JPH01297918A - Immunity testing circuit - Google Patents

Abstract

PURPOSE:To reduce a noise voltage to an opposite device side and to accurately measure characteristics by connecting impedance circuits which are equal in value to one another between a balanced couple of transmission lines between a transformer and a common mode choke coil. CONSTITUTION:The impedance circuits Z1 and Z2 which are nearly equal in value to each other are connected between the ground and the lines of the balanced couple of transmission lines L between the transformer T and common mode choke coil CH. While the output level of a noise generator G, the fre quency or waveform of the generated noise voltage is varied, the error of a digital signal transmitted and received between devices Q1 and Q2 through the transmission line L is observed. At this time, a noise applied to the genera tor G is effective to only the device Q1 to be tested and exerts no influence upon the opposite device Q2. Thus, the characteristics are accurately tested.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is utilized for testing digital communication equipment 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 a device under test that is inserted into a balanced pair transmission line between a device under test connected to a balanced pair transmission line and a counterpart device that is a communication partner connected to the balanced pair transmission line. In this device, the characteristics of the device under test can be accurately tested by preventing noise voltage from reaching the device under test and not reaching the other device.

[Conventional technology]

Digital communications equipment connected to balanced-pair transmission lines can receive induced noise from power lines and other sources in overhead cables or indoor wiring, which is caused by large voltages between the balanced-pair wires and ground rather than between the balanced-pair wires. It appears. As a general rule, the housing and each mounted circuit of a digital communication device are grounded, so if the noise voltage between the balanced pair wire and the ground is large, it will affect the communication device circuit and cause code errors. This may cause malfunction or other quality deterioration.

In order to test this, a conventional method is known in which a noise voltage is applied between the balanced pair transmission line and the ground, and the device under test is tested for code errors and other conditions according to the type and level of the noise voltage. .

FIG. 7 shows a conventional example circuit, in which the output of a noise generator G is connected to the midpoint of a coil T1 inserted in a balanced pair transmission path connecting a device under test Q1 and a device Q2 with which it communicates. A common mode choke coil CH is inserted into the balanced pair transmission path of the partner device to prevent this noise from being transmitted. In this circuit, the error rate of the transmitted signal is measured while applying a noise voltage between the balanced pair transmission line for the device under test Q1 and the ground.

Since this circuit is grounded at the center point at the coil T, the conditions are somewhat different from those of a practical balanced pair transmission line.As an improvement to this, the circuit shown in FIG. 8 is used. This circuit is also a conventional circuit, and is the device under test Q1.
A transformer T is inserted into the balanced pair transmission line connecting the communication partner device Q2, and is equipped with a secondary winding that is balanced with respect to the balanced pair transmission line on the side of the device under test. Connect a noise generator G that applies a noise voltage to the primary winding of the transformer, and connect a common mode choke coil CH so that the output of this noise generator G is not transmitted to the balanced pair transmission path of the partner device Q2. This is the circuit.

[Problem that the invention seeks to solve]

This circuit is an excellent circuit that can float the noise generator G with respect to ground, but the common mode choke coil CH has frequency characteristics, so it cannot be used in a wide frequency range or in many types of pulse noise. Then, the other device Q
There is a drawback that leakage of noise to the second side cannot be prevented.

In other words, if the output noise of the noise generator G leaks into the balanced transmission path on the side of the target device Q2, it will be difficult to determine whether the error in the observed transmission signal occurred in the device under test Q1 or the target device Q2. Therefore, it becomes impossible to accurately measure the characteristics of the device under test Q1.

The present invention is an improvement on this, and an object of the present invention is to provide a circuit that can reduce the leakage of noise voltage to the other device side and accurately measure the characteristics of a device under test.

[Means for solving problems]

The present invention provides a structure in which a transformer that applies noise to the balanced pair transmission line and a common mode choke coil that prevents leakage of noise to the other device are connected between each line of the balanced pair transmission line and the ground, which are substantially equal to each other. value impedance circuit (Zl,
Z2).

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.

[Effect]

Common mode choke coils have frequency characteristics, but
By appropriately setting the value of the impedance circuit,
This frequency characteristic can be flattened. In addition, by connecting an impedance circuit to ground on the other device's side, a noise current flows through this impedance circuit, lowering the noise voltage, and reducing the noise voltage transmitted to the other device's side. . Furthermore, the frequency characteristics of common mode choke coils often have sharp resonances and anti-resonances, and by using a resistor in the impedance circuit, these sharp resonances and anti-resonances can be alleviated and the noise transmitted to the other device can be reduced. The voltage can be reduced.

As a result, the noise voltage is applied only to the device under test, and it becomes possible to measure errors in the observed transmission signal as having occurred from the device under test.

[Embodiment] FIG. 1 is a block diagram of a circuit according to an embodiment of the present invention. This circuit is inserted into a balanced pair transmission line L connecting the device under test Q1 and its communication partner Q2, and connects a balanced secondary winding to the balanced pair transmission line on the device under test side. a noise generator G that applies a noise voltage to the primary winding of the transformer T, and a common mode choke coil c inserted into the balanced pair transmission path of the partner device.
In the circuit provided with H, impedance circuits Zl and Z2 having substantially equal values are connected between each line of the balanced pair transmission line between the transformer T and the common mode choke coil CH and the ground, respectively. It is characterized by having been.

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

An example of the impedance circuits Zl and Z2 is a series circuit of a capacitor C and a resistor R, as shown in FIG. The capacitor C is for direct current blocking, and its value is selected to have sufficiently low impedance over the frequency band to be used. Further, the value of the resistor R is preferably set to be high enough to not cause interference with the terminal impedance of the counterpart device Q2, and low with respect to the impedance in the frequency band used by the common mode choke coil CH. Further, it is preferable that the values of the two impedance circuits z1 and Z2 are set to match as accurately as possible so as not to lose the balance of the balanced transmission line.

The influence of this impedance circuit on the terminal impedance of the other device Q2 is that (Z+ +z, , 2Z) is inserted in parallel, and the influence on the noise voltage of the balanced transmission path is due to the parallel connection of the two impedance circuits. This means that the circuit (habo z/2) is inserted between it and the ground.

A practical value is to set the frequency band of interest to 10 kHz to 1
0M) Iz, the value of capacitor C is 0.1 μF
~10 μF, and the value of resistor R is 1000 to 1Ω.

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

In such a circuit, the noise voltage applied by the transformer T does not appear between the pair of balanced pair transmission lines, but appears between the balanced pair transmission line and ground. This noise voltage is a pseudo-noise signal for noise induced from power lines and other sources in practical cables. This noise voltage is transmitted from the transformer T to the device under test Q, but is transmitted to the other device Q2 after being attenuated by the impedance circuits Z+, Z2 and the common mode choke coil CH.

While changing the output level of the noise generator G or the frequency or waveform of the generated noise voltage, the two devices Q,
Errors in digital signals transmitted and received via this balanced pair transmission path between Q2 and Q2 are observed. At this time, the noise applied from this circuit is the device under test Q1
It is effective only for the other device Q2, and has no effect on the other device Q2. In other words, since the error in the digital signal observed due to the applied noise voltage may be assumed to occur in the device under test Ql, the accurate characteristics of the device under test Q can be tested.

FIG. 4 shows the results of actually measuring the characteristics of this example circuit.

Voltage V. -V3 is as indicated in FIG. Impedance circuits Z1 and Z2 are capacitors 1.5μ
F, a series circuit with a 200 Ω resistor was used. From this figure, the output voltage V of the noise generator G.

is applied to the device under test Q+ as a voltage V1 without being attenuated, and is applied to the device under test Q2 as a large voltage V3 (with attenuation). Voltage V1 is applied as voltage V3 It has an advantage of about 40 dB over a wide frequency band.

FIG. 5 shows similar actual measurement results for the conventional circuit shown in FIG. 8 as a comparative example. Voltage V. -■3 is as written in Figure 8. It can be seen that there is a significant improvement in the low frequency range.

FIG. 6 is a diagram showing the results of measuring the balance of the circuit of the above embodiment. Regarding the circuit of the above embodiment, each terminal is terminated with a resistor as shown in FIG. 3, the horizontal voltage Va and the vertical voltage Vb are measured, and the ratio thereof is expressed as a degree of balance and expressed in decibels. It can be seen that this circuit maintains a practically sufficient level of balance over a wide frequency range from several kHz to several tens of MHz.

〔Effect of the invention〕

As explained above, according to the present invention, the noise voltage to be applied is effective only to the device under test and is applied to the other device in a highly attenuated state. Errors can be evaluated as occurring in the device under test, which has the effect of allowing accurate evaluation.

[Brief explanation of the drawing]

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 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 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...device under test, Q2...other device, L...
Balanced pair transmission line, ■...Circuit of the present invention, T...Transformer, G...Noise generator, CH...Common mode choke Koinope Z+, Z2...Impedance circuit. Patent applicant: Nippon Telegraph and Telephone Corporation. Agent Patent Attorney Ide Nao Takashi → Zhou Trayi () (z) → Zhou and Lei (Hz) Conventional example tube I Shenggong 5 times frequency (Hz) Measurement of equilibrium degree Zhao Xian shoulder 6 reasons

Claims (1)

[Claims] 1. Inserted into the balanced pair transmission path (L) connecting the device under test (Q_1) and the other device (Q_2) with which it communicates, and which is balanced with respect to the balanced pair transmission path on the device under test side. A transformer (T) equipped with a secondary winding, a noise generator (G) that applies a noise voltage to the primary winding of this transformer, and a common mode choke coil ( In the immunity test circuit, an impedance circuit (Z
_1, Z_2) are connected.