JP3147987B2 - Equilibrium system characteristic parameter measuring device and measuring method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for measuring a characteristic parameter of a balanced system using an unbalanced measuring apparatus such as a network analyzer. The present invention relates to the above-described measuring device and measuring method capable of determining characteristic parameters such as impedance at the measuring device.

[0002]

2. Description of the Related Art A balanced device such as a balanced cable is used in a balanced state in which terminals are driven by a differential signal to keep a constant potential with respect to the ground. If the characteristics of such a balanced device are measured in an unbalanced state in which one terminal is always at the ground potential, the measurement result will be different from the equilibrium state, which is the original operating state. Impedance analyzers and network analyzers used for measuring impedance are generally unbalanced measuring instruments, and the measurement terminals are unbalanced with one side grounded. It is not originally suitable for measuring characteristic parameters such as impedance of a balanced device. Therefore, when measuring the impedance or the like of a balanced device using these measuring devices in the past, a balanced-unbalanced conversion circuit is inserted between the device to be measured and the measuring device, and a measuring terminal for connecting the device to be measured is used. Is kept in equilibrium.

FIG. 4 is a configuration diagram of a conventional balanced system impedance measuring device using a transformer circuit as a balanced-unbalanced conversion circuit. In the figure, an unbalanced terminal pair 21 (both terminals are indicated by 21a and 21b) of an unbalanced measuring device 20 is connected to both terminals of a primary winding of a transformer circuit 22, and a secondary A balanced system terminal pair 23 (both terminals 23a and 23
(indicated by b) is connected to the device under test 10. The unbalanced measuring device 20 is configured such that the line on the unbalanced side terminal 21b side is grounded (maintained at the ground potential), and a signal for measurement is applied to the other terminal 21a.
By knowing the voltage applied to 1a and the current flowing through the device under test 10, the impedance of the device under test 10 can be measured.

Now, as shown in FIG.
Assuming that a voltage signal of + V is applied during 1b, this voltage causes an induced voltage in the secondary winding of the transformer circuit 22. Since the middle point of the secondary winding of the transformer circuit 22 is grounded, if the turn ratio of the transformer circuit 22 is 1: 1, the terminals 23a and 23b are connected to + V / 2 and -V / 2.
Is induced. A balanced current flows through the device under test 10 by these balanced differential voltages, and this current is converted into an unbalanced current via the transformer circuit 22. By measuring this current with the unbalanced measuring device 20, the current flowing through the device under test 10 can be known, and therefore, the impedance of the device under test 10 in the unbalanced system can be obtained.

In the above circuit, the balanced system terminal pair 23
Is transmitted to the unbalanced terminal pair 21 via the transformer circuit 22, the impedance measured by the unbalanced measuring instrument 20 is the impedance of the device under test 10 And the winding impedance of the transformer circuit 22. For this reason, since the measurement result includes an error due to the winding impedance of the transformer circuit 22, the impedance characteristics and the transmission characteristics of the transformer circuit 22 in the measurement frequency band are reduced to such an extent that the measurement accuracy is not significantly affected. It needs to be restricted. However, generally, the transformer circuit 2
In the case of No. 2, the frequency band that can be used in a state where the impedance characteristics and the transmission characteristics are stable is limited.
The measurement of a balanced system using the transformer circuit 22 for unbalanced conversion has a problem that the measurable frequency range is limited.

In the case where high accuracy is required so that the error due to the influence of the transformer circuit 22 cannot be ignored, or when the winding ratio of the transformer circuit 22 is not 1: 1, the impedance characteristic and the transmission characteristic of the transformer circuit 22 are Correction is needed to remove the effects of such factors. The correction coefficient used for this error correction is a calibration standard device (for example, open (0
S), short (0 Ω)) and reference load resistance. However, in a balanced system, traceability has been established, and there is no standard device whose accuracy is guaranteed.Therefore, a correction coefficient is obtained from the measurement results using an unbalanced standard device, or a new balanced system standard is created. There must be. Since an unbalanced standard is designed to have a specified impedance in an unbalanced state, accuracy is not guaranteed when used in a balanced system, and the impedance measurement value is also inaccurate. Therefore, when an unbalanced standard device is used to derive a correction coefficient for a balanced system, sufficient correction cannot be performed.

