JP3062506B1 - Impedance measuring device - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To stabilize a reference voltage with high responsiveness while sufficiently suppressing a ripple in a control voltage when controlling the amplitude of a sine wave reference voltage to be constant. SOLUTION: A reference voltage generation circuit 14 generates a sine-wave reference voltage and applies the voltage to a measurement target 13, whereby the impedance of the measurement target 13 is calculated by an impedance calculation circuit 29 from a current flowing through the measurement target 13. I do. At this time, the amplitude of the reference voltage is controlled to be constant by the automatic level control circuit 22 based on the voltage generated at the measurement target 13. In the automatic level control circuit 22 described above, the frequency of the voltage generated in the measuring object 13 is multiplied by the frequency multiplying circuit 29, and the output voltage of the frequency multiplying circuit 29 is converted to direct current by the AC-DC conversion circuit 24. And removes the ripple of the output voltage of the AC-DC conversion circuit 24 and supplies it to the reference voltage generation circuit 14 as a control voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of applying a reference voltage of a sine wave having a constant amplitude to a measuring object such as a resistor, a capacitor, or an inductor, and a current flowing through the measuring object. The impedance is calculated, or a reference current of a sine wave having a constant amplitude is applied to the object to be measured, and the voltage (voltage drop between both ends of the object to be measured) generated in the object to be measured is measured. The present invention relates to an impedance measuring device for calculating impedance.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional impedance measuring device for calculating the impedance of a measuring object from a current flowing through the measuring object by applying a sine wave reference voltage having a constant amplitude to the measuring object. Show.

In this impedance measuring apparatus, as shown in FIG. 4, a measuring object (impedance Zx) 13 such as a resistor, a capacitor, or an inductor is connected between a pair of measuring terminals 11 and 12. .

In this impedance measuring device, a reference voltage e ₀ of a sine wave having a constant amplitude output from a reference voltage generating circuit 14 is applied from one measuring terminal 11 to a measuring object 13. Measuring object 1
The current i flowing through 3 is detected from the other measurement terminal 12 and converted into a voltage by the current / voltage conversion circuit 15.

Further, the output voltage of the current / voltage conversion circuit 15 is phase-detected by the phase detection circuit 16 based on the sine wave reference voltage e ₀ , so that the current / voltage conversion circuit 15
, A component in phase with the reference voltage e ₀ , that is, a voltage component corresponding to the resistance component of the measuring object 13 is extracted.

The output of the phase detection circuit 16 is A
By being converted into a digital value by the / D conversion circuit 17,
A voltage component corresponding to the resistance component of the measurement target 13 is obtained as a digital value.

The reference voltage generating circuit 14 comprises, for example, a sine wave oscillator 18 oscillating at a frequency f ₀ and a variable gain amplifier 19 for amplifying the oscillation output. The current / voltage conversion circuit 15 includes, for example, an operational amplifier 20 and a resistor 21 connected between the output terminal and the inverting input terminal.

The current / voltage conversion circuit 15, the phase detection circuit 16 and the A / D conversion circuit 17 constitute an impedance calculation circuit 28 for calculating the impedance Zx of the measurement object 13 from the current i flowing through the measurement object. I have.

By inputting the reference voltage e ₀ to the phase detection circuit 16 with the phase advanced by 90 degrees, the output voltage of the current / voltage conversion circuit 15 is advanced by 90 degrees from the reference voltage e _0. Components of phase, ie, object 1 to be measured
A voltage component corresponding to the capacitive reactance component of No. 3 is extracted and obtained as a digital value.

Further, by inputting the reference voltage e ₀ to the phase detection circuit 16 with the phase delayed by 90 degrees, the output voltage of the current / voltage conversion circuit 15 is delayed by 90 degrees from the reference voltage e _0. A phase component, that is, a voltage component corresponding to the inductive reactance component of the measurement target 13 is extracted and obtained as a digital value.

In order to accurately measure the impedance, it is necessary to control the amplitude of the sine wave reference voltage e ₀ output from the reference voltage generation circuit 14 to be constant. Here, the automatic level control circuit 22 for controlling the amplitude of the reference voltage e ₀ output from the reference voltage generation circuit 14 to be constant based on the voltage generated at the measurement target 13 will be described.

