JPH0227848A - Immunity test circuit - Google Patents

Abstract

PURPOSE:To measure a device duration force of a communication equipment to be tested only accurately by adding a coil with a mid-point tap and an impedance element so as to suppress the voltage applied to an opposite communication equipment to a level not causing malfunction. CONSTITUTION:A coil 30 is provided newly and a mid-point 33 of the coil 31 with a mid-point tap is connected to ground and an impedance element 35 of an impedance Z is connected between common connecting points A, B of the secondary winding 272 of a coupling transformer 26 and a common mode choke coil 17 and the coil 31 with the mid-point tap. Then the voltage induced in the secondary winding 272 of the coupling transformer 26 is applied to the communication equipment 11 to be tested and the induced voltage is reduced by the common mode choke coil 17 and the impedance element 35. Thus, the voltage applied to the opposite communication equipment 13 is suppressed to measure the code error and malfunction of the communication equipment 11 to be tested is measured accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to imi-unity (i+uiunty) test circuits, which include at least one pair of test circuits that communicate with each other and operate with a common potential point (for example, the earth) as a reference. For example, one communication device to be tested for noise tolerance, etc. is the communication device under test, and the other communication device is the opposite communication device, and the communication line connected to the communication device under test and a common potential point (e.g., earth) are connected. This invention relates to an immunity test circuit for testing transmission quality deterioration and malfunctions such as code errors in digital transmission occurring in communication devices by applying a voltage between the two.

[Conventional technology]

Conventionally, before the operation of a communication device (for example, during the development stage of the device, before installation of the device, etc.), for example, a certain pattern is transmitted from one device that is the communication device under test to the other device that is the opposing communication device. However, code errors in digital transmission during this time are verified, and tests for transmission quality deterioration, malfunction, etc. in the communication line of the communication device 1 are sometimes performed. Immunity tests were used to examine the extent to which such operational tests could be performed against noise, that is, the equipment tolerance of communication equipment.

When performing such an immunity test, the circuit that applies the immunity test voltage (suspicious noise source) between the communication line connected to the communication device under test and the ground is as follows:
There was something like the one shown in Figure 9. Here, the communication device under test 11 and the opposing communication device 1 that communicates with it
3 is a two-conductor communication line 15, and a common moat coil 17 is inserted into each of the communication lines 15 on the opposing communication device 13 side. A voltage injection coil 20 is inserted between the two communication lines 15, and the center point 2 of the coil 21 with a center point tap forming the voltage injection coil 20 is inserted.
This circuit applies a voltage for immunity testing between the voltage generating device 25 and the ground. Voltages for this test include sinusoidal alternating current voltage, amplitude modulated or frequency modulated signal voltage, surge voltage, and the like.

In this circuit, the common mode circuit coil 17 is inserted into the communication line 15 because the same voltage is applied not only to the communication device under test 11 which is originally subjected to the immunity test, but also to the opposing communication device 13. This is to reduce the voltage applied to the opposing communication device 13.

In this circuit, another conventional example is shown in FIG. 10, as in the case of FIG. 9, the communication line 15 connecting two communication devices is
In the case of a conductor, a coupling transformer 26 is provided between the communication device under test 11 and the opposing communication device 13 that communicates with it, and the secondary winding 27g of this coupling transformer 26
is inserted into each communication line 15, and a voltage is applied to the primary winding 271 of the coupling transformer 26 by the voltage generator 25 for immunity testing. In this circuit as well, a common mode choke coil 17 is inserted so as to reduce the voltage applied to the opposing communication device 13.

[Problem to be solved by the invention]

However, in the conventional circuit shown in FIG. 9 described above, when performing an immunity test,
A common mode choke coil 17 is inserted in order to reduce the effect of the voltage applied to the , when the device resistance of the opposing communication device 13 is low, the opposing communication device 13
The problem was that code errors and malfunctions occurred, making it impossible to conduct accurate tests.

Furthermore, even in the circuit shown in FIG. 1θ, the opposing communication device 1
Although a common mode choke coil 17 is inserted to reduce the voltage applied to the circuit 3, the effect is small at low frequencies, similar to the circuit shown in FIG. Therefore, when the equipment tolerance of the opposing communication device 13 is low, code errors and malfunctions occur in the opposing communication device 13, resulting in a problem that the equipment tolerance of the communication device under test 11 cannot be evaluated correctly.

