KR101001865B1 - Contactless sensor circuit - Google Patents

Abstract

The present invention provides a contactless sensor circuit. This sensor circuit can measure the electric potential of a measuring object in electrical and physical contact with a measuring object. The sensor circuit includes a measuring electrode for capacitively coupling with a measurement object, a coupling capacitor connected in series with the measuring electrode, a first negative input terminal and a first positive input terminal connected to the coupling capacitor and inputting a measurement signal to the first positive input terminal. And a first amplifier for amplifying the measured signal and outputting the measured signal to a first output terminal, and an impedance circuit connected between the first node and the first output terminal to increase an input impedance, wherein the first amplifier has its own input resistance Ri. And a self capacitance Ci, wherein the coupling capacitance of the coupling capacitor may be smaller than the equivalent capacitance formed by the measurement target and the measurement electrode.

Contactless sensors, potential sensors, biosignal amplifiers, high input impedance, low input capacitance

Description

Non-contact sensor circuit {CONTACTLESS SENSOR CIRCUIT}

The present invention relates to a sensor circuit. More structurally, it relates to a contactless sensor circuit.

In bioelectrical signal measurement, an electrode is attached to the skin of a subject for signal detection. It is connected to the signal amplifier using a wire connected to the electrode, and the signal sensed by the electrode is sufficiently amplified and measured. Here, the electrode causes the inconvenience of the measurement process and the discomfort of the subject. In addition, the electrode is also a major obstacle to the explosive demand for bioelectric signal utilization today. A solution to this problem is to implement a specific circuit capable of measuring a signal in a non-contact manner by including a signal amplifier with a much higher input impedance even when the signal source has a high impedance.

The present invention is derived from a study performed as part of the 21st century frontier R & D project of the Ministry of Education, Science and Technology [Task No.-M103KV010019-06K2201-01910, Task name: Development of brain-machine connecting device].

One technical problem to be solved by the present invention is to provide a non-contact sensor circuit that can measure the potential of the signal source without physically and / or electrically contacting the signal source.

The non-contact sensor circuit according to the exemplary embodiment of the present invention may measure the electric potential of the measurement target in electrical and physical non-contact with the measurement target. The sensor circuit includes a measurement electrode for capacitively coupling the measurement object, a coupling capacitor connected in series with the measurement electrode, a first negative input terminal, and a first positive input terminal connected to the coupling capacitor, and configured to measure the first signal with the first positive signal. A first amplifier which is input to an input terminal of the amplifier and amplifies the output signal and outputs it to a first output terminal, and an impedance circuit unit connected between the first node and the first output terminal to increase an input impedance; Includes a self input resistance Ri and a self capacitance Ci, and a coupling capacitance of the coupling capacitor may be smaller than an equivalent capacitance formed by the measurement object and the measurement electrode.

In one embodiment of the present invention, the first negative input terminal of the first amplifier may be connected to the first output terminal.

In one embodiment of the present invention, it may include a guard portion wrapped around at least one of the coupling capacitor and the measurement electrode and connected to the first output terminal.

In one embodiment of the present invention, a first node positioned between the first positive input terminal and the coupling capacitor of the first amplifier and the first output terminal of the first amplifier are connected to each other to stabilize the first amplifier. It may further comprise a bias circuit portion for providing an operation.

In example embodiments, the bias circuit part includes a bias resistor Rb connected between the first node and a fourth node, a fourth amplifier including a fourth output terminal connected to the fourth node, and the fourth node. And a capacitor (C) coupled between the fourth negative input terminal of the fourth amplifier and a resistor (R) coupled between the fourth negative input terminal of the fourth amplifier and the first output terminal of the first amplifier. The fourth positive input terminal of the fourth amplifier may be connected to a ground terminal.

In one embodiment of the present invention, the bias circuit portion may include an integrating circuit having a bias resistor and an inverting amplifier circuit providing a negative feedback through the bias resistor Rb.

In one embodiment of the present invention, the impedance circuit portion is connected between the first node and the first output terminal capacitive current circuit portion to reduce the effective input capacitance of the sensor circuit, and the first node and the first It may include at least one of the resistive current circuit portion connected between the output terminal to increase the effective input resistance of the sensor circuit.

In an embodiment of the present invention, the impedance circuit part includes a feedback capacitor Cf connected between the first node N1 and a third node N3, and a third output terminal connected to the third node N3. A third amplifier, a first resistor R1 connected between the third negative input terminal of the third amplifier and a ground terminal, and between the third node N3 and the third negative input terminal of the third amplifier. A second resistor R2 and a capacitor C1 connected in series, the third positive input terminal of the third amplifier is connected to the first output terminal of the first amplifier,

Can meet.

In an embodiment of the present invention, the impedance circuit part includes a feedback capacitor Cf connected between the first node N1 and a third node N3, and a third output terminal 435c connected to the third node N3. A third amplifier comprising a third amplifier, a first resistor R1 connected between the third negative input terminal and the ground terminal of the third amplifier, and a third negative terminal of the third node N3 and the third amplifier. A second resistor (R2) and a capacitor (C1) connected in series between the input terminals, wherein the third positive input terminal of the third amplifier is connected to the first output terminal of the first amplifier,

Can meet.

In one embodiment of the present invention, the impedance circuit portion includes a feedback resistor Rf connected between the first node N1 and the second node N2 and a second output terminal connected to the second node N2. A second amplifier, a first capacitor C1 connected between the second negative input terminal of the second amplifier and a ground terminal, and between the second node N2 and the second negative input terminal of the second amplifier. A resistor (R1) and a second capacitor (C2) connected in series, wherein a second positive input terminal of the second amplifier is connected to the first output terminal of the first amplifier,

Can meet.

In an example embodiment, the impedance circuit part includes a feedback resistor Rf connected between the first node N1 and the second node N2 and a second output terminal connected to the second node N2. A second amplifier, a first capacitor C1 connected between the second negative input terminal of the second amplifier and a ground terminal, and between the second node N2 and the second negative input terminal of the second amplifier. A resistor (R1) and a second capacitor (C2) connected in series, wherein a second positive input terminal of the second amplifier is connected to the first output terminal of the first amplifier,

Can meet.

In an embodiment of the present invention, the impedance circuit part includes a feedback capacitor Cf connected between the first node N1 and a third node N3, and a third output terminal connected to the third node N3. A third amplifier, a first resistor R1 connected between the third negative input terminal of the third amplifier and a ground terminal, and between the third node N3 and the third negative input terminal of the third amplifier. And a third resistor R2 and a capacitor C1 connected in series, and a third positive input terminal of the third amplifier may be connected to the first output terminal of the first amplifier.

