JP2009049711A - Circuit device for converting minute-amplitude alternating current signal to large-amplitude voltage signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the performance of a circuit device which converts a minute-amplitude alternating current signal to a large-amplitude voltage signal using an integration circuit. <P>SOLUTION: An output voltage from an integration circuit operational amplifier is stored in a first capacitor 6 at a first phase in a period of an input alternating current signal, and the output voltage from the integration circuit operational amplifier is stored in a second capacitor 8 at a second phase with a shift of 180 degrees from the first phase. Then, the stored voltages of the first capacitor 6 and the second capacitor 8 are read to be added at a third phase, and a stored voltage of a third capacitor 10 is subtracted from the added voltage. The voltage that is the subtraction result is stored in the third capacitor 10, and a correction current is inputted as an inverting input of the integration circuit operational amplifier based on the stored voltage of the third capacitor 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention takes a small amplitude alternating current signal output from a capacitance type sensor, a piezoelectric element type sensor or the like as an input, converts it into a large amplitude voltage signal, outputs it, and performs AD conversion / microcomputer circuit, etc. In particular, the present invention relates to a circuit technology for realizing highly accurate and stable operation with a simple configuration.

  For example, in vibratory gyros disclosed in JP-A-4-324311, JP-A-5-96629, JP-A-8-29178, JP-A-11-142157, etc., they are excited at a constant period. An alternating current signal with a minute amplitude is output from the piezoelectric element type sensor. The output waveform is a sine wave synchronized with the excitation period.

  As is well known, it is necessary for a vibrating gyroscope to detect a change in the maximum amplitude value or peak-to-peak value of a sensor output with high accuracy. For this purpose, the sensor output is usually amplified with high accuracy and high stability by a pre-processing circuit called a sense amplifier and supplied to the subsequent AD conversion / microcomputer circuit.

=== Introduction part of the invention ===
The above preprocessing circuit corresponds to a circuit device that is an object of the present invention. As is well known to engineers in this field, it is not easy to realize a highly accurate and highly stable circuit that converts an alternating current signal having a small amplitude into a voltage signal having a large amplitude. The smaller the input signal, the greater the difficulty.

  As a rational circuit for amplifying a minute alternating current signal having a positive / negative symmetrical waveform such as a sine wave, the well-known integration circuit shown in FIG. This integrating circuit has a simple configuration including an operational amplifier and a capacitor, and a large gain can be obtained.

  As shown in FIG. 1, for example, when a sine wave AC current signal from a piezoelectric element type sensor is applied to an inverting input of an integration circuit operational amplifier via an input resistor, an AC voltage signal of cosine wave obtained by integrating the input is output from the operational amplifier. Is output. As is well known, the gain is inversely proportional to the product of the input resistance value and the feedback capacitor capacitance value, and the change in the maximum amplitude value of the input signal is faithfully reflected in the maximum amplitude value of the output signal.

=== Problems to be solved by the invention ===
The integration circuit of FIG. 1 operates as described above in an ideal state where the disturbance is completely ignored. In the ideal state, the symmetry of the positive half wave and the negative half wave of the input signal is maintained, and the charge stored in the feedback capacitor becomes zero every period of the input signal. However, when actually testing with the circuit shown in FIG. 1, it is obvious that leakage current due to external factors will flow into and out of the operational amplifier, and that there are offsets in the operational amplifier. Positive and negative symmetry is not maintained.

  In other words, since the input waveform is symmetrical, the stored charge in the feedback capacitor becomes zero for each period. However, when a very weak DC level leakage current is added to or subtracted from the input current due to a disturbance factor, the positive or negative DC input component is integrated, and the center line of the cosine wave of the integrated output is not zero volts, and positive or negative Swinging to one side, the operational amplifier will soon saturate positively or negatively. Even if the leakage current and the offset are minimal, it is assumed that the input signal is a current signal with a very small amplitude. Therefore, if no measures are taken, it is inevitable that the operational amplifier will be saturated.

