JP3389528B2 - Impedance / voltage converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an operational amplifier to convert impedance into a corresponding voltage.
The present invention relates to a voltage (Z / V) conversion device, and more particularly to a Z / V conversion device capable of preventing an output voltage drift due to an environmental change due to temperature change or the like or heat generation of the device itself.

[0002]

2. Description of the Related Art FIG. 8 is a schematic diagram showing a configuration of a capacitance-voltage (C / V) converter disclosed in Japanese Patent Laid-Open No. 61-14578. In the device of this conventional example, stray capacitance is superimposed on a signal line for connecting an unknown capacitance Cx to a C / V converter, and the stray capacitance changes due to movement or bending of the signal line. This is proposed in order to solve the problem that accurate C / V conversion cannot be performed, and as shown in the figure, the signal line L1 is provided between the AC signal generator OS and the operational amplifier OP. And L
An unknown capacitance Cx is connected via 2 and these signal lines L
By shielding 1 and L2 with the shield means s1 and s2, it is intended to reduce the influence of the stray capacitances Cs1, Cs2, and Cs3. A feedback circuit composed of a parallel circuit of a resistor Rf and a capacitor Cf is connected between the output terminal and the inverting input terminal of the operational amplifier OP, and the non-inverting input terminal of the inverting amplifier and the AC signal generator OS are connected. The end and the shields s1 and s2 are grounded.

In the C / V conversion device of FIG. 8 having such a configuration, the two input terminals of the operational amplifier OP are in an imaginary short state due to the nature of the operational amplifier having the negative feedback circuit, which results in The two input terminals have almost the same potential (the inverting input terminal has a virtual ground potential), and the stray capacitance Cs2 is not charged. The stray capacitance Cs3 is
It can be considered as the coupling capacitance of the two shield means s1 and s2, but since they are both grounded, they too are not charged. Therefore, the influence of the stray capacitance of the cable connecting the unknown capacitance Cx is reduced, so that the same charge as the charge induced in the capacitance Cx is induced in the capacitor Cf of the feedback circuit, and eventually the capacitance is increased. Voltage Vo = − (Cx / Cf) Vi proportional to Cx, where Vi is the output voltage of the AC signal generator OS.

[0004]

However, in the C / V conversion device of FIG. 8, when the unknown capacitance becomes small, the effect of the stray capacitance becomes apparent, and there is a problem that accurate C / V conversion cannot be performed. is there. Further, since the feedback circuit of the operational amplifier OP is configured by the parallel circuit of the resistor Rf and the capacitor Cf, when it is actually integrated into one chip,
The process for forming the parallel circuit is required, which complicates the manufacturing process and increases the chip size. Further, when one electrode of the electrostatic capacitance Cx is biased to a certain potential, AC cannot be applied to the electrostatic capacitance, so that there is a problem that C / V conversion is impossible. Further, in the C / V converter shown in FIG. 8, no measures are taken against the drift of the output voltage Vo due to environmental changes such as temperature changes, heat generation of the device itself, or aged changes of the device. Therefore, for example, although the capacitance Cx to be measured does not change, the level of the output voltage Vo differs between when the measurement environment is high temperature and when it is low temperature. It may not be possible to obtain the corresponding output voltage exactly. The present invention has been proposed in order to solve such a problem, and an object thereof is to provide an impedance / voltage (Z / V) converter for converting an impedance to be measured into a voltage, depending on the surrounding environment or the like. The purpose of this is to effectively reduce the drift of the output voltage that occurs and to obtain an output voltage that corresponds to the impedance to be measured with high accuracy.