In the conventional circuit shown in Fig. 10, for example, the results of measuring the characteristics of the applied voltage when certain circuit constants are determined are shown in the first diagram.
Shown in Figure 1. Here, the voltage v0 applied by the voltage generator 25 of the circuit shown in FIG.
The voltage ■1 applied to the terminal is indicated by an X mark, the voltage vz applied to the common connection point B (common mode choke coil 17) is indicated by a Δ mark, and the voltage V applied to the opposing communication device 13 is indicated by a mouth mark.

Here, the voltage v2 applied to the common connection point B is approximately equal to the voltage v0 supplied from the voltage generator 25, and a voltage equivalent to the voltage Vl applied to the communication device under test 11 is applied to the common mode choke coil 17. . As described above, the common mode choke coil 17 has little effect on the voltage applied to the common mode choke coil 17 below several hundred kHz. Therefore, if the device resistance of the opposing communication device 13 is low, code errors, malfunctions, etc. may occur.

The present invention was created in consideration of these points, and it is possible to accurately measure the equipment strength of only the communication device under test by suppressing the voltage applied to the opposing communication device to a level that does not cause code errors or malfunctions. The purpose is to provide an immunity test circuit that can perform measurements.

[Means to solve the problem]

(i terminal 11) In order to achieve the above-mentioned object, in the invention as claimed in claim 1, a desired test is to be performed on one of the at least one pair of communication devices that are in a relationship such that they communicate with each other. In an immunity test circuit in which a communication device is the communication device under test and the other communication device is the opposing communication device, a common mode choke coil is inserted into each of the two conductors of the communication line interposed between the pair of communication devices, and the common A secondary winding of a coupling transformer is inserted into each of the two conductors of the communication line between the mode choke coil and the communication device under test, and a voltage is supplied from the primary winding of the coupling transformer by a voltage supply source. A coil with a center point tapped connected to a common potential point is provided, and an impedance element is inserted between the common connection point of the common mode chiroak coil and the secondary winding of the coupling transformer and both ends of the coil with a center point tapped. The communication device under test is configured to apply a voltage from a voltage supply source to the communication device under test via a coupling transformer for immunity testing.

According to U.2 In order to achieve the above-mentioned object, in the invention according to claim 2, for at least a pair of communication devices that are in a relationship such that they communicate with each other, one of the communication devices to be subjected to a desired test is provided. In an immunity test circuit in which the device is the communication device under test and the other communication device is the opposite communication device, a common moat coil is inserted into each of the two conductors of one signal line interposed between the pair of communication devices, and the A secondary winding of a coupling transformer is inserted into each of the two conductors of the communication line between the common mode choke coil and the communication device under test, and a voltage is supplied from the primary winding of the coupling transformer by a voltage supply source. An impedance element is connected to a coil with a center tap and another coil wound around the same core, and another impedance element is inserted between the midpoint of the coil with a center tap and a common potential point. A capacitive element is inserted between the coil with point taps and the communication line,
The configuration is such that a voltage is applied from a voltage supply source to the communication device under test via a coupling transformer for immunity testing.

[For production]

(i) Invention according to Claim 1 In the present invention, voltage is supplied from the primary winding of the coupling transformer by a voltage supply source, and the voltage induced in the secondary winding of the coupling transformer is applied to the communication device under test. applied. This induced voltage is reduced by a common mode choke coil. It is also reduced by an impedance element between the midpoint tapped coil and the secondary winding of the coupling transformer, whose midpoint is connected to a common potential point. Therefore, it does not affect the opposing communication device.

Therefore, in the immunity test, it becomes possible to accurately measure the equipment strength of only the communication device under test.

ii) In the invention according to claim 2 according to claim 1, resonance caused by the center-tapped coil is prevented by an impedance element connected to another coil wound around the same core as the center-tapped coil of the transformer. Prevented.

Therefore, in the immunity test, it becomes possible to more accurately measure the equipment strength of only the communication device under test.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows the configuration of an immunity test circuit in one embodiment of the present invention. In the figure, the same reference numerals as in FIG. 1θ indicate the same elements, and detailed explanation thereof will be omitted here.

In FIG. 1, a coil section 30 is newly provided, and a center point 33 of a coil 31 with a center point tap that forms the coil section 30 is shown.
Ground. An impedance element 35 having the same impedance 2 is connected between the respective common connection points A and B of the secondary winding cotton 27 □ of the coupling transformer 26 and the common mode choke coil 17 and both center-tapped coils 31. are doing.