=== Known measures ===
As a countermeasure, a countermeasure A for connecting a high resistance in parallel with the feedback capacitor and a countermeasure B for short-circuiting the feedback capacitor at an appropriate interval in accordance with the zero cross point of the input signal are known. In either case, the integrated charge due to the direct current component does not accumulate in the feedback capacitor.

  Measure A is not preferred because it requires a high resistance that cannot be built into the IC and that the high resistance itself becomes a noise source. Measure B is difficult to detect before amplifying the zero-cross point of a minute input signal, and if there is no environment that can obtain a signal synchronized with the phase of the input signal by another method, Measure B should be adopted. I can't.

=== Prerequisites for Invention ===
In the circuit device premised on the following items (a) to (c), a new countermeasure different from the above-described known countermeasures A and B is taken by the drift correction circuit.
(A) a circuit device that includes an integration circuit and a drift correction circuit and converts a small amplitude alternating current signal input from a signal source into a large amplitude voltage signal; and (b) the alternating current signal has a constant period. (C) The integrating circuit has an operational amplifier in which a signal source is connected to an inverting input, an inverting input and an output of the operational amplifier. Provide a feedback capacitor to be connected and output a voltage signal obtained by integrating an alternating current signal input from a signal source

=== Operation principle of new countermeasures ===
The drift correction circuit according to the present invention stores the output voltage of the integrating circuit operational amplifier at two points separated by a half cycle of the alternating current signal. The stored voltage is called a first voltage value and a second voltage value. Since the alternating current signal to be input is “the current absolute values at two points different in phase by 180 degrees within one period are equal”, the first voltage value and the second voltage can be obtained if the positive / negative symmetry of the integration operation is maintained. Adds the value to zero. This state is referred to as having zero deviation.

  If the positive / negative symmetry of the integration operation is not maintained, the addition result of the first voltage value and the second voltage value (this is regarded as a deviation) does not become zero. Based on this deviation, the drift correction circuit applies a correction current or charge to the inverting input of the integration circuit operational amplifier, and executes feedback control in a direction in which the deviation is suppressed.

=== Gist of the first invention ===
The circuit device according to the first aspect of the invention is specified by the following items (1) to (8).
(1) A circuit device that includes an integration circuit and a drift correction circuit, and converts a minute amplitude alternating current signal input from a signal source into a large amplitude voltage signal. (2) The alternating current signal has a constant period. (2) The integrating circuit has an operational amplifier in which a signal source is connected to the inverting input, and the inverting input and output of the operational amplifier. (4) The drift correction circuit stores the voltage in each of the first to third capacitors and each capacitor and stores the voltage signal obtained by integrating the alternating current signal input from the signal source. A first to a third peripheral circuit for reading a voltage, and a control circuit for controlling the operation timing of each peripheral circuit in a unified manner. (5) The control circuit has a first cycle of an alternating current signal. (6) The control circuit stores the output voltage of the integration circuit in the second capacitor in a second phase that is 180 degrees out of phase with the first phase. (7) The control circuit reads and adds the storage voltage of the first capacitor and the storage voltage of the second capacitor in the third phase of the cycle of the alternating current signal, and stores the storage voltage of the third capacitor from the addition voltage. Subtract the voltage and store the voltage of the subtraction result in the third capacitor. (8) The storage voltage of the third capacitor gives a correction current to the inverting input of the integrating circuit operational amplifier.

=== Configuration and Operation of the First Embodiment ===
FIG. 2 shows the configuration of one embodiment of the first invention, and FIG. 3 shows the operation timing thereof. A piezoelectric element type sensor 1 of a vibration gyro which is a signal source is connected to an inverting input of an integrating circuit operational amplifier 3 via an input resistor 2. A feedback capacitor 4 is connected to the operational amplifier 3. This circuit configuration is the same as in FIG. A switch 5 connected in parallel to the feedback capacitor 4 is provided to short-circuit the feedback capacitor 4 at the start of operation and determine the initial state of the integrating circuit.

  In FIG. 2, except for the configuration of the integration circuit, a drift correction circuit is provided. The drift correction circuit includes a first capacitor 6 and a first peripheral circuit (switches 7a to 7d), a second capacitor 8 and a second peripheral circuit (switches 9a to 9d), a third capacitor 10 and a third peripheral circuit (switch). 11a to 11d and the second operational amplifier 12).

