JP2008085745A - Correction coefficient acquisition method and impedance measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure impedance with higher precision than the prior art in an impedance measuring instrument comprising an analog/digital converter for detecting a vector ratio. <P>SOLUTION: An impedance measuring instrument (10) comprising the analog/digital converter (430) for performing digital conversion on a signal representing a voltage to be applied to an object to be measured and a signal representing a current flowing through the object to be measured is provided with: a storage means (520) for storing a correction coefficient G; and a means (510) which uses the correction coefficient G stored in the storage means to correct output data of the analog/digital converter. The correction coefficient G is acquired before measurement using the impedance measuring instrument (10). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for correcting a measurement error of an impedance measuring apparatus, and more particularly to a technique for correcting a measurement error caused by the linearity of an analog / digital converter.

  In recent measuring instruments, analog / digital converters are frequently used. For example, the impedance measuring device applies a measurement signal to the device under test, measures the current flowing through the device under test and the voltage applied to the device under test, and obtains the impedance of the device under test based on those measurement results. Thus, the impedance of the object to be measured is measured. In the impedance measuring device, the voltage is digitized by an analog / digital converter in a vector ratio detector (VRD), and the current is converted into a voltage by the current / voltage converter and then converted to the same analog / digital converter. Digitized by the instrument.

Japanese Patent Laid-Open No. Hei 10-108041 (pages 2 to 4, FIG. 1) JP-A-Heisei 11-346153 (pages 2 to 4, FIG. 1)

  The linearity error of the analog / digital converter is one of the causes of measurement errors. For example, even though a 14-bit analog-digital converter has good performance, its SFDR (spurious-free dynamic range) is about 90 to 100 dB. If a signal of 1/5 of full scale is input to such an analog-digital converter, an error of about 50 to 150 ppm occurs. This value is unacceptable in current impedance measuring devices. In order to reduce this error, it is necessary to use an analog / digital converter having higher resolution and excellent linearity characteristics. Generally, as the resolution of the analog / digital converter increases, the conversion speed of the analog / digital converter decreases. When such a low-speed analog / digital converter measures a high-speed, that is, high-frequency signal, a mixer or a local signal source for frequency conversion (down conversion) is required. These additional components increase the circuit scale and cost.

  In order to solve the above problems, the present invention applies a signal under measurement generated by an impedance measuring device to an element whose impedance changes according to the frequency, and applies a voltage applied to the element or a current flowing through the element. Alternatively, the impedance of the element is measured with an impedance measuring device. These measured values vary depending on the impedance of the element. The impedance of the element is controlled by changing the frequency of the measurement signal during the measurement. The coefficient for correcting the linearity error of the analog / digital converter provided in the impedance measuring apparatus is obtained from the measured value and true value of voltage, current, or impedance. The correction coefficient G is stored in the storage means so that it can be used in the impedance measuring apparatus. On the other hand, the impedance measuring device corrects the output data of the analog / digital converter in the impedance measuring device using the stored correction coefficient G.

  In short, the first invention is an analog-to-digital converter provided in an impedance measuring apparatus, which is an analog / digital converter for digitally converting a signal representing a voltage applied to a device under test and a signal representing a current flowing through the device under test. A method for obtaining a coefficient for correcting a linearity error of a digital converter, wherein the impedance changes with frequency and the frequency-impedance characteristic is known and is connected to the measuring device as a device under test. And while changing the frequency of the measurement signal while maintaining the impedance of the element to which the measurement signal generated by the measurement device is applied, or the current flowing through the element, the voltage applied to the element is substantially constant, A first step of measuring with the measuring device; a measured value in the first step; and Using the true value of the current flowing through the true value or the element of the impedance and is characterized in that it comprises a second step of obtaining the correction coefficient.

  Further, the second invention is an analog / digital converter provided in the impedance measuring device, and digitally converts a signal representing a voltage applied to the device under test and a signal representing a current flowing through the device under test. A method for obtaining a coefficient for correcting a linearity error of an analog / digital converter, wherein the impedance changes according to the frequency and the frequency-impedance characteristic is known, and is connected to the measuring apparatus as a device under test. The impedance of the element to which the measurement signal generated by the measurement apparatus is applied or the current flowing through the element is changed while the frequency applied to the element is kept substantially constant while the frequency of the measurement signal is changed. A first step of measuring with the measuring device, and a resistance value is known and connected to the measuring device as an object to be measured. In addition, the impedance of the resistor to which the measurement signal generated by the measurement device is applied or the current flowing through the resistor is changed while the voltage applied to the resistor is kept substantially constant, and the frequency of the measurement signal is changed. The second step of measuring with the measuring device, the measured value in the first and second steps, and the true value of the impedance of the element and the resistor or flowing through the element and the resistor And a third step of obtaining the correction coefficient using the true value of the current.

