JP2698615B2 - Circuit element measuring device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a circuit element measuring device for performing four-terminal pair measurement.

(Prior Art and its Problems) In recent years, demands for high-precision measurement of circuit elements have been increasing. Some measuring devices employ four-terminal pair measurement for such measurement.

FIG. 4 is a schematic circuit diagram of a conventional circuit element measuring device for performing four-terminal pair measurement.

Four lines that make up a four-terminal pair, CL ₁ , CL ₂ , CL ₃ , CL ₄
The circuit element under test _ZX is converted into a signal source SS constituting a measuring instrument by
Connect to voltmeter VM, ammeter AM and zero detection amplifier A.

The measured circuit element Z _X and referred to as element Z _X below, also represented by Z _X the impedance value.

The lines CL ₁ , CL ₂ , CL ₃ , CL ₄ are generally, but not limited to, coaxial cables, and their jacket elements Z _X side terminals g ₁₁ , g ₂₁ , g ₃₁ , g ₄₁ are connected together and at reference potential. Line CL _1, elements of the central conductor of CL ₂ Z _X terminal l _11, l ₂₁ is connected to one terminal of the element Z _X. Track CL
_3, elements of the central conductor of CL ₄ Z _X terminal l _31, l ₄₁ is connected to the other terminal of the element Z _X.

Terminals opposite to the center conductor of the lines CL ₁ , CL ₂ , CL ₃ , and CL ₄ and the element Z _{X of the} jacket (the measuring device side) are terminals l ₁₂ , g ₁₂ , and l, respectively.
_{22, g 22, l 32,} g 32, l 42, a g _42.

Between the terminal l _12, g ₁₂ direct circuit of the signal source SS and the signal source resistance R _s is connected.

A voltmeter VM is connected between the terminals l ₂₂ and g ₂₂ .

The terminals l ₃₂ and g ₃₂ are connected to the inverting input terminal and the non-inverting input terminal of the zero detection amplifier A, respectively. A feedback resistor _Rf is connected between the inverting input terminal and the output terminal of the zero detection amplifier A.
The output is introduced to a narrow band amplification / phase compensation amplifier NBA (hereinafter referred to simply as NBA), and finally a voltage-controlled current source VC
C controls the output current (complex current).

The NBA performs complex detection on the input signal and outputs a detection output, which is the same as that used for 4274A and 4275A described above. Terminal
l _42, Between g ₄₂ resistor R _c and a current meter and a voltage controlled current meter VCC
Are connected in parallel. Note that the voltage control current source VC
C, the resistor R _c , and the ammeter AM may be replaced with a Thevenin-equivalent voltage-controlled voltage source, a resistor, and a voltmeter.

In the circuit of FIG. 4, the voltage between terminals l ₃₂ and g ₃₂ is substantially zero, that is, the current flowing through l ₃₂ is substantially zero.
Automatically controlled. As a result, the voltage V _X, which is applied to the element Z _X
There is obtained as an indication of the voltmeter V _M. Further current I _X flowing in the element Z _X is obtained as an indication of the ammeter AM. Voltmeter VM,
Nagarekei AM is because measuring the complex voltage or heterocyclic current detection power of the signal SS as a reference, Z _X is determined according to the following formula in the complex value.

Z _x = V _x / I _X complex voltage, are known for measurement of the current, along with meter overall operation, e.g. supra 4274A, are disclosed in 4275A. The calibration is performed by a known method by replacing the device under test with a short circuit and an open circuit (furthermore, a known third impedance may be used).

Although the circuit element measuring device described in detail above operates very well at low frequencies, the following problems become apparent as the signal frequency increases. The premise is described first, and the problems are described next.

First, referring to FIG. 2, the transfer characteristic of the line CL (characteristic impedance Z _o , line length l, propagation constant γ) is given by the following equation.

Assuming that the voltage between the terminals l ₁ and g ₁ is V ₁ , the voltage between the terminals l ₂ and g ₂ is V _2, and the terminating impedance of the receiving end is Z ₂ , Also, if the impedance seen from the terminals l ₁ and g ₁ on the line CL side is Z _i , In the line CL ₂ of FIG. 4, the indicated voltage V _{12 of the} voltmeter VM
Is the voltage between terminals l ₁₁ and g _{11 by} setting Z ₂ = ∞ from the above equation of V ₂
From V _11, the _{V 12 = V 11 / coshγ 1} l 1. Here, l ₁ and γ ₁ are the line length and the propagation constant of the line CL ₁ .