  The output of the second operational amplifier 12 is connected to the inverting input of the integrating circuit operational amplifier 3 through a resistor voltage dividing circuit (resistors 13a to 13c). Between the inverting input and the output of the second operational amplifier 12, a reset switch 14 and a capacitor 15 for absorbing noise with a minute capacitance value are connected. In order to understand the basic operation of this embodiment, the switch 14 and the capacitor 15 can be ignored.

  A control circuit for uniformly controlling the first to third peripheral circuits is not shown. The control circuit operates in synchronization with the excitation circuit of the vibration gyro and operates as follows (the phase is free) with the same cycle as the alternating current signal generated from the piezoelectric element type sensor 1.

(A) First, as an initial state of description, it is assumed that the switches 11c and 11d of the third peripheral circuit are on, the switches 11a and 11b are off, and all the switches of the first peripheral circuit and the second peripheral circuit are off. In this state, the second operational amplifier 12 supplies an output current based on the storage voltage of the third capacitor 10 to the inverting input of the integrating circuit operational amplifier 3, and a voltage of a substantially cosine wave obtained by integrating the input sine wave from the integrating circuit operational amplifier 3. A signal is output.
(B) In the first phase in one cycle in the above state (A), the switches 7a and 7b of the first peripheral circuit are instantaneously turned on, and the output voltage (first voltage) of the integrating circuit operational amplifier 3 in the first phase Value) is stored in the first capacitor 6.
(C) In a second phase that is 180 degrees out of phase with the first phase, the switches 9a and 9b of the second peripheral circuit are instantaneously turned on, and the output voltage (second voltage value) of the integrating circuit operational amplifier 3 in the second phase Is stored in the second capacitor 7.
(D) Next, in the third phase in one cycle, the switches 11c and 11d of the third peripheral circuit are turned off, the switches 11a and 11b are turned on, and the connection direction of the third capacitor 10 to the second operational amplifier 12 is reversed. To do. At the same time, the switches 7c and 7d of the first peripheral circuit and the switches 9c and 9d of the second peripheral circuit are instantaneously turned on at the same timing, and the first voltage value from the first capacitor 6 and the second voltage from the second capacitor 8 are The voltage value is read and the charge is transferred to the third capacitor 10. In this circuit operation, the first voltage value and the second voltage value are added, and the storage voltage of the third capacitor 10 in the state (A) is subtracted from the added voltage, and the voltage of the subtraction result is used as the third capacitor. 10 is equivalent to storing it in 10.
(E) The state after the circuit operation in the state (D) is completed corresponds to the initial state (A) described. The above operation is repeated according to the output cycle of the piezoelectric element type sensor 1.

=== Functional Effects of the First Embodiment ===
A non-zero voltage is stored in the third capacitor 10, and a correction current based on the stored voltage is applied from the second operational amplifier 12 to the integration circuit operational amplifier 3. In this state, a DC current due to a disturbance factor is canceled, and the integration circuit operational amplifier 3. Suppose that a cosine wave having positive and negative symmetry is stably output from.

  The drift correction circuit reads and adds the storage voltage of the first capacitor 6 and the storage voltage of the second capacitor 8 for each input / output cycle, and subtracts the storage voltage of the third capacitor 10 from the added voltage, The operation of “store the voltage of the subtraction result in the third capacitor 10” is repeated.

  The stable state is a state in which the storage voltage does not change even when the storage voltage update operation of the third capacitor 10 is repeated. If the accumulated charge amount of the third capacitor 10 in this stable state is 1, it means that the sum of the accumulated charge amount of the first capacitor 6 and the accumulated charge amount of the second capacitor 8 is kept at 2 in the stable state. To do. Since 2-1 = 1 and the storage voltage update operation of the third capacitor 10 is repeated, the amount of accumulated charge in the third capacitor 10 remains 1 and does not change.

  The state in which the sum of the accumulated charge amount of the first capacitor 6 and the accumulated charge amount of the second capacitor 8 is almost 2 is a state that is almost zero, and the sign of the cosine wave signal output from the integrating circuit operational amplifier 3 is positive or negative. The symmetry is very high.