In an example embodiment, the impedance circuit part includes a feedback resistor Rf connected between the first node N1 and the second node N2 and a second output terminal connected to the second node N2. A second amplifier, a first capacitor C1 connected between the second negative input terminal of the second amplifier and a ground terminal, and between the second node N2 and the second negative input terminal of the second amplifier. A resistor R1 and a second capacitor C2 connected in series may be included, and the second positive input terminal of the second amplifier may be connected to the first output terminal of the first amplifier.

 A sensor circuit according to an embodiment of the present invention provides a design guide of an amplifier, a method of increasing the effective input resistance of the sensor circuit, a method of reducing the effective input capacitance, and a bias method for correct operation of the amplifier. To provide. Accordingly, the sensor circuit can provide signal measurement in a non-contact manner for various signal sources. In particular, in bioelectrical signal measurement, signal measurement can be performed in a non-contact manner without an electrolyte electrode.

Moreover, contactless bioelectrical signal metrology can be avoided from the contact bioelectrical signal measuring method, which will greatly contribute to the activation of metrology equipment and industrialization in the field of bioelectrical signal measuring. The sensor circuit according to an embodiment of the present invention provides a theoretical and practical way in which bioelectrical signals such as brain waves and electrocardiograms can be measured without skin contact of electrodes. The sensor circuit according to an embodiment of the present invention can be utilized as a non-contact sensor in all electrical signal measurement as well as bioelectrical signal measurement.

The sensor circuit according to an embodiment of the present invention can provide the potential signal measurement without the electrical and physical contact from the voltage signal source. For example, the sensor circuit may be utilized for measuring bioelectrical signals. When the impedance of the signal source is large, the voltage signal of the signal source can be measured without loss when the input impedance of the amplifier of the sensor circuit is very high. When an operational amplifier (OP AMP) is used as the amplifier, the input impedance of the sensor circuit may be almost determined by the input impedance of the operational amplifier. In particular, the input impedance of the operational amplifier used in the bioelectric signal measurement field may be the input impedance of the sensor circuit. Thus, other circuit elements may contribute little to the increase in the impedance of the sensor circuit. Typically, in the field of contact bioelectrical signal metrology, the input impedance of the operational amplifier itself alone can achieve a lossless measurement.

The input impedance of the operational amplifier of the sensor according to an embodiment of the present invention can be controlled. That is, the input impedance of the sensor circuit may be determined regardless of the input impedance value of the operational amplifier itself.

The principle of measuring the potential of the voltage signal source without electrical and physical contact with the voltage signal source is described below.

[Physical situation of non-contact potential measurement]

1 is a view for explaining the operating principle of the sensor circuit according to an embodiment of the present invention. FIG. 2 is an equivalent circuit diagram of the sensor circuit of FIG. 1. FIG. 3 is a diagram illustrating a frequency characteristic of the sensor circuit of FIG. 2.

1 to 3, the electric potential (Vs) of the voltage signal source 102 may be capacitively coupled to the measuring electrode 103 in a non-contact manner. The measurement voltage Vm or the measurement signal induced in the measurement electrode 103 may be measured through the amplifier 106 having a gain A. The voltage signal source 102 and the measurement electrode 103 may form an electrically capacitive coupling. The capacitive coupling can be represented by measuring capacitor 104 having an equivalent capacitance Cs. The voltage signal source 102 and the amplifier 106 may be modeled with the equivalent capacitance Cs, its own input resistance Ri, and its own input capacitance Ci.

The amplifier 106 may amplify and output the measurement potential Vm of the measurement electrode 103 to the gain A. The amplifier 106 may be an operational amplifier. The measurement potential Vm may have the following relationship with the generation potential Vs of the voltage signal source 102.

Where ω is the angular frequency of the generation potential Vs of the voltage signal source 102. Considering the situation where the angular frequency is very large, Equation 1 may be expressed as follows.

g _m is a condition to obtain the maximum magnitude of the measurement potential (Vm).

The equivalent capacitance Cs may vary according to the non-contact distance and the opposing area of the voltage signal source 102 and the measurement electrode 103. Typically, the equivalent capacitance Cs may have a value of 1 pF or less. Meanwhile, the input capacitance Ci of the amplifier 106 may be about 10 pF. In this case, according to Equation 2, the measurement potential (Vm) may be less than 1/10 of the generation potential (Vs). Therefore, when the equivalent capacitance Cs is small and the self input capacitance Ci of the amplifier 106 is large, measurement of the measurement potential Vm in a non-contact manner is difficult. Moreover, when the signal frequency is low (1 Hz level), such as a bioelectric signal, the contactless measurement may be more difficult because the frequency characteristic is worse.

Referring to FIG. 3, the measurement potential Vm is the same as a high pass filter in terms of frequency dependency. The cut-off frequency (ω _c ) of the high pass filter may be given as follows.

When the equivalent capacitance Cs is 1pF and the amplifier's own input capacitance is 10pF, the self-input resistance of the amplifier 106 for obtaining the cutoff frequency ω _c of the high pass filter to 1 Hz is obtained. Ri) can be seen that the level of about 140TΩ according to equation (3). Typically, the self input resistance of the amplifier 106 is on the order of 1TΩ. Therefore, when the self input resistance Ri of the amplifier 106 has 100 TΩ or more and the self input capacitance Ci of the amplifier 106 has 1 pF or less, the measurement of the measurement potential Vs without contacting It may be possible.

[Effect of equivalent capacitance (Cs) between voltage signal source and measuring electrode]

There is a need to consider ways to reduce the effect of electrical coupling between the voltage signal source 102 and the measurement electrode 103 on the sensor circuit.

4 is a circuit diagram illustrating a sensor circuit according to another embodiment of the present invention.

Referring to FIG. 4, the sensor circuit may measure a potential of the measurement target by physically contacting the measurement target 102. The sensor circuit may include a first amplifier 106 and a coupling capacitor 112. The first amplifier 106 may include an input terminal 105 connected to a measurement electrode (not shown) which is capacitively coupled to the measurement object 102 to generate a measurement signal Vm. In order for the sensor circuit to be in physical contact with the measurement object, air, clothes, a dielectric, or the like may be interposed between the measurement electrode and the measurement object. The first amplifier 106 may include its own input resistance Ri and its own input capacitance Ci.