In the automatic level control circuit 22, the voltage (that is, the reference voltage e ₀ ) generated in the measuring object 13 is amplified by the buffer amplifier 23, and the output of the buffer amplifier 23 is subjected to AC-DC conversion comprising an absolute value circuit or the like. The DC voltage is converted by a circuit 24, and the DC voltage is further passed through a filter circuit 27 including a resistor (resistor R) 25 and a capacitor (capacitance C) 26 to remove the ripple component, and then the gain control of the amplifier 19 of the reference voltage generating circuit 14 is performed. A control voltage is applied to the input terminal. Thereby, the amplitude of the reference voltage e ₀ output from the reference voltage generation circuit 14 is controlled to be constant.

FIG. 5 is a block diagram of a conventional impedance measuring apparatus for calculating the impedance of a measuring object from a voltage generated in the measuring object by flowing a sine wave reference current having a constant amplitude through the measuring object.

In this impedance measuring device, as shown in FIG. 5, a measuring object (impedance is Zx) 33 such as a resistor, a capacitor or an inductor is connected between a pair of measuring terminals 31 and 32. .

[0015] Then, in the impedance measuring device, the reference current i ₀ of the sine wave of constant amplitude output from the reference current generation circuit 34 is passed through the measuring object 33 from one measurement terminal 31, the reference current i ₀ Is the other measurement terminal 3
2 and is converted to a voltage by the current / voltage conversion circuit 35, and at the same time, a voltage (voltage drop due to the measurement target 33) generated in the measurement target 33 due to the supply of the reference current i _0.
e is detected from one of the measurement terminals 31.

Further, the phase detection circuit 36 detects the voltage e generated in the measuring object 33 based on the voltage corresponding to the sine wave reference current i ₀ output from the current / voltage conversion circuit 35. Accordingly, a component having the same phase as the reference current i ₀ , that is, a voltage component corresponding to the resistance component of the measurement target 33, is extracted from the voltage e generated in the measurement target 33.

The output of the phase detection circuit 36 is A
By being converted into a digital value by the / D conversion circuit 37,
A voltage component corresponding to the resistance component of the measurement target 33 is obtained as a digital value.

The reference current generating circuit 34 includes a sine wave oscillator 38 oscillating at a frequency f ₀ , for example, and a variable gain amplifier 39 for amplifying the oscillation output. The current / voltage conversion circuit 35 includes, for example, an operational amplifier 40 and a resistor 41 connected between the output terminal and the inverting input terminal.

The current / voltage conversion circuit 35, the phase detection circuit 36 and the A / D conversion circuit 37 constitute an impedance calculation circuit 48 for calculating the impedance Zx of the object 33 from the voltage e generated at the object. I have.

Note that a reference current is supplied to the phase detection circuit 36.
i₀Is input with the phase advanced by 90 degrees.
In the output voltage of the current / voltage conversion circuit 35,
Current i ₀More 90-degree advanced component, ie, object 3
The voltage component corresponding to the capacitive reactance component of
And it is obtained as a digital value. Also rank
The reference current i for the phase detection circuit 36₀Delays the phase by 90 degrees
Input with the current / voltage conversion circuit
At the output voltage of the path 35, the reference current i₀90 degrees slower
Ingredient of the phase, that is, the inductive reactant of the measurement object 33
Voltage component corresponding to the
Obtained as tall value.

In order to accurately measure the impedance, it is necessary to control the amplitude of the sinusoidal reference current i ₀ output from the reference current generating circuit 34 to be constant. Here, an automatic level control circuit 42 for controlling the amplitude of the reference current i ₀ output from the reference current generation circuit 34 to be constant based on the current flowing through the measurement target 33 will be described.

In the automatic level control circuit 42, a voltage generated at both ends of the resistor 41 by a current flowing through the measuring object 33 (that is, the reference current i ₀ ) is supplied to the buffer amplifier 43.
, And the output of the buffer amplifier 43 is converted to DC by an AC-DC conversion circuit 44 composed of an absolute value circuit and the like, and further a resistor (resistance R) 45 and a capacitor (capacitance C) 46
After removing the ripple component by passing through a filter circuit 47 composed of a filter circuit 47, a reference voltage is applied to the gain control input terminal of the amplifier 39 of the reference current generating circuit 34 as a control voltage. Thus, the amplitude of the reference current i ₀ output from the reference current generation circuit 34 is controlled to be constant.

