JP2675583B2 - Immunity test circuit - Google Patents

Description

The present invention relates to an immunity test circuit,
Of at least a pair of communication devices having a relationship of communicating with each other, one communication device to be tested for noise immunity or the like is a communication device under test, and the other communication device is an opposite communication device. The present invention relates to an immunity test circuit for applying a voltage (longitudinal voltage) to a connected communication line and performing a test for deterioration of transmission quality such as code error of digital transmission occurring in a communication device and malfunction.

[Conventional technology]

Conventionally, before operating a communication device (for example, in the development stage of a device, before installing a device, etc.), a device that is one of the communication devices under test transmits, for example, a certain pattern to a device that is the other opposite communication device. However, a code error or the like of digital transmission in the meantime may be verified, and a test such as deterioration of transmission quality or malfunction in a communication device or a communication line may be performed. The immunity test was conducted in order to examine the extent to which such an operation test can be performed against noise, that is, the device durability of the communication device.

A circuit for applying a voltage (pseudo noise source) for the immunity test between the communication line connected to the communication device under test and the ground when performing such an immunity test is as shown in FIG. There was something. Here, the communication device under test 11 and the opposite communication device for communicating with the communication device 11 under test.
This is the case where the communication line 15 to and from 13 is a two conductor, and the communication line 15
Is a common mode choke coil on the opposite communication device 13 side.
17 has been inserted. A voltage injection coil 20 is inserted between two communication lines 15, and a voltage generator is provided between the midpoint 23 of the coil 21 with a midpoint tap forming the voltage injection coil 20 and the ground.
It is a circuit that applies a voltage for immunity test by 25. The voltage for this test is a sinusoidal AC voltage,
Amplitude-modulated or frequency-modulated signal voltage, surge voltage, etc. are available.

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

FIG. 10 shows another conventional example. In this circuit as well, as in the case of FIG. 9, the communication line 15 connecting the two communication devices has two conductors, and the communication device under test 11 and the opposite communication device 13 that communicates in opposition thereto. A coupling transformer 26 is provided in between, the secondary winding 27 ₂ of this coupling transformer 26 is inserted into each communication line 15, and a voltage is applied to the primary winding 27 ₁ of the coupling transformer 26 by the pressure generator 25 for the immunity test. It is a circuit to apply. Also in this circuit, the common mode choke coil 17 is provided so as to reduce the voltage applied to the opposite communication device 13.
Is inserted.

[Problems to be solved by the invention]

However, in the conventional circuit shown in FIG. 9 described above, when performing the immunity test, the opposite communication device 13
In order to reduce the influence of the voltage applied to the common mode choke coil 17, the common mode choke coil 17 can reduce the voltage at high frequencies.
The effect is low at low frequencies. Therefore, the opposite communication device
If the device endurance of 13 is low, there is a problem that a code error or malfunction occurs in the opposite communication device 13 and an accurate test cannot be performed.

Further, even in the circuit shown in FIG. 10, the opposite communication device 13
Although the common mode choke coil 17 is inserted so as to reduce the voltage applied to, the effect is small at low frequencies as in the circuit of FIG. Therefore, if the device resistance of the opposite communication device 13 is low, a code error may occur in the opposite communication device 13.
There is a problem that malfunction occurs, and the device yield strength of the communication device under test 11 cannot be evaluated correctly.

In the conventional circuit of FIG. 10, for example, the result of measuring the characteristics of the applied voltage when a certain circuit constant is determined is shown in FIG.
Shown in the figure. Here, the voltage generator 25 of the circuit shown in FIG.
The applied voltage V ₀ is indicated by ○, the voltage V ₁ applied to the communication device under test 11 is indicated by X, the voltage V ₂ applied to the common connection point B (common mode choke coil 17) is indicated by Δ, and the voltage applied to the opposite communication device 13 is indicated. V ₃ is shown by □. Here, common connection point B
The voltage V ₂ applied to the common mode choke coil 17 is substantially equal to the voltage V ₀ supplied from the voltage generator 25, and a voltage equivalent to the voltage V ₁ applied to the communication device under test 11 is applied. Thus, with respect to the voltage applied to the common mode choke coil 17, the effect of the common mode choke coil 17 is scarce at several hundred kHz or less. Therefore, the opposite communication device 1
If the device endurance of item 3 is small, code errors and malfunctions may occur.

