JP2002090394A - Voltage measurement circuit and its calibration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage measuring circuit capable of obtaining highly accurate data over a wide frequency band. SOLUTION: An attenuator circuit 1 loweres input voltage 101 from a voltage input terminal to a transient-decay AC voltage 103 at an attenuation factor D, and inputs the transient-decay AC voltage 103 passed through a buffer amplifier 2 in a correction amplifier 3. The correction amplifier 3 calibrates frequency characteristics based on control DC voltage 102, amplifies the transient-decay AC voltage 103 to correction AC voltage 104 at a amplification degree G and inputs in a voltage measuring part 4. The voltage measuring part 4 converts the correction AC voltage 104 into measuring data and stores in a correction memory 5. A control part 6 refers a stored content of the correction memory 5, produces control DC voltage 102 from the measured data under a specified condition and inputs to the correction amplifier 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage measuring circuit and a method for calibrating the same, and more particularly, to a voltage measuring circuit for correcting a frequency characteristic of an input AC voltage and a method for calibrating the same.

[0002]

2. Description of the Related Art A voltage measuring circuit measures a DC voltage or an AC voltage via an attenuator circuit and a buffer amplifier in an input stage. Since the input stage of the voltage measurement circuit has a parasitic capacitance and affects the attenuation rate of the attenuator circuit, the measured value of the AC voltage differs between a low frequency and a high frequency. Therefore, the voltage measurement circuit generally has a function of correcting the frequency characteristics.

FIG. 8 is a block diagram of a frequency characteristic correction circuit described in Japanese Utility Model Laid-Open No. 6-58617. The input stage of this voltage measurement circuit receives the AC voltage from the voltage input terminal,
Capacitor C ₈₁ and resistor R _81, a capacitor C ₈₂ and resistor R _82, ~, n pieces of parallel circuit of the capacitor C _8n and the resistor R _8n are input to the attenuator circuit connected in series. Attenuator circuit, by turning on any one of the changeover switches S ₈₁ to S _8n-1, which is connected to the series circuits, to step down an input AC voltage at a predetermined attenuation rate, the parasitic capacitance C _s
To the input terminal of the buffer amplifier 81 having

The buffer amplifier 81 amplifies the attenuated AC voltage and inputs the amplified AC voltage to an input terminal of a voltage measuring unit 82. The input terminal and the output terminal of the buffer amplifier 81 are connected via _a variable amplifier 83 and a correction resistor Ra. The AC voltage measuring unit 82 measures the amplified AC voltage and inputs the measured value to the control unit 84. The control unit 84 converts the measured value into correction data and inputs the data to the correction memory 85 and the variable amplifier 83.

[0005] The variable amplifier 83 is operated in accordance with correction data.
It has a variable resistance function that changes the valence resistance. Control unit 84
Corrects the correction data and adjusts the resistance R of the attenuator circuit.
₈₁~ R _8n, The equivalent resistance of the variable amplifier 83, and the correction resistance
R_aAnd the capacity of the attenuator circuit
Sita C₈₁~ C_8nAnd the parasitic capacitance C_sConsisting of volumetric attenuation
Match the rate.

[0006]

In the above conventional voltage measuring circuit, the resistance decay rate is adjusted to a predetermined value so that the resistance decay rate and the capacity decay rate coincide with each other to correct the frequency characteristics. However, the parasitic capacitance C _s has many factors that fluctuate due to aging or the like. According to the method of adjusting the resistance decay rate to the capacitance decay rate, the attenuation rate at the input stage of the voltage measurement circuit may also fluctuate. The capacitors C ₈₁ to C _81
8n is more difficult to set with high precision than the resistors R _{81 to} R _8n , which has affected parts procurement and cost reduction.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and provides a voltage measurement circuit capable of acquiring high-precision measurement data in a wide frequency band and a calibration method thereof. The purpose is to do.

