltage Vout corresponding to the capacitance Cs of the capacitance 14 to be measured is output from the signal output terminal 18. By performing various signal processes on the output voltage Vout, the capacitance Cs of the measured capacitance 14 is obtained.

In the third embodiment, as described above, the voltage supply circuit 1 for applying the alternating voltage for fixing the potential is provided to the signal line 17 connecting the capacitor 14 and the fixed capacitor 15. Since the electric potential of the output terminal 5 of the voltage supply circuit 1 is set to be equal to the electric potential Vin of the operation signal applied to the signal line 17, the entry and exit of the current to the signal line 17 is lost. It is possible to prevent the charge amount of the signal line 17 from changing. In addition, by including the high impedance of the first high resistance 3 and the second high resistance 4 in the voltage supply circuit 1, a part of the current flowing in the signal line 17 is supplied to the voltage supply circuit 1 side. Flowing in can be effectively prevented by the high impedance. This also prevents the charge amount of the signal line 17 from changing. As a result, in the capacitance measuring apparatus of Example 3, even if the potential of the signal line 17 connecting the measured capacitance 14 and the fixed capacitance 15 is fixed, the sensitivity of the capacitance measuring apparatus does not decrease. Accurate dose measurement can be performed.

(Example 4)

5 is a circuit diagram showing a capacitance measuring device having a potential holding device including a voltage supply circuit according to a fourth embodiment of the present invention. Referring to FIG. 5, in the voltage supply circuit 1 of the fourth embodiment, in the configuration of the above-described third embodiment, the signal line 17 is replaced on the input side of the amplifier 2 in place of the AC voltage generator 7. The example in the case where the AC voltage generator 13 for applying the operation signal Vin is connected is shown. In addition, the other structure of Example 4 is the same as that of Example 3. As shown in FIG.

In the fourth embodiment, as described above, the AC voltage generator 13 of the third embodiment is connected to the input side of the amplifier 2 by connecting the AC voltage generator 13 for applying the operation signal Vin to the signal line 17. Since 7) can be omitted, the circuit configuration can be simplified as compared with the third embodiment.

Further, in the fourth embodiment, similarly to the third embodiment, the amplification degree A of the amplifier 2, the resistance value Ra1 of the first high resistance 3, the resistance value Ra2 of the second high resistance 4 and the terminal 6 By adjusting the voltage Vs), the voltage Va at the output terminal 5 of the voltage supply circuit 1 can be easily set to be equal to the voltage Vin of the operation signal of the signal line 17. Specifically, by setting the resistance values of the resistors 22 and 23 of the amplifier 2 shown in FIG. 2 to R1 = R2, the amplification degree A of the amplifier 2 is set to A = 2, and Vs = 0V. By setting Ra1 = Ra2, the voltage Va of the output terminal 5 of the voltage supply circuit 1 can be easily set to the voltage Vin and the coincidence of the operation signal of the signal line 17.

Thus, by setting the voltage Va at the output terminal 5 of the voltage supply circuit 1 to be equal to the voltage Vin of the operation signal of the signal line 17, the signal line 17 similarly to Example 3 mentioned above. Since no current flows in and out, it is possible to effectively prevent the charge amount of the signal line 17 from changing. As a result, even when the potential of the signal line 17 is fixed by the capacitance measuring device, since the sensitivity of the capacitance measuring device does not decrease, accurate capacitance measurement can be performed. For example, when Cs = 20pF, Cf = 1pF, amplifier amplification degree A = 2, and Vin is set to 500mV and several tens of mVrms, Ra1 = Ra2 = 1mV, the voltage sensitivity at Cs is-. On the other hand, when Ra1 = Ra2 = 100 ms, it is -5 ms and an improvement of about 10 ms is seen.

In addition, it should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is shown not by the description of the above embodiments but by the claims, and includes all changes within the scope and meaning equivalent to the scope of the claims.

For example, in the said embodiment, although the 1st high resistance 3 and the 2nd high resistance 4 were used as the high impedance of the voltage supply circuit 1, this invention is not limited to this, As a high impedance, For example, the reverse bias characteristic of the diode may be used, or the off state of the transistor may be used.