Further, the impedance Z _i1 corresponding to the above Z ₁ in CL ₁ is Z _i1 = Z _o cosh γ ₁ l ₁ / sinh γ ₁ l ₁ .

If the line is lossless, γ ₁ is a pure imaginary number, and if it is close to lossless, when l ₁ is 1/4 of the guide wavelength (the line resonates), V ₂ becomes very large, and Z _i1 becomes It approaches 0. Therefore, the circuit of FIG. 4 becomes unstable and inaccurate. Sometimes Z _i1
Becomes very small, the voltage is not applied to the element Z _x. According to the same consideration, the line length of the line CL ₃ is CL ₃
When will the tube quarter of the wavelength, the current flowing into the line CL ₃ becomes very small, the loop gain of the feedback circuit including the NBA is extremely small. Therefore, the operation of the circuit shown in FIG. 4 becomes unstable, and accurate measurement becomes difficult.

(Object of the Invention) An object of the present invention is to terminate each line used to connect a device under test at the time of performing a four-terminal pair measurement with a characteristic impedance or the like, thereby providing stable and stable operation over a wide band. An object of the present invention is to provide a circuit element measuring device capable of performing accurate measurement.

(Summary of the Invention) In one embodiment of the present invention, a line for connecting a device to be measured is terminated at each characteristic impedance to eliminate or reduce the influence of line resonance, thereby achieving a wide band and high accuracy. Enables four-terminal pair measurement. Also,
To keep the accuracy at low frequencies high, the termination can be asymptotically done only at high frequencies.

FIG. 1 shows a circuit element measuring apparatus according to an embodiment of the present invention.
The purpose of this apparatus is the same as that of the apparatus shown in FIG. 4, and parts having the same functions and performances as those in FIG. 4 are given the same reference numerals.

In FIG. 1, resistors R ₁ , R ₂ , R ₃ , and R ₄ are respectively connected to lines.
_{CL 1, CL 2, CL 3} , chosen equal to the characteristic impedance of the CL _4.

In this way, the transfer function of each line (output / input)
And the input impedance is as follows, corresponding to (Equation 1) and (Equation 2). (Equation 1), (Equation 2) for simplicity
It will be explained by.

In FIG. (Equation 4)... Z ₁ = Z _o Therefore, if the loss of the line CL is small, V ₂ is a phase-shifted version of V ₁ and the amplitude is kept the same.

Therefore, since only the phase shift of the circuit changes depending on the frequency, the stability of the negative feedback loop including the NBA can be maintained if the phase compensation of the NBA is performed by a known technique. Therefore, accurate measurement can be performed over a wide band.

The phase shift due to the change of the element Z _x 18.4 DEG ±, it is sufficient to consider only the compensation of the phase shift due to frequency.

Next, FIG. 3 shows an embodiment in which the circuit of FIG. 1 is improved.
First, check the circuit of FIG. Conventional (as shown in FIG. 4) no current flows through the center conductor of the line CL _2, error due to the contact resistance of said central conductor and the element Z _x did not occur. However, current flows in the circuit of FIG. 1, so that the voltage applied to the element Z _x is measured also have a slight error in the low frequency. Similarly, the terminal l ₄₁ of the center conductor of the line CL ₄ and the element Z _x
Ammeter A that measures the current flowing through element Z _x
Affect the instructions. Thus, the circuit of FIG. 1 has increased stability and improved accuracy at high frequencies, but has the point of improving accuracy at low frequencies.