  Assume that the disturbance factor has changed from the stable state described above, and the positive / negative symmetry of the output signal of the integrating circuit operational amplifier 3 has been disturbed. Then, the sum of the accumulated charge amount of the first capacitor 6 and the accumulated charge amount of the second capacitor 8 becomes 4, for example, and the accumulated charge amount of the third capacitor 10 becomes 4-1 = 3.

  As a result, the correction current changes and feedback control acts so as to reverse the positive / negative asymmetry of the output signal. In the next cycle, the sum of the accumulated charge amount of the first capacitor 6 and the accumulated charge amount of the second capacitor 8 is calculated. For example, −2 and the accumulated charge amount of the third capacitor 10 is −2−1 = −3.

  As a result, the correction current changes and feedback control acts so as to reverse the positive / negative asymmetry of the output signal again. In the next cycle, the sum of the accumulated charge amount of the first capacitor 6 and the accumulated charge amount of the second capacitor 8 is added. Is 3, for example, and the accumulated charge amount of the third capacitor 10 is 3-1 = 2.

  As described above, the vibration phenomenon converges to the above-described stable state while repeating several cycles. The present invention envisions drift that changes very slowly due to leakage current and offset, and under such realistic conditions, a large damped oscillation phenomenon is observed from when the power is turned on until it converges to the above stable state. However, once it has converged to the stable state, the sum of the accumulated charge amount of the first capacitor 6 and the accumulated charge amount of the second capacitor 8 is almost 2 due to the feedback control of the extremely high loop gain. The stable state in which the amount of charge stored in the capacitor 10 is approximately 1 continues.

  Note that the noise absorbing capacitor 15 connected to the second operational amplifier 12 is extremely small to prevent the input / output of the second operational amplifier 12 from being opened even for a moment when the connection direction of the third capacitor 10 is reversed. It is a capacitor with a capacitance, and prevents noise caused by being released for a moment. Further, the switch 5 and the switch 14 are used for resetting to discharge the capacitor by short-circuiting at the start of operation, and can be omitted when the time until stabilization immediately after the start of operation may be long.

=== Gist of the second invention ===
The circuit device according to the second invention is specified by the following items (21) to (28).
(21) A circuit device that includes an integration circuit and a drift correction circuit and converts a small amplitude alternating current signal input from a signal source into a large amplitude voltage signal. (22) The alternating current signal has a constant period. (2) The integrating circuit has an operational amplifier with a signal source connected to the inverting input, and the inverting input and output of the operational amplifier. (24) A drift correction circuit that stores a voltage in each of the first to third capacitors and each capacitor, and outputs a voltage signal obtained by integrating an alternating current signal input from a signal source. A first to a third peripheral circuit for reading a voltage, and a control circuit that controls the operation timing of each peripheral circuit in a unified manner. (25) The control circuit has a first phase of a cycle of an alternating current signal. (26) The control circuit stores the output voltage of the integration circuit in the second capacitor in a second phase that is 180 degrees out of phase with the first phase. (27) The control circuit reads and adds the storage voltage of the first capacitor and the storage voltage of the second capacitor in the third phase of the cycle of the alternating current signal, and stores the addition voltage in the third capacitor. (28) The storage voltage of the third capacitor gives a correction charge to the inverting input of the integrating circuit operational amplifier.

=== Configuration and Operation of Second Embodiment ===
FIG. 4 shows the configuration of one embodiment of the second invention, and FIG. 5 shows the operation timing thereof. The configuration of the piezoelectric element type sensor 1, the input resistor 2, the integrating circuit operational amplifier 3, the feedback capacitor 4, and the reset switch 5 is the same as the circuit of FIG. 2, and the other circuit is a drift correction circuit.

  The drift correction circuit includes a first capacitor 16 and a first peripheral circuit (switches 17a and 17b), a second capacitor 18 and a second peripheral circuit (switches 19a and 19b), a third capacitor 20 and a third peripheral circuit (switches). 21a and 21b) and a resistor 22. The resistor 22 is a limiting resistor for preventing the integrating circuit operational amplifier from becoming unstable due to the influence of the third capacitor 20, and is not necessary for the basic circuit operation of this system.