[0023]

In the above-described automatic level control circuit 22 of the impedance measuring apparatus shown in FIG. 4, the AC-DC conversion circuit 24 is constituted by an absolute value circuit, and its output voltage is a sine wave voltage. Becomes a pulsating wave voltage as if the full-wave rectified waveform was obtained. Therefore, in order to control the amplitude of the reference voltage of the reference voltage generation circuit 14 to be constant with the output voltage of the AC-DC conversion circuit 24, it is necessary to minimize the ripple component included in the output voltage of the AC-DC conversion circuit 24 as much as possible. is necessary.

The reason is that if the control voltage Ec to the reference voltage generation circuit 14 includes the ripple er as shown by the waveform Ec 'in FIG. 6A, the amplitude is controlled by the control voltage Ec. The reference voltage e ₀ of the sine wave of the reference voltage generation circuit 14 has a waveform that is amplitude-modulated by the ripple er as shown by a measurement signal waveform e ₀ ′ in FIG. 7A. Therefore, high-precision impedance measurement cannot be performed.

Therefore, the resistor 25 and the capacitor 26
The time constant of the filter circuit 27 is made as large as possible so that the ripple does not appear in the control voltage Ec to the reference voltage generating circuit 14.

However, in order to eliminate ripples, a filter is required.
If the time constant of the filter circuit 27 is set to a large value,
Sine wave reference voltage e due to power supply voltage fluctuation₀Sudden change of
Motion or when the impedance of the measuring object 13 is low.
Reference voltage e₀If a sudden change in
The control voltage Ec to the reference voltage generation circuit 14 is
As shown by the waveform Ec ″ in FIG.
At this time, since the time constant of the filter circuit 27 is large,
The time t required until the control voltage Ec is stabilized becomes longer.
At this time, the sine wave reference voltage e₀Is measured in Fig. 7 (b).
Signal waveform e₀Is modulated by the control voltage Ec.
And the reference voltage e₀Long time to stabilize
Will be required. In FIG. 7B, a solid line
Is the reference voltage e ₀Shows the measurement signal waveform of
e₀Measurement signal waveform e₀″ Shows the envelope
You.

The automatic level control circuit 42 of the impedance measuring apparatus of FIG. 5 has the same problem as the automatic level control circuit 22 of FIG.

Accordingly, an object of the present invention is to control the reference voltage or the reference current with good responsiveness while sufficiently suppressing the ripple in the control voltage when controlling the amplitude of the sine wave reference voltage or the reference current to be constant. An object of the present invention is to provide an impedance measuring device that can be stabilized.

[0029]

According to a first aspect of the present invention, there is provided an impedance measuring apparatus for generating a reference voltage of a sine wave and applying the reference voltage to a measuring object, and a reference voltage generating circuit for measuring the measuring object based on a current flowing through the measuring object. It comprises an impedance calculation circuit for calculating impedance and an automatic level control circuit for controlling the amplitude of the reference voltage to be constant based on the voltage generated at the object to be measured.

The above-mentioned automatic level control circuit comprises a frequency multiplying circuit for multiplying the frequency of the voltage generated in the object to be measured, an AC-DC converting circuit for converting the output voltage of the frequency multiplying circuit into DC, and an AC-DC converting circuit. And a filter circuit that removes a ripple component of the output voltage and provides the control voltage to the reference voltage generation circuit.

Here, the AC-DC conversion circuit comprises, for example, an absolute value circuit. The frequency multiplying circuit includes, for example, a phase shift circuit that generates first and second voltages whose phases are shifted from each other by 90 degrees based on a voltage generated in the object to be measured, and first and second output signals from the phase shift circuit. And an analog multiplier for multiplying the voltage. The phase shift circuit includes, for example, a resistor and a capacitor.

According to the configuration of the first invention, before the voltage generated in the object to be measured is converted into DC by the AC-DC converter, the frequency is multiplied by the frequency multiplier, so that the necessary ripple can be reduced. In order to obtain the function, the time constant of the filter circuit can be made smaller than in the conventional example.
As a result, the reference voltage can be stabilized with good responsiveness while suppressing the ripple in the control voltage when controlling the amplitude of the sine wave reference voltage to be constant. For example, in order to obtain the same ripple reduction function, the time constant of the filter circuit can be reduced to a reciprocal multiple of the multiplication ratio. As described above, since the time constant of the filter circuit can be reduced without lowering the ripple reduction function, the reference voltage can be stabilized with good responsiveness.

