JP2957596B2 - Circuit element measuring device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit element measuring device, and more particularly to a device capable of performing stable and accurate measurement over a wide band.

[Prior Art and its Problems] In recent years, demands for high-precision measurement of circuit elements have been increasing. As an apparatus for performing such a measurement, there are 4274A and 4275A multi-frequency LCR meters marketed by Yokogawa Hewlett-Packard Co., Ltd., which perform four-terminal pair measurement.

FIG. 7 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 (also referred to as less DUT) under test circuit element signal source constituting the instrument a Z _x SS, voltmeter VM, ammeter AM, connected to zero detection amplifier A.

The measured circuit element Z _x is referred to as element Z _x hereinafter, 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 to each other and at the reference potential. Terminals l ₁₁ and l ₂₁ on the element Z _x side of the center conductor of the lines CL ₁ and CL ₂ are connected to one terminal of the element Z _x . line
Element Z _x side terminals l ₃₁ and l ₄₁ of the center conductor of CL ₃ and CL ₄ are elements Z _x
Is connected to the other terminal.

The central conductors of the lines CL ₁ , CL ₂ , CL ₃ , CL _{4 and} the terminals (measuring devices) on the opposite side of the element Z _{x of the} jacket are terminals l ₁₂ , g ₁₂ ,
_{l 22, g 22, l 32} , g 32, l 42, g 42, is.

Terminal l _12, g _12, between the series 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. Its output is a narrow band amplification / phase compensation amplifier NBA (N
BA), and finally controls the output current (complex current) of the voltage-controlled current source VCC. The NBA performs complex detection on the input signal and outputs a detection output.
It is the same as that used for 275A. A series circuit of a resistor _RC , an ammeter, and a voltage-controlled ammeter VCC is connected in parallel between the terminals l ₄₂ and g ₄₂ . In addition, voltage control current source VCC, resistance R _C , ammeter A
M may be replaced with a Thevenin-equivalent voltage-controlled voltage source, resistance, or voltmeter.

In the circuit of FIG. 7, the terminal l _32, g ₃₂ between voltage substantially zero, i.e. so that the current flowing through the l ₃₂ becomes substantially zero,
Automatically controlled. As a result, the voltage V _X applied to the element Z _x
Is obtained as an indication of the voltmeter VM. Further, the current _IX flowing through the element Zx is obtained as an indication of the ammeter AM. Voltmeter VM,
Since ammeter AM measures the complex voltage or heterocyclic current output 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 (further, 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. 8, the transmission of the line CL (characteristic impedance Z ₀ , 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 , The impedance seen from the terminals l ₁ and g ₁ to the line CL side is Z _i , In the line CL ₂ of FIG. 7, 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 the V _11, the _{V 12 = V 11 / coshγ 1} 1. Here, l ₁ and γ ₁ are the line length and the propagation constant of the line CL ₂ .

Further, the Z _i corresponding to the impedance Z _i1 in CL _2, the _{Z i1 = Z 0 coshγ 1 1} / sinhγ 1 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 ₁₂ becomes very large, and Z _i1 becomes It approaches 0. Therefore, the circuit of FIG. 7 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. 7 becomes unstable, and accurate measurement becomes difficult.

Therefore, in the prior art disclosed in Japanese Patent Application No. 63-167061, in order to eliminate this drawback, the line for measuring the element to be measured is matched with its characteristic impedance when performing four-terminal pair measurement, so There has been proposed a method for achieving stable measurement over a wide range.

However, in this method, since the input impedance of the voltage measurement circuit and the input impedance of the current measurement circuit are reduced by the matching resistance, the measurement accuracy is deteriorated by the combination of the contact resistance between the element to be measured and the center conductor of the measurement line,
In the low frequency range, the accuracy is lower than that of the prior art.

To compensate for this drawback, as shown in FIG. 3, that is, FIG. 9 of Japanese Patent Application No. 63-167061, capacitors are further inserted in series with the matching resistors of the voltage measuring circuit and the current measuring circuit, respectively. Thus, the impedance of both input terminals of the voltage measurement circuit and the current measurement circuit is increased in the low frequency range, and the measurement accuracy in the low frequency range is improved. FIG. 10 shows the voltage measurement circuit of FIG. 3 of Japanese Patent Application No. 63-167061. In the circuit of FIG. 10, for example, by setting R1 = 50Ω and C1 = 1500 pF on the measurement line having a line length of 2 m and setting the cutoff frequency to 2 MHz, the ripple of the voltage transmission characteristic can be suppressed within ± 1 dB.