 The first amplifier 106 may receive the measurement signal Vm through the input terminal 105, amplify the measurement signal Vm, and output the amplified measurement signal Vm to the first output terminal 107. The coupling capacitor 112 may be connected between the measurement electrode and the input terminal 105 of the first amplifier 106. The coupling capacitance Cc of the coupling capacitor 112 may be smaller than the equivalent capacitance Cs formed by the measurement target 102 and the measurement electrode.

The equivalent capacitance Cs may vary depending on the extent to which the measurement electrode 103 is close to the voltage signal source 102. Accordingly, the measurement potential Vm may depend on the equivalent capacitance Cs. The dependence of the equivalent capacitance Cs on the measurement potential Vm may make measurement of the measurement potential Vm difficult. Since the change in the equivalent capacitance Cs occurring during the measurement process can be introduced into the noise, the capacitance Cs dependency needs to be suppressed. In order to reduce the equivalent capacitance Cs dependency, a coupling capacitor 112 connected between the equivalent capacitance Cs and the input terminal 105 of the first amplifier 106 may be disposed. The coupling capacitor 112 may have the coupling capacitance Cc. The total capacitance C _{T of} the coupled capacitor 112 and the equivalent capacitance Cs connected in series is always less than each capacitance. Therefore, when the coupling capacitance Cc is sufficiently smaller than the equivalent capacitance Cs, the total capacitance C _T is smaller than the coupling capacitance Cc, so that the equivalent capacitance Cs dependency is reduced. can do. The total capacitance C _T may be expressed as follows.

Here, it can be seen that if the coupling capacitance Cc is sufficiently smaller than the equivalent capacitance Cs, the total capacitance C _T is almost equal to the coupling capacitance Cc. That is, if this condition is satisfied, the effect of the equivalent capacitance Cs between the voltage signal source 102 and the measurement electrode on the measurement potential Vm can be ignored. For example, when the equivalent capacitance Cs is at a level of 1 pF, the coupling capacitance Cc may be at a level of 0.1 pF to ignore the dependency of the equivalent capacitance Cs.

[Increase input resistance of sensor]

The self input resistance Ri of the amplifier may be preferably 1 TΩ or more, and the self input capacitance Ci of the amplifier may be preferably 0.1 pF or less. Now, let's discuss how to achieve this high input resistance and this low capacitance.

5 is an equivalent circuit diagram of a sensor circuit according to another embodiment of the present invention.

Referring to FIG. 5, the sensor circuit may measure the potential of the measurement target by physically contacting the measurement target. The sensor circuit may include a first amplifier 106 and a coupling capacitor 112. The first amplifier 106 may include its own input resistance Ri and its own input capacitance Ci.

The first amplifier 106 includes a first positive input terminal 106a and a first negative input terminal 106b connected to a measurement electrode (not shown) which is capacitively coupled to the measurement object 102 to generate a measurement signal. can do. The first amplifier 106 may receive the measured voltage signal Vm through the first positive input terminal 106a to amplify the measured voltage signal Vm and output the amplified measurement voltage signal Vm to the first output terminal 107. The coupling capacitor 112 may be connected between the measurement electrode and the first positive input terminal 106a of the first amplifier 106. The coupling capacitance Cc of the coupling capacitor 112 may be smaller than the equivalent capacitance Cs formed by the measurement target 102 and the measurement electrode. The first negative input terminal 106b of the first amplifier 106 may be connected to the first output terminal 107.

The effective input resistance Ri of the sensor circuit is defined as a value obtained by dividing the measured voltage signal Vm by the measured current Im. For convenience, the input capacitance of the first amplifier 106 is considered to be absent. The measurement current Im may flow through the coupling capacitor 112.

As the measured current Im approaches zero, the effective input resistance Ri of the sensor circuit increases. The measurement current Im flows through the input resistance Ri of the first amplifier 106 by the measurement voltage signal Vm. Thus, the effective input resistance Ri of the sensor circuit may be its own input resistance Ri of the first amplifier 106. However, if a current flows in its own input resistance Ri of the first amplifier 106 by an impedance circuit 120 which provides another current instead of the measured current Im by the measured voltage signal Vm. The effective input resistance Ri of the sensor circuit may be modified. The impedance circuit unit 120 may include a resistance voltage source 20 for providing the feedback resistors 121 and Rf and the resistance feedback voltage Vrf.

The feedback resistors 121 and Rf lie between the self input resistance Ri of the first amplifier 106 and the resistance voltage source 20.

The current Ii flowing through the first input resistance Ri of the first amplifier is not the current Im due to the measurement potential Vm but may be a resistance current If by the resistance voltage source 20. have. In this case, the measurement current Im can be suppressed while maintaining the measurement voltage signal Vm. If this condition is satisfied, the input resistance Ri of the sensor circuit may be infinite in theory. The measurement current Im may be expressed as follows.

The measurement current Im may vary according to the magnitude of the potential Vrf of the resistance voltage source 20. The effective input resistance Ri of the sensor circuit can be expressed as follows.

In the condition that the effective input resistance Ri of the sensor circuit should be greater than or equal to zero, a limit condition of the resistance voltage source 20 may be given as follows.

In Equation 8, when the equal sign is established, the effective input resistance Ri of the sensor circuit may be infinite.

6 is a circuit diagram illustrating a sensor circuit according to another embodiment of the present invention.

The sensor circuit according to another embodiment of the present invention is an example of implementing Equation 7.

Referring to FIG. 6, the first amplifier 106 may be a voltage follower. The first negative input terminal 106b of the first amplifier 106 may be connected to the first output terminal 107 of the first amplifier 106. Since the first amplifier 106 is wired with a voltage flow, the measured voltage signal Vm may appear at the first output terminal 107 of the first amplifier 106 as it is. The impedance circuit unit 120 may include a feedback resistor Rf 121 and a resistor voltage source 20. The first node N1 may be located between the first positive input terminal 106a of the first amplifier 106 and the coupling capacitor 112. The first amplifier 106 may include its own input resistance Ri and its own capacitance Ci. The capacitance of the coupling capacitor 112 may be smaller than the equivalent capacitance Cs formed by the measurement target and the measurement electrode.