According to a second aspect of the present invention, there is provided an impedance measuring apparatus comprising:
A reference current generation circuit that generates a sine wave reference current and flows the measurement object, an impedance calculation circuit that calculates the impedance of the measurement object from a voltage generated in the measurement object,
An automatic level control circuit for controlling the amplitude of the reference current to be constant based on the current flowing through the object to be measured.

The automatic level control circuit includes a frequency multiplying circuit for multiplying the frequency of a voltage corresponding to the current flowing through the object to be measured, an AC-DC converting circuit for converting the output voltage of the frequency multiplying circuit into DC, and an AC-DC converting circuit. And a filter circuit for removing a ripple component of the output voltage of the DC conversion circuit and applying the ripple as a control voltage to the reference current generation circuit.

Here, the AC-DC conversion circuit comprises, for example, an absolute value circuit. Further, the frequency multiplier circuit outputs, for example, a phase shift circuit that generates first and second voltages having phases shifted from each other by 90 degrees based on a voltage corresponding to a current flowing through the object to be measured, and output from the phase shift circuit. An analog multiplier for multiplying the first and second voltages. The phase shift circuit includes, for example, a resistor and a capacitor.

According to the configuration of the second invention, before the voltage corresponding to the current flowing through the object to be measured is converted to DC by the AC-DC converter, the frequency is multiplied by the frequency multiplier, so that the frequency is multiplied. It is possible to make the time constant of the filter circuit smaller than that of the conventional example in order to obtain the required ripple reduction function. As a result, while controlling the amplitude of the sine wave reference current to be constant, the ripple in the control voltage can be suppressed sufficiently low, and the reference current can be stabilized with good responsiveness. For example, in order to obtain the same ripple reduction function, the time constant of the filter circuit can be reduced to a reciprocal multiple of the multiplication ratio. As described above, the time constant of the filter circuit can be reduced without deteriorating the ripple reduction function, so that the reference current can be stabilized with good responsiveness.

[0037]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] The present invention calculates the impedance of a measuring object from a current flowing through the measuring object by applying a sine wave reference voltage having a constant amplitude to the measuring object in FIG. 1 is a block diagram of an impedance measuring device according to a first embodiment of the present invention.

As shown in FIG. 1, this impedance measuring apparatus uses an automatic level control circuit 22A in place of the automatic level control circuit 22 of FIG. 4, and the other configuration is the same as that of FIG.

In the automatic level control circuit 22A, between the buffer amplifier 23 and the AC-DC conversion circuit 24, 2 ⁿ
A frequency doubler (n is an integer of 1 or more) 29 is inserted,
The difference from the automatic level control circuit 22 in FIG. 4 is that a filter circuit 27A is used instead of the filter circuit 27.

The 2 ⁿ -times frequency multiplying circuit 29 includes n multiplying circuits 291 to 29 ^{n for} doubling the frequency of the input signal.
When the frequency of the output signal of the buffer amplifier 23 is f ₀ , for example, the first-stage multiplication circuit 2
The frequency of the output signal of 91 is 2f ₀ , and the frequency of the output signal of the final stage multiplier 29n is 2 ⁿ f ₀ .

The multiplying circuits 291 to 29n have the same configuration.
For example, as shown in FIG. 3, a phase shift circuit 51 that generates first and second voltages whose phases are shifted from each other by 90 degrees based on a voltage generated in the measurement target 13, and a second phase shift circuit 51 that is output from the phase shift circuit 51. Analog multiplier 52 for multiplying the first and second voltages
Consists of

The phase shift circuit 51 includes, for example, a resistor (resistance r).
53 and a series circuit of a capacitor (capacitance c) 54, and the time constant is set so as to satisfy 2πf ₀ = 1 / cr when the frequency of the input signal is f ₀ .

As the analog multiplier 52, for example, MPY634 or an analog
AD633 or the like manufactured by Devices Inc. is used. And
In the analog multiplier 52, a first voltage (in phase with a sine wave input signal having a frequency f ₀ ) generated at both ends of a resistor 53 is applied between terminals X ₁ and X ₂ , and a first voltage generated at both ends of a capacitor 54 is provided. A voltage of 2 (90 degrees advanced with respect to the input signal) is applied between the terminals Y ₁ and Y ₂ , and multiplies the first and second voltages in an analog manner. Then, the result of the multiplication is obtained from the terminal W. The output signal from this terminal W is
The frequency is 2f _0. The terminal Z is provided to apply an offset voltage. In this example, the terminal Z is grounded, and the first and second voltages have a phase of 9
Since it differs by 0 degrees, the DC component of the output signal from this terminal W is zero.