  Further, the third invention is an analog / digital converter provided in the impedance measuring apparatus, which digitally converts a signal representing a voltage applied to the device under test and a signal representing a current flowing through the device under test. A method for obtaining a coefficient for correcting a linearity error of an analog / digital converter, wherein the impedance changes according to the frequency and the frequency-impedance characteristic is known, and is connected to the measuring apparatus as a device under test. The impedance of the element to which the measurement signal generated by the measurement device is applied or the voltage applied to the element is changed while changing the frequency of the measurement signal while keeping the current flowing through the element substantially constant. , A first step of measuring with the measuring device, a measured value in the first step, and the element True value of the impedance or with the true value of the voltage applied to the element, and comprising a, a second step of deriving the correction coefficient.

  Still further, the fourth invention is an analog / digital converter provided in the impedance measuring apparatus, wherein the signal representing the voltage applied to the object to be measured and the signal representing the current flowing through the object to be measured are digitally converted. A method for obtaining a coefficient for correcting a linearity error of an analog / digital converter, the impedance of which varies with frequency, the frequency-impedance characteristics are known, and the measurement device is used as a device under test. The impedance of the element to which the measurement signal generated by the measurement device is applied or the voltage applied to the element is changed while changing the frequency of the measurement signal while keeping the current flowing through the element substantially constant. However, the first step of measuring with the measuring device, the resistance value is known, and the measuring device as the object to be measured The impedance of the resistor to which the measurement signal generated by the measurement device is applied or the voltage applied to the resistor is maintained at a substantially constant current through the resistor, while the frequency of the measurement signal is maintained. The second step of measuring with the measuring device while changing the value, the measured values in the first and second steps, and the true value of the impedance of the element and the resistor or the element and the resistor And a third step of obtaining the correction coefficient by using a true value of the voltage applied to.

  The fifth invention is characterized in that, in any one of the first to fourth invention methods, the element is a capacitor or an inductor.

  Furthermore, the sixth invention is characterized in that, in the first to fifth invention methods, the correction coefficient is a multiplier or a divisor for the output data of the analog-digital converter. It is.

  Furthermore, the seventh invention provides an impedance measuring apparatus comprising an analog / digital converter for digitally converting a signal representing a voltage applied to a device under test and a signal representing a current flowing through the device under test. Storage means storing a correction coefficient obtained by any one of the first to sixth methods, and arithmetic means for correcting the output data of the analog / digital converter using the correction coefficient stored in the storage means These are provided.

  Further, the present invention relates to an impedance measurement apparatus comprising an analog / digital converter for digitally converting a signal representing a voltage applied to a device under test and a signal representing a current flowing through the device under test. Storage means for correcting a linearity error of the converter and storing a correction coefficient that is a multiplier or a divisor for the output data of the analog / digital converter, and output data of the analog / digital converter And a calculation means for multiplying the correction coefficient by the correction coefficient.

  According to the present invention, it is possible to obtain a coefficient for correcting a linearity error of an analog / digital converter without separately preparing a high-accuracy voltage source. The correction coefficient G is acquired with an accuracy depending on the control accuracy of the frequency of the measurement signal. Then, the impedance measuring device can correct the linearity error of the analog / digital converter by using the correction coefficient G. As a result, a higher-speed analog-to-digital converter can be used in the impedance measuring apparatus without impairing the measurement accuracy.

  The present invention has the effect of reducing not only the linearity error of the analog / digital converter but also the linearity error of the front circuit of the analog / digital converter.

  Hereinafter, the present invention will be described based on preferred embodiments shown in the accompanying drawings. The first embodiment of the present invention is an impedance measuring apparatus 10. First, the configuration and operation of the impedance measuring apparatus 10 will be described. After that, acquisition of a correction coefficient used in the impedance measuring apparatus 10 will be described.

(Configuration of impedance measuring apparatus 10)
Reference is now made to FIG. FIG. 1 is a diagram illustrating a configuration of the impedance measuring apparatus 10. In FIG. 1, an impedance measuring device 10 is a device that measures the impedance of a device under test 100 by an automatic balanced bridge method. The impedance measuring device 10 includes a signal source 200, a current-voltage converter 300, a vector ratio detector 400, and a correction device 500.

  The device under test 100 is a device under test having at least two terminals. When the DUT 100 has three or more terminals, two of these terminals are used for measurement. The device under test 100 is connected to the impedance measuring apparatus 10 via four terminals (Hpot, Hcur, Lpot, Lcur).

  The signal source 200 is a signal generator that generates a measurement signal S to be applied to the device under test 100. The measurement signal S is a sine wave signal. The frequency f of the measurement signal S is variable by a PLL (Phase Locked Loop) technique or a DDS (Direct Digital Synthesizer) technique. Therefore, the frequency f is controlled with an absolute accuracy of 50 ppm or a relative accuracy of 10 ppm. Hereinafter, the frequency f of the measurement signal S is referred to as a measurement frequency f. The signal source 200 is connected to the device under test 100 via the Hcur terminal. The signal source 200 is also connected to the vector ratio detector 400 via the Hcur terminal and the Hpot terminal. Element 210 represents the output impedance of signal source 200 and exhibits a substantially constant 50 ohm impedance Zo regardless of frequency.

  The current-voltage converter 300 is a device that converts the current flowing through the DUT 100 into a voltage. Therefore, a voltage signal representing the current flowing through the DUT 100 appears at the output terminal of the current-voltage converter 300. The current-voltage converter 300 includes a null amplifier 310 and a range resistor 320. The null amplifier 310 and the range resistor 320 form a feedback loop 330. The feedback loop 330 is also referred to as a null loop.