  A control circuit for uniformly controlling the first to third peripheral circuits is not shown. The control circuit operates in synchronization with the excitation circuit of the vibration gyro and operates as follows (the phase is free) with the same cycle as the alternating current signal generated from the piezoelectric element type sensor 1.

(A) First, as an initial state of the description, all the switches are off, and the accumulated charges of the first capacitor 16, the second capacitor 18, and the third capacitor 20 are all zero.
(B) The switch 17a of the first peripheral circuit is instantaneously turned on in the first phase in one cycle in the above state (A), and the output voltage (first voltage value and the output voltage of the integrating circuit operational amplifier 3 in the first phase is set. Is stored in the first capacitor 16.
(C) In the second phase that is 180 degrees out of phase with the first phase, the switch 19a of the second peripheral circuit is instantaneously turned on, and the output voltage of the integrating circuit operational amplifier 3 in the second phase (set to the second voltage value) Is stored in the second capacitor 18.
(D) Next, at the third phase in one cycle, the switches 17b and 19b are simultaneously turned on for a moment, and the first voltage value from the first capacitor 16 and the second voltage value from the second capacitor 18 are read out. Charges are distributed to the three capacitors 20. This circuit operation corresponds to storing the added voltage of the first voltage value and the second voltage value in the third capacitor 30. Immediately after this, the switch 21 b is turned on, and a correction charge based on the voltage newly stored in the third capacitor 30 is given to the integration circuit operational amplifier 3.
(E) Then, when the switch 21a is turned on for a moment and the residual charge in the third capacitor 20 is discharged, the initial state (A) of the description is obtained. In general, even if the switch 21a is not turned on, all the charge of the third capacitor 20 is transferred to the integrating circuit operational amplifier, so that the switch 21a can be omitted. The above operation is repeated according to the output cycle of the piezoelectric element type sensor 1.

=== Functional Effects of Second Embodiment ===
Compared with the first embodiment (FIG. 2), the circuit of the second embodiment is different in that the charge stored in the third capacitor 20 is discharged every cycle and is not reflected in the feedback control of the next cycle. . Based on the sum of the first voltage stored in the first capacitor 16 and the second voltage stored in the second capacitor 18, feedback control is performed at the start of the next cycle. As a result, the accuracy and continuity are inferior to those of the first embodiment, but a simple circuit device that realizes almost the same control action is obtained, and the configuration of the second embodiment is sufficient for some applications.

=== Gist of the third invention ===
The circuit device according to the third aspect of the invention is specified by the following items (31) to (38).
(31) A circuit device that includes an integration circuit and a drift correction circuit and converts a small amplitude alternating current signal input from a signal source into a large amplitude voltage signal. (32) The alternating current signal has a constant period. The absolute current values of two points that are 180 degrees out of phase within one cycle are equal to each other (33) The integrating circuit has an operational amplifier with a signal source connected to the inverting input, and the inverting input and output of the operational amplifier. (34) A drift correction circuit that stores a voltage in each of the first to third capacitors and each capacitor, and outputs a voltage signal obtained by integrating an alternating current signal input from a signal source. The first to third peripheral circuits for reading the voltage, and a control circuit that controls the operation timing of each peripheral circuit in a unified manner (35) The control circuit is provided for each half cycle of the alternating current signal. (36) The control circuit reads the storage voltage of the first capacitor and adds it to the storage voltage of the second capacitor for each half cycle of the alternating current signal, and stores the output voltage of the integration circuit in the first capacitor. (37) The control circuit reads the storage voltage of the second capacitor and stores it in the third capacitor every half cycle of the alternating current. (38) The storage voltage of the third capacitor is the integration circuit operational amplifier. Applying a correction charge to the inverting input of

=== Configuration and Operation of Third Embodiment ===
FIG. 6 shows the configuration of one embodiment of the third invention, and FIG. 7 shows the operation timing thereof. The configuration of the piezoelectric element type sensor 1, the input resistor 2, the integrating circuit operational amplifier 3, the feedback capacitor 4, and the reset switch 5 is the same as the circuit of FIG. 2, and the other circuit is a drift correction circuit.