On the other hand, when a balanced standard device is prepared, extra cost is added, and it is difficult to guarantee the valuation of the standard device and the traceability of accuracy in the balanced system. There is also a problem that many types of transformer circuits 22 for balanced-unbalanced conversion must be prepared.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems. The present invention is based on the characteristic parameters of a device under measurement in an unbalanced state measured using an unbalanced characteristic parameter measuring apparatus. It is an object of the present invention to provide an equilibrium system characteristic parameter measuring device and a measuring method capable of obtaining characteristic parameters such as impedance in a system.

[0009]

SUMMARY OF THE INVENTION A balanced system characteristic parameter measuring device according to the present invention comprises an unbalanced measuring device, a directional bridge connected to each of two ports of the unbalanced measuring device, and the unbalanced measuring device. Connecting means to the two terminals of the device under test having four terminals via the directional bridge, and connecting the terminals of the device under test to which the directional bridge is not connected with a predetermined impedance. Terminating means for terminating, and characteristic parameter deriving means for deriving a characteristic parameter in a desired balanced system from a characteristic parameter in an unbalanced system of the device under test measured by the unbalanced measuring apparatus, It is characterized by having. Further, in the balanced system characteristic parameter measuring device according to the present invention, the unbalanced measuring device measures an S parameter in an unbalanced system of a device under test connected via the directional bridge, and the characteristic parameter deriving means. By converting the S-parameters in the unbalanced system measured by the unbalanced measuring device into Z or Y parameters in the unbalanced system and then diagonalizing, the S-parameters in the balanced system of the device-under-test are converted. Request Z or Y Pas Ramee also characterized in that. Furthermore, the equilibrium system characteristic parameter measuring device of the present invention, the device, via a twisted pair cable,
Being connected to the two directional bridges .
You. The balanced system characteristic parameter measuring method according to the present invention derives a 2-port unbalanced S-parameter test set by performing full 2-port calibration of a resistive divider type directional bridge connected to each of two ports of an unbalanced measuring device. In advance, the connection terminals of the device under test to which the port is connected via the resistance-divider type directional bridge are sequentially switched to measure the S parameter in the unbalanced system of the device under test, The S parameter is set to Z or Y in an unbalanced system.
Diagonalizing after converting to the parameter, the Z in the equilibrium system of the measuring device to determine the Y parameters, characterized in that.

The outline of the present invention will be described below. Of the present invention
The equilibrium system characteristic parameter measurement device is a network analyzer.
Unbalanced measurements, such as an analyzer or impedance analyzer
A directional bridge is connected to each of the two ports of the device.
It is composed. For example, twisted pair cable or multi-conductor
Unbalanced type measurement as a device to be measured
Connected to a device port via a directional bridge (specifically
Uses connection means such as cables, clips, connectors, etc.
Connected). The S-parameter of the directional bridge is obtained in advance by the unbalanced measuring device, and the measuring device is fully 2-port calibrated based on the parameter to derive a 2-port unbalanced S-parameter test set. Then, a measurement signal is output to the device under test via the directional bridge, and a response signal from the device under test is input.
I do. Then, the characteristic parameter deriving means measures the S parameter of the device under test from these signals. Ma
Further, the terminating means includes the terminal among the terminals of the device under test.
If there is a terminal to which no directional bridge is connected,
The terminal is terminated with a predetermined impedance.

When the device to be measured is a multiconductor system, the error correction is performed by multiport calibration when measuring the S parameter. Thereafter, the matrix based on the S parameter is converted into the balanced system Z by the unbalanced measuring device.
Alternatively, it is converted into a matrix of balanced characteristic parameters such as Y parameters, and the characteristic parameters of the device under test in the balanced system are obtained. Normally, this conversion is performed by converting the S parameter to a Z or Y parameter, and then diagonalizing to convert the balanced system to a Z or Y parameter.
This is performed by obtaining parameters.

As the unbalanced measuring device, a network analyzer or an impedance analyzer, which is a general-purpose measuring device used in a high frequency band, is preferably used. By using these analyzers, characteristic parameters (impedance, etc.) over a wide band (several Hz to several tens of GHz) can be obtained as compared with a conventional measurement device using a balanced-unbalanced transformer. Further, since the analyzer can easily guarantee traceability using a standard device, it is possible to obtain a highly reliable measurement result.