The feedback resistor Rf and 121 may be connected between the first node N1 and the second node N2. The resistance voltage source 20 may include a second amplifier 124, first resistors R1 and 123, and second resistors R2 and 122. The second amplifier 124 may be an operational amplifier. The resistance voltage source 20 may be a non-inverting amplifier circuit. The second positive input terminal 124a of the second amplifier 124 may be connected to the first output terminal 107 of the first amplifier 106. The second output terminal 124c of the second amplifier 124 may be connected to the second node N2. The second resistors R2 and 122 may be connected between the second node N2 and the second negative input terminal 124b of the second amplifier 124. The first resistors R1 and 123 may be connected between the second negative input terminal 124b of the second amplifier 124 and the ground terminal.

The second amplifier 124 may receive the output signal Vout of the first output terminal 107 of the first amplifier 106 and provide a positive feedback output signal Vrf. Considering the gain of the second amplifier 124, the effective input resistance Ri of the sensor circuit may be expressed as follows.

The effective input resistance Ri of the sensor circuit may depend on the resistors Rf, R1, and R2 of the impedance circuit unit 120. Referring to Equation 9, the effective input resistance Ri may be zero or more. Therefore, the impedance circuit unit 120 may have the following conditions.

In consideration of the error of the resistance values, the feedback resistor Rf and the self input resistance Ri of the first amplifier 106 preferably have similar magnitudes.

[Reduce input capacitance of sensor circuit]

The input capacitance of the sensor circuit can be reduced in a manner similar to the increase of the input resistance of the sensor circuit described above.

7 is a circuit diagram illustrating a sensor circuit according to another embodiment of the present invention.

For convenience, the first amplifier 106 does not have its own input resistance Ri.

Referring to FIG. 7, the first amplifier 106 may be a voltage follower. The first negative input terminal 106b of the first amplifier 106 may be connected to the first output terminal 107 of the first amplifier 106. Since the first amplifier 106 is wired with a voltage flow, the measured voltage signal Vm may appear at the first output terminal 107 of the first amplifier 106 as it is. Impedance circuitry 130 may include feedback capacitors 131 and Cf and capacitive voltage source 30. The first node N1 may be located between the coupling capacitor 112 and the first positive input terminal 106a of the first amplifier 106. The capacitance of the coupling capacitor 112 may be smaller than the equivalent capacitance Cs formed by the measurement target and the measurement electrode. The capacitive voltage source 30 may be connected in series with the feedback capacitors 131 and Cf to provide the capacitive feedback voltage Vcf.

The effective input capacitance Cie of the sensor circuit includes the amount of charge Qm accumulated in the first positive input terminal 106a of the first amplifier 106 by the measured voltage signal Vm and the measured voltage signal Vm. It can be defined as divided by.

When the measured charge amount Qm accumulated by the measured voltage signal Vm becomes zero, the effective input capacitance Cie of the sensor circuit may be zero. The measured charge amount Qm may be accumulated in the input capacitance Ci of the first amplifier 106 by the measured voltage signal Vm. Thus, the effective input capacitance Cie of the sensor circuit may be the input capacitance Ci of the first amplifier 106. However, the charge amount Qi accumulated in the input capacitance Ci of the first amplifier 106 is not due to the measured voltage signal Vm, but the potential Vcf and feedback of the other capacitance voltage source 30. It may be due to the capacitance (Cf, 131). In this case, the effective input capacitance Cie of the sensor circuit may be zero. The measured charge amount Qm may be expressed as follows.

The capacitive voltage source 30 and the feedback capacitors 131 and Cf may change the measured charge amount Qm accumulated in the first positive input terminal 106a of the first amplifier 106. The feedback capacitance Cf and the potential Vcf of the capacitance voltage source 30 may control the measured charge amount Qm. In this case, the effective input capacitance Cie of the sensor circuit may be expressed as follows.

The effective input capacitance Cie of the sensor circuit may be zero or more. Accordingly, the impedance circuit 130 may have the following conditions.

In this equation, when the equal sign is true, the effective input capacitance Cie of the sensor circuit may be zero.

8 is a circuit diagram illustrating a sensor circuit according to another embodiment of the present invention.

The sensor circuit according to another embodiment of the present invention is an example of implementing Equation 14.

Referring to FIG. 8, the first amplifier 106 may be a voltage follower. The first negative input terminal 106b of the first amplifier 106 may be connected to the first output terminal 107 of the first amplifier 106. Since the first amplifier 106 is connected with the voltage flow, the measured voltage signal Vm may be displayed at the first output terminal 107 of the first amplifier 106 as it is. The impedance circuit unit 130 may include a feedback capacitor Cf 131 and a capacitive voltage source 30. The first node N1 may be located between the first positive input terminal 106a of the first amplifier 106 and the coupling capacitor 112. The feedback capacitor Cf and 131 may be connected between the first node N1 and the third node N3. The capacitive voltage source 30 may be connected to the third node N3 to provide a capacitive feedback voltage Vcf. The impedance circuit unit 130 may reduce the effective input capacitance Cie of the sensor circuit.

The capacitive voltage source 30 may include a third amplifier 135, third resistors R3 and 134, and fourth resistors R4 and 133. The third amplifier 135 may be an operational amplifier. The capacitive voltage source 30 may be a non-inverting amplifier circuit. The third positive input terminal 135a of the third amplifier 135 may be connected to the first output terminal 107 of the first amplifier 106. The third output terminal 135c of the third amplifier 135 may be connected to the third node N3. The fourth resistors R4 and 133 may be connected between the third node N3 and the third negative input terminal 135b of the third amplifier. The third resistors R3 and 134 may be connected between the third negative input terminal 135b of the third amplifier 135 and the ground terminal.

The third amplifier 135 may receive the output signal Vout of the first output terminal 107 of the first amplifier 106 and provide a positive feedback output signal Vcf. Considering the gain of the third amplifier, the effective input capacitance Cie of the sensor circuit can be expressed as follows.

It can be seen that the effective input capacitance Cie of the sensor circuit is controlled by resistors R3 and R4 that determine the gain of the third amplifier providing positive feedback. The effective input capacitance of the sensor circuit may be zero or more. Therefore, the resistors R3 and R4 of the third amplifier may be limited as follows.

In consideration of the error of the resistance values, the feedback capacitance Cf and the input capacitance Ci of the first amplifier 106 preferably have a similar magnitude.

[Bias for Stable Operation of Operational Amplifiers]

The impedance circuit portion that increases the effective input resistance (Rie) of the sensor circuit or the impedance circuit portion that reduces the effective input capacitance (Cie) may not guarantee the normal operation of the sensor circuit. For stable operation of the sensor circuit, an input bias current path of the first amplifier 106 needs to be secured.