The present invention was created in view of such a point, and suppresses the voltage applied to the opposite communication device to a level at which code error and malfunction do not occur, so that the device strength of only the communication device under test can be accurately measured. It is intended to provide an immunity test circuit that enables measurement.

[Means for solving the problem]

(I) Invention according to Claim 1 In order to achieve the above-mentioned object, in the invention according to Claim 1, a desired test should be performed on at least a pair of communication devices that are in a relationship of communicating with each other. In an immunity test circuit in which one communication device is a device under test and the other communication device is an opposite communication device, a common mode choke coil is inserted into two conductors of a communication line interposed between a pair of communication devices, and the common Insert the secondary winding of the coupling transformer into each of the two conductors of the communication line between the mode choke coil and the communication device under test, and supply the voltage from the primary winding of the coupling transformer by the voltage supply source. Provide a coil with a midpoint tap connected to the desired potential point,
Insert an impedance element between the common connection point of the common mode choke coil and the secondary winding of the coupling transformer and both ends of the coil with a midpoint tap, and connect it to the communication device under test from the voltage supply source via the coupling transformer. It is configured to apply a voltage for the immunity test.

(Ii) The invention according to claim 2 In order to achieve the above-mentioned object, in the invention according to claim 2, a desired test should be performed on at least a pair of communication devices that are in a relationship of communicating with each other. In an immunity test circuit in which one communication device is a device under test and the other communication device is an opposite communication device, a common mode choke coil is inserted into two conductors of a communication line interposed between a pair of communication devices, and the common Insert the secondary winding of the coupling transformer into each of the two conductors of the communication line between the mode choke coil and the communication device under test, and supply the voltage from the primary winding of the coupling transformer by the voltage supply source. Connect an impedance element to the coil with a point tap and another coil wound on the same core as that, and between the midpoint of this coil with a midpoint tap and the desired potential point. In addition to inserting an impedance element, insert a capacitive element between the coil with the midpoint tap and the communication line, and apply a voltage for immunity test from the voltage supply source to the communication device under test via the coupling transformer. Is configured.

(Operation)

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

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

(Ii) The invention according to claim 2 In the invention according to claim 2, the coil with the midpoint tap is formed by an impedance element connected to another coil wound on the same core as the coil with the midpoint tap of the transformer. Resonance is prevented.

Therefore, in the immunity test, the device yield strength of only the communication device under test can be measured more accurately.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

I. First Embodiment (i) Configuration of First Embodiment FIG. 1 shows a configuration of an immunity test circuit according to an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 10 indicate the same elements and the like, and the detailed description thereof will be omitted here.

In FIG. 1, a coil portion 30 is newly provided, and a midpoint 33 of a coil 31 with a midpoint tap forming the coil portion 30 is grounded. Between the secondary winding 27 ₂ and two common connection points A, B and both the midpoint tapped coil 31 of the common mode choke coil 17 of the coupling transformer 26, connect the impedance element 35 having the same impedance Z doing.

(Ii) Operation of the First Embodiment The operation of the embodiment thus configured will be described below.

In FIG. 1, the communication device under test 11 and the opposite communication device 13
The voltage V ₀ for the immunity test generated from the voltage generator 25 while transmitting a signal to and is supplied to the primary winding 27 ₁ of the coupling transformer 26 and is induced in the secondary winding 27 ₂ thereof. A voltage is applied to the communication device under test 11.

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

This 2Z + jωL impedance is the communication device under test 1
1, from the communication device under test 11 to the opposite communication device by making it sufficiently larger than the input / output impedance of the opposite communication device 13.
The effect on the signal transmission to 13 is negligible.

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 The voltage generated in the secondary winding 27 ₂ of 26 is
It can be efficiently applied to the communication device under test 11.

Generally, as the impedance element 35 having the impedance Z, a capacitive element is inserted in order to prevent a DC power supply current of, for example, −48 (V) of the communication line 15 from flowing into the coil section 30, and In order to prevent the impedance between lines from becoming almost zero due to resonance between the capacitive element and the coil 31 with the midpoint tap of the coil portion 30, a resistive element is inserted in series and formed.