(ii) Operation of the first embodiment The operation of the embodiment configured in this manner will be described below.

In FIG. 1, the communication device under test 11 and the opposing communication device 1
The immunity test voltage Vo generated from the voltage generator 25 while transmitting signals between the primary winding 27.3 of the coupling transformer 26 and the primary winding 27. and its secondary winding 27.
A voltage induced by the voltage is applied to the communication device under test 11.

In this circuit, between the two conductors of the communication line 15, 2Z
This means that an impedance of +jωL is inserted. Here, L is the overall impedance of the coil section 30.

This impedance of 2Z+jωL is the impedance of the communication device under test 11. By making the input/output impedance sufficiently larger than the input/output impedance of the opposite communication device 13, the influence on signal transmission from the communication device under test 11 to the opposite communication device 13 can be ignored.

Furthermore, the vertical impedance between the communication line 15 and the ground is approximately Z/2, and by making Z/2 smaller than the impedance between the communication line terminal of the communication device under test 11 and the ground, the coupling transformer is The voltage generated in the 26 secondary windings 27 and 2 can be efficiently applied to the communication device under test 11.

- For boat fishing, the impedance element 35 having an impedance Z is, for example, -48 (V) of the communication line 15.
A capacitive element is inserted in order to prevent the DC power supply current from flowing into the coil part 30, and a resistive element is connected in series to prevent resonance between this capacitive element and the center-tapped coil 31 of the coil part 30. It is formed by inserting it.

The common mode choke coil 17 is connected to a coupling transformer 26
This reduces the voltage applied to the opposite communication device 13 from the opposite communication device ff113, thereby eliminating transmission quality deterioration and malfunction in the opposite communication device ff113.

Furthermore, if there is a difference in impedance between the two impedance elements 35, a voltage will be generated between the two communication lines 15, but
This can be prevented by making the difference between the two impedances 2 sufficiently small. In addition, by winding the center-tapped coil 31 of the coil section 30 in a well-balanced manner, the voltage generated between the communication lines 15 in the immunity test circuit section is suppressed to a low level, so that it does not affect signal transmission. be able to.

FIG. 2 shows the voltage generator 2 in the circuit shown in FIG.
Vertical voltage V between each of the communication line terminal of the communication device under test 11, the common connection point B, and the communication line terminal of the opposite communication device 13 and the ground with respect to the voltage V, (marked O) supplied from 5.
, (X mark), Vz (Δ mark) and V2 (in the mouth) are shown.

The coupling transformer 26 in FIG. 1 has, for example, a toroidal core wound with a primary winding nine times and a secondary winding nine times. Moreover, the impedance Z of the impedance element 35
is a 200 (Ω) resistive element and a 0°1 (μF) capacitive element connected in series, and this capacitive element prevents the DC supply current from flowing to the impedance element 35. , the difference in impedance Z is 0.1%
I am doing the following.

By the way, under the same conditions (coupling transformer 2
6. FIG. 11 shows the measurement results for the conventional circuit shown in FIG. 10 using a common mode choke coil 17, etc.).

Comparing both figures, it can be seen that in both the present embodiment and the conventional example, the voltage V1 applied to the communication device under test 11 is the voltage (2) supplied from the voltage generator 25. It can be seen that a voltage approximately equal to that is efficiently applied.

In the characteristics of this embodiment shown in FIG. 2, the voltage ■2 applied to the common connection point B in FIG. 1 is 10 (kHz), and the voltage ■1
It is about 40 (dB) smaller than that. Furthermore, 1 (MH
At high frequencies between z) and 10 (MHz), the voltage at the common connection point B becomes large, but the common motor tituta coil 1
7 is used to reduce the voltage V applied to the opposite communication device 13, and overall, the voltage V applied to the opposite communication device 13 from low frequency to high frequency is compared to the voltage V applied to the communication device under test 11. It is about 40 (dB) to 50 (dB) lower.

On the other hand, in the conventional circuit shown in FIG. 11, the voltage v2 applied to the common connection point B in FIG. A voltage equivalent to V is applied to the common mode choke coil 17. With respect to this voltage, the common mode choke coil 17 has almost no effect below several hundred kHz, and a voltage v3 approximately equivalent to the voltage (2) applied to the communication device under test 11 is applied to the opposing communication device 13. Therefore, in the conventional circuit, if the device resistance of the opposing communication device 13 is low, code errors, malfunctions, etc. may occur.