[0005]

In order to achieve the above object, the impedance / voltage (Z / V) converter of the present invention is an AC voltage having an amplitude corresponding to the value of the impedance connected to the input terminal. AC voltage output means for outputting, dummy impedance of known value, and dummy
A switch circuit for selectively connecting the impedance and the measured impedance to the input terminal of the AC voltage output means,
AC / DC conversion circuit for converting the AC voltage from the AC voltage output means into a DC voltage corresponding to its amplitude, a sample hold circuit for sampling and holding the DC voltage from the AC / DC conversion circuit, and an AC / DC conversion circuit A subtraction circuit for subtracting the voltage held in the sample-hold circuit from the DC voltage from, and a control circuit for controlling the operation of the switch circuit, the sample-hold circuit, and the subtraction circuit. The hold circuit is controlled so that the dummy impedance is connected to the input terminal of the AC voltage output means, and the DC voltage corresponding to the dummy impedance from the AC / DC conversion circuit is held by the sample hold circuit, and then the switch circuit. And the subtraction circuit are controlled to measure the input terminal of the AC voltage output means. A control circuit that connects the impedance and controls to subtract the voltage held in the sample-hold circuit from the DC voltage corresponding to the measured impedance from the AC / DC conversion circuit. It is characterized in that it can be obtained.

In the impedance / voltage converter described above, a bias voltage generating circuit for generating a voltage having the same absolute value and opposite polarity as the bias voltage of the DC voltage from the AC / DC converting circuit is used instead of the sample-hold circuit. However, an addition circuit may be used instead of the subtraction circuit. Further, it is preferable that the measured impedance and the dummy impedance both have the same characteristic and are placed under the same condition. By using these impedances as capacitances, a capacitance / voltage conversion device can be configured, which is suitable for detecting electrostatic capacitances.

Further, the AC voltage output means is connected to an operational amplifier having a feedback impedance connected between an inverting input terminal serving as an input terminal of the AC voltage output means and an output terminal, and a non-inverting input terminal of the operational amplifier. A second signal line connecting the switch circuit and the impedance to be measured, the shield being provided on at least a part of the first signal line connecting the switch circuit and the inverting input terminal of the operational amplifier. Of at least one shield of at least a part of the shield provided on at least a part of the third signal line connecting the switch circuit and the dummy impedance to the non-inverting input terminal of the operational amplifier. Is preferably connected to. By doing so, it is possible to effectively eliminate the influence of the stray capacitance of the signal line due to the imaginary short state of the two input terminals of the operational amplifier.

[0008] Impedance /
In the voltage converter, an AC voltage output means for outputting an AC voltage having an amplitude corresponding to the impedance value connected to the input terminal, and a ground terminal and an impedance to be measured are selectively input terminals of the AC voltage output means. A switch circuit connected to the AC voltage converter, an AC / DC converter circuit for converting into a DC voltage corresponding to the amplitude of the AC voltage from the AC voltage output means, and a DC voltage from the AC / DC converter circuit having the same absolute value but opposite polarity. Voltage generating circuit for generating the voltage of the above as a bias voltage, an adding circuit for adding a DC voltage from the AC / DC converting circuit and a bias voltage from the bias voltage generating circuit, a switch circuit, a bias voltage generating circuit and an adding circuit A control circuit for controlling the AC voltage output by controlling the switch circuit and the bias voltage generation circuit immediately after the start of measurement. The ground terminal is connected to the input terminal of the stage, and the bias voltage is set based on the DC voltage from the AC / DC conversion circuit at that time, and then the switch circuit and the addition circuit are controlled to control the AC voltage output means. It consists of a control circuit that connects the impedance to be measured to the input terminal and controls to add the bias voltage to the DC voltage corresponding to the impedance to be measured from the AC / DC conversion circuit, and obtains the output from which the drift component has been removed. It is characterized by being able to do.

According to the present invention which does not use the above dummy impedance, it is possible to output a voltage corresponding to only the value of the impedance to be measured. Also in this impedance / voltage conversion device, instead of the sample-hold circuit, a bias voltage generation circuit that generates a voltage having the same absolute value as the DC voltage from the AC / DC conversion circuit but opposite polarity is used as the bias voltage. An addition circuit may be used instead of the subtraction circuit. Further, if the impedance to be measured is a capacitance, it is suitable for detecting the electrostatic capacitance, and it is possible to set the impedance to be measured and the ground terminal connected to the AC voltage generating means via the switch circuit under the same condition. It is more effective to reduce.