5 to 8 again, in order for the first amplifier 106 to operate stably, an input bias current path needs to be formed in a circuit. The impedance circuit unit may provide an input bias current path by gain determining resistors and a circuit wiring method. However, the input bias current path of the first amplifier 106 which performs the main function of the sensor circuit may not be guaranteed.

9 is a circuit diagram illustrating a sensor circuit according to another embodiment of the present invention.

Referring to FIG. 9, the first amplifier 106 may be a voltage follower. The first negative input terminal 106b of the first amplifier 106 may be connected to the first output terminal 107 of the first amplifier 106. Since the first amplifier 106 is connected with the voltage flow, the measured voltage signal Vm may be displayed at the first output terminal 107 of the first amplifier 106 as it is. The first node N1 may be located between the first positive input terminal 106a of the first amplifier 106 and the coupling capacitor 112. The first amplifier 106 may include its own input resistance Ri and its own capacitance Ci. The capacitance of the coupling capacitor 112 may be smaller than the equivalent capacitance Cs formed by the measurement target and the measurement electrode.

The bias circuit unit 140 may include an integration circuit including a negative feedback. The bias circuit unit 140 may include bias resistors Rb and 141, fourth amplifiers 144, integral resistors R and 143, and integral capacitors C and 142. The bias resistors Rb and 141 may be connected between the first node N1 and the fourth node N4. The integral capacitors C and 142 may be connected between the fourth node N4 and the fourth negative input terminal 144b of the fourth amplifier 144. The integration resistors R and 143 may be connected between the fourth negative input terminal 144b of the fourth amplifier 144 and the output terminal 107 of the first amplifier 106. The fourth output terminal 144c of the fourth amplifier 144 may be connected to the fourth node N4. The fourth positive input terminal 144a of the fourth amplifier 144 may be grounded.

The input bias current Ib of the first amplifier 106 may flow through its own input resistance Ri of the first amplifier 106. Accordingly, the DC offset voltage V _offset at the first positive input terminal 106a of the first amplifier 106 may be Ib x Ri. When the DC offset voltage V _offset is within a driving voltage Vcc of the first amplifier 106, the operation of the first amplifier 106 may be guaranteed. However, when a direct current fluctuation occurs in the output of the first amplifier 106, the operation of the first amplifier 106 may be unstable.

Although the bias current path by the feedback resistor may be considered, the feedback resistance value may have a value substantially equal to the input resistance Ri of the first amplifier 106, and thus, the first of the first amplifier 106. The DC offset voltage V _offset may be formed at the positive input terminal 106a.

In addition, since the input bias current Ib and the input resistance Ri may be different according to the first amplifier 106, the DC offset voltage V _offset is always the driving voltage of the first amplifier 106. Vcc) may not be guaranteed to be in the range. In addition, the DC offset voltage V _offset present in the first positive input terminal 106a of the first amplifier 106 may make the effective input resistance Rie of Equation 9 meaningless.

As the effective input resistance (Rie) of the sensor circuit is increased, the non-contact potential measurement according to the embodiment of the present invention may be enabled. However, when the DC offset voltage V _offset is present at the first positive input terminal 106a of the first amplifier 106, the output Vout of the first amplifier 106 may be saturated. Therefore, it is necessary to secure a separate input bias current path in order to stably operate the first amplifier 106 while keeping the effective input resistance Rie of the sensor circuit at a high value (theoretical infinity). have. For example, the bias circuit unit 140 may apply the first positive input terminal 106a of the first amplifier 106 to a reference potential (eg, to prevent the DC offset voltage V _offset ) from appearing at the first output terminal 107. For example, it can be maintained at 0 V). To this end, the bias circuit unit 140 may provide a negative feedback signal Vb. In addition, the feedback signal Vb may be provided to always maintain the reference potential regardless of the magnitude of the output Vout of the first amplifier 106. Thus, the bias circuit unit 140 may include an integration circuit.

 A positive (negative) DC offset voltage Voffset may be generated at the first output terminal 107 by the input bias current Ib of the first amplifier 106. In this case, the inflow (outflow) of the current through the integration resistors R and 143 of the fourth amplifier 144 of the bias circuit unit 140 may charge the integration capacitors C and 142. Accordingly, a negative voltage may be generated at the fourth output terminal 144c of the fourth amplifier 144. Subsequently, the fourth amplifier 144 may absorb (generate) the DC bias current Ib through the bias resistors Rb and 141. Therefore, generation of the DC offset voltage Voffset at the first positive input terminal 106a of the first amplifier 106 can be suppressed.

 Measurement current may also flow through the bias circuit unit 140. However, due to the frequency characteristic of the bias circuit unit 140, the high frequency component of the measurement current may not pass through the bias circuit unit 140. The resistance value R of the integration resistor 143 and the capacitance C of the integration capacitor 142 may be appropriately selected according to the frequency band of the signal. The 1 / RC value can be chosen to be much smaller than the angular frequency of the signal. Nevertheless, the bias resistor Rb 141 may affect the effective input resistance Ri of the sensor circuit. The configuration of the sensor circuit considering this effect is discussed.

[Sensor Circuit Configuration]

10 is a circuit diagram illustrating a sensor circuit according to another embodiment of the present invention.

 Referring to FIG. 10, the non-contact sensor circuit may measure the potential of the measurement object in electrical and physical contact with the measurement object. The sensor circuit may include a first amplifier 106 and a coupling capacitor 112.

The non-contact sensor circuit includes a measurement electrode capacitively coupled to the measurement object, a coupling capacitor 112 connected in series with the measurement electrode, a first negative input terminal and a first positive input terminal connected to the coupling capacitor, and a measurement signal ( A first amplifier 106 for receiving Vm) through the first positive input terminal 106a and amplifying the measured signal Vm to a first output terminal 107; and the first node N1 and the It may include an impedance circuit 150 is connected between the first output terminal 107 to increase the input impedance. The coupling capacitance Cc of the coupling capacitor 112 may be smaller than the equivalent capacitance formed by the measurement target and the measurement electrode.

The first amplifier 106 may include its own input resistance Ri and its own capacitance Ci. The first negative input terminal 106b of the first amplifier 106 may be connected to the first output terminal 107. The bias circuit unit 140 includes a first node N1 located between the first positive input terminal 106a of the first amplifier 106 and the coupling capacitor 112 and the first node of the first amplifier 106. It is connected between the first output terminal 107 can provide a stable operation of the first amplifier 106.