  The drift correction circuit includes a first capacitor 23 and a first peripheral circuit (switches 24a to 24d), a second capacitor 25 and a second peripheral circuit (second operational amplifier 26 / switch 27), a third capacitor 28 and a third peripheral circuit. A circuit (switches 29a and 29b) and a resistor 30 are included. The resistor 30 is a limiting resistor for preventing the integrating circuit operational amplifier from becoming unstable due to the influence of the third capacitor 28, and is not necessary for the basic circuit operation of this system.

  A control circuit for uniformly controlling the first to third peripheral circuits is not shown. The control circuit operates in synchronization with the excitation circuit of the vibration gyro and operates as follows (the phase is free) with the same cycle as the alternating current signal generated from the piezoelectric element type sensor 1.

(A) First, as an initial state of description, all the switches are turned off.
(B) In the above state (A), the switches 24a and 24b of the first peripheral circuit and the switch 27 of the second peripheral circuit are instantaneously turned on in the first phase in one cycle of the alternating current signal, and the first phase The output voltage of the integrating circuit operational amplifier 3 in (1) is stored in the first capacitor 23 and the second capacitor 25 is reset.
(C) In the second phase immediately after the first phase, the switches 24c and 24d of the first peripheral circuit are turned on instantaneously, and the first voltage value is transferred to the second capacitor 25.
(D) Then, in the third phase 180 degrees from the first phase, the switches 24a and 24b are instantly turned on in the same manner as the first phase, and the integration circuit operational amplifier 3 in the fifth phase delayed 180 degrees from the first phase. The output voltage (referred to as the second voltage value) is stored in the first capacitor 23.
(E) In the fourth phase immediately after the third phase, the switches 24c and 24d of the first peripheral circuit are instantaneously turned on, and the second voltage value is added to the stored voltage value of the second capacitor 25.
(F) Immediately after the fourth phase, in the fifth phase, the switch 29a of the third peripheral circuit is instantaneously turned on, and the storage voltage of the second capacitor is stored in the third capacitor 28.

(G) In the sixth phase immediately after the fifth phase, the switch 29b of the third peripheral circuit is instantaneously turned on, and a correction charge is given to the inverting input of the integrating circuit operational amplifier.
(F) Immediately after the sixth phase, the first phase is reached again when 180 degrees from the third phase. The above operation is repeated according to the output cycle of the piezoelectric element type sensor 1.

=== Functional Effects of Third Embodiment ===
Compared with the second embodiment (FIG. 4), in the circuit of the third embodiment, the output voltage of the integrating circuit is stored in the first capacitor every half cycle of the input alternating current signal and then transferred to the second capacitor. This method is different from the sampling method in which the storage voltage for two times is sequentially added by the second capacitor. The feedback control performance is equivalent to that of the second embodiment.

Configuration diagram of integration circuit for explanation Circuit configuration diagram of the first embodiment Timing explanatory diagram of the first embodiment Circuit configuration diagram of the second embodiment Timing explanatory diagram of the second embodiment Circuit diagram of the third embodiment It is timing explanatory drawing of 3rd Example.

Explanation of symbols

6 1st capacitor 8 2nd capacitor 10 3rd capacitor 16 1st capacitor 18 2nd capacitor 20 3rd capacitor 23 1st capacitor 25 2nd capacitor 28 3rd capacitor

Claims (7)