Further, even in the present invention which does not use the dummy impedance described above, in order to effectively eliminate the influence of the stray capacitance on the signal line, the AC voltage output means is connected to the input terminal of the AC voltage output means. An operational amplifier having a feedback impedance connected between the inverting input terminal and the output terminal, and an oscillator connected to the non-inverting input terminal of the operational amplifier, and connecting the switch circuit and the inverting input terminal of the operational amplifier. A shield provided on at least a part of the first signal line, a shield provided on at least a part of the second signal line connecting the switch circuit and the impedance to be measured, and a connection provided on the switch circuit with the dummy impedance At least one of the shields applied to at least a part of the third signal line is a non-inverting input terminal of the operational amplifier. It is preferably connected.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the principle configuration of a Z / V converter according to the present invention. In this Z / V converter, a measured impedance 6 of an object whose impedance value Zx is to be measured is connected to an inverting input terminal of an operational amplifier 1 via a signal line 5 provided with a shield 7, and the calculated impedance is calculated. The feedback impedance 3 having a known impedance value Zf is connected between the output terminal of the amplifier 1 and the inverting input terminal (−), and the oscillator 4 and the shield 7 are connected to the non-inverting input terminal (+).
Are connected. The output terminal of the operational amplifier 1 has an AC / DC conversion circuit (AC) composed of a rectifying / smoothing circuit or the like.
/ DC) 2 is connected. In the Z / V converter shown in FIG. 1, due to the nature of the operational amplifier having the negative feedback circuit, the inverting and non-inverting input terminals of the operational amplifier 1 are in an imaginary short state, so that they are substantially the same potential. Become. Therefore, since the signal line 5 and the shield 7 have the same potential, the stray capacitance generated between them is not charged and the input terminal of the operational amplifier 1 is not affected by the stray capacitance. This is established regardless of the length of the signal line 5, and is established regardless of the movement or bending of the signal line 5.

Explaining in more detail, Z / shown in FIG.
In the V conversion circuit, since the two input terminals of the operational amplifier 1 are in an imaginary short state, the voltage Vm at the inverting input terminal becomes equal to the oscillation output voltage Vi of the oscillator 4. Then, the current i ₁ flowing through the measured impedance 6
The current i ₂ flowing in the feedback impedance 3 is expressed as follows, where Vo is the AC voltage output from the operational amplifier 1. i ₁ = −Vm / Zx = −Vi / Zx i ₂ = (Vm−Vo) / Zf = (Vi−Vo) / Zf Here, the operational amplifier has a high input impedance characteristic by its nature. , I ₁ = i ₂ , and Vo = Vi (1 + Zx / Zf) (1) is obtained. When the circuit element of the measured impedance Zx is the electrostatic capacitance Cx and the circuit element of the feedback impedance Zf is the resistor Rf, the Z / V converter of FIG.
It becomes a V converter, and the AC voltage Vo in that case can be obtained from the equation (1) as follows. Vo = Vi (1 + jωCxRf) (2) [where ω is the angular frequency of Vi]

Therefore, according to the Z / V converter of FIG. 1, the AC voltage Vo represented by the equation (1) can be output from the operational amplifier 1, and the input terminal of the operational amplifier is imaginarily shorted. , The stray capacitance generated in the signal line 5 does not appear between the input terminals, so that the AC voltage V that exactly corresponds to the value of the impedance Zx to be measured.
o can be output. Then, the AC voltage Vo from the operational amplifier 1 is supplied to an AC / DC (AC / DC) of a rectifying / smoothing circuit or the like.
DC) conversion circuit 2 so that the AC voltage Vo
The DC voltage Vout corresponding to the amplitude of is output. The change state of the measured impedance Zx can be detected by the change of the level of the DC output voltage Vout, and further, the value of the measured impedance Zx can be calculated by adding an appropriate calculation means as necessary. Can be calculated backwards. As described above, Z / in FIG. 1 proposed by the applicant
According to the V converter, it is possible to more accurately output the AC voltage Vo and the DC voltage Vout corresponding to the measured impedance Zx, as compared with the known C / V converter shown in FIG.