The aforementioned prior art has the following disadvantages. FIG. 11, FIG.
FIG. 12 shows the voltage transmission characteristics (a) and the frequency characteristics (a) of the impedance Z1 when the above values are used in FIG. No.
As shown in FIG. 11, the ripple of the voltage transmission characteristic is within ± 1 dB. However, the impedance Z1 of the voltage measuring circuit as shown in FIG. 12 is a 100Ω at 1 MHz, it can not be obtained sufficiently measurement accuracy due to the influence of the contact resistance of the element Z _x. In other words, in order to ensure stability, the R ₁ C ₁
It is necessary to increase the C _1, does not become sufficiently high impedance at low frequencies, the measurement accuracy is degraded compared with a method to measure not consistent. The same can be said for the current measurement circuit.

[Object of the Invention] An object of the present invention is to provide a circuit element measuring apparatus which solves the above-mentioned drawbacks and is characterized by being stable at a high frequency and having little accuracy deterioration even at a low frequency.

According to one embodiment of the present invention, a series circuit of a parallel resonance circuit and a switch or a parallel circuit of a series resonance circuit and a switch is connected in series with a matching impedance of a line.
The switch changes its open / closed state (open (OFF) or closed (ON)) depending on the magnitude relationship between the resonance frequency of the resonance circuit and the measurement signal frequency.

In a series circuit of a parallel resonance circuit and a switch, the switch is opened at a high frequency and closed at a low frequency.

In a parallel circuit of a series resonance circuit and a switch, the switch is closed at a high frequency and opened at a low frequency.

In the simplified circuit, the parallel resonance circuit can be short-circuited and the series resonance circuit can be opened.

In order to cope with various line lengths, a plurality of resonance circuits can be sequentially switched and used.

The use of the switch prevents precision deterioration at low frequencies and enables measurement of wideband circuit elements.

FIG. 1 shows an embodiment of the present invention.

SS supplies a measurement signal from the H _C terminal measurement signal source, VM measures the voltage across the voltage or DUTZ _x of H _p pin vector voltmeter, L _p by the loop including the NBA, the potential of L _c Set to 0. AM measures the current flowing through DUTZ _x with a vector ammeter.

R1, R2, R3, R4, R s, R p, is equal to the characteristic impedance of the line at the matching resistor. Also, the cutoff frequency ω
_{0 is set} to an appropriate value (the highest possible frequency that is stable even if used without matching the line) To switch at measurement frequency lower than or equal to ω ₀
SW1, SW3 are closed switches SW2, SW4 are open, and at measurement frequencies higher than ω ₀ , switches SW2, SW4 are closed switches SW
1, SW3 opens. At a sufficiently low frequency, Z1 and Z3 are equal to the characteristic impedance of the cable, and Z2 and Z4 are very high impedances. L1 and C1 form a parallel resonance circuit, and L2 and C2 and L4 and C4 form a series resonance circuit. Therefore, when the frequency approaches ω ₀ , Z 1 rapidly increases, and Z 2 and Z 4 approach the characteristic impedance. When the measurement frequency reaches ω ₀ , Z 1 becomes infinite, and Z 2 and Z 4 match the characteristic impedance.

When the measurement frequency is slightly higher than ω ₀ , the switch SW
2, SW4 is closed and switches SW1 and SW3 are open, but originally,
When each LC resonance circuit is resonating, switch
Since switching the SW, it is not that the impedance of Z1, Z2, Z4 is little change before and after the measurement frequency ω _0. That is, voltmeter, ammeter, each terminal to the signal source, _Hp ,
The impedance that allows for L _c and H _c changes smoothly with frequency. Thus, the gain of the voltage measurement circuit and a current measuring circuit, the rate of change with respect to the measurement line (contact impedance with and H _p L _c and DUT) (element sensitivity),
Since the frequency characteristic is smooth with respect to the change in frequency, the frequency characteristic of the measured value does not take a jump value when the line or the like changes as compared with the case where the line has been calibrated (corrected) in advance.
Further, the parallel circuit of the terminals H _p to the terminal H _c and voltmeter to the signal source so forms a constant resistance circuit, the impedance of the expectation of the DUTZ _x side measuring signal source is constant regardless of the frequency .