[0008]

In order to achieve the above object, a voltage measuring circuit according to the present invention has an attenuation rate corresponding to a plurality of measurement ranges, and reduces an input voltage based on a selected attenuation rate. An attenuator, and a voltage measurement circuit having a voltage measurement unit that measures an input voltage based on an output voltage of the attenuator, a storage unit that stores a correction value for each measurement range, the attenuator, the voltage measurement unit, And a correction amplifier having a variable capacitor that is controlled based on the correction value and determines the amplification degree.

In the voltage measuring circuit according to the present invention, the correction amplifier adjusts the value of the variable capacitor as a constituent element based on the correction value to cope with a high frequency region where the influence of the capacitor appears, thereby correcting the frequency characteristic. Therefore, highly accurate measurement data can be obtained in a wide frequency band.

A method of calibrating a voltage measuring circuit according to the present invention is a method of calibrating a voltage measuring circuit as described above, wherein a reference voltage having a low frequency equal to or lower than a predetermined value is inputted, and 1 is measured for each of the measurement ranges, and a second output voltage is measured by the voltage measurement unit based on a reference input voltage having a frequency higher than a predetermined value for each of the measurement ranges.
The variable capacitor is set so that the difference between the output voltage of the second output voltage and the second output voltage is equal to or less than a predetermined range, a correction value is determined based on the setting, and the correction value is stored in the storage unit. And

In the method for calibrating a voltage measuring circuit according to the present invention, good calibration is performed by making the difference between the first output voltage and the second output voltage equal to or less than a predetermined difference.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a voltage measuring circuit according to the present invention will be described with reference to the drawings based on an embodiment of the present invention. FIG. 1 is a block diagram of a voltage measuring circuit according to an embodiment of the present invention. The voltage measurement circuit includes an attenuator circuit 1, a buffer amplifier 2, a correction amplifier (correction amplifier)
3, a voltage measurement unit 4, a correction memory (storage unit) 5, and a control unit 6.

The attenuator circuit 1 includes resistors R _{1 to} R _{n + 1} ,
The capacitors C _{1 to} C _{n + 1} and the changeover switches S _{1 to} S _n
Composed of The input terminal of the attenuator circuit 1 constitutes the voltage input terminal of the present voltage measurement circuit, and the resistor R ₁
And via a capacitor C _1, it is connected to the output terminal of the attenuator 1. Output terminals of the attenuator circuit 1 is connected to each one end of the selector switch S ₁ to S _n, is connected to an input terminal of the buffer amplifier 2. Changeover switch S ₁
The other end of each of the to S _n, the resistance R ₂ ~R _{n + 1} and the capacitor C ₂ ~
Each is connected to one end of C _{n + 1} . The other end of the resistor R ₂ ~R n + ₁ and the capacitor C ₂ ~C n + ₁ are all connected to ground.

An output terminal of the buffer amplifier 2 is connected to an AC input terminal of the correction amplifier 3. An AC output terminal of the correction amplifier 3 is connected to an input terminal of the voltage measurement unit 4. An output terminal of the voltage measuring unit 4 is connected to an input terminal of the correction memory 5. An output terminal of the correction memory 5 is connected to an input terminal of the control unit 6. The output terminal of the control unit 6 is connected to the DC input terminal of the correction amplifier 3.

FIG. 2 shows a specific example of the attenuator circuit 1, the buffer amplifier 2, and the correction amplifier 3 of FIG. Attenuator circuit 1 is shown a state in which the changeover switch S ₁ is turned on, resistors R _1, R ₂ capacitors C ₁ and,, C ₂
Only shown. Buffer amplifier 2 is a voltage follower Wow including the operational amplifier OP _1. Operational amplifier OP
_One non-inverting input terminal is connected to the output terminal of the attenuator circuit 1. The output terminal of the operational amplifier OP ₁ is connected to the inverting input terminal.