In FIG. 3, a series circuit of terminals l _12, g resistor R ₁₀ is between ₁₂ and inductor L _10, a series circuit of a resistor R ₂ and capacitor C ₂₀ is between terminals l _22, g _22, the terminal l ₄₂ , G ₄₂ has a resistance R
Inserting a serial circuit of ₄ and the capacitor C _40. Also terminal ₃₂
If the between the inverting terminal of the zero detection amplifier resistor R ₃₀ and the inductor L
A series circuit of ₃₀ to insert the resistor R ₃ in parallel. These values are also represented by reference symbols of each element, and the values are determined as follows. Here and _{R 10 = R 2, L 10} / C 20 = R 2 2, 1 / (2πC
The value of ₂₀ R ₂ ) is selected to be large enough not to lack high frequency stability. The value is a typical 50Ω coaxial line, the line length is
It is about 3MHz even at 2m. In this way, the element Z _x
Is maintained substantially constant regardless of the signal frequency. The reason is because the parallel connection of the series circuit of the series circuit R ₂ and C ₂₀ in R ₁₀ and L ₁₀ is constant resistance circuit. Track CL ₁
Better results if you choose to those same specification CL ₂ and is obtained. In that case, R ₁₀ = R ₂ = R ₁ .

The size of the _{R 30 = R 4, L 30} / C 40 = R 4 2 and then 2πC ₄₀ R ₄ is selected in the same manner as 2πC ₂₀ R _2. Unlike shown a series circuit of R ₃₀ and L _30, it may be to insert between the terminal l _32, g _32. If the illustrated method of measuring the element Z _x high impedance, degradation of the signal-to-noise ratio is less advantageous aspect.

By the above selection, the accuracy of the low frequency is improved without impairing the stability of the control loop including the NBA. The reason is R
Parallel connection of the series circuit ₃₀ and the series circuit R ₄ and C ₄₀ of the L ₃₀ is always a constant resistance. Having the lines CL ₃ and CL ₄ of the same specification gives better results. Needless to say, it is convenient if all the tracks have the same specifications. Therefore, the circuit shown in FIG. 3 can provide a circuit element measuring device which has a small deterioration in accuracy even at the operation at a low frequency and does not lose the stability at the high frequency.

(A) and (b) of FIG. 5 are schematic circuits for replacing the corresponding parts of FIG. 1 or FIG.

In FIG. 5, reference numeral _A51 denotes a high input impedance inverting amplifier including an NBA and having an amplification degree capable of making the voltage between the terminals l ₃₂ and g ₃₂ substantially zero.

(Effects of the Invention) As described above, by implementing the present invention, it is possible to improve stability and accuracy at high frequencies while minimizing deterioration in accuracy at low frequencies. Therefore, measurement over a wide band is possible even if the distance between the measuring instrument and the device under test is large.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of a circuit element measuring device according to one embodiment of the present invention, FIG. 2 is a circuit diagram for explaining a transfer characteristic of a line, and FIG. 3 is an improvement of the circuit element measuring device of FIG. FIG. 4 is a schematic circuit diagram of a prior art circuit element measuring device, and FIG. 5 is a further alternative embodiment of the present invention in which a part of the device of FIGS. 1 and 3 is replaced. It is a schematic circuit diagram of a circuit for obtaining the example circuit element measuring device. Z _x : Circuit element under test CL ₁ , CL ₂ , CL ₃ , CL ₄ : Line SS: (Measurement) signal source VM: (Complex) voltmeter NBA: Narrow band amplification / phase compensation amplifier VCC: Voltage control current source AM: (complex) ammeter A: Zero detection amplifier A ₅₁ : High input impedance inverting amplifier

Claims (2)

(57) [Claims] 1. A first line connecting one terminal to a signal source for applying an applied voltage to one terminal of a device under test, and the one terminal connected to a voltmeter for measuring the applied voltage. A second line for detecting the voltage of the other terminal of the device under test, a third line connecting the other terminal to the zero detection amplifier, and a second line for detecting the voltage of the zero detection amplifier. A fourth line for connecting to the other terminal a voltage-controlled current source for attracting a current flowing through the device to be measured to reduce the voltage of the other terminal to zero, and A circuit element measuring device for performing a four-terminal pair measurement, wherein each of the second, third, and fourth lines has a terminating element equal to the characteristic impedance at the end of each measuring instrument. 2. The terminal element of the second line is connected in series with a second resistor and a capacitor, and the terminal element of the first line is connected in series with a first resistor and an inductor. 2. The circuit element measuring device according to claim 1, wherein the resistance values of the second resistors are equal, and the square of the resistance value is equal to a ratio of the value of the inductor to the value of the capacitor.