The impedance circuit unit 150 is connected between the first node N1 and the first output terminal 107 to reduce the effective input capacitance Cie of the sensor circuit. At least one of the resistive current circuit unit 120 connected between the first node (N1) and the first output terminal 107 to increase the effective input resistance (Rie) of the sensor circuit.

The resistive current circuit unit 120 includes a feedback resistor Rf and 121 connected between the first node N1 and the second node N2 and a second output terminal 124c connected to the second node N2. A second amplifier 124, a first resistor R1 and 123 connected between the second negative input terminal 124b of the second amplifier 124 and a ground terminal, and the second node N2 and the The second resistor 124 may include second resistors R2 and 122 connected between the second negative input terminal 124b of the second amplifier 124. The second positive input terminal 124a of the second amplifier 124 may be connected to the first output terminal 107 of the first amplifier 106. The resistive current circuit unit 120 may include a non-inverting amplifier circuit having a positive feedback. The second output terminal 124c of the second amplifier 124 may provide a resistance feedback potential Vrf.

The capacitive current circuit unit 130 includes a feedback capacitor Cf and 131 connected between the first node N1 and the third node N3 and a third output terminal 135c connected to the third node N3. And a third resistor 135 including a third resistor R3 and 134 connected between the third negative input terminal 135b and the ground terminal of the third amplifier 135, and the third node N3. Fourth resistors R4 and 133 connected between the third negative input terminal 135b of the third amplifier 135 may be included. The third positive input terminal 135a of the third amplifier 135 may be connected to the first output terminal 107 of the first amplifier 106. The capacitive current circuit unit may include a non-inverting amplifier circuit having a positive feedback. The third output terminal 135c of the third amplifier 135 may provide the capacitive feedback potential Vcf.

The bias circuit unit 140 includes a bias resistor Rb connected between the first node N1 and the fourth node N4, and a fourth output terminal 144c connected to the fourth node N4. A capacitor C, 142 connected between the amplifier 144, the fourth node N4 and the fourth negative input terminal 144b of the fourth amplifier 144, and the fourth of the fourth amplifier 144. It may include a resistor (R, 143) connected between the four negative input terminal 144b and the first output terminal 107 of the first amplifier 106. The fourth positive input terminal 144a of the fourth amplifier 144 may be connected to ground. The bias circuit unit 140 may include an integrating circuit including an inverting amplifying circuit having a negative feedback. The fourth output terminal 144c of the fourth amplifier 144 may provide a bias potential Vb.

Hereinafter, an operation according to the coupling of the bias circuit unit 140 and the impedance circuit unit 150 will be described.

The design conditions of the sensor circuit are shown through examples. In the above description, a large modification may be an effective input resistance Rie due to the introduction of the bias resistor Rb of the bias circuit unit 140. Referring to Equation 9, in view of the measured voltage signal Vm and the feedback resistor Rf, the bias resistor Rb may be regarded as being connected in parallel with the input resistance Ri of the first amplifier 106. have. In this case, the effective input resistance Rie of Equation 9 may be modified as follows.

Similarly, referring to Equation 10, the constraints of the resistors R1 and R2 that determine the gain of the second amplifier 124 which provides the feedback signal Vrf to the feedback resistor Rf are modified as follows. Can be.

Equations 15 and 16 associated with the feedback capacitor Cf may be useful as they are. That is, the bias circuit 140 may not affect the effective input capacitance Cie of the sensor circuit.

The guard unit 115 may be wrapped around the coupling capacitor 112 and / or the measuring electrode and connected to the first output terminal 107. The self input capacitance Ci of the first amplifier 106 may be modified by electrical wiring in an actual circuit wiring process. The self input resistance Ri of the first amplifier 106 may be modified by electrical wiring in an actual circuit wiring process. In order to reduce the influence of the electrical wiring, a guard 115 may be disposed in the signal input path. For example, if a potential different from the measurement voltage signal Vs is formed around the signal input line in the printed circuit board PCB, a leakage current due to the potential difference may be generated. The leakage current may affect the self input resistance Ri and the self input capacitance Ci of the first amplifier 106. In addition, the leakage current may modify the input bias current Ib of the first amplifier 106. To reduce this effect, the signal input line may be surrounded by a metal lead having a potential equal to the measured voltage signal Vs.

The driving signal of the guard unit 115 may be provided from the output signal Vout of the first amplifier 106. Accordingly, the first amplifier 106 may be protected by a guard unit in a low impedance state that suppresses the inflow of external noise. The guard unit 115 may be connected to a guard connection terminal 116 disposed around the signal input terminal 118. The guard connection terminal 116 may also serve as a guard of a measurement electrode (not shown) for signal detection. The input terminal unit 119 may include a signal input terminal 118, a reference ground terminal 117, and a guard connection terminal 116. The input terminal unit 119 may be configured to facilitate mounting of the measurement electrode.

  The frequency response characteristic of the output signal Vout of the sensor circuit with respect to the voltage signal Vs to be measured can be obtained as follows.

I denotes a complex number, ω denotes an angular frequency of the voltage signal Vs to be measured, Cc denotes a coupling capacitance, Cie denotes an effective input capacitance of the sensor circuit (see Equation 15), and Rb denotes a bias resistor. Where R is the integral resistance, C is the capacitance of the integrating capacitor, Rie is the effective input resistance of the sensor circuit (see Equation 17), and _o is the natural angular frequency of the sensor circuit. The natural angular frequency ω _o of the sensor circuit may be set to be much lower than the lowest frequency of the voltage signal Vs to be measured. In this case, the sensor circuit may operate as a high pass filter as shown in Equation 19. When the angular frequency ω of the voltage signal Vs to be measured is much larger than the natural angular frequency ω _o , the input / output signal size ratio may be approximated as follows, similar to Equation (1).

If Rie is replaced with Ri and Cie is replaced with Ci, equation (20) is the same as that of equation (1). However, the effective input capacitance Cie (see Equation 15) and the effective input resistance Rie (see Equation 17) may be adjusted by the capacitive current circuit unit 130 and the resistive current circuit unit 140, respectively. For example, the effective input capacitance Cie may be adjusted by gain resistance values R3 and R4 of the third amplifier 135 of the capacitive current circuit unit 130, and the effective input resistance ( Rie) may be controlled by gain resistance values R1 and R2 of the second amplifier 124 of the resistive current circuit unit 120. As a result, the sensor circuit can reduce the effective input capacitance Cie and increase the effective input resistance Ri, so that the sensor circuit can measure the potential of the measurement target in a non-contact manner.

The control of the effective input resistance Ri and the effective input capacitance Cie of the sensor circuit can widen the selection of the coupling capacitance 112. Accordingly, non-contact potential measurement may be possible regardless of the degree of capacitive coupling between the measurement object and the measurement electrode.

Hereinafter, a modified embodiment of the present invention will be described. The modified embodiment operates similarly to the sensor circuit described in FIG.

11 is a circuit diagram illustrating a sensor circuit according to another embodiment of the present invention.

Referring to FIG. 11, the non-contact sensor circuit may measure the potential of the measurement object in electrical and physical contact with the measurement object. The sensor circuit may include a first amplifier 106 and a coupling capacitor 112.

The non-contact sensor circuit includes a measurement electrode capacitively coupled to the measurement object, a coupling capacitor 112 connected in series with the measurement electrode, a first negative input terminal and a first positive input terminal connected to the coupling capacitor, and a measurement signal ( A first amplifier 106 for receiving Vm) through the first positive input terminal 106a and amplifying the measured signal Vm to a first output terminal 107; and the first node N1 and the It may include an impedance circuit unit 450 connected between the first output terminal 107 to increase the input impedance. The coupling capacitance Cc of the coupling capacitor 112 may be smaller than the equivalent capacitance formed by the measurement target and the measurement electrode.

The first amplifier 106 may include its own input resistance Ri and its own capacitance Ci. The first negative input terminal 106b of the first amplifier 106 may be connected to the first output terminal 107. The bias circuit unit 140 includes a first node N1 located between the first positive input terminal 106a of the first amplifier 106 and the coupling capacitor 112 and the first node of the first amplifier 106. It is connected between the first output terminal 107 can provide a stable operation of the first amplifier 106.

The measuring electrode may be mounted on the signal input end 118. The first negative input terminal 106b of the first amplifier 106 may be connected to the first output terminal 107. The sensor circuit may include an impedance circuit unit 450. The impedance circuit unit 450 may control the impedance of the sensor circuit.

The bias circuit unit 140 includes a bias resistor Rb connected between the first node N1 and the fourth node N4, and a fourth output terminal 144c connected to the fourth node N4. A capacitor C, 142 connected between the amplifier 144, the fourth node N4 and the fourth negative input terminal 144b of the fourth amplifier 144, and the fourth of the fourth amplifier 144. It may include a resistor (R, 143) connected between the four negative input terminal 144b and the first output terminal 107 of the first amplifier 106. The fourth positive input terminal 144a of the fourth amplifier 144 may be connected to ground. The bias circuit unit 140 may include an integrating circuit including an inverting amplifying circuit having a negative feedback.

The impedance circuit unit 450 may be connected between the first node and the first output terminal to increase an input impedance. The impedance circuit 450 includes a feedback capacitor Cf and 431 connected between the first node N1 and the third node N3 and a third output terminal 435c connected to the third node N3. A third resistor 435, a first resistor R1, 434 connected between the third negative input terminal 435b of the third amplifier 435 and a ground terminal, and the third node N3 and the third resistor; The third resistor 435 may include a second resistor (R2, 437) and a capacitor (C1, 436) connected in series between the third negative input terminal (435b). The third positive input terminal 435a of the third amplifier 435 may be connected to the first output terminal 107 of the first amplifier 106.

The effective input resistance Ri of the sensor circuit by the impedance circuit unit 450 may be obtained next instead of Equation 17.

By the condition that the effective resistance (Rie) value may be zero or more, the circuit element of the sensor circuit may have the following conditions.

This is a condition similar to the above expression (18).

The input capacitance Cie of the sensor circuit by the impedance circuit unit 450 is obtained next instead of equation (15).

Under the condition that the effective capacitance Cie may be equal to or greater than zero, the circuit element of the sensor circuit may have the following condition.

This is a condition similar to the above equation (16).

12 is a circuit diagram illustrating a sensor circuit according to another embodiment of the present invention.

Referring to FIG. 12, the non-contact sensor circuit may measure the potential of the measurement object in electrical and physical contact with the measurement object. The sensor circuit may include a first amplifier 106 and a coupling capacitor 112.

The non-contact sensor circuit includes a measurement electrode capacitively coupled to the measurement object, a coupling capacitor 112 connected in series with the measurement electrode, a first negative input terminal and a first positive input terminal connected to the coupling capacitor, and a measurement signal ( A first amplifier 106 for receiving Vm) through the first positive input terminal 106a and amplifying the measured signal Vm to a first output terminal 107; and the first node N1 and the An impedance circuit unit 550 connected between the first output terminal 107 to increase an input impedance may be included. The coupling capacitance Cc of the coupling capacitor 112 may be smaller than the equivalent capacitance formed by the measurement target and the measurement electrode.

The first amplifier 106 may include its own input resistance Ri and its own capacitance Ci. The first negative input terminal 106b of the first amplifier 106 may be connected to the first output terminal 107. The bias circuit unit 140 includes a first node N1 located between the first positive input terminal 106a of the first amplifier 106 and the coupling capacitor 112 and the first node of the first amplifier 106. It is connected between the first output terminal 107 can provide a stable operation of the first amplifier 106.

The measuring electrode may be mounted on the signal input end 118. The first negative input terminal 106b of the first amplifier 106 may be connected to the first output terminal 107. The sensor circuit may include an impedance circuit unit 550. The impedance circuit unit 550 may control the impedance of the sensor circuit.

The bias circuit unit 140 includes a bias resistor Rb connected between the first node N1 and the fourth node N4, and a fourth output terminal 144c connected to the fourth node N4. A capacitor C, 142 connected between the amplifier 144, the fourth node N4 and the fourth negative input terminal 144b of the fourth amplifier 144, and the fourth of the fourth amplifier 144. It may include a resistor (R, 143) connected between the four negative input terminal 144b and the first output terminal 107 of the first amplifier 106. The fourth positive input terminal 144a of the fourth amplifier 144 may be connected to ground. The bias circuit unit 140 may include an integrating circuit including an inverting amplifying circuit having a negative feedback.