The analog multiplier 52 has terminals X ₁ ,
When the voltages of X ₂ , Y ₁ , Y ₂ , W, and Z are represented by the same symbols as the respective terminals, W = (X ₁ −X ₂ ) · (Y ₁ −Y ₂ ) / 10 [V] The operation indicated by + Z is performed.

The filter circuit 27A comprises a resistor (resistor R ') 25A and a capacitor (capacitance C') 26A, and its time constant is set to, for example, 1/2 ⁿ of the time constant of the filter circuit 27. That is, for example, it is set so as to satisfy the relationship of R′C ′ = RC / 2 ⁿ .

The number n of multiplication circuits in the 2 ⁿ -times frequency multiplication circuit 29 may be any number as long as it is one or more. When the time constant of the filter circuit 27A is constant, the larger the number of stages, the more ripple is suppressed. Great ability. On the other hand, when the time constant is set to be small as in the condition of the above equation, the suppression capability of the ripple becomes the same as that of the conventional example shown in FIG. in this case,
Since the time constant of the filter circuit 27A is 1/2 ⁿ of the time constant of the filter circuit 27, the response is 2 ⁿ times faster than the conventional example.

As a result, when a sudden change in the sine wave reference voltage e ₀ due to a temperature change or a change in the power supply voltage, or a sudden change in the reference voltage e ₀ which occurs when the impedance of the measuring object 13 is low, occurs. Then, the control voltage Ec to the reference voltage generating circuit 14 changes suddenly in a pulse shape. At this time, since the time constant of the filter circuit 27A is small, the time t (see FIG. 6B) required until the control voltage Ec is stabilized becomes short. At this time, the sine wave reference voltage e ₀ is
The waveform is modulated by the control voltage Ec, and the time t (see FIG. 7B) until the reference voltage e ₀ stabilizes is also shortened.

It should be noted that the time constant of the filter circuit 27A is not restricted by the value of the number of stages n of the multiplication circuit, and the time constant of the
7, the time t required for the control voltage Ec to stabilize can be made shorter than in the conventional example.
Therefore, the time t until the reference voltage e ₀ is stabilized can be shortened.

The configuration and operation other than those described above are the same as those described in the conventional example of FIG.

As described above, according to the impedance measuring apparatus of the first embodiment of the present invention, before the voltage generated in the measuring object 13 is converted to DC by the AC-DC conversion circuit 24, the frequency is increased by 2 ⁿ times. Since the frequency is multiplied by the multiplying circuit 29, the time constant of the filter circuit 27A can be made smaller than that of the conventional example in order to obtain a necessary ripple reducing function. As a result, the reference voltage can be stabilized with good responsiveness while the ripple in the control voltage when the amplitude of the sine wave reference voltage is controlled to be constant is sufficiently suppressed.

[0052] For example, the time constant of the filter circuit 27A becomes possible to reduce the reciprocal of the multiplication factor to achieve the same ripple reduction function, since the time constant of the filter circuit 27A can be reduced, the reference voltage e ₀ Responsiveness can be stabilized.

As described above, the 2 ⁿ frequency multiplier 2
9 and the value of the time constant of the filter circuit 27A are:
It is not necessary to interlock with each other, and at least the frequency is doubled, and the time constant of the filter circuit 27A is set smaller than the time constant of the filter circuit 27 of the conventional example, thereby controlling the amplitude of the sine wave reference voltage to be constant. The reference voltage can be stabilized with good responsiveness while suppressing the ripple component in the control voltage at this time sufficiently.

[Second Embodiment] In FIG. 2, an impedance of a measurement object is calculated from a voltage generated in the measurement object by flowing a sine wave reference current having a constant amplitude through the measurement object. FIG. 4 is a block diagram of an impedance measuring device according to a second embodiment.

As shown in FIG. 2, this impedance measuring apparatus uses an automatic level control circuit 42A in place of the automatic level control circuit 42 shown in FIG. 5, and the other configuration is the same as that of FIG.