The circuit device includes an integration circuit and a drift correction circuit, and converts a minute amplitude alternating current signal input from a signal source into a voltage signal having a large amplitude,
The alternating current signal has a positive and negative symmetrical waveform with a constant period, and the current absolute values at two points different in phase by 180 degrees within one period are equal.
The integrating circuit includes an operational amplifier whose signal source is connected to the inverting input, a feedback capacitor that connects the inverting input and the output of the operational amplifier, and outputs a voltage signal obtained by integrating the alternating current signal input from the signal source,
The drift correction circuit includes first to third capacitors, first to third peripheral circuits for storing a voltage in each capacitor and reading the stored voltage, and a control circuit that controls the operation timing of each peripheral circuit in a unified manner And
The control circuit stores the output voltage of the integration circuit in the first capacitor in the first phase of the cycle of the alternating current signal,
The control circuit stores the output voltage of the integration circuit in the second capacitor in the second phase different from the first phase by 180 degrees.
The control circuit reads and adds the storage voltage of the first capacitor and the storage voltage of the second capacitor in the third phase of the period of the alternating current signal, and subtracts the storage voltage of the third capacitor from the added voltage, The voltage of the subtraction result is stored in the third capacitor,
The memory voltage of the third capacitor provides a correction current to the inverting input of the integrating circuit operational amplifier. The third peripheral circuit includes a second operational amplifier, and a third capacitor can be reversibly connected between the inverting input and the output of the second operational amplifier under the control of the control circuit,
The circuit device according to claim 1, wherein the second operational amplifier provides an output current based on a storage voltage of the third capacitor to an inverting input of the integrating circuit operational amplifier. The circuit device according to claim 2, wherein an output of the second operational amplifier is connected to an inverting input of the integrating circuit operational amplifier via a resistance voltage dividing circuit. The circuit device according to claim 2, wherein the second operational amplifier has a noise absorbing capacitor connected between the inverting input and the output. The circuit device includes an integration circuit and a drift correction circuit, and converts a minute amplitude alternating current signal input from a signal source into a voltage signal having a large amplitude,
The alternating current signal has a positive and negative symmetrical waveform with a constant period, and the current absolute values at two points different in phase by 180 degrees within one period are equal.
The integrating circuit includes an operational amplifier whose signal source is connected to the inverting input, a feedback capacitor that connects the inverting input and the output of the operational amplifier, and outputs a voltage signal obtained by integrating the alternating current signal input from the signal source,
The drift correction circuit includes first to third capacitors, first to third peripheral circuits for storing a voltage in each capacitor and reading the stored voltage, and a control circuit that controls the operation timing of each peripheral circuit in a unified manner And
The control circuit stores the output voltage of the integration circuit in the first capacitor in the first phase of the cycle of the alternating current signal,
The control circuit stores the output voltage of the integration circuit in the second capacitor in the second phase different from the first phase by 180 degrees.
The control circuit reads and adds the storage voltage of the first capacitor and the storage voltage of the second capacitor in the third phase of the cycle of the alternating current signal, and stores the addition voltage in the third capacitor,
The memory voltage of the third capacitor gives a correction charge to the inverting input of the integrating circuit operational amplifier. The circuit device includes an integration circuit and a drift correction circuit, and converts a minute amplitude alternating current signal input from a signal source into a voltage signal having a large amplitude,
The alternating current signal has a positive and negative symmetrical waveform with a constant period, and the current absolute values at two points different in phase by 180 degrees within one period are equal.
The integrating circuit includes an operational amplifier whose signal source is connected to the inverting input, a feedback capacitor that connects the inverting input and the output of the operational amplifier, and outputs a voltage signal obtained by integrating the alternating current signal input from the signal source,
The drift correction circuit includes first to third capacitors, first to third peripheral circuits for storing a voltage in each capacitor and reading the stored voltage, and a control circuit that controls the operation timing of each peripheral circuit in a unified manner And
The control circuit stores the output voltage of the integrating circuit in the first capacitor every half cycle of the alternating current signal,
The control circuit reads the storage voltage of the first capacitor every half cycle of the alternating current signal, adds it to the storage voltage of the second capacitor, and stores it in the second capacitor.
The control circuit reads the storage voltage of the second capacitor and stores it in the third capacitor every half cycle of the alternating current,
The memory voltage of the third capacitor gives a correction charge to the inverting input of the integrating circuit operational amplifier. The second peripheral circuit includes a second operational amplifier in which a second capacitor is connected between the inverting input and the output, and integrates voltages sequentially read from the first capacitor by the second capacitor.
The circuit device according to claim 6, wherein the third peripheral circuit stores the voltage in the third capacitor by the output of the second operational amplifier based on the storage voltage of the second capacitor.

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