FIG. 2 is a schematic diagram showing a first embodiment of the Z / V conversion device of the present invention. In FIG. 2, the same or similar components as those in FIG. 1 are designated by the same reference numerals. is doing. In the first embodiment of the present invention, the Z / V converter of FIG.
A sample hold for sampling and holding the impedance 8, the switch impedance 9 for selectively connecting the measured impedance 6 and the dummy impedance 8 to the inverting input terminal of the operational amplifier 1, and the output of the AC / DC conversion circuit 2. A circuit (SH) 10, a subtraction circuit 11 to which the output of the sample and hold circuit and the output Vout of the AC / DC conversion circuit 2 are input, and control for controlling the operations of the switch circuit 9, the sample and hold circuit 10 and the subtraction circuit 11. It is characterized in that the circuit 12 is added to prevent the output drift. The switch 15 connected in parallel with the feedback impedance 3 is for performing initialization by setting the output of the operational amplifier and the inverting input terminal to the same potential before operating the Z / V converter. It is a thing.

In FIG. 2, the switch circuit 9 is the device under test.
Of the signal line connecting the impedance 6 and the operational amplifier 1
Signals on both sides of the switch circuit 9 are connected to the middle section
Line 5 ₁5,₂To shield 7₁, 7₂And these signals
To reduce the effects of stray capacitance between the wire and the shield.
To protect, shield 7₁And 7₂Is connected to the oscillator 4
It is connected to the non-inverting input terminal of the amplifier 1. And da
Same impedance as measured impedance 6
Since it is preferable to place it in the environment,
-Signal line 5 connecting to impedance 8_dThe signal
Line 5₁Has the same length as the non-inverting input of the operational amplifier 1.
Shield 7 connected to the input terminal (and oscillator 4)_dAt sea
I'm rude. The dummy impedance 8 and
The measured impedances 6 are resistances or capacitances.
It is preferable to be a teacher. Also, switch circuit 9
Close to the input terminal of the operational amplifier 1 or the impeder under test
Place it close to the impedance 6 and the dummy impedance 8.
You can also In the former case, signal line 5₂And shield
7₂Is unnecessary, and in the latter case, the signal line 5 ₁5,_das well as
Shield 7₁, 7_dIs unnecessary.

FIG. 3 shows the output timing of the control signals S ₉ , S ₁₀ and S ₁₁ output from the control circuit 13 of the Z / V converter shown in FIG. The control signal S ₉ is supplied to the switch circuit 9 so that the inverting input terminal of the operational amplifier 1 is connected to the dummy impedance 8 side when the level is high and to the measured impedance 6 side when the level is low. Control the switch circuit. The control signal S ₁₀ is supplied to the sample hold circuit 10, and when the signal is at a high level, the sample hold circuit is operated to operate the AC / DC conversion circuit 2
The output Vout of is sampled and held. The control signal S ₁₁ is supplied to the subtraction circuit 11 and controls the subtraction circuit 11 to execute the subtraction operation when it is at a high level.

With reference to FIGS. 2 and 3, the first aspect of the present invention is described.
The operation of the embodiment will be described. First, turn on the switch 15.
After turning off and initialization, the measurement operation is performed at time t₀Start with
Then, the control circuit 12 causes the control signal S₉To a high level
Switch circuit 9 to the dummy impedance 8 side (point
Line position) and at time t ₁In
Signal S_TenTo high level, and sample and hold circuit 1
Sampling and hold operation by turning on the gate in 0
Let the work run. This allows dummy impedance
DC voltage Vout (= Vout-d (t)) corresponding to Zd
Output from the flow / DC converter circuit 2
It is stored or held in the capacitor of path 10. Next
At time t₂At the control signal S₉Back to low level
Switch circuit 9 to the measured impedance 6 side
The measured impedance Z from the AC / DC conversion circuit 2
DC voltage Vout (= Vout-x (t)) corresponding to x is output
It At this time, the control signal S_TenHas a low level
Therefore, the gate of the sample hold circuit 10 is in the off state.
Hold, and therefore the hold voltage is a dummy impeder
The voltage Vout-d (t) corresponding to the resistance Zd is held.