[0013]

FIG. 1 shows an embodiment of the present invention. In the present embodiment, a network analyzer is used as an unbalanced measuring device. In FIG. 1, two terminals of a device under test 10 are connected to a terminal pair 2 (indicated by terminals 2a and 2b) of a network analyzer 1 via connection means . In addition, a signal source (voltage sources 3 and 4 in the figure) in the analyzer 1 applies a voltage + V to each signal terminal of the terminal pair 2.
/ 2 and -V / 2, and the current flowing through each terminal 2a, 2b is measured to find the S parameter in the unbalanced system.
The impedance of the device under test 10 in the balanced system is determined from the parameters.

FIG. 2 shows the principle of conversion of characteristic parameters from an unbalanced system to a balanced system by the network analyzer 1.
This will be described with reference to FIG. First, the voltage sources 3 and 4
Add each voltages _{V 1} and _{V 2} terminal 2a, through 2b to the device under test 10. Here, it is assumed that the device under test 10 is a balanced device (usually a device used in a balanced state) and has two terminal pairs.
At this time, assuming that the common mode component and the differential component of the voltage between the terminals 2a and 2b are V _u and V _b, and the common mode component and the differential component of the current are I _u and I _b , The relationship is established.

[0015]

(Equation 1)

Here, the relationship between V ₁ , V ₂ and I ₁ , I ₂ is as follows when a two-port pair circuit is represented using an impedance matrix [Z] and an admittance matrix [Y].

[0017]

(Equation 2)

By using (Equation 1) and (Equation 2), V _b , I
_When the relation between _b and V _u , I _u is obtained, the following (Equation 3) and (Equation 4) are obtained.

[0019]

(Equation 3)

[0020]

(Equation 4)

The impedance Z [i-balance] of the device under test 10 in a balanced current driving state is V _b at I _u = 0.
Since the ratio between the I _b, the first row of the matrix of equation (3) 1
Given by the elements of the sequence:

[0022]

[Equation 5] Z [i-balance] = z ₁₁ −z ₁₂ −z ₂₁ + z ₂₂

On the other hand, the admittance of the balanced voltage drive state so the ratio between _{V b} and _{I b} in _V u = 0, is given by the following equation (Equation 4).

[0024]

Z [v-balance] = {(y ₁₁ −y ₁₂ −y ₂₁ + y ₂₂ ) / 4} ⁻¹

That is, when the device under test 10 is of a balanced type, if the impedance matrix and the admittance matrix when the device under test is viewed as a two-port circuit are known, the balanced voltage drive state and the balanced current The impedance in the driving state can be obtained. Here, the impedance matrix [Z] and the admittance matrix [Y] of the two-port pair circuit can be obtained by conversion calculation if the S parameter matrix of the circuit is obtained. The S-parameter matrix of the two-terminal pair device under test can be measured by the network analyzer 1 and the S-parameter test set. By equipping the network analyzer 1 with the conversion calculation function based on the above formula and the result display function, the characteristic parameters of the equilibrium system can be easily known.

The device under test 10 may be inductive or capacitive as long as it is a balanced device. Although the voltage sources 3 and 4 are used as signal sources in FIG. 1, it goes without saying that a current source can be used.
Hereinafter, an embodiment in which the impedance of a twisted pair cable is obtained according to the present invention will be described with reference to FIGS. 3 (A) and 3 (B). In FIG. 1A, resistance divider-type directional bridges 6a and 6b are connected to two ports 5a and 5b of the network analyzer 1, respectively. Here, it is assumed that these bridges 6a and 6b have been calibrated to a 50Ω system by full two-port calibration.

Here, the device to be measured (in this case,
In order to obtain the S parameter of the twisted pair cable 7), the four terminals 8a, 8b,
For 8c and 8d, S matrix measurement is performed with six types of connections. In these measurements, twisted pair cable 7
The Not to be measured terminal pin should be grounded at terminator (termination resistors z _{0 (50} [Omega in this case)). Note that FIG.
In (A), the jacket at both ends of the twisted-pair cable 7 also are grounded at terminal resistor z _0.