The correction amplifier 3 includes an operational amplifier OP _2, variable capacitor C _11, the capacitor C _{1 2,} resistors R _11, and, an inverting amplifier consisting of R _12. Correction amplifier 3
The input terminal, via a resistor R ₁₁ and variable capacitor C _11, is connected to the inverting input terminal of the operational amplifier OP _2. The non-inverting input terminal of the operational amplifier OP ₂ is connected to ground. The output terminal of the operational amplifier OP ₂ is connected to a resistor R ₁₂
And via a capacitor C _12, it is connected to the inverting input terminal of the operational amplifier OP _2.

[0017] Although using the varicap diode capacitance between two terminals is changed based on the control DC voltage 102 which is input as a variable capacitor C ₁₁ in FIG. 2, not limited to this, for example, FET May be used as a diode to utilize the input capacitance and feedback capacitance of the FET, which change according to the voltage applied between the gate, drain and source. By using an FET as a diode, the problem of the reproducibility of the capacitance with respect to the control DC voltage in the case of a varicap diode can be greatly improved. In addition, the same type of variable capacitance element may be used.

The control unit 6 recognizes the key input operation and sends necessary instructions to each circuit. Attenuator circuit 1 in accordance with an instruction from the control unit 6, and on either one of the changeover switch S ₁ to S _n, is set to the attenuation factor D corresponding to the measurement range. The output terminal of the attenuator circuit 1, the input capacitance of the buffer amplifier 2, the stray capacitance to the connection line buffer amplifier 2, and the parasitic capacitance C _s is present consisting of the input capacitance of the changeover switch S ₁ to S _n. The value of the capacitor C ₂ ~C n + ₁ is designed itself as a value including the parasitic capacitance C _s.

In the attenuator circuit 1, the impedance of the parallel circuit composed of the resistor R ₁ and the capacitor C ₁ is Z ₁ , the impedance of the parallel circuit composed of the resistor R ₂ and the capacitor C ₂ is Z _2, and the angle of the input AC voltage 101 is Assuming that the frequency is ω, it is shown as follows. Z ₁ = 1 / {(1 / R ₁ ) + jωC ₁ } (1) Z ₂ = 1 / {(1 / R ₂ ) + jωC ₂ } (2) The attenuator circuit 1 The input AC voltage 101 from the input terminal is reduced to an attenuated AC voltage 103, and the attenuated AC voltage 103 is input to the correction amplifier 3 via the buffer amplifier 2. Attenuated AC voltage 10 for input AC voltage 101
The decay rate D of 3 is obtained from Expressions (1) and (2) as follows. _{D = Z 2 / (Z 1} + Z 2) ···· (3)

The attenuation rate D is determined by the resistance attenuation rate D _R due to the resistance of the attenuator circuit 1 and the attenuator circuit 1
The capacitance decay rate D _C due to the reactance component of The respective attenuation rates D _R and D _C are expressed as follows: D _R = R ₂ / (R ₁ + R ₂ ) (4) D _C = C ₁ / (C ₁ + C ₂ ) (5) It is.

[0021] When the input AC voltage 101 is low frequency close to direct current, since the reactance attenuator circuit 1 becomes a high impedance, negligible capacity fade rate D _C.
The value of the attenuation factor D is determined as the value of the resistance attenuation rate D _R as shown in equation (4).

[0022] When the input AC voltage 101 is high frequency, because the reactance of the attenuator circuit 1 becomes low impedance, not negligible capacity fade rate D _C. here,
If resistivity decay rate D _R and fade rate D _C are equal damping condition is satisfied, the value of the attenuation factor D is determined as the value of the resistance attenuation rate D _R as shown in equation (4).

FIG. 3 is a diagram showing a frequency characteristic of the attenuated AC voltage 103. FIG. 3A is a table of the measurement results of the attenuated AC voltage 103. Resistors R ₁ , R ₂ , capacitor C ₁ ,
And C ₂ is 10 MΩ, 1.11 MΩ, 11.1 P, respectively.
F and 100 PF (0 ± 5%), and the attenuation factor D of the attenuator circuit 1 is set to 0.1. The input AC voltage 101 from the voltage input terminal has a predetermined amplitude serving as a reference for calibration, and has several types of frequencies of 100 Hz or more. Capacitor C ₂ is assumed actual voltage measurement circuit error occurs, ± 0% to a value designed, + 5%, and, -5% of variation is added. The measurement result is 100
It is obtained as a relative ratio of the measurement data obtained at another frequency to the measurement data obtained at the frequency of Hz.