In the automatic level control circuit 42 A, a 2 ⁿ frequency multiplier (n is an integer of 1 or more) 49 is inserted between the buffer amplifier 43 and the AC-DC converter 44, and is replaced with the filter circuit 47. The difference from the automatic level control circuit 42 of FIG. 5 is that a filter circuit 47A is used.

The 2 ⁿ -times frequency multiplying circuit 49 includes n multiplying circuits 491 to 49n for doubling the frequency of the input signal.
When the frequency of the output signal of the buffer amplifier 43 is f ₀ , for example, the first stage multiplication circuit 4
The frequency of the output signal of 91 is 2f ₀ , and the frequency of the output signal of the final stage multiplier 49n is 2 ⁿ f ₀ . The configuration of the above-mentioned doublers 491-49n is the same as that shown in FIG.

The filter circuit 47A comprises a resistor (resistance R ') 45A and a capacitor (capacitance C') 46A, and its time constant is set to, for example, 1/2 ⁿ of the time constant of the filter circuit 47. That is, for example, it is set so as to satisfy the relationship of R′C ′ = RC / 2 ⁿ .

The number n of multiplication circuits in the 2 ⁿ -times frequency multiplication circuit 49 may be any number as long as it is one or more. When the time constant of the filter circuit 47A is constant, the larger the number of stages, the more ripple is suppressed. Great ability. On the other hand, if the value is set to be small as in the condition of the above formula, the suppression capability for the ripple becomes the same as that of the conventional example shown in FIG. In this case, the time constant of the filter circuit 47A is 1/1 / the time constant of the filter circuit 47.
2 ⁿ , and the response is 2 ⁿ times faster than the conventional example.

As a result, when a sudden change in the sine wave reference current i ₀ due to a temperature change or a change in the power supply voltage, or a sudden change in the reference current i ₀ which occurs when the impedance of the measuring object 33 is low, occurs. Then, the control voltage Ec to the reference voltage generation circuit 34 changes suddenly in a pulse shape. At this time, since the time constant of the filter circuit 47A is large, the time required until the control voltage Ec is stabilized becomes short. At this time, the sine wave reference current i ₀ has a waveform modulated by the control voltage Ec, and the time required for the reference current i ₀ to stabilize is also shortened.

It should be noted that the time constant of the filter circuit 47A is not limited to the value of the number of stages n of the multiplying circuit, and the time constant of the filter circuit 47A is not limited.
By setting the time constant smaller than 7, the time required for the control voltage Ec to stabilize can be shorter than that of the conventional example, and therefore, the time required for the reference current i ₀ to stabilize can be shortened.

The configuration and operation other than those described above are the same as those described in the conventional example of FIG.

As described above, according to the impedance measuring apparatus of the second embodiment of the present invention, before the voltage corresponding to the current flowing through the measuring object 33 is converted to DC by the AC-DC conversion circuit 44, Since the frequency is multiplied by the ²ⁿ frequency multiplier 49, the time constant of the filter circuit 47A can be made smaller than that of the conventional example in order to obtain a necessary ripple reduction function. As a result, while controlling the amplitude of the sine wave reference current to be constant, the ripple in the control voltage can be suppressed sufficiently low, and the reference current can be stabilized with good responsiveness.

[0064] For example, the time constant of the filter circuit 47A becomes possible to reduce the reciprocal of the multiplication factor to achieve the same ripple reduction function, since the time constant of the filter circuit 47A can be reduced, the reference current i ₀ Responsiveness can be stabilized.

As described above, the 2 ⁿ frequency multiplier 4
9 and the value of the time constant of the filter circuit 47A are:
It is not necessary to interlock with each other, and at least the frequency is doubled, and the time constant of the filter circuit 47A is set smaller than the time constant of the filter circuit 47 of the conventional example, so that the amplitude of the sine wave reference voltage is controlled to be constant. The reference current can be stabilized with good responsiveness while suppressing the ripple component in the control voltage at this time sufficiently.

[0066]

According to the impedance measuring apparatus of the first invention, before the voltage generated in the object to be measured is converted into a direct current by the AC-DC conversion circuit, the frequency is multiplied. In order to obtain the function, the time constant of the filter circuit can be made smaller than in the conventional example.
As a result, the reference voltage can be stabilized with good responsiveness while suppressing the ripple in the control voltage when controlling the amplitude of the sine wave reference voltage to be constant.