In addition, although the said Example demonstrated the capacitance measuring apparatus which has a circuit structure shown to FIG. 1, FIG. 3, FIG. 4 and FIG. 5, this invention is not limited to this, The same also applies to the capacitance measuring apparatus which has another circuit structure. Applicable

Moreover, in the said Example, although the case where the electric potential of the signal line 17 which connects the to-measured capacitance 14 and the fixed capacitance 15 in a capacitance measurement apparatus was demonstrated, this invention is not limited to this, It is also widely applicable to the case where the potential of the device other than the capacitance measuring device including the circuit configuration in which the first capacitor and the second capacitor are directly connected are fixed.

As described above, according to the present invention, when the potential of the connection line between the first capacitor and the second capacitor is fixed, it is possible to prevent the charge amount of the connection line between the first capacitor and the second capacitor from changing. As a result, even when the potential of the connecting line between the first capacitance and the second capacitance is fixed in the capacitance measuring device, for example, since the sensitivity of the capacitance measuring device does not decrease, accurate capacitance measurement can be performed.

As described above, the potential holding device, the potential holding method, and the capacitance measuring device according to the present invention are useful as circuits and devices for detecting capacitance, and in particular, capacitances whose capacitances change at various frequencies such as condenser microphones. It is suitable as a detection circuit and a detection device of a type sensor.

Claims (9)

A potential fixing device for fixing a potential of a connection line between a first capacitor and two capacitors of a second capacitor directly connected to the first capacitor, And a voltage supply means having at least two high impedances and maintaining a potential of the connection line between the two capacitances while maintaining a total total charge amount between the first capacitance and the second capacitance, An output terminal of the voltage supply means is connected to a connection line between the two capacitances, The voltage supply means, A first high resistance as the two high impedances and a second high resistance directly connected to the first high resistance, And voltage dividing means for outputting a potential divided by the first high resistance and the second high resistance. Potential fixing device. A potential fixing device for fixing a potential of a connection line between a first capacitor and two capacitors of a second capacitor directly connected to the first capacitor, A voltage supply means having at least two high impedances and outputting a potential equal to a potential of an operation signal applied to the connection line; An output terminal of the voltage supply means is connected to a connection line between the two capacitances, The voltage supply means, A first high resistance as the two high impedances and a second high resistance directly connected to the first high resistance, And voltage dividing means for outputting a potential divided by the first high resistance and the second high resistance. Potential fixing device. delete The method according to claim 1 or 2, The voltage supply means further includes an amplifier, a predetermined voltage applying means, and the output terminal, One end of the first high resistance is connected to the amplifier, The other end of the first high resistance and one end of the second high resistance are connected, The output terminal is connected between the other end of the first high resistance and one end of the second high resistance, The other end of the second high resistance and the predetermined voltage application means are connected. Potential fixing device. A capacity measuring device comprising the potential holding device according to claim 1 or 2, The potential holding device further comprises a first operational amplifier, The first dose is the dose to be measured, The connection line between the two capacitances is a signal line, The input terminal of the first operational amplifier is connected to the signal line. Capacity measuring device. The method of claim 5, wherein The potential holding device further comprises a second operational amplifier, An output terminal of the second operational amplifier is connected to the second capacitance Capacity measuring device. A potential fixing method for fixing a potential of a connection line between a first capacitor and two capacitors of a second capacitor directly connected to the first capacitor, The output potential is applied to the connection line between the two capacitances, with the potential divided by using at least two high impedances as the output potential, and the output potential is applied to an output potential at which the current does not enter the connection line. Fixed, A potential divided by the first high resistance as the two high impedances and the second high resistance directly connected to the first high resistance is applied as the output potential to the connection line. Potential fixation method. A potential fixing method for fixing a potential of a connection line between a first capacitor and two capacitors of a second capacitor directly connected to the first capacitor, An operation in which the output potential is applied to the connection line between the two capacitances, and the output potential is applied to the connection line between the two capacitances, with the potential divided by using at least two high impedances as the output potential. Is set equal to the potential of the signal, A potential divided by the first high resistance as the two high impedances and the second high resistance directly connected to the first high resistance is applied as the output potential to the connection line. Potential fixation method. The method according to claim 7 or 8, A potential fixing method using either the first dose or the second dose as a dose to be measured.

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