Although not described in detail, the diagonal elements among the elements of the S-parameter matrix are measured three times each, and which of the duplicated data is used depends on how the error is included. Consider and decide. For this reason, if a random error is expected, it is a matter of course that the error can be reduced by averaging the measured values. In a measurement in which the port connected by the core wire forms the port to be measured, the load resistance and the core impedance that terminate a port that is not the port to be measured are reflected and measured, and the measurement error increases due to the reflection coefficient error of the load resistance. . Therefore, according to the data in the measurement (see the connection mode of FIG. 3A) performed between the terminals (8a and 8c, 8b and 8d) connected by the core wire,
Preferably, the diagonal elements are determined.

As described above, if the measured S parameter matrix in the unbalanced system is converted into Z or Y parameters by the characteristic parameter deriving means based on (Equation 5) or (Equation 6), The impedance and the like can be easily obtained. FIG. 3B is a diagram showing the frequency characteristic of the characteristic impedance in the above measurement. In the figure, the calculated values are shown together with the actually measured values. As can be seen from FIG. 7B, in the frequency range from 100 kHz to 100 MHz, the measured values show almost the same characteristics as the calculated values of the cable parameters based on the theoretical formula.
Note that in a frequency range of less than 100 kHz or a frequency range of more than 100 MHz, the measured value and the calculated value are different. In this case, the terminal impedance or the connection method is appropriately changed, or the core wire is pulled out. It is also possible to correct the error.

In FIGS. 3A and 3B, the twisted pair cable has been described. However, the present invention can be extended to a multi-conductor case, such as a real line or a heavy line in the case of a four-wire transmission line. It can also be applied to measurement of ground lines.

[0031]

As is apparent from the above description, according to the present invention, the characteristics of the device under test are obtained from the measurement results of the S parameters in the unbalanced state when the device under test is viewed as a two-port circuit. Parameters (e.g., balanced impedance) can be determined. In addition, since a balanced-unbalanced conversion circuit, which is required for the measurement of a balanced system, is not required, it is not necessary to prepare various types of balanced-unbalanced transformers according to the frequency as in the related art. In addition, since the measuring instrument can be calibrated with the existing unbalanced standard device, highly reliable accuracy can be guaranteed. In addition, it is necessary to change the method of measuring the balanced impedance depending on whether it is defined as the constant current type or the constant voltage type.In the present invention, however, since the balanced impedance is obtained by calculation, the It is possible to quickly and easily provide a measuring device that also supports such a definition.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a diagram for explaining a principle of converting characteristic parameters from an unbalanced system to a balanced system in the present invention.

3A and 3B are explanatory diagrams showing an embodiment in which the present invention is applied to a twisted pair cable, wherein FIG. 3A is a circuit configuration diagram, and FIG. 3B is a graph showing measured and calculated values of characteristic impedance.

FIG. 4 is an explanatory view showing a conventional measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Unbalanced measuring device 3, 4 Voltage signal source 5a, 5b Unbalanced measuring device port 6 Directional bridge 7 Twisted pair cable 8a-8d Twisted pair cable terminal

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 27/28

Claims (5)

(57) [Claims] An unbalanced measuring device; a directional bridge connected to each of two ports of the unbalanced measuring device; and a device under test connected to the unbalanced measuring device via the directional bridge. Connecting means for connecting to the device to be measured, when there is a terminal to which the directional bridge is not connected, and terminating means for terminating the terminal with a predetermined impedance, Characteristic parameter deriving means for deriving a Z parameter or a Y parameter in a balanced system of the measured device by a predetermined conversion from a characteristic parameter of the device to be measured in the unbalanced system measured by the mold measuring apparatus. characteristic parameter S parameters in the unbalanced system, der either Z parameter or Y parameter
That equilibrium systems characteristic parameter measurement device. 2. The balanced system characteristic parameter measuring device according to claim 1, wherein the characteristic parameter in the unbalanced system is an S parameter. 3. The apparatus according to claim 1, wherein the device under test is connected to the two directional bridges via a twisted pair cable. 4. The equilibrium system characteristic parameter measuring device according to claim 1, wherein said directional bridge is a resistance voltage divider type directional bridge for which S parameters have been determined in advance. 5. A two-port unbalanced S-parameter test set is derived by performing full two-port calibration of a resistive voltage divider type directional bridge connected to each of two ports of an unbalanced measuring device. The connection terminals of the device under test to which the above port is connected via the voltage divider type directional bridge are sequentially switched to measure the S parameter in the unbalanced system of the device under test. Calculating a Z parameter or a Y parameter in the balanced system of the device under test by conversion.