  The null amplifier 310 is a device that outputs a signal that makes the current flowing into the input terminal of the null amplifier 310 zero by balancing the current flowing through the range resistor 320 and the current flowing through the device under test 100. When the current flowing through the range resistor 320 and the current flowing through the DUT 100 are balanced, the Lpot terminal is virtually grounded. Although not shown, the null amplifier 310 is generally composed of a zero detector, a vector detector, a narrowband amplifier, and a vector modulator.

  Although not shown in detail in the drawing, the range resistor 320 is composed of one resistor or a plurality of resistors having different resistance values. The plurality of resistors are selected according to the impedance to be measured.

  The vector ratio detector 400 includes a buffer 410, a buffer 411, a switch 420, and an analog / digital converter 430. The buffer 410 receives a signal at the Hpot terminal, that is, a signal applied to the device under test 100. An output signal of the current-voltage converter 300 is input to the buffer 411. The switch 420 selectively connects either the output terminal of the buffer 410 or the output terminal of the buffer 411 to the input terminal of the analog / digital converter 430. In the figure, “Edit” represents the voltage of the signal applied to the device under test 100. Err represents the voltage of the output signal of the current-voltage converter 300. Data output from the analog / digital converter 430 is supplied to the correction device 500. When the analog / digital converter 430 requires a hold circuit, a sample-and-hold circuit (not shown) or the like is appropriately provided before the analog / digital converter 430.

  The correction device 500 is a device that corrects data output from the analog / digital converter 430. The correction device 500 includes a processor 510 and a storage device 520. The processor 510 is a device having a data processing function. The processor 510 is, for example, a CPU, MPU, DSP, RISC, or an FPGA or ASIC including at least one of them. In the present embodiment, the processor 510 controls other components in the impedance measuring apparatus 10. Note that the processor 510 may be separate from a device that controls other components in the impedance measuring apparatus 10. Further, the processor 510 or the correction device 500 can be replaced with a computer provided in the impedance measurement device 10 or an external computer connected to the impedance measurement device 10 by wired communication means or wireless communication means. The storage device 520 is a storage device that stores at least one correction coefficient G. The correction coefficient G is a value (data) necessary for correcting the data output from the analog / digital converter 430. The correction coefficient G is an addend, subtract, multiplier, divisor, coefficient of each term of the polynomial, or the like. The storage device 520 may be any device that has a function of storing the correction coefficient G, and is configured by, for example, a flash memory.

(Operation of impedance measuring apparatus 10)
Next, the measurement operation of the impedance measuring apparatus 10 will be described below. Reference is now made to FIG. 2 in addition to FIG. FIG. 2 is a flowchart showing a procedure for measuring the impedance of the object to be measured using the impedance measuring apparatus 10.

  First, in step S <b> 10, the DUT 100 is connected to the impedance measuring device 10. One end of the device under test 100 is connected to the Hpot terminal and the Hcur terminal, and the other end of the device under test 100 is connected to the Lpot terminal and the Lcur terminal.

  Next, in step S11, the measurement signal S is output from the signal source 200, the voltage applied to the device under test 100 is measured, and the current flowing through the device under test 100 is measured. When the switch 420 selects the terminal a, the analog / digital converter 430 digitally converts a signal representing a voltage applied to the device under test 100. When the switch 420 selects the terminal b, the analog / digital converter 430 digitally converts a signal representing the current flowing through the device under test 100. The selection state of the switch 420 is switched every time a current or voltage is measured, every time a predetermined number of currents or voltages are measured, or every predetermined time.

  In step S12, the conversion result output from the analog / digital converter 430 is corrected. The processor 510 performs correction using the correction coefficient G stored in the storage device 520. Here, it is assumed that the output data of the analog / digital converter 430 is X. The correction coefficient G is an array G (i) of multipliers for the data. Note that i is an element number. For example, when the correction coefficient G (1) corresponding to the output data X1 of the analog / digital converter 430 exists in the storage device 520, X1 is corrected as shown in the following equation, and corrected data Y1 is obtained. .

  Y1 = X1 · G (1)

  When the corresponding correction coefficient G does not exist, the corresponding correction coefficient G is calculated by linear interpolation using the correction coefficient G existing in the storage device 520. For example, the correction coefficient G corresponding to the output data X6 of the analog / digital converter 430 does not exist, but instead, the correction coefficient G (2) corresponding to the output data X4 and the correction coefficient corresponding to the output data X8 When G (3) exists and the output data X6 is a value between X4 and X8, X6 is corrected as shown in the following equation, and corrected data Y6 is obtained.

  Y6 = X6. (G (2). (X8-X6) + G (3). (X6-X4)) / (X8-X4)

  Finally, in step S13, the impedance of the DUT 100 is obtained. Specifically, the impedance is obtained by calculation from the corrected current measurement data and voltage measurement data obtained in step S12. Needless to say, the impedance is derived by dividing the voltage measurement (data) by the current measurement (data). Although not described in detail, in this step, correction using a calibration coefficient obtained in advance by calibration is also performed. The impedance obtained in this step is output as an impedance measurement value of the device under test 100 to an output device such as a display device, a communication device, or a storage device (not shown).

(Method and procedure for obtaining correction coefficient G)
Now, the correction coefficient G stored in the storage device 520 is acquired by the impedance measuring apparatus 10 before measuring the DUT 100. Acquisition of the correction coefficient G is performed by measuring an element whose impedance changes according to the frequency with the impedance measuring apparatus 10. Hereinafter, an element whose impedance changes according to the frequency is also referred to as a reactive element. First, the voltage applied to the element or the current flowing through the element is changed by changing the impedance of the reactive element by controlling the measurement frequency f. Then, a correction coefficient G is obtained based on the measured value of the changing voltage or current, or the measured impedance value of the reactive element, and the true value of the voltage, current, or impedance.

  During measurement, the voltage applied to the reactive element or the current flowing through the element is kept substantially constant. More specifically, the variation in linearity error of the analog-to-digital converter 430 included in the measured value of the voltage due to the variation in the voltage applied to the reactive element is smaller than a predetermined value. That voltage is maintained. Alternatively, the current is maintained so that the fluctuation of the linearity error of the analog / digital converter 430 included in the measured value of the current due to the fluctuation of the current flowing through the reactive element becomes smaller than a predetermined value. The This allows the linearity error of the analog / digital converter 430 caused by the measurement of the voltage Edut and the linearity error of the analog / digital converter 430 caused by the measurement of the voltage Err to be handled separately. It is to do. The predetermined value is determined according to the accuracy with which a coefficient for correcting the linearity error of the analog / digital converter 430 is obtained.

  In addition, according to the above method, the correction coefficient may include frequency dependency. This frequency dependence is not related to the linearity error of the analog-to-digital converter 430. In order to remove the frequency dependence from the correction coefficient, a resistor is further measured instead of the reactive element. Then, the correction coefficient G from which the frequency dependency is removed is obtained based on the measured value and true value of the voltage, current, or impedance of the reactive element and the resistor.

  There are roughly four methods for obtaining the correction coefficient G. That is, (1) a method of using a measured impedance value of the element when the voltage applied to the reactive element is substantially constant and a true value of the impedance, or (2) a current flowing through the element is substantially (3) A method of using the measured impedance value of the same element and the true value of the impedance when it is made constant, (3) A method of using the measured value of the current flowing through the element and the true value of the current, or (4) There is a method of using a measured value of a voltage applied to an element and a true value of the voltage.

<Method 1>
First, a specific mode for obtaining the correction coefficient G by the method (1) will be described below. In the following, reference is made to FIG. 1 and FIG. FIG. 3 is a flowchart showing a procedure for obtaining the correction coefficient G using the impedance measuring apparatus 10.

  First, in step S20, the element 110 whose impedance changes according to the frequency is connected to the impedance measuring apparatus 10 as an object to be measured. In this embodiment, the element 110 is a standard capacitor (product model number: 16386A) manufactured by Agilent. The frequency-impedance characteristic of the capacitor standard can be derived by calculation using a known capacitance value C (= 100 picofarads) provided as a specification, ie, known.

  Next, in step S21, the impedance of the element 110 is measured while changing the measurement frequency f while keeping the voltage applied to the element 110 substantially constant. This is because the amount of change in linearity error of the analog / digital converter 430 included in the measured value of the voltage applied to the element 110 is made smaller than a predetermined value. The predetermined value is set small enough to detect the linearity error of the analog / digital converter 430 included in the measured value of the current flowing through the element 110 with a desired accuracy.

  In step S21, the set value of the output voltage level of the signal source 200 is fixed in order to keep the voltage applied to the element 110 substantially constant. In addition, the variable range of the measurement frequency f is selected so that the impedance of the element 110 is sufficiently larger than the impedance of the element 210. This is because the output voltage of the signal source 200 is applied to the element 110 with almost no attenuation. For example, in this embodiment, when the impedance of the element 110 is 200 times or more the impedance of the element 210, the measurement frequency f is set to about 159 kHz or less. Also, the set value of the output voltage level of the signal source 200, the characteristics of the element 110, or the variable range of the measurement frequency f is such that the maximum value of the voltage of the signal input to the analog / digital converter 430 is the analog / digital converter. It is set to be around 430 full scale.

  Next, in step S22, the resistor 120 is connected to the impedance measuring apparatus 10 as an object to be measured. The resistance value of the resistor 120 is known. In this embodiment, the resistor 120 is a standard resistor (product model number: 42038A) manufactured by Agilent. This standard resistor has a resistance value R of 10 kilohms.

  Next, in step S23, the impedance of the resistor 120 is measured while changing the measurement frequency f while keeping the voltage applied to the resistor 120 substantially constant. Note that the measurement frequency f in this step changes in the same manner as the measurement frequency f in step S21. In order to keep the voltage applied to the resistor 120 substantially constant, the set value of the output voltage level of the signal source 200 is fixed. The output voltage level setting value or the characteristic of the resistor 120 is such that the maximum value of the voltage of the signal input to the analog / digital converter 430 is close to the full scale of the analog / digital converter 430. Is set.

  Next, in step S24, a correction coefficient G is obtained. The correction coefficient G is obtained using the measured value obtained in step S21 and step S23 and the true value of each impedance of the element 110 and the resistor 120. Specifically, the correction coefficient G (i) at the measurement point i is obtained by the following equation.

G (i) = Gk (i) / Gn
Gk (i) = (Zc (i) / Zct (i)) / (Zr (i) / Zrt (i))
Zct (i) = − j / (2π · f (i) · C)
Zrt (i) = R / (1 + 2π · f (i) · Cp · R)

  Note that i is a number for distinguishing each measurement point, and is an element number for distinguishing each element of the numerical array corresponding to each measurement point. f (i) is the measurement frequency f at the measurement point i. Zc (i) is an impedance measurement value of the element 110 at the measurement point i. Zr (i) is an impedance measurement value of the resistor 120 at the measurement point i. Zct (i) is a theoretical true value with respect to Zc (i), and is a true value of the impedance of the element 110 at the measurement point i. Zrt (i) is a theoretical true value for Zr (i), and is a true value of the impedance of the resistor 120 at the measurement point i. Cp is a known parasitic capacitance of the resistor 120. Gn is Gk (i) at the maximum measurement frequency.

  As a precaution, the derivation process of the above equation is shown below. First, the measured impedance value Za can be expressed by the following general formula.

Za = Va / Ia
Va = Vo · (1 + efv) (1 + eav)
Ia = Io · (1 + efi) (1 + eai)

  However, Va is a measured value of the voltage applied to the object to be measured. Ia is a measured value of the current flowing through the device under test. Vo is a voltage applied to the object to be measured. Io is a current flowing through the object to be measured. efv is a frequency error that occurs when measuring the voltage applied to the device under test. efi is a frequency error that occurs when measuring the current flowing through the device under test. eav is a linearity error that occurs when measuring the voltage applied to the object to be measured. eai is a linearity error that occurs when measuring the current flowing through the device under test.

  The impedance Zo of the device under test is Zo = Vo / Io. Further, since the voltages applied to the element 110 and the resistor 120 are kept substantially constant, the frequency errors efv and efi and the linearity error eav do not change regardless of the frequency of the measurement signal S. Therefore, the relationship between Zc and Zct, and the relationship between Zr and Zrt are expressed by the following equations.

Zc = Zct · ((1 + e1) / (1 + e2)) · ((1 + e3) / (1 + eaic))
Zr = Zrt · ((1 + e1) / (1 + e2)) · ((1 + e3) / (1 + air))

  However, e1 is the frequency error efv at the measurement frequency f (i). e2 is a frequency error efi at the measurement frequency f (i). e3 is a linearity error eav at the measurement frequency f (i). eaic is a linearity error eai that occurs when measuring the current flowing through the element 110 at the measurement frequency f (i). eair is a linearity error eai that occurs when measuring the current flowing through the resistor 120 at the measurement frequency f (i).

  Substituting one of the above two formulas into the other and further transforming it yields the following formula. The equation is Gk.

(1 + air) / (1 + eaic)
= (Zc / Zct) / (Zr / Zrt)
= Gk

  Gk includes a linearity error eair. However, since the voltages applied to the resistors 120 are each kept substantially constant, the linearity error eair is also constant. Here, Gk at the measurement point i is Gk (i). Then, one of all Gk (i) is selected as Gn, and all Gk (i) are normalized by the Gn. Then, the normalized Gk (i) is set as a correction coefficient G (i).

Gk (i) / Gn = G (i)

  G (i) represents a relative change in the linearity error eaic. This normalization makes it possible to ignore the linearity error eair. Further, an error in the definition value (known characteristic value) of the object to be measured, that is, an error in the capacitance value C or the resistance value R can be ignored. The correction coefficient G (i) is stored so that the impedance measuring apparatus 10 can be used. For example, the correction coefficient G (i) is stored in the storage device 520.

  In the acquisition of the correction coefficient by the method 1, the true impedance values Zct (i) and Zrt (i) in the equation for obtaining Gk may be replaced with the true values of the currents flowing through the element 110 and the resistor 120, respectively. it can.

<Method 2>
Next, a specific mode for obtaining the correction coefficient G by the method (2) will be described below. In the following, reference is made to FIGS. FIG. 4 is a flowchart showing a procedure for obtaining the correction coefficient G using the impedance measuring apparatus 10.

  Next, in step S30, the element 130 is connected to the impedance measuring apparatus 10 as an object to be measured. In the present embodiment, the element 130 is an inductor. The frequency-impedance characteristic of the inductor can be derived by calculation using a known inductance value L (= 100 millihenries), that is, is known.

  Next, in step S31, the impedance of the element 130 is measured while changing the measurement frequency f while keeping the current flowing through the element 130 substantially constant. This is because the change amount of the linearity error of the analog / digital converter 430 included in the measured value of the current flowing through the element 130 is made smaller than a predetermined value. The predetermined value is set small enough to detect the linearity error of the analog / digital converter 430 included in the measured value of the voltage applied to the element 130 with a desired accuracy.