FIG. 2B shows frequency characteristics of the attenuated AC voltage 103. If there is no capacitor C ₂ of variation, said damping condition is satisfied, the magnitude of the relative ratio at all frequencies, becomes 0.00 dB. If there is a variation in the capacitor C _2, not satisfied the above attenuation conditions, the magnitude of the relative ratio is larger than 0.00dB with increasing frequency. Therefore, the attenuated AC voltage 103 depends on the frequency.

When the impedance of the parallel circuit composed of the resistor R ₁₁ and the capacitor C ₁₁ is Z ₃ and the impedance of the parallel circuit composed of the resistor R ₁₂ and the capacitor C ₁₂ is Z ₄ , the correction amplifier 3 is expressed as follows. It is. _{Z 3 = 1 / {(1} / R 11) + jωC 11} ···· (6) Z 4 = 1 / {(1 / R 12) + jωC 12} ···· (7) correction amplifier 3, following Attenuated AC voltage 1 with amplification G shown in
03 to the corrected AC voltage 104, and the corrected AC voltage 10
4 is input to the voltage measuring unit 4. G = Z ₄ / Z ₃ (8) Equation (8) shows only the size.

The voltage measuring section 4 converts the corrected AC voltage 104 into analog data and converts the measured data into the correction memory 5 and a display section (not shown). The display unit displays the amplitude of the input AC voltage 101 to the measurer based on the measurement data. The correction memory 5 temporarily stores the measurement data.

In the calibration mode, the control unit 6 converts the measured data into a control DC voltage 102 while changing the measured data in the correction memory 5 and, when a predetermined condition is satisfied, uses the measured data as range data as the correction memory. 5 is stored.
In the case of the measurement mode, the range data in the correction memory 5 is DA-converted into the control DC voltage 102. The control unit 6 inputs the control DC voltage 102 to the correction amplifier 3.

Here, a calibration method for the voltage measurement circuit will be described. When recognizing that the control mode is the calibration mode, the control unit 6 executes a calibration method of the voltage measurement circuit. The measurement range of the voltage measurement circuit is selected to an arbitrary range, and an input AC voltage 101 having a predetermined amplitude value serving as a reference for calibration is applied from the calibration device to a voltage input terminal of the voltage measurement circuit. First, the input AC voltage 101 is set to a low frequency close to DC. The amplitude of the input AC voltage 101 of the low frequency measured by the voltage measuring unit 4 as the measurement data A _1, calibrating the display unit to indicate the predetermined amplitude value.

Next, the input AC voltage 101 is set to a high frequency. Measured as measurement data A ₂ the amplitude of the input AC voltage 101 of high frequency voltage measuring unit 4.

The magnitude of the difference between the measurement data A ₁ and the measurement data A ₂ is determined as the accuracy of the measurement range, and it is determined whether the accuracy of the measurement range is within a predetermined range. If “NO”,
The control DC voltage 102 is adjusted, and the measurement of the measurement data A ₁ and A ₂ and the determination on the accuracy of the measurement range are performed again.
If "YES", since measurement accuracy is calibrated in a predetermined range, the measurement range data data A ₂ (correction value) as is stored in the correction memory 5.

Further, the calibration method of the voltage measurement circuit is performed for all the measurement ranges in the same manner as described above.