The common mode choke coil 17 reduces the voltage applied from the coupling transformer 26 to the opposite communication device 13 and eliminates the deterioration of transmission quality and malfunction of the opposite communication device 13.

If there is a difference in impedance between the two impedance elements 35, a voltage is generated between the two communication lines 15, but
This can be prevented by making the difference between the two impedances Z sufficiently small. Also, by winding the coil 31 with the midpoint taps in a well-balanced manner, the voltage between the communication lines 15 generated in the immunity test circuit part can be suppressed to a small value so as not to affect the signal transmission. be able to.

FIG. 2 is a circuit diagram of the voltage generator in the circuit shown in FIG.
With respect to the voltage V ₀ (marked with ○) supplied from 25, the communication line terminal of the communication device under test 11, the common connection point B, and the opposite communication device 13
Vertical voltage V ₁ (×
(Marked), V ₂ (marked) and V ₃ (marked) are shown.

The coupling transformer 26 in FIG. 1 is, for example, a toroidal core wound with nine primary windings and nine secondary windings. The impedance Z of the impedance element 35 is
A resistance element of 200 (Ω) and a capacitive element of 0.1 (μF) are connected in series, and this capacitive element prevents a DC power supply current from flowing to the impedance element 35. The difference in Z is 0.1% or less.

By the way, the same condition (coupling transformer
26, a common mode choke coil 17), and FIG. 11 shows the result of measurement in the conventional circuit shown in FIG.

By comparing both figures, the voltage V ₁ applied to the communication device under test 11 is the voltage generator in both the present embodiment and the conventional example.
It can be seen that a voltage substantially equal to the voltage V ₀ supplied from 25 is efficiently applied.

In the characteristic of this embodiment shown in FIG. 2, the voltage V ₂ applied to the common connection point B in FIG. 1 is 10 (kHz), and the voltage V ₁ is 40 (d
B) becomes smaller. Furthermore, although the voltage V ₂ at the common connection point B increases at high frequencies of 1 (MHz) to 10 (MHz), the voltage V ₃ applied to the opposite communication device 13 is reduced by using the common mode choke coil 17. However, in total, the voltage V ₃ applied to the opposite communication device 13 from low frequency to high frequency is the communication device under test.
It is about 40 (dB) to 50 (dB) lower than the voltage V ₁ applied to 11.

On the other hand, in the conventional circuit shown in FIG. 11, the voltage V ₂ applied to the common connection point B in FIG. 10 is almost equal to the voltage V ₀ supplied from the voltage generator 25 and is applied to the communication device under test 11. A voltage equivalent to the voltage V ₁ is applied to the common mode choke coil 17. With respect to this voltage, the effect of the common mode choke coil 17 is almost several hundreds kHz or less, and the voltage V _{3 which} is almost equal to the voltage V ₁ applied to the communication device under test 11 is applied to the opposite communication device 13. Therefore, in the conventional circuit, if the device resistance of the opposite communication device 13 is small, there is a possibility that a code error, a malfunction, or the like may occur.

FIG. 3 shows a measuring circuit for obtaining the degree of balance λ of the circuit in the circuit of this embodiment shown in FIG. Further, FIG. 4 shows the measured results.

In the circuit shown in FIG. 3, the voltage (lateral voltage) Va generated between the communication device under test 11 and the conductor of the communication line 15 is Va.
When the voltage (longitudinal voltage) Vb generated between the communication line 15 and the ground is measured, the balance λ is expressed by λ = 20log (Vb / Va) (dB).

According to FIG. 4, the degree of balance λ (dB) in this embodiment is 5
(KHz) to 10 (MHz), the minimum is 60 (dB) or more, which is a sufficiently good characteristic compared to the communication line used for actual signal transmission. This means that the voltage applied between the communication line 15 connected to the communication device under test 11 and the ground is sufficient for the lateral voltage generated in the coupling transformer 26 portion as compared with that generated in the actual communication line. It can be seen that the test can be accurately measured by separating the code error and malfunction that occur in the communication device under test 11 by the vertical voltage.