  In step S31, the set value of the output voltage level of the signal source 200 is fixed in order to keep the current flowing through the element 130 substantially constant. In addition, the variable range of the measurement frequency f is selected so that the impedance of the element 130 is sufficiently smaller than the impedance of the element 210. This is so that the output current of the signal source 200 hardly changes regardless of the measurement frequency f. For example, in this embodiment, when the impedance of the element 130 is set to 1/200 or less of the impedance of the element 210, the measurement frequency f is set to about 15.9 kHz or less. In addition, the set value of the output voltage level of the signal source 200, the characteristics of the element 130, or the variable range of the measurement frequency f is such that the maximum value of the voltage of the signal input to the analog / digital converter 430 is the analog / digital converter. It is set to be around 430 full scale.

  Next, in step S32, the resistor 120 is connected to the impedance measuring apparatus 10 as a device under test.

  Next, in step S33, the impedance of the resistor 120 is measured while changing the measurement frequency f while keeping the current flowing through the resistor 120 substantially constant. Note that the measurement frequency f in this step changes in the same manner as the measurement frequency f in step S31. In order to keep the current flowing through the resistor 120 substantially constant, the set value of the output voltage level of the signal source 200 is fixed. The output voltage level setting value or the characteristic of the resistor 120 is such that the maximum value of the voltage of the signal input to the analog / digital converter 430 is close to the full scale of the analog / digital converter 430. Is set.

  Next, in step S34, a correction coefficient G is obtained. The correction coefficient G is obtained using the measured value obtained in step S31 and step S33 and the true value of each impedance of the element 130 and the resistor 120. Specifically, the correction coefficient G (i) at the measurement point i is obtained by the following equation.

G (i) = Gk (i) / Gn
Gk (i) = (Zr (i) / Zrt (i)) / (Zd (i) / Zdt (i))
Zdt (i) = j · 2π · f (i) · L

  Zd (i) is an impedance measurement value of the element 130 at the measurement point i. Zdt (i) is a theoretical true value for Zd (i), and is a true value of the impedance of the element 130 at the measurement point i.

  G (i) represents a relative change in the linearity error eavc. By this normalization, the linearity error eavr can be ignored. Further, the error of the definition value of the object to be measured can be ignored. The correction coefficient G (i) is stored so that the impedance measuring apparatus 10 can be used. For example, the correction coefficient G (i) is stored in the storage device 520.

  In the acquisition of the correction coefficient by the method 2, the true values of impedance Zdt (i) and Zrt (i) in the equation for obtaining Gk are the true values of the voltages applied to the element 110 and the resistor 120, Vdt ( i) and Vrt (i) can also be substituted.

<Method 3>
Next, a specific mode for obtaining the correction coefficient G by the method (3) will be described below. In the following, reference is made to FIG. 1 and FIG. FIG. 5 is a flowchart showing a procedure for obtaining the correction coefficient G using the impedance measuring apparatus 10.

  First, in step S40, the element 110 is connected to the impedance measuring apparatus 10 as an object to be measured.

  Next, in step S41, the current flowing through the element 110 is measured while changing the measurement frequency f while keeping the voltage applied to the element 110 substantially constant.

  In step S41, the set value of the output voltage level of the signal source 200 is fixed in order to keep the voltage applied to the element 110 substantially constant. The variable range of the measurement frequency f is selected so that the impedance of the element 110 is sufficiently larger than the impedance of the element 210. This is because the output voltage of the signal source 200 is applied to the element 110 with almost no attenuation. For example, in this embodiment, when the impedance of the element 110 is 200 times or more the impedance of the element 210, the measurement frequency f is set to about 159 kHz or less. Also, the set value of the output voltage level of the signal source 200, the characteristics of the element 110, or the variable range of the measurement frequency f is such that the maximum value of the voltage of the signal input to the analog / digital converter 430 is the analog / digital converter. It is set to be around 430 full scale.

  Next, in step S42, the resistor 120 is connected to the impedance measuring apparatus 10 as an object to be measured.

  Next, in step S43, the current flowing through the resistor 120 is measured while changing the measurement frequency f while keeping the voltage applied to the resistor 120 substantially constant. Note that the measurement frequency f in this step changes in the same manner as the measurement frequency f in step S41. Further, in order to keep the voltage applied to the resistor 120 substantially constant, the set value of the output voltage level of the signal source 200 is fixed.

  Next, in step S44, a correction coefficient G is obtained. The correction coefficient G is obtained using the measured value obtained in step S41 and step S43 and the true value of the current flowing through each of the element 110 and the resistor 120. Specifically, the correction coefficient G (i) at the measurement point i is obtained by the following equation.

G (i) = Gk (i) / Gn
Gk (i) = (Ir (i) / Irt (i)) / (Ic (i) / Ict (i))
Ict (i) = E / (Zo + Zct (i)) ≈E / Zct (i)
Irt (i) = E / (Zo + Zrt (i)) ≈E / Zrt (i)

  Here, Ic (i) is a measured value of the current flowing through the element 110 at the measurement point i. Ict (i) is the theoretical true value for Ic (i). Ir (i) is a measured value of the current flowing through the resistor 120 at the measurement point i. Irt (i) is a theoretical true value for Ir (i), and is a true value of the current flowing through the resistor 120 at the measurement point i. E is the output voltage level of the signal source 200. Zo is a known impedance value (50 ohms) of the element 210.

  G (i) represents a relative change in the linearity error eaic. This normalization makes it possible to ignore the error in the definition value of the object to be measured. The correction coefficient G (i) is stored so that the impedance measuring apparatus 10 can be used. For example, the correction coefficient G (i) is stored in the storage device 520.

  In the acquisition of the correction coefficient by the method 3, the current true values Ict (i) and Irt (i) in the equation for obtaining Gk are the true values Zct (i) and Zrt of the impedances of the element 110 and the resistor 120, respectively. It can also be replaced with (i).

<Method 4>
Next, a specific mode for obtaining the correction coefficient G by the method (4) will be described below. In the following, reference is made to FIG. 1 and FIG. FIG. 6 is a flowchart showing a procedure for obtaining the correction coefficient G using the impedance measuring apparatus 10.

  First, in step S50, the element 130 is connected to the impedance measuring apparatus 10 as an object to be measured.

  Next, in step S51, the voltage applied to the element 130 is measured while changing the measurement frequency f while keeping the current flowing through the element 130 substantially constant.

  In this step, the set value of the output voltage level of the signal source 200 is fixed in order to keep the current flowing through the element 130 substantially constant. In addition, the variable range of the measurement frequency f is selected so that the impedance of the element 130 is sufficiently smaller than the impedance of the element 210. This is because the output current of the signal source 200 hardly changes regardless of the measurement frequency f. For example, in this embodiment, when the impedance of the element 130 is set to 1/200 or less of the impedance of the element 210, the measurement frequency f is set to about 15.9 kHz or less. In addition, the set value of the output voltage level of the signal source 200, the characteristics of the element 130, or the variable range of the measurement frequency f is such that the maximum value of the voltage of the signal input to the analog / digital converter 430 is the analog / digital converter. It is set to be around 430 full scale.

  Next, in step S52, the resistor 120 is connected to the impedance measuring apparatus 10 as an object to be measured.

  Next, in step S53, the voltage applied to the resistor 120 is measured while changing the measurement frequency f while keeping the current flowing through the resistor 120 substantially constant. Note that the measurement frequency f in this step changes in the same manner as the measurement frequency f in step S51. Further, in order to keep the current flowing through the resistor 120 substantially constant, the set value of the output voltage level of the signal source 200 is fixed.

  Next, in step S54, a correction coefficient G is obtained. The correction coefficient G is obtained using the measured value obtained in step S51 and step S53 and the true value of the voltage applied to each of the element 130 and the resistor 120. Specifically, the correction coefficient G (i) at the measurement point i is obtained by the following equation.

G (i) = Gk (i) / Gn
Gk (i) = (Vr (i) / Vrt (i)) / (Vd (i) / Vdt (i))
Vdt (i) = E · Zdt (i) / (Zo + Zdt (i))
≒ E ・ Zdt (i) / Zo
Vrt (i) = E · Zrt (i) / (Zo + Zrt (i))
≒ E ・ Zrt (i) / Zo

  Here, Vd (i) is a measured value of the voltage applied to the element 130 at the measurement point i. Vdt (i) is a theoretical true value with respect to Vd (i), and is a true value of a voltage applied to the element 130 at the measurement point i.

  G (i) represents a relative change in the linearity error eavc. This normalization makes it possible to ignore the error in the definition value of the object to be measured. The correction coefficient G (i) is stored so that the impedance measuring apparatus 10 can be used. For example, the correction coefficient G (i) is stored in the storage device 520.

  In the acquisition of the correction coefficient by the method 4, the true voltage values Vdt (i) and Vrt (i) in the equation for obtaining Gk are the true values Zdt (i) and Zrt of the impedances of the element 110 and the resistor 120, respectively. It can also be replaced with (i).

  When the correction coefficient is given as a divisor for the output data of the analog / digital converter 430, the reciprocal Gd (i) of G (i) obtained by the above method may be obtained. And the correction | amendment in step S12 follows Y1 = X1 / Gd (1). Even when the correction coefficient is an addend or subtract to the output data of the analog / digital converter 430, it can be obtained from G (i).

  Each step in each of FIGS. 3 to 6 is performed by controlling the impedance measuring device 10 by a control device such as a processor built in the impedance measuring device 10 by executing a program prepared in advance. Is. Alternatively, a control device such as a computer externally connected to the impedance measurement device 10 controls the impedance measurement device 10 by executing a program prepared in advance.

  In the present embodiment, the element 110 can be replaced with the element 130. Conversely, the element 130 can be replaced with the element 110. When these replacements are made, the variable range of the measurement frequency f will change.