FIG. 3 shows a measuring circuit for determining the circuit balance λ in the circuit of the present embodiment shown in FIG. Also, the fourth
The figure shows the measured results.

In the circuit shown in FIG. 3, the voltage (lateral voltage) generated between the communication device under test 11 and the conductor of the communication line 15
When the voltage (vertical voltage) vb generated between Va, the communication line 15, and the ground is measured, the degree of balance λ is λ=201! , og (Vb/Va) (dB).

From FIG. 4, the balance degree λ (dB) in this example is 5 (
It has a minimum of 60 (dB) or more in the frequency range (kHz) to 10 (MHz), and exhibits sufficiently better characteristics than communication lines used for actual signal transmission. This means that the lateral voltage generated in the coupling transformer 26 due to the voltage applied between the communication line 15 connected to the communication device under test 11 and the ground is sufficient compared to that generated in the actual communication line. It can be seen that the test can isolate and accurately measure code errors and malfunctions occurring in the communication device under test 11 due to the vertical voltage.

Further, FIG. 5 shows the impedance ZAI between the common connection point A and the common connection point B in the circuit shown in FIG. This impedance ZAI is at frequency 1 (kHz
z) to 1 (MHz), it becomes a large value of 400 (Ω) or more. Therefore, almost no transmission signal current flows through the impedance element 35 and the center-tapped coil 31.
This shows that even in the immunity test, the influence on the transmission signal is small.

By the way, as can be seen from Figure 5, approximately 1.5 (kH)
Resonance occurs at z). In order to prevent the influence of such resonance, in the circuit of the first embodiment, a resistor is connected in series with the capacitive element in the impedance element 35 inserted between the communication line 15 and the center-tapped coil 31. need to be inserted. However, this resonance prevention resistor needs to be one for high precision and high power use. An immunity test circuit that eliminates such drawbacks will be described next.

11,'M2a Figure 6 shows another embodiment of the present invention. In the figure, the first
The difference from the circuit shown in the figure is that a transformer 40 with a center tap is provided in place of the coil section 30. Two capacitors 45 are interposed between the two center-tapped coils 41 forming the center-tapped transformer 40 and the communication line 15 to prevent the feeding current from flowing.
In addition, the center point 43 of the center tapped coil 41 is connected to the resistor 4.
It is grounded via 7. Coil 41 with center tap
Another coil 49 is wound around the same core and terminated with a resistor 51 as an impedance element to prevent series resonance between the center-tapped coil 41 and the capacitor 45.

In the circuit of this second embodiment, the terminating resistor 51 of the resonance prevention coil 49 may be used for low power, and the impedance Z□ between the common connection points A, B and the ground is set to the midpoint. There is an advantage that the resistor 47 inserted between the tapped coil 41 and the ground can be freely set.

FIG. 7 shows the impedance 2□ between the common connection point A and the common connection point B in the circuit shown in FIG. From this, the impedance ZAI between the common connection points A and B is even larger than that in the circuit of the first embodiment near 1 and 5 (kHz) where resonance occurs. Moreover, the impedance ZAI is HkΩ) or more at 1 (kHz) to 1 (MHz), and the coil 41 with a center tap
Resonance between the capacitor 45 and the capacitor 45 is well suppressed, and the impedance ZAII becomes approximately constant.

Furthermore, in Fig. 8, common connection points A, B and point 0 (midpoint 43
), the impedance ZAI-C becomes a very small value and becomes the value of the resistor 47. Therefore, this impedance Z□ can be freely set by the resistor 47. By the way, this impedance ZAI is the impedance seen between the common connection points A and B and the 0 point, assuming that they are short-circuited.

In the circuit of the second embodiment, the terminating resistor 51 of the coil 49 for preventing resonance can be a low-power resistor, so there is no need to use a high-precision high-power resistor for resonance prevention.

mAdditional ζ Modification As mentioned above, the number of secondary windings 273 equal to the number of conductors of the communication line 15 is inserted between the communication device under test 11 and the opposing communication device 13 that communicates with it. . Also, the opposing communication device 13 of the secondary winding 27t of the coupling transformer 26
An impedance element 35 having the same impedance value is connected to each pair on the side, and this is connected to the coil 3 with a center point tapped.
The main feature is that a common mode choke coil 17 is inserted between the impedance element 35 and the opposite communication device 13, and the middle point 33 is grounded.

Further, a transformer 40 with a center point tapped is provided in which a separate coil 49 is wound around the same core as the coil 41 with a center point tapped, and this separate coil 49 is terminated with a resistor 51.