Further, FIG. 5 shows the impedance Z _AB between the common connection point A and the common connection point B in the circuit shown in FIG. This impedance Z _AB has a frequency of 1 (kHz) to 1
It becomes a large value of 400 (Ω) or more at (MHz). for that reason,
Almost no transmission signal current flows through the impedance element 35 and the coil 31 with the midpoint tap. From this, it can be seen that even in the immunity test, the influence on the transmission signal is small.

By the way, as you can see from Fig. 5, about 1.5 (kHz)
Resonance occurs and the impedance at this frequency is very small without a resistive element. In order to prevent the influence of such low impedance, in the circuit of the first embodiment, the communication line 15 and the coil 31 with the middle point tap are used.
In the impedance element 35 inserted between and, it is necessary to insert a resistor in series with the capacitive element. But,
As this resonance preventing resistor, one for high precision and high power is required. An immunity test circuit that eliminates such drawbacks will be described below.

II. Second Embodiment FIG. 6 shows another embodiment of the present invention. In the figure, the difference from the circuit of FIG. 1 is that a transformer 40 with a midpoint tap is provided in place of the coil section 30. Two capacitors 45 are inserted between the two midpoint tapped coils 41 forming the midpoint tapped transformer 40 and the communication line 15 in order to prevent the feed current from flowing, and the midpoint tapped The midpoint 43 of the coil 41 is grounded via a resistor 47. Another coil 49 is wound around the same core as the coil 41 with a midpoint tap, and a resistor 51 as an impedance element.
, And prevents series resonance between the coil 41 with the midpoint tap and the capacitor 45.

In the circuit of the second embodiment, the termination resistor 51 of the resonance prevention coil 49 may be for low power, and the common connection point A,
The impedance Z _AB between B and the ground has the advantage that it can be freely set by the coil 41 with the midpoint tap and the resistor 47 inserted between the ground.

FIG. 7 shows the impedance Z _AB between the common connection point A and the common connection point B in the circuit shown in FIG. As a result, the impedance Z _AB between the common connection points A and B is even greater in the vicinity of 1.5 (kHz) where resonance occurs than in the circuit of the first embodiment. Also, the impedance
Z _AB is 1 (kΩ) or more in the range of 1 (kHz) to 1 (MHz), resonance between the coil 41 with the midpoint tap and the capacitor 45 is well suppressed, and the impedance Z _AB becomes substantially constant.

Further, FIG. 8 shows that the impedance Z _AB-C between the common connection points A and B and the point C (middle point 43) has a very small value,
It is almost the value of the resistor 47. Therefore, this impedance
Z _AB-C can be freely set by the resistor 47. By the way, this impedance Z _AB-C is the impedance seen between the common connection points A and B and the point C, assuming that the common connection points A and B are short-circuited.

In the circuit of the second embodiment, since the termination resistor 51 of the coil 49 for resonance prevention may be for low power, it is not necessary to use a resistor for high precision and high power for resonance prevention.

III. Summary of Embodiments As described above, the same number of secondary windings 27 ₂ as the number of conductors of the communication line 15 are provided between the communication device under test 11 and the opposite communication device 13 which communicates with the communication device under test 11. insert. Also, connect the impedance element 35 having the same impedance value for each pair in opposite communication device 13 side of the secondary winding 27 ₂ of the coupling transformer 26, and connect it to both ends of the midpoint tapped coil 31, this The most important feature is to ground the midpoint 33 and insert the common mode choke coil 17 between the impedance element 35 and the opposite communication device 13.

Further, it is characterized in that a transformer 40 with a midpoint tap in which another coil 49 is wound around the same core as the coil 41 with a midpoint tap is provided, and the other coil 49 is terminated by a resistor 51.

In the conventional circuit, the same number of secondary windings 27 ₂ as the number of conductors of the communication line 15 are inserted between the device under test 11 and the opposite communication device 13, and a common mode choke coil is provided on this side and the opposite communication device 13 side. Only insert 17.

In the present invention embodiment, all connecting the impedance element 35 of the same impedance value, which midpoints tapped coil for each pair 31 between the secondary winding 27 ₂ and the common mode choke coil 17 of the coupling transformer 26 It is connected to both ends of (coil part 30). This midpoint tapped coil 31 midpoint 33
Is grounded, the voltage applied to the opposite communication device 13 is reduced to a level at which the opposite communication device 13 does not cause a code error or malfunction.