It is a figure which shows the structure of the impedance measuring apparatus 10 of this invention. 3 is a flowchart showing the operation of the impedance measuring apparatus 10. It is a flowchart which shows the procedure for acquiring a correction coefficient. It is a flowchart which shows the procedure for acquiring a correction coefficient. It is a flowchart which shows the procedure for acquiring a correction coefficient. It is a flowchart which shows the procedure for acquiring a correction coefficient.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Impedance measuring apparatus 100 Device under test 110,130,210 Element 120 Resistor 200 Signal source 300 Current voltage converter 310 Null amplifier 320 Range resistor 330 Feedback loop 400 Vector ratio detector 410,411 Buffer 420 Switch 430 Analog / digital conversion 500 Correction device 510 Processor 520 Storage device

Claims (8)

An analog-to-digital converter provided in an impedance measuring device, wherein a linearity error of an analog-to-digital converter that digitally converts a signal representing a voltage applied to a device under test and a signal representing a current flowing through the device under test A method for obtaining a coefficient for correcting
The impedance of an element whose impedance changes with frequency and whose frequency-impedance characteristics are known and is connected to the measurement apparatus as a device under test and to which a measurement signal generated by the measurement apparatus is applied or the current flowing through the element A first step of measuring with the measuring device while changing the frequency of the measurement signal while keeping the voltage applied to the element substantially constant;
A second step of obtaining the correction coefficient using the measured value in the first step, and the true value of the impedance of the element or the true value of the current flowing through the element;
The correction coefficient acquisition method characterized by including. An analog-to-digital converter provided in an impedance measuring device, wherein a linearity error of an analog-to-digital converter that digitally converts a signal representing a voltage applied to a device under test and a signal representing a current flowing through the device under test A method for obtaining a coefficient for correcting
The impedance of an element whose impedance changes with frequency and whose frequency-impedance characteristics are known and is connected to the measurement apparatus as a device under test and to which a measurement signal generated by the measurement apparatus is applied or the current flowing through the element A first step of measuring with the measuring device while changing the frequency of the measurement signal while keeping the voltage applied to the element substantially constant;
The impedance of a resistor having a known resistance value and connected to the measuring device as an object to be measured and to which a measurement signal generated by the measuring device is applied or the current flowing through the resistor is applied to the resistor A second step of measuring with the measuring device while changing the frequency of the measurement signal while keeping the voltage substantially constant;
Thirdly, the correction coefficient is obtained by using the measured values in the first and second steps and the true value of the impedance of the element and the resistor or the true value of the current flowing through the element and the resistor. And the steps
The correction coefficient acquisition method characterized by including. An analog-to-digital converter provided in an impedance measuring device, wherein a linearity error of an analog-to-digital converter that digitally converts a signal representing a voltage applied to a device under test and a signal representing a current flowing through the device under test A method for obtaining a coefficient for correcting
Impedance varies with frequency and frequency-impedance characteristics are known and connected to the measuring device as an object to be measured, and a measurement signal generated by the measuring device is applied to the impedance of the device or applied to the device A first step of measuring with the measuring device while changing the frequency of the measurement signal while maintaining the current flowing through the element substantially constant;
A second step of deriving the correction factor using the measured value in the first step and the true value of the impedance of the element or the true value of the voltage applied to the element;
The correction coefficient acquisition method characterized by including. An analog-to-digital converter provided in an impedance measuring device, wherein a linearity error of an analog-to-digital converter that digitally converts a signal representing a voltage applied to a device under test and a signal representing a current flowing through the device under test A method for obtaining a coefficient for correcting
Impedance varies with frequency and frequency-impedance characteristics are known and connected to the measuring device as an object to be measured, and a measurement signal generated by the measuring device is applied to the impedance of the device or applied to the device A first step of measuring with the measuring device while changing the frequency of the measurement signal while maintaining the current flowing through the element substantially constant;
A resistance value is known and connected to the measuring device as an object to be measured, and the impedance of a resistor to which a measurement signal generated by the measuring device is applied or a voltage applied to the resistor flows through the resistor. A second step of measuring with the measuring device while changing the frequency of the measurement signal while keeping the current substantially constant;
The correction coefficient is obtained using the measured values in the first and second steps and the true value of the impedance of the element and the resistor or the true value of the voltage applied to the element and the resistor. The third step,
The correction coefficient acquisition method characterized by including.   The correction coefficient acquisition method according to claim 1, wherein the element is a capacitor or an inductor.   6. The correction coefficient acquisition method according to claim 1, wherein the correction coefficient is a multiplier or a divisor for the output data of the analog / digital converter. In an impedance measuring apparatus comprising an analog / digital converter for digitally converting a signal representing a voltage applied to a device under test and a signal representing a current flowing through the device under test,
Storage means for storing a correction coefficient obtained by the method according to any one of claims 1 to 6;
An arithmetic means for correcting the output data of the analog / digital converter using the correction coefficient stored in the storage means;
An impedance measuring device comprising: In an impedance measuring apparatus comprising an analog / digital converter for digitally converting a signal representing a voltage applied to a device under test and a signal representing a current flowing through the device under test,
Storage means for storing a correction coefficient that is a coefficient for correcting a linearity error of the analog-digital converter and is a multiplier or a divisor for the output data of the analog-digital converter;
Arithmetic means for multiplying the output data of the analog-digital converter by the correction coefficient;
An impedance measuring device comprising:

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