According to the impedance measuring apparatus of the second invention, the voltage corresponding to the current flowing through the object to be measured is converted to an AC-
Since the frequency is multiplied before the DC conversion is performed by the DC conversion circuit, the time constant of the filter circuit can be made smaller than that of the conventional example in order to obtain a necessary ripple reduction function. As a result, while controlling the amplitude of the sine wave reference current to be constant, the ripple in the control voltage can be suppressed sufficiently low, and the reference current can be stabilized with good responsiveness.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an impedance measuring device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an impedance measuring device according to a second embodiment of the present invention.

FIG. 3 is a block diagram illustrating an example of a specific configuration of a multiplier circuit.

FIG. 4 is a block diagram showing a configuration of a first conventional impedance measuring device.

FIG. 5 is a block diagram showing a configuration of a second conventional impedance measuring device.

FIG. 6 is a waveform chart showing an operation of the automatic level control circuit.

FIG. 7 is a waveform diagram showing a reference voltage of a reference voltage generation circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Measurement terminal 12 Measurement terminal 13 Measurement object 14 Reference voltage generation circuit 15 Current / voltage conversion circuit 16 Phase detection circuit 17 A / D conversion circuit 18 Sine wave oscillator 19 Amplifier 20 Operational amplifier 21 Resistor 22A Automatic level control circuit 23 Buffer Amplifier 24 AC-DC conversion circuit 25A Resistor 26A Capacitor 27A Filter circuit 28 Impedance calculation circuit 29 ²ⁿ frequency multiplier 31 Measurement terminal 32 Measurement terminal 33 Measurement object 34 Reference current generation circuit 35 Current / voltage conversion circuit 36 Phase detection Circuit 37 A / D conversion circuit 38 Sine wave oscillator 39 Amplifier 40 Operational amplifier 41 Resistor 42A Automatic level control circuit 43 Buffer amplifier 44 AC-DC conversion circuit 45A Resistor 46A Capacitor 47A Filter circuit 48 Impedance calculation Circuit 49 2 ⁿ times the frequency multiplier circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 27/00 H03G 3/20

Claims (6)

(57) [Claims] 1. A reference voltage generating circuit for generating a sine wave reference voltage and applying the reference voltage to a measurement target; an impedance calculation circuit for calculating an impedance of the measurement target from a current flowing through the measurement target; An automatic level control circuit that controls the amplitude of the reference voltage to be constant based on a voltage generated in the object; a frequency multiplying circuit that multiplies a frequency of the voltage generated in the measurement object; and An AC-DC converter circuit for converting the output voltage of the frequency multiplier circuit into DC,
An impedance measuring apparatus, comprising: a filter circuit that removes a ripple component of an output voltage of the AC-DC conversion circuit and provides the control voltage to the reference voltage generation circuit. 2. The impedance measuring device according to claim 1, wherein the AC / DC conversion circuit comprises an absolute value circuit. 3. A frequency multiplying circuit comprising: a phase shifter for generating first and second voltages having phases shifted from each other by 90 degrees based on a voltage generated on an object to be measured; and a second phase shifter output from the phase shifter. The impedance measuring device according to claim 1, further comprising an analog multiplier that multiplies the first and second voltages. 4. A reference current generating circuit for generating a sine wave reference current and flowing the same to an object to be measured, an impedance calculating circuit for calculating an impedance of the object to be measured from a voltage generated in the object to be measured, and An automatic level control circuit that controls the amplitude of the reference current to be constant based on a current flowing through the object, wherein the automatic level control circuit multiplies a frequency of a voltage corresponding to the current flowing through the object to be measured. A circuit, and an AC for converting the output voltage of the frequency multiplying circuit into DC.
An impedance measuring apparatus, comprising: a DC conversion circuit; and a filter circuit that removes a ripple component of an output voltage of the AC-DC conversion circuit and provides a control voltage to the reference current generation circuit. 5. The impedance measuring device according to claim 1, wherein the AC-DC conversion circuit comprises an absolute value circuit. 6. A frequency multiplying circuit, comprising: a phase shifter for generating first and second voltages having phases shifted from each other by 90 degrees based on a voltage corresponding to a current flowing through an object to be measured; 2. The impedance measuring device according to claim 1, further comprising an analog multiplier for multiplying the output first and second voltages.