When the control unit 6 recognizes that the measurement mode is set, the control unit 6 measures the normal AC voltage. The gain DG of the corrected AC voltage 104 with respect to the input AC voltage 101 is
Equations (3) and (8) show the following. DG = Z ₂ Z ₄ / {(Z ₁ + Z ₂ ) × Z ₃ } (9) The value of the variable capacitor C ₁₁ is calculated by the following equations (1), (2),
It is obtained from Expressions (6), (7), and (9) as shown below. C ₁₁ = DG / ｛(1 / R ₁ ) ² + (ωC ₁ ) ² ｝ [｛(1 / R ₁ R ₁₂ ) + ω ² C ₁ C ₁₂ ｝ (C ₁ + C ₂ ) + ｛(C ₁₂ / R ₁ ) − (C ₁ / R ₁₂ ) {(1 / R ₁ ) + (1 / R ₂ )}] (10) The control unit 6 reads out the range data from the correction memory 5, Based on the variable capacitor C ₁₁
Is set to the value shown in equation (10).

FIG. 4 is a diagram showing a frequency characteristic of the corrected AC voltage 104. As shown in FIG. 3A, a measurement result of the corrected AC voltage 104 is obtained in the same manner as in FIG. As shown in FIG. (B), regardless of the variation of the capacitor C _2, is at all frequencies the magnitude of the relative ratio, approximately 0.00d
Become B. Therefore, the corrected AC voltage 104 does not depend on the frequency.

FIG. 5 is a first example showing another specific example of FIG. The attenuator circuit 1A is a modified example of the attenuator circuit 1 of FIG. Attenuator circuit 1A, the voltage input terminal is connected to one end of a resistor R ₁ and capacitor C _1. The other end of the resistor R ₁ and capacitor C ₁ is connected to the output terminal through the switch S _1, it is connected to one end of the resistor R ₂ and capacitor C _2. Resistance R ₂ and capacitor C ₂
The other end is connected to the output terminal through the switch S _2, it is connected to one end of a resistor R ₃ and capacitor C _3. In the same manner, the resistance and the other end of R _n and the capacitor C _n is connected to the output terminal through the switch S _n, the resistance R _{n + 1}
And one end of the capacitor C _{n + 1} . The other ends of the resistor R _{n + 1} and the capacitor C _{n + 1} are connected to the ground.

The attenuator circuit 1A includes a changeover switch S
_{One of 1 to} Sn is turned on to set a predetermined attenuation rate D.

FIG. 6 is a second example showing another specific example of FIG. Attenuator 1B includes an operational amplifier OP ₃ Unlike attenuator circuit 1 in FIG. 1, configured as an inverting amplifier. Attenuator 1B, a voltage input terminal is connected to one end of a resistor R ₁ and capacitor C _1. The other end of the resistor R ₁ and capacitor C ₁ is connected to the inverting input terminal of the operational amplifier OP _3, is connected to all of the one end of the changeover switch S ₁ to S _n. The other end of the change-over switch S ₁ ~S _n is,
They are respectively connected to one end of the resistor R ₂ ~R n + ₁ and the capacitor C ₂ ~C n + _1. The operational amplifier OP ₃ has a non-inverting input terminal connected to the ground, the output terminal is connected to all of the other end of the resistor R ₂ ~R n + ₁ and the capacitor C ₂ ~C n + _1.

The attenuator circuit 1B includes a switch S
_{One of 1 to} Sn is turned on to set a predetermined attenuation rate D.

FIG. 7 is a third example showing another specific example of FIG. The buffer amplifier 2A shown in FIG.
Unlike, variable capacitor C _11, a capacitor C _12, resistor R ₁₁ and have the R _12. Input terminal of the buffer amplifier 2A is connected to the non-inverting input terminal of the operational amplifier OP _1. The output terminal of the operational amplifier OP ₁ becomes the output terminal of the buffer amplifier 2A, is connected to one end of a resistor R ₁₁ and variable capacitor C _11. Operational amplifier OP ₁
The inverting input terminal, the resistor R ₁₁ and a variable capacitor C
Is connected to the other end of ₁₁ is connected to one end of a resistor R ₁₂ and capacitor C _12. The other end of the resistor R ₁₂ and capacitor C ₁₂ is connected to the ground.

The variable capacitor C _11, based on a control DC voltage 102 from the control unit 6, the value is adjusted, it can be omitted correction amplifier 3.