Further, in the second embodiment, resonance is prevented especially by the coil 49 and the resistor 51 of the transformer 40 with the midpoint tap.

IV. Modified Embodiment of the Invention In the embodiment described above, the communication device under test 1
1, the opposite communication device 13 is shown connected to the ground,
It is not limited to this. For example, it may be connected to the ground of the building. Further, it is not necessary to directly connect to the ground or the like, and in that case, it is connected to the ground through a so-called stray capacitance.

Further, those skilled in the art can easily contemplate that the present invention has various modifications.

〔The invention's effect〕

As described above, according to the present invention, in the immunity test, the voltage supplied for the test can be efficiently applied to the communication device under test, and the voltage applied to the opposite communication device can be suppressed. Code error of test communication device,
The malfunction characteristic can be accurately measured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an immunity test circuit according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of an applied voltage in the circuit shown in FIG. 1, and FIG. 3 is a balance degree λ in the circuit shown in FIG. Fig. 4 is a circuit diagram showing a measurement circuit of Fig. 4, Fig. 4 is an explanatory diagram showing measurement results in the circuit shown in Fig. 3, and Fig. 5 is an impedance Z _AB between common connection points A and B in the circuit shown in Fig. 1. 6 is a characteristic block diagram of an immunity test circuit according to another embodiment of the present invention, and FIG. 7 is a characteristic diagram of impedance Z _AB between common connection points A and B in the circuit shown in FIG. FIG. 8 shows common connection points A, B and C in the circuit shown in FIG.
Characteristic diagram of the impedance Z _AB-C between the point, Figure 9 is a circuit diagram showing a conventional example, FIG. 10 is a circuit diagram showing another conventional example, FIG. 11 prior art example shown in FIG. 10 It is a characteristic view which shows the measurement result of the application of the voltage in a circuit. In the figure, 11 is a communication device under test, 13 is an opposite communication device, 15 is a communication line, 17 is a common mode choke coil, 20 is a voltage injection coil, 21 is a coil with a midpoint tap, 25 is a voltage generator, and 26 is a voltage generator. Coupling transformer, 30 is coil part, 31 is coil with midpoint tap, 35 is impedance element, 40 is transformer with midpoint tap, 41 is coil with midpoint tap, 47 is resistor, 49 is coil, 51 is resistor Is.

Claims (2)

(57) [Claims] 1. An immunity test circuit for at least a pair of communication devices having a relationship of communicating with each other, wherein one communication device to be subjected to a desired test is a communication device under test and the other communication device is an opposite communication device. In a common mode choke coil inserted into two conductors of a communication line interposed between the pair of communication devices, and two conductors of the communication line between the common mode choke coil and the communication device under test. A secondary winding of the coupling transformer inserted in the, a voltage supply source for supplying a voltage from the primary winding of the coupling transformer, a coil with a midpoint tap whose midpoint is connected to a desired potential point, and the common mode Two in-lines inserted between a common connection point of each of the choke coil and the secondary winding of the coupling transformer and both ends of the coil with the midpoint tap. Comprising a-impedance element, and immunity test circuit, characterized by being configured to apply a voltage for immunity test device under test communication device from the voltage supply through the coupling transformer. 2. An immunity test circuit for at least a pair of communication devices having a relationship of communicating with each other, wherein one communication device to be subjected to a desired test is a communication device under test and the other communication device is an opposite communication device. In a common mode choke coil inserted into two conductors of a communication line interposed between the pair of communication devices, and two conductors of the communication line between the common mode choke coil and the communication device under test. A secondary winding of the coupling transformer inserted in the coil, a voltage supply source for supplying a voltage from the primary winding of the coupling transformer, a coil with a midpoint tap and another coil wound on the same core as the coil, A transformer in which an impedance element is connected to another coil, and another impedance inserted between the midpoint of the coil with the midpoint tap and the desired potential point And children, were inserted between the communication line and the tapped coil 2
An immunity test circuit comprising: one capacitive element; and a voltage for applying an immunity test from the voltage supply source to the communication device under test via the coupling transformer.