Regarding the stability of the circuit, the input of the voltmeter and ammeter circuits is matched with the characteristic impedance of the cable at a frequency higher than ω ₀ , so that the frequency characteristic of the gain of the voltage measurement and measurement circuit becomes flat. Further, since the _Lp terminal is also matched, the amplitude characteristic of the loop including the NBA is kept constant irrespective of the frequency, and the stability of the loop is maintained.

In the present invention, the input impedance of the voltmeter circuit and the ammeter circuit is devised so as to be high in the low frequency region, so that the measurement accuracy in the low frequency region is improved. This utilizes the fact that the impedance of the LC series resonance circuit changes drastically near the resonance frequency (that is, ω ₀ ).

As described above, a measurement device that improves the measurement accuracy by increasing the input impedance of the voltmeter circuit and current circuit at low frequencies while ensuring the stability of the method proposed in Japanese Patent Application No. 63-167061. Can be realized.

As an example, the characteristics of the voltmeter circuit in the above invention and those in the present invention will be compared. FIG. 2 shows a measuring circuit of the present invention. The characteristic impedance of the measuring cable is 50Ω and the length is
At 2 m, ω ₀ / 2π = 5 MHz, R2 = 50Ω, L2 = 6.8μ
H and C2 may be set to 300 pF. As shown by (b) in FIG. 11, the ripple of the voltage transmission characteristic at this time is within ± 1 dB, which is not much different from the characteristic (a) of the circuit of FIG.
As shown in Fig. 12, the impedance characteristic of Z2 (b)
It can be seen that is improved about 5 times higher than the characteristic (a) of Z1 at low frequency.

Various modifications are conceivable utilizing the concept of the present invention.
Below are some of them.

 The LC resonance circuit is omitted.

The matching circuits Z1, Z2, and Z3 are shown in FIGS.
Even if the LC circuit is omitted as in (C), stability and measurement accuracy do not deteriorate. This is because characteristics equivalent to those obtained when the Q value of the LC circuit is made infinite are obtained.

 Each switch resistance is added.

When a resistor is added to each switch as shown in FIGS. 4A and 4B, a change in matching impedance when the switch is switched can be reduced. This allows the switching frequency of the switch to be exactly ω
There is no need to set it to _zero . The resistance connected in parallel to SW1 and SW3 should be a multiple of the matching resistance, and the resistance connected in series to SW2 and SW4 should be selected to be a fraction of the matching resistance.

A large number of LC resonance circuits are switched by switches to handle several types of lines.

In order to make the measurement line length correspond to several types, as shown in Fig. 5, each cable length has an optimum resonance frequency.
Prepare an LC resonance circuit and switch with a switch. SWn1
~ Only one of SWnm is closed and the corresponding switch SW1l ~
The value of omega ₀ of the basic configuration example of FIG. 1 by opening the only one of the SW1m can be switched.

An accurate value of the resonance frequency ω ₀ is obtained by measurement, and switching is performed at that frequency.

In the LC resonance circuit, there is a body difference of ω _{0 due to} variations in L and C. Therefore, by measuring an accurate value of ω ₀ of each manufactured model and switching the switch at that frequency, the amount of change in the matching impedance due to the switching can be minimized. For this purpose, a method is conceivable in which the switching frequencies of the switches of the voltmeter circuit and the ammeter circuit are not intentionally made the same.

Although the measure of omega ₀ There are various ways, voltage, current measures each switch by adding a suitable circuit to the instrument outside ON, by changing the frequency while OFF, ON, measurement by OFF Is one of the methods for obtaining ω ₀ as the frequency at which the change in.

Source simplification H _c circuit of the H _c circuits is also conceivable to simplify the matching circuitry does not directly related to the measurement accuracy.

The _Lp circuit has a frequency characteristic. The _Lp circuit is not directly related to the measurement accuracy, and the simplified circuit does not significantly impair the stability of the loop including the NBA. Although not, L _c by using a parallel resonance circuit equivalent to the H _c circuit
Forming a circuit and a constant resistance circuit further increases the stability of the loop. Also, _{if Zf} in FIG. 1 is replaced with a one-port pair circuit having frequency characteristics instead of resistance, the amplitude frequency characteristics of the loop can be corrected.