It is to be noted that a configuration incorporating an oscillator may be employed. The built-in oscillator generates an input AC voltage 101 having a low frequency and a high frequency, and inputs the AC voltage 101 to the attenuator circuit 1 via a changeover switch. In this case, since the frequency characteristics can be corrected by the built-in oscillator, automatic calibration that does not require an external calibration device can be performed.

According to the above embodiment, the correction amplifier adjusts the value of the variable capacitor as a constituent element based on the correction value, and adjusts the frequency characteristic by coping with the high frequency region where the influence of the capacitor appears. Therefore, highly accurate measurement data can be obtained in a wide frequency band. In addition, by making the difference between the first output voltage and the second output voltage equal to or smaller than a predetermined difference, good calibration is performed.

Although the present invention has been described based on the preferred embodiment, the voltage measuring circuit and the calibration method of the present invention are not limited to the configuration of the above-described embodiment, and are not limited thereto. A voltage measurement circuit obtained by making various modifications and changes from the configuration of the embodiment and a calibration method thereof are also included in the scope of the present invention.

[0043]

As described above, in the voltage measuring circuit according to the present invention, the correction amplifier adjusts the value of the variable capacitor which is a component on the basis of the correction value to cope with the high frequency region where the influence of the capacitor appears. By doing so, the frequency characteristics are corrected, so that highly accurate measurement data can be obtained in a wide frequency band.

Further, by making the difference between the first output voltage and the second output voltage equal to or less than a predetermined difference, good calibration is performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a voltage measuring circuit according to an embodiment of the present invention.

FIG. 2 is a specific example of an attenuator circuit 1, a buffer amplifier 2, and a correction amplifier 3 of FIG.

FIG. 3 is a diagram illustrating frequency characteristics of an attenuated AC voltage 103;

FIG. 4 is a diagram illustrating a frequency characteristic of a corrected AC voltage 104;

FIG. 5 is a first example showing another specific example of FIG. 2;

FIG. 6 is a second example showing another specific example of FIG. 2;

FIG. 7 is a third example showing another specific example of FIG. 2;

FIG. 8 is a block diagram of a frequency characteristic correction circuit described in Japanese Utility Model Laid-Open No. 6-58617.

[Explanation of symbols]

Reference Signs List 1 attenuator circuit 2, 81 buffer amplifier 3 correction amplifier (compensation amplifier) 4 voltage measurement unit 5, 85 correction memory 6, 84 control unit 82 AC voltage measurement unit 83 variable amplifier 101 input AC voltage 102 control DC voltage 103 attenuated AC voltage 104 correcting the alternating voltage _{R 1 ~R n + 1, R} 81 ~R 8n resistance _{C 1 ~C n + 1, C} 81 ~C 8n capacitor C _s parasitic capacitance C ₁₁ variable capacitors S ₁ ~S _n, S ₈₁ ~S _8n changeover switch OP ₁ ~OP ₃ op-amp

Claims (2)

[Claims] 1. An attenuator having an attenuation rate corresponding to a plurality of measurement ranges and stepping down an input voltage based on a selected attenuation rate, and a voltage measuring unit measuring an input voltage based on an output voltage of the attenuator. And a storage unit for storing a correction value for each measurement range, connected between the attenuator and the voltage measurement unit,
A voltage measuring circuit, comprising: a correction amplifier having a variable capacitor that is controlled based on the correction value to determine an amplification degree. 2. The method for calibrating a voltage measurement circuit according to claim 1, wherein a reference voltage having a low frequency equal to or less than a predetermined frequency is input, and the first output voltage is measured by the voltage measurement unit. For each measurement range, a second output voltage is measured by the voltage measurement unit based on a reference input voltage having a frequency higher than a predetermined value, and a difference between the first output voltage and the second output voltage is equal to or less than a predetermined range. A method for calibrating a voltage measurement circuit, comprising: setting a variable capacitor so as to obtain a correction value based on the setting; and storing the correction value in the storage unit.