In the conventional circuit, the communication device under test 11 and the opposing communication device 13
The number of secondary windings 27□ is the same as the number of conductors of the communication line 15.
It is only necessary to insert the common mode rotor coil 17 between this and the opposing communication device 13 side.

In the embodiment of the present invention, the secondary winding 27□ of the coupling transformer 26
Impedance elements 35 having the same impedance value are connected between the common mode choke coil 17 and the common mode choke coil 17,
A coil 31 with a center point tapped with a center point 33 is attached to each pair.
(The coil part 30) is connected to both ends of the coil part 30. By grounding the center point 33 of this center-tapped coil 31, the voltage applied to the opposing communication device 13 is reduced to a level at which code errors and malfunctions do not occur in the opposing communication device 13.

Further, in the second embodiment, resonance is particularly prevented by the coil 49 and resistor 49 of the center-tapped transformer 40.

IV! 1(7)iiJ41 Woodcutter The present invention is not limited to the above-mentioned embodiments,
Those skilled in the art will easily guess that there are various modifications.

〔Effect of the invention〕

As described above, according to the present invention, in an immunity test, the voltage supplied for testing can be efficiently applied to the communication device under test, and the voltage applied to the opposing communication device can be suppressed. Code errors and malfunction characteristics of the test communication device can be accurately measured.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of an immunity test circuit according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of applied voltage in the circuit shown in FIG. 1, and FIG. 3 is a balance diagram of the circuit shown in FIG. 1. 4 is an explanatory diagram showing the measurement results in the circuit shown in FIG. 3, and FIG. 5 is a diagram showing the impedance ZAI between the common connection points A and B in the circuit shown in FIG. 6 is a configuration block diagram of an immunity test circuit according to another embodiment of the present invention. FIG. 7 is a characteristic diagram of impedance ZAl between common connection points A and B in the circuit shown in FIG. 6. The figure shows common connection point A in the circuit shown in FIG. Characteristic diagram of impedance ZA and A between point B and 0, Fig. 9 is a circuit diagram showing the conventional example, Fig. 1O is a circuit diagram showing another conventional example, Fig. 11 is the conventional example shown in Fig. 1O. FIG. 3 is a characteristic diagram showing measurement results of voltage application in an example circuit. In the figure, II is the communication device under test, 13 is the opposing communication device, 15 is the communication line, 17 is the common mode choke coil, 20 is the voltage injection coil, 21 is the center-tapped coil, 25 is the voltage generator, and 26 is the voltage generator. Coupling transformer, 30 is a coil section, 31 is a coil with a center tap, 35 is an impedance element, 40 is a transformer with a center tap, 41 is a coil with a center tap, 47 is a resistor, 49 is a coil, 51 is a resistor It is.

Claims (2)

[Claims] (1) For at least a pair of communication devices that communicate with each other and operate with a common potential point as a reference, one communication device to be tested is the communication device under test, and the other communication device is the opposite communication device. In an immunity test circuit that is a communication device, a common mode choke coil inserted into each of two conductors of a communication line interposed between the pair of communication devices, and between the common mode choke coil and the communication device under test. a secondary winding of a coupling transformer inserted into each of the two conductors of the communication line, a voltage supply source supplying voltage from the primary winding of the coupling transformer, and a midpoint connected to the common potential point. a coil with a center point tapped; two impedance elements inserted between respective common connection points of the common mode choke coil and the secondary winding of the coupling transformer and both ends of the coil with a center point tap; , and is configured to apply a voltage for immunity testing from the voltage supply source to the communication device under test via the coupling transformer. (2) For at least a pair of communication devices that communicate with each other and operate with a common potential point as a reference, one communication device to be subjected to the desired test is the communication device under test, and the other communication device is the opposite communication device. In an immunity test circuit that is a communication device, a common mode choke coil inserted into each of two conductors of a communication line interposed between the pair of communication devices, and between the common mode choke coil and the communication device under test. a secondary winding of a coupling transformer inserted into each of the two conductors of the communication line; a voltage supply source supplying voltage from the primary winding of the coupling transformer; a transformer having a separate coil with an impedance element connected to the separate coil; a separate impedance element inserted between the midpoint of the center-tapped coil and the common potential point; two capacitive elements inserted between a tapped coil and the communication line, and applying a voltage from the voltage supply source to the communication device under test via the coupling transformer for immunity testing. An immunity test circuit characterized by comprising: