JP2603513B2 - Immunity test circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is used for testing a digital communication device connected to a balanced pair transmission line. The present invention relates to an apparatus for applying a noise voltage between a balanced pair transmission line and ground.

The present invention is directed to a balanced pair transmission line inserted between a device under test connected to the balanced pair transmission line and a partner device that is a communication partner connected to the balanced pair transmission line. In this apparatus, the noise voltage reaches the device under test and the noise voltage does not reach the partner device so that the characteristics of the device under test can be accurately tested.

[Conventional technology]

Digital communication equipment connected to a balanced pair transmission line may receive inductive noise from the power line each time in an overhead cable or indoor wiring, which is greater between the balanced pair and the ground than the balanced pair. Appears as voltage.
In digital communication equipment, the housing and each mounted circuit are grounded in principle, so if the noise voltage between the balanced pair and ground is large, the circuit of the communication equipment will be affected and code errors will occur. It may cause malfunction and other quality deterioration.

In order to test this, conventionally, there has been known a method of applying a noise voltage between a balanced pair transmission line and ground and testing a code error or the like of a device under test according to the type and level of the noise voltage. .

FIG. 7 is its conventional circuits, balanced pair transmission line L that connects the partner device Q ₂ to which a device under test Q ₁ and its communication partner
In the inserted midpoint of the coil T _1, by connecting the output of the noise generator G giving noise voltage between the ground, the balanced pair transmission line L of the counterpart apparatus so that the noise is not transmitted To
The common mode choke coil CH is inserted. In this circuit, while providing noise voltage between the ground and the balanced pair transmission line with respect to the test device Q _1, to measure the error rate of the transmission signal.

Since this circuit rather conditions a practical balanced pair transmission line for the midpoint grounded coil T ₁ is different from the circuit shown in FIG. 8 as to improve this have been used. This circuit also, a conventional circuit, balanced pair transmission line L that connects the partner device Q ₂ to which a device under test Q ₁ and its communication partner
And a noise generator G for applying a noise voltage of a primary membrane wire of the transformer using a transformer T having a secondary winding balanced with respect to the balanced pair transmission line on the side of the device under test. a circuit connected to the common mode choke coil CH as the output of the noise generator G to a balanced pair transmission line L of the counterpart apparatus Q ₂ is not transmitted.

[Problems to be solved by the invention]

This circuit is an excellent circuit that allows the noise generator G to float with respect to the ground, but the common mode choke coil CH has frequency characteristics, and can be used for wide frequency characteristics or various types of pulse noise. And the other device Q ₂
There is a drawback that noise leakage to the side cannot be prevented.

That is, when the output noise of the noise generator G to a balanced pair transmission line L of the partner device Q ₂ side leaks, whether those errors observed transmission signals is generated by the device under test Q _1, generated by the other unit Q ₂ It is no longer possible to distinguish between
The characteristics for Q ₁ can not be accurately measured.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a circuit capable of reducing the leakage of a noise voltage to a partner device and accurately measuring characteristics of the device under test.

[Means for solving the problem]

According to the present invention, each line of a balanced pair transmission line between a transformer for applying noise to the balanced pair transmission line and a common mode choke coil for preventing noise leakage to a partner device and the ground are substantially equal to each other. impedance circuit (Z ₁ value,
Z ₂ ) is connected.

This impedance circuit is, for example, a series circuit of a DC blocking capacitor and a resistor, and it is desirable that the values of the two impedance circuits be set to match as much as possible.

[Action]

The common mode choke coil has a frequency characteristic. By appropriately setting the value of the impedance circuit, the frequency characteristic can be flattened. Further, by connecting an impedance circuit to the ground on the side of the partner device, a noise current flows through this impedance circuit, thereby reducing the noise voltage and reducing the noise voltage transmitted to the partner device side. . Furthermore, the frequency characteristics of common mode choke coils often have sharp resonances and anti-resonances, and the use of resistors in the impedance circuit reduces these sharp resonances and anti-resonances.
The noise voltage transmitted to the partner device can be reduced.

As a result, the noise voltage is applied only to the device under test, and the observed transmission signal error can be measured as having occurred from the device under test.

〔Example〕

FIG. 1 is a block diagram of a circuit according to an embodiment of the present invention.
This circuit is inserted in the balanced pair transmission line L that connects the partner device Q ₂ to which a device under test Q ₁ and its communication partner, the equilibrium secondary winding with respect to the balanced-to-transmission path of the device under test side A transformer T having a wire, a noise generator G for applying a noise voltage to the primary winding of the transformer T, and a common mode choke coil CH inserted into the balanced pair transmission line L on the partner device side. In the circuit, impedance circuits Z ₁ and Z ₂ having substantially the same value are connected between each line of the balanced pair transmission path between the transformer T and the common mode choke coil CH and the ground, respectively. It is characterized by.

Although the circuit of FIG. 1 is shown only for a pair of balanced transmission lines, it is possible to mount a plurality of balanced pair transmission lines in one device.

One example of the impedance circuits Z ₁ and Z ₂ is a series circuit of a capacitor C and a resistor R as shown in FIG.
The capacitor C is for blocking direct current, and its value is selected to have a sufficiently low impedance over the used frequency band. The value of resistor R is high enough without interference to the terminal impedance of the partner device Q _2, it is possible to set lower than the impedance at the frequency band to be used for the common mode choke coil CH. Also, it is exactly aligned as much as possible the value of the two impedance circuits Z ₁ and Z _2, may be set so as not to lose balance of the balanced pair transmission line.

The effect on the terminal impedance of the partner device Q ₂ of the impedance circuit (Z ₁ + Z _2, substantially 2Z) will be connected in parallel, effect on the noise voltage of the balanced pair transmission line L is two impedance circuit Parallel circuit (almost Z /
2) has been inserted between it and the ground.

A practical value is that if the frequency band of interest is 10 kHz to 10 MHz, the value of the capacitor C is 0.1 μF to 10 μF,
The value of the resistor R is between 100Ω and 1kΩ.

The noise generator G can be floated with respect to ground, or its output midpoint potential can be grounded if necessary.

In such a circuit, the noise voltage applied from the transformer T does not appear between the pair of the balanced pair transmission line but appears between the balanced pair of the transmission line and the ground. This noise voltage is a pseudo-noise signal for noise caused by induction from a power line or the like in a practical cable. The noise voltage is transmitted to the device under test Q ₁ from the transformer T, on the side of the other unit Q ₂ are impedance circuits Z _1, Z ₂ and the common mode choke coil CH
Is transmitted after being attenuated.

While changing the output level of the noise generator G or the frequency or waveform of the generated noise voltage, the two devices Q ₁
And between the by Q ₂ via the balanced pair transmission line L observing the error in the digital signal transmitted and received. At this time, noise is applied from the circuit is used only for the device under test Q _1, not its effect on the other unit Q _2. That is, the error of the digital signal observed by the noise voltage applied is so good as occurring at the device under test Q _1, it is possible to test the precise characteristics of the device under test Q _1.

FIG. 4 shows the results of actually measuring the characteristics of the circuit of this embodiment. Voltage V ₀ ~V ₃ are as entered in Figure 1. Impedance circuit Z ₁ and Z ₂ using a series circuit of a capacitor 1.5MyuF, resistors 200 [Omega. From this figure, it can be seen that the output voltage V ₀ of the noise generator G has almost no attenuation.
Is applied to the device under test Q ₁ as V _1, it can be seen that the applied receiving greatly attenuated as the voltage V ₃ to the counterpart device Q _2. Voltage V ₁ was some superiority about 40dB over a wide frequency band with respect to the voltage V _3.

FIG. 5 shows the same measured results as those of the conventional circuit shown in FIG. 8 as a comparative example. Voltage V ₀ ~V ₃ are as entered in FIG. 8. It can be seen that there is a significant improvement in the lower frequency range.

FIG. 6 is a view showing the result of measuring the degree of balance of the circuit of the embodiment. As shown in FIG. 3, each terminal of the circuit of the embodiment was terminated with a resistor, the horizontal voltage Va and the vertical voltage Vb were measured, and the ratio was expressed in decibels as the degree of balance. It can be seen that this circuit has a practically sufficient degree of balance in a wide frequency range from several kHz to several tens of MHz.

〔The invention's effect〕

As described above, according to the present invention, the applied noise voltage is effective only for the device under test, and is applied to the partner device after being greatly attenuated. May be evaluated as occurring in the device under test, which has the effect of allowing accurate evaluation.

[Brief description of the drawings]

FIG. 1 is a block diagram of a circuit according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration example of an impedance circuit. FIG. 3 is a circuit diagram for measuring the degree of balance of the circuit according to the embodiment of the present invention. FIG. 4 is a characteristic measurement diagram of the circuit according to the embodiment of the present invention. FIG. 5 is a characteristic measurement diagram of the conventional circuit (FIG. 8). FIG. 6 is an actual measurement diagram of the degree of balance of the circuit according to the embodiment of the present invention. FIG. 7 is a configuration diagram of a conventional circuit. FIG. 8 is a configuration diagram of a conventional circuit. Q ₁ … under test device, Q ₂ … partner device, L… balanced transmission line, I… circuit of the present invention, T… transformer, G… noise generator, CH… common mode choke coil , Z ₁ , Z ₂ …
... impedance circuit.

Claims (1)

(57) [Claims] 1. A balanced pair transmission line (L) for connecting a device under test (Q ₁ ) and a partner device (Q ₂ ) to communicate with the device under test (Q ₁ ). A transformer (T) having a secondary winding balanced with respect to the noise, a noise generator (G) for applying a noise voltage to the primary winding of the transformer, and a transformer inserted into the balanced pair transmission line on the partner device side. In an immunity test circuit including a common mode choke coil (CH), an impedance having a value substantially equal to each other between a balanced pair between the transformer and the common mode choke coil and each line of the transmission path and the ground. An immunity test circuit to which circuits (Z ₁ , Z ₂ ) are connected.