Then, the control circuit 12 sets the control signal S ₁₁ to a high level at the time point t ₃ , so that the subtraction circuit 11 samples and holds from the DC voltage Vout-x (t) corresponding to the impedance Zx to be measured. The voltage Vout-d (t) held in the circuit 10 is subtracted, and the difference voltage VV = Vout-x (t) -Vout-d (t) (3) is output. The time lag between the time points t ₀ and t ₁ and the time lag between the time points t ₂ and t ₃ require time from the switching of the switch circuit 9 until the output voltage of the AC / DC conversion circuit 2 stabilizes. It is provided.

By the way, Vout-x (t) and Vout-d (t) in the equation (3) include a drift component caused by a change in environmental temperature. The drift component is Vou.
Both tx (t) and Vout-d (t) have the same value ΔV (t). That is, Vout-x (t) = Vout-x + ΔV (t) Vout-d (t) = Vout-d + ΔV (t) ∴V = Vout-x-Vout-d (4) However, Vout-x and Vout-d Is the true measured impedance Z when the output voltage Vout does not include a drift component.
Let us denote the output voltage corresponding to x and Zd. This is true regardless of the value of the measured impedance Zx (and the dummy impedance Zd). Therefore, the voltage V (equation (4)) represented by the difference between Vout-x and Vout-d does not include a drift component caused by a change in the environment, so that the subtraction circuit 11 changes the measured impedance Zx. It is possible to obtain the output voltage V that changes following the change. In addition, when it is necessary to continuously monitor the change in the impedance Zx to be measured, at the time t ₄ , considering that the hold voltage Vout-d (t) of the sample hold circuit 10 decreases due to spontaneous discharge or the like. It suffices to reconnect the switch circuit 9 to the dummy impedance Zd side and repeat the above operation at an appropriate cycle. As a result, the hold voltage Vout-d (t) always accurately corresponds to the dummy impedance Zd.

In the Z / V converter according to the first embodiment shown in FIG. 2, the output voltage Vout-d corresponding to the dummy impedance Zd and containing no drift component has a reference temperature (for example, 25 It can be obtained in advance by using in an environment such as (° C). Therefore, Vout-x = V-Vout-d (5) is obtained from the equation (4), and the measured impedance Zx is obtained from the equation (5).
It is possible to obtain a voltage Vout-x that corresponds to the above and does not include a drift component. Needless to say, when it is sufficient to monitor only the state of change in the measured impedance Zx, the output V may be monitored without the process represented by the equation (5).

FIG. 4 shows a Z / V converter according to the second embodiment of the present invention. The second embodiment is different from the first embodiment shown in FIG. 2 in that a bias voltage generating circuit 13 and an adding circuit 14 are used instead of the sample hold circuit 10 and the subtracting circuit 11. is there. When the control signal S ₁₃ from the control circuit 12 becomes a high level, the bias voltage generation circuit 13 outputs a voltage having the same absolute value and the opposite polarity as the output of the AC / DC conversion circuit 2 at that time. It is intended to occur. The control signal S ₁₃ is generated at the same timing as the control signal S ₁₀ (FIGS. 2 and 3) and is controlled to be high level when the control signal S ₉ is high level. A bias voltage -Vout-d (t) having the same absolute value and opposite sign as the output voltage Vout-d (t) when switched to the impedance 8 side is set. The adder circuit 14 is generated at the same timing as the control signal S ₁₁ (FIGS. 2 and 3), and executes the addition operation when the control signal S ₁₄ is at a high level, and the voltage Vout corresponding to the measured impedance Zx. -x
The bias voltage −Vout-d (t) is superimposed on (t).

That is, at the start of measurement, the switch circuit 9 is switched so that the signal line 5 _d is connected to the dummy impedance 8 side by the control signal S ₉ , and the corresponding output voltage Vout-d (t) is converted into AC / DC. Output from the circuit 2. After the output voltage Vout-d (t) becomes stable, the control signal S ₁₃ sets −Vout-d (t) in the bias circuit 13. And
The switch circuit 9 is switched to the measured impedance 6 side, the voltage Vout-x (t) is output from the AC / DC conversion circuit 2, and the following addition is executed in the adder circuit 14, similar to the case of the first embodiment. The drift component is removed, and it is possible to obtain the output voltage V that changes in accordance with the change in the impedance Zx to be measured. V = Vout-x (t) + (-Vout-d (t)) = Vout-x-Vout-d Note that the bias voltage of the bias voltage generating circuit is AC /
Although the polarity of the output voltage of the DC conversion circuit 2 has been described as being inverted, it is also possible to make the polarity the same, in which case the adder circuit 14 is configured as a subtractor circuit. Therefore, the embodiment of FIG. 2 and the embodiment of FIG. 4 are functionally the same although the realizing means are different.

FIG. 5 shows a third embodiment of the present invention. In the third embodiment, the signal line 5d is grounded via the switch circuit 9 and the second embodiment shown in FIG. (That is, the dummy impedance Zd = 0). In the third embodiment, the output voltage Vout-g (t) corresponding to the zero impedance when the switch circuit 9 is switched to the ground terminal is output from the AC / DC conversion circuit 2 and supplied to the bias circuit 13. −
Vout-g (t) is set as the bias voltage. Since Vout-g (t) at this time corresponds to zero impedance, it is only the drift component and the DC component Vidc corresponding to the oscillation output Vi of the oscillator 4 (from the equation (1)). 13 outputs -Vout-g (t) =-ΔV (t) -Vidc as a bias voltage.

When the switch circuit 9 is switched to the measured impedance 6 side, the addition circuit 14 performs the following addition. V = Vout-x (t) + (-Vout-g (t)) ∴V = Vout-x + ΔV (t) -ΔV (t) -Vidc = Vout-x-Vidc = Vidc (1 + Zx / Zf) -Vidc = Vidc · Zx / Zf With this, it is possible to obtain the voltage V corresponding to the measured impedance Zx and including no drift component. In addition,
Of course, the sample hold circuit 10 and the subtraction circuit 11 shown in FIG. 2 may be used instead of the bias voltage generation circuit 13 and the addition circuit 14.

In FIG. 6, in the first embodiment of the present invention shown in FIG. 2, the impedance to be measured 6 is a capacitance component such as capacitance, the dummy impedance 8 is a capacitance, and the feedback impedance 3 is a capacitance 3. _{1 /} resistor 3 ₂ parallel circuit is adopted,
The case where it is a voltage (C / V) converter is shown. According to the C / V conversion device having such a configuration, it is possible to correct the phase shift that occurs in the output Vo due to a factor such as an operational amplifier. Further, if at least one of the capacitance 3 ₁ and the resistance 3 ₂ is variable, more preferable phase correction can be performed. The measured impedance 6 and the feedback impedance 3 of the second embodiment of the present invention shown in FIG.
It is needless to say that by setting as shown in FIG. 6, it is possible to obtain the same effect as the above.

FIG. 7 shows the C / V conversion device of the present invention shown in FIG. 6 and the Z / V conversion device shown in FIG. 1 configured as a C / V conversion device. The results are displayed in a graph. Note that the same capacitance Cx to be measured is used, and the conditions are the same, and Cx
Was measured and the amount of change was determined. In the graph, the plot points indicated by squares (□) are the test measurement results according to the present invention, and appear almost along the straight line (A). on the other hand,
Plot points indicated by circles (∘) are test results by the apparatus of FIG. 1, and appear almost along the straight line (B). As is clear from this graph, according to the present invention, it is understood that the drift component can be suppressed because the measured value is almost constant.

Since the present invention is configured as described above, in the Z / V converter, it is possible to compensate the output drift due to the change of the measurement environment, and to connect the impedance Zx to be measured. Since it is possible to reduce the influence of stray capacitance on the line, it is possible to perform Z / V conversion with extremely high accuracy, and the utility is extremely high.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a principle configuration of a Z / V conversion device of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a Z / V conversion device according to a first embodiment of the present invention.

FIG. 3 is a timing chart showing a generation timing of a control signal in the Z / V conversion device shown in FIG.

FIG. 4 is a circuit diagram showing a configuration of a Z / V conversion device according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of a Z / V conversion device according to a third embodiment of the present invention.

FIG. 6 shows the Z / V conversion device shown in FIG.
It is a circuit diagram which shows the structure at the time of using as a / V) conversion device.

FIG. 7 is a graph showing the measurement results of actual device tests of the C / V conversion device shown in FIG. 6 and the case where the Z / V conversion device shown in FIG. 1 is used as the C / V conversion device.

FIG. 8 is a circuit diagram showing a configuration of a conventional C / V conversion device.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI G01D 5/24 K (72) Inventor Toshiyuki Matsumoto 1-8 Fuso-cho, Amagasaki-shi, Hyogo Sumitomo Metal Industries Co., Ltd. 56) References JP-A-9-280806 (JP, A) JP-A-2-302628 (JP, A) JP-A-61-82103 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 27/26 G01R 27/02 G01R 35/00 G01D 5/24

Claims (13)

(57) [Claims] 1. An impedance / voltage converter for converting an impedance value to be measured into a voltage, an AC voltage output means for outputting an AC voltage having an amplitude corresponding to a value of an impedance connected to an input terminal, and a known value. And a switch circuit that selectively connects the dummy impedance and the measured impedance to the input terminal of the AC voltage output means, and converts the AC voltage from the AC voltage output means into a DC voltage corresponding to its amplitude. AC / DC conversion circuit, sample / hold circuit for sampling / holding DC voltage from AC / DC conversion circuit, and subtraction for subtracting voltage held in sample / hold circuit from DC voltage from AC / DC conversion circuit AC voltage by controlling the circuit, switch circuit and sample hold circuit A dummy impedance is connected to the input terminal of the force means, and a DC voltage corresponding to the dummy impedance from the AC / DC conversion circuit is held by the sample hold circuit, and then the switch circuit and the subtraction circuit are controlled to change the AC voltage. And a control circuit for connecting the impedance to be measured to the input terminal of the voltage output means, and controlling so as to subtract the voltage held in the sample hold circuit from the DC voltage corresponding to the impedance to be measured from the AC / DC conversion circuit. An impedance / voltage conversion device characterized in that an output from which a drift component is removed can be obtained. 2. An impedance / voltage converter for converting an impedance value to be measured into a voltage, an AC voltage output means for outputting an AC voltage having an amplitude corresponding to a value of an impedance connected to an input terminal, and a known value. And a switch circuit that selectively connects the dummy impedance and the measured impedance to the input terminal of the AC voltage output means, and converts the AC voltage from the AC voltage output means into a DC voltage corresponding to its amplitude. An AC / DC converter circuit, a bias voltage generator circuit that generates a voltage having the same absolute value and opposite polarity as the bias voltage from the AC / DC converter circuit, and a DC voltage from the AC / DC converter circuit. An adder circuit for adding the bias voltage from the bias voltage generating circuit, a switch circuit and a bias voltage The raw circuit is controlled to connect the dummy impedance to the input terminal of the AC voltage output means, and the bias voltage is set based on the DC voltage from the AC / DC conversion circuit at that time, and then the switch circuit and the addition circuit are added. Control the circuit and connect the impedance to be measured to the input terminal of the AC voltage output means,
And a control circuit for controlling to add a bias voltage to a DC voltage corresponding to the impedance to be measured from the AC / DC conversion circuit, and it is possible to obtain an output from which a drift component is removed. Impedance / voltage converter. 3. The impedance according to claim 1 or 2.
In the voltage converter, the impedance to be measured and the dummy impedance have the same characteristic, and the impedance / voltage converter is characterized. 4. The impedance / voltage conversion device according to claim 1, wherein the impedance to be measured and the dummy impedance are placed under the same condition. 5. The impedance / voltage conversion device according to claim 1, wherein the AC voltage output means has a feedback impedance between an inverting input terminal serving as an input terminal of the AC voltage output means and an output terminal. Applied to at least a part of the first signal line connecting the switch circuit and the inverting input terminal of the operational amplifier, which includes an operational amplifier connected to the operational amplifier and an oscillator connected to the non-inverting input terminal of the operational amplifier. A shield is provided on at least a part of the second signal line connecting the switch circuit and the impedance to be measured, and a shield is provided on at least a part of the third signal line connecting the switch circuit and the dummy impedance. Impedance / voltage conversion, characterized in that at least one of the two shields is connected to the non-inverting input terminal of the operational amplifier. Location. 6. An impedance / voltage converter for converting a measured impedance value into a voltage, wherein a dummy impedance having a known value, an operational amplifier, and the dummy impedance and the measured impedance are selectively inverted. A switch circuit connected to the input terminal, a feedback impedance connected between the output terminal of the operational amplifier and the inverting input terminal, and an oscillator connected to the non-inverting input terminal of the operational amplifier. A shield applied to at least a part of the first signal line connecting the inverting input terminal of the switch, a shield applied to at least a part of the second signal line connecting the switch circuit and the impedance to be measured, and a switch Shield applied to at least a part of the third signal line connecting the circuit and the dummy impedance At least one shield is non-inverting impedance / voltage conversion apparatus characterized by being connected to an input terminal of the operational amplifier of the inner. 7. The impedance / voltage converter according to claim 6, wherein the measured impedance and the dummy impedance have the same characteristics. 8. The impedance according to claim 6 or 7.
In the voltage converter, the impedance to be measured and the dummy impedance are both placed under the same condition. 9. An impedance / voltage converter for converting a measured impedance value into a voltage, an AC voltage output means for outputting an AC voltage having an amplitude corresponding to the value of the impedance connected to an input terminal, and a ground terminal. A switch circuit for selectively connecting the impedance to be measured to the input terminal of the AC voltage output means, an AC / DC conversion circuit for converting to a DC voltage corresponding to the amplitude of the AC voltage from the AC voltage output means, and an AC / DC A bias voltage generating circuit that generates a voltage having the same absolute value and opposite polarity as the bias voltage from the conversion circuit, and the DC voltage from the AC / DC conversion circuit and the bias voltage from the bias voltage generation circuit are added. Control the adder circuit, the switch circuit and the bias voltage generating circuit, and input the voltage to the input terminal of the AC voltage output means. And the bias terminal is set based on the DC voltage from the AC / DC conversion circuit at that time, and then the switch circuit and the addition circuit are controlled to measure the input voltage to the input terminal of the AC voltage output means. A control circuit for connecting the impedance and controlling to add a bias voltage to the DC voltage corresponding to the measured impedance from the AC / DC conversion circuit, so that an output from which the drift component is removed can be obtained. An impedance / voltage converter characterized in that 10. The impedance / voltage conversion device according to claim 9, wherein the impedance to be measured and the ground terminal connected to the AC voltage generating means via the switch circuit are placed under the same condition. Impedance / voltage converter. 11. The impedance / voltage conversion device according to claim 9 or 10, wherein the AC voltage output means has a feedback impedance connected between an inverting input terminal serving as an input terminal of the AC voltage output means and an output terminal. An operational amplifier and an oscillator connected to the non-inverting input terminal of the operational amplifier, and a shield and a switch applied to at least a part of a first signal line connecting the switch circuit and the inverting input terminal of the operational amplifier. A shield applied to at least a part of the second signal line connecting the circuit and the impedance to be measured, and a shield applied to at least a part of the third signal line connecting the switch circuit and the dummy impedance. At least one of the shields is connected to the non-inverting input terminal of the operational amplifier. 12. An impedance / voltage converter for converting a measured impedance value into a voltage, an operational amplifier, a switch circuit for selectively connecting a ground terminal and the measured impedance to an inverting input terminal of the operational amplifier, and an operational circuit. A feedback impedance connected between an output terminal and an inverting input terminal of the amplifier; and an oscillator connected to a non-inverting input terminal of the operational amplifier, the first circuit connecting the switch circuit and the inverting input terminal of the operational amplifier A shield provided on at least a part of the signal line, a shield provided on at least a part of the second signal line connecting the switch circuit and the impedance to be measured, and a shield provided on the switch circuit and the dummy impedance. Of at least one of the shields applied to at least a part of the signal line 3 of the operational amplifier. It is connected to the inverting input terminal impedance / voltage conversion device according to claim. 13. The impedance / voltage conversion device according to claim 12, wherein the impedance to be measured and the ground terminal are both placed under the same condition.