For example, when the _Lp circuit of FIG. 1 is replaced as shown in FIG. 6, a device having increased stability and a flat amplitude-frequency characteristic of the loop can be obtained. Switches SW3 and SW _3f are switched in conjunction with each other. Further, R _p / R3 = R _3f and L3C3 = L _3f C _3f .

Voltage measuring circuit for inserting a CR series circuit in parallel with the Z2 of H _p matching circuit low as flat frequency described above
When SW2 is open, the gain becomes very large at high frequencies. For this reason, the fact that the measurement signal contains high-frequency noise is emphasized at the voltmeter VM terminal, which may hinder voltage measurement. By inserting a serial circuit of a relatively small C a relatively large R in parallel Z2 To avoid this, the high frequency component is emphasized by the VM terminal when measuring at frequencies below omega ₀ To prevent

Further, it is not necessary to make the LC resonance frequencies equal.

[Effects of the Invention] The following effects can be obtained by implementing the present invention. Since the matching termination can be realized at a high frequency, the instability of the measurement circuit due to the measurement line length is prevented. Also, at low frequencies, the matching circuit is removed by the switch, so that the circuit impedance increases and errors due to contact resistance and the like due to the measurement current are reduced.

Further, the switch is arranged in series with the parallel resonance circuit or in parallel with the series resonance circuit, and performs switching near the resonance frequency of the accompanying circuit, thereby reducing the influence of switch switching.

[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 schematic circuit diagram of a voltage measuring circuit portion of the embodiment of FIG. 1, and FIG. FIG. 4 is a switch circuit diagram in which a resistor is added to reduce the influence of the switch, and FIG. 5 is a matching circuit provided with a large number of matching circuits so as to correspond to various lines. , FIG. 6 is a circuit diagram of an embodiment in which a resonance circuit is introduced into a zero detection circuit, FIG. 7 is a schematic diagram of a conventional circuit element measuring device, and FIG. 8 is a voltage measuring portion of FIG. FIG. 9 is a schematic circuit diagram of another embodiment of the prior art, and FIG.
FIG. 10 is a schematic circuit diagram of the voltage measuring part of FIG. 9, FIG. 11 is a graph showing the voltage transmission characteristics of the circuit of FIG. 2 and FIG.
FIG. 12 is a graph showing the frequency characteristic of the impedance of the matching circuit in FIGS. 2 and 10. DUT: measured circuit elements _{H c, H p, L p} , L c: measuring signal source, a voltmeter, a zero detection circuit, DUT terminal connection to the ammeter lines _{CL 1, CL 2, CL 3} , CL 4 SS: Signal source VM: (Complex) voltmeter NBA: Narrow band amplification / phase compensation amplifier VCC: Voltage suppression current source AM: (Complex) ammeter A: Zero detection amplifier

Claims (6)

(57) [Claims] A first line connecting the one terminal to a signal source for applying a measurement voltage having a desired measurement frequency to one terminal of the device under test; and a first line for measuring the measurement voltage. A second line for connecting one terminal to the voltmeter, a third line connecting the other terminal to the zero detection amplifier for detecting the voltage of the other terminal of the device under test, A fourth line for connecting to the other terminal a voltage-controlled current source for drawing a current flowing through the device under test in response to the output of the zero detection amplifier to make the voltage of the other terminal zero; A circuit element measuring device comprising: a matching circuit that terminates each of the lines by a matching circuit connected by a relay on a side opposite to the side where the device under test is connected, and the measurement frequency is equal to or less than a predetermined value. At low frequencies, the matching circuit A circuit element measuring device for performing four-terminal pair measurement, wherein the circuit element is removed by opening and closing the relay. 2. The circuit element measuring device according to claim 1, wherein the matching circuit is a characteristic impedance of the line to which the matching circuit is connected. 3. At least one of the matching circuits terminating the first and third lines is a series connection of a characteristic impedance of the line to which the one matching circuit is connected and a parallel resonance circuit. The circuit element measuring device according to claim 1, wherein: 4. A series resonance circuit is connected in parallel to at least one of the relays connected to the matching circuits terminating the second and fourth lines, respectively. The circuit element measuring device according to (1) or (2). 5. The circuit element measuring device according to claim 3, wherein the resonance frequency of the parallel resonance circuit has the predetermined value. 6. The circuit element measuring device according to claim 4, wherein the resonance frequency of the series resonance circuit has the predetermined value.