The impedance circuit unit 550 may be connected between the first node and the first output terminal to increase an input impedance. The impedance circuit unit 550 includes a feedback resistor Rf 521 connected between the first node N1 and the second node N2, and a second output terminal 524c connected to the second node N2. A second amplifier 524, a first capacitor C1, 525 connected between the second negative input terminal 524b and the ground terminal of the second amplifier 524, and the second node N2 and the first node; It may include a resistor (R1, 522) and the second capacitor (C2, 526) connected in series between the second negative input terminal (524b) of the two amplifier (524). The second positive input terminal 524a of the second amplifier 524 may be connected to the first output terminal 107 of the first amplifier 106.

The effective input resistance Ri of the sensor circuit by the impedance circuit unit 550 can be obtained next instead of Equation 17.

Under the condition that the effective resistance (Rie) value may be zero or more, the circuit element of the sensor circuit may have the following condition.

This is a condition similar to the above expression (18).

The input capacitance Cie of the sensor circuit by the impedance circuit unit 550 is obtained next instead of the equation (15).

Under the condition that the effective capacitance Cie may be equal to or greater than zero, the circuit element of the sensor circuit may have the following condition.

This is a condition similar to the above equation (16).

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

1 is a view for explaining the operating principle of the sensor circuit according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the sensor circuit of FIG. 1.

FIG. 3 is a diagram illustrating a frequency characteristic of the sensor circuit of FIG. 2.

4 to 12 are circuit diagrams illustrating a sensor circuit according to embodiments of the present invention.

Claims (13)

In the non-contact sensor circuit for measuring the potential of the measurement object in electrical and physical non-contact with the measurement object, A measurement electrode capacitively coupled to the measurement object; A coupling capacitor connected in series with the measuring electrode; A first amplifier including a first negative input terminal and a first positive input terminal connected to the coupling capacitor, and receiving a measurement signal through the first positive input terminal and amplifying the measurement signal and outputting the measured signal to a first output terminal; And An impedance circuit portion connected between a first node and the first output terminal to increase an input impedance, The first amplifier includes a self input resistance Ri and a self capacitance Ci; The coupling capacitance of the coupling capacitor is smaller than the equivalent capacitance formed by the measurement object and the measurement electrode. According to claim 1, And said first negative input end of said first amplifier is coupled to said first output end. According to claim 1, And a guard portion wrapped around at least one of the coupling capacitor and the measurement electrode and connected to the first output terminal. According to claim 1, A bias circuit portion coupled between a first node positioned between the first positive input terminal of the first amplifier and the coupling capacitor and the first output terminal of the first amplifier to provide stable operation of the first amplifier Contactless sensor circuit. 5. The method of claim 4, The bias circuit portion: A bias resistor Rb coupled between the first node and a fourth node; A fourth amplifier including a fourth output terminal connected to the fourth node; A capacitor C coupled between the fourth node and a fourth negative input terminal of the fourth amplifier; And A resistor (R) coupled between the fourth negative input terminal of the fourth amplifier and the first output terminal of the first amplifier, And a fourth positive input terminal of said fourth amplifier is connected to a ground terminal. 5. The method of claim 4, And the bias circuit portion includes an integrating circuit having a bias resistor and an inverting amplification circuit providing a negative feedback through the bias resistor (Rb). According to claim 1, The impedance circuit portion: A capacitive current circuit portion connected between the first node and the first output terminal to reduce an effective input capacitance of the sensor circuit; And And at least one of a resistive current circuit portion connected between the first node and the first output terminal to increase an effective input resistance of the sensor circuit. The method according to claim 6, The impedance circuit portion: A feedback capacitor Cf connected between the first node N1 and a third node N3; A third amplifier including a third output terminal connected to the third node N3; A first resistor (R1) connected between the third negative input terminal and the ground terminal of the third amplifier; And A second resistor R2 and a capacitor C1 connected in series between the third node N3 and a third negative input terminal of the third amplifier, A third positive input terminal of the third amplifier is connected to the first output terminal of the first amplifier,

Meet and Rb is the bias resistor, and Ri is the self input resistor. According to claim 1, The impedance circuit portion: A feedback capacitor Cf connected between the first node N1 and a third node N3; A third amplifier including a third output terminal 435c connected to the third node N3; A first resistor (R1) connected between the third negative input terminal and the ground terminal of the third amplifier; And A second resistor R2 and a capacitor C1 connected in series between the third node N3 and a third negative input terminal of the third amplifier, A third positive input terminal of the third amplifier is connected to the first output terminal of the first amplifier,

Meet and Ci is a contactless sensor circuit, characterized in that the self input capacitance. The method according to claim 6, The impedance circuit portion: A feedback resistor Rf connected between the first node N1 and the second node N2; A second amplifier including a second output terminal connected to the second node N2; A first capacitor C1 connected between the second negative input terminal and the ground terminal of the second amplifier; And A resistor R1 and a second capacitor C2 connected in series between the second node N2 and the second negative input terminal of the second amplifier, A second positive input terminal of the second amplifier is connected to the first output terminal of the first amplifier,

Meet and Rb is the bias resistor, and Ri is the self input resistor. According to claim 1, The impedance circuit portion: A feedback resistor Rf connected between the first node N1 and the second node N2; A second amplifier including a second output terminal connected to the second node N2; A first capacitor C1 connected between the second negative input terminal and the ground terminal of the second amplifier; And A resistor R1 and a second capacitor C2 connected in series between the second node N2 and the second negative input terminal of the second amplifier, A second positive input terminal of the second amplifier is connected to the first output terminal of the first amplifier,

Meet and Ci is the self-capacitance, characterized in that the contactless sensor circuit. According to claim 1, The impedance circuit portion: A feedback capacitor Cf connected between the first node N1 and a third node N3; A third amplifier including a third output terminal connected to the third node N3; A first resistor (R1) connected between the third negative input terminal and the ground terminal of the third amplifier; And A second resistor R2 and a capacitor C1 connected in series between the third node N3 and a third negative input terminal of the third amplifier, And a third positive input terminal of the third amplifier is connected to the first output terminal of the first amplifier. According to claim 1, The impedance circuit portion: A feedback resistor Rf connected between the first node N1 and the second node N2; A second amplifier including a second output terminal connected to the second node N2; A first capacitor C1 connected between the second negative input terminal and the ground terminal of the second amplifier; And A resistor R1 and a second capacitor C2 connected in series between the second node N2 and the second negative input terminal of the second amplifier, And a second positive input terminal of the second amplifier is connected to the first output terminal of the first amplifier.

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