TWI514799B - Cable equivalent circuit and test system - Google Patents

Description

Cable equivalent circuit and test system

This case is about a circuit and an electronic system. In particular, a cable equivalent circuit and test system.

With the rapid development of information technology, various types of network devices have been widely used in people's lives, such as servers, routers and switches.

In general, a test system for a network device includes a test device and a device under test. In the network device test, in order to simulate the actual test environment, a cable (for example, 100 meters in length) is coupled between the test device and the device under test. However, since the cable is bulky and cumbersome, it often causes inconvenience in testing and thus leads to inefficient execution of the test operation.

In view of this, a solution is proposed.

One aspect of the invention is a cable equivalent circuit. According to an embodiment of the invention, the cable equivalent circuit includes a low pass filter and a first resistor element. The low pass filter includes a first input. The low pass filter has a line resistance value. The first resistive element is coupled between the first input end of the low pass filter and a ground potential. The resistance value of the first resistance element is equal to a component resistance value.

Another aspect of the invention is a test system. The test system includes a cable equivalent circuit, a test device, and a device under test. The cable equivalent circuit includes a low pass filter and a first resistive element. The low pass filter includes a first input and a first output. The low pass filter has a line resistance value. The first resistive element is coupled between the first input of the low pass filter and the ground potential. The resistance value of the first resistance element is equal to a component resistance value. The test device is coupled to the first input end of the low pass filter for providing a test signal to the low pass filter, and the device under test is coupled to the first output end of the low pass filter for receiving the test through the low pass filter Signal and provide a response signal to the test device through a low pass filter.

In summary, by applying the above embodiment, a cable equivalent circuit can be realized. By adjusting the value of the component resistance and/or the value of the line resistance value, the circuit characteristics of the cable equivalent circuit can be fine-tuned so that the cable equivalent circuit can more accurately simulate the physical cable. In this way, in the test system, the cable equivalent circuit can be used to replace the traditional physical cable, thereby reducing the inconvenience of testing, reducing the test cost, and improving the execution efficiency of the test operation.

100‧‧‧Test system

110‧‧‧Testing device

120‧‧‧Device under test

130‧‧‧ Cable equivalent circuit

132‧‧‧ low pass filter

RO1-RO4‧‧‧resistive components

VG‧‧‧Virtually

P1, P2‧‧‧ current path

RI1-RI8‧‧‧ resistance

RS1, RS2‧‧‧ resistance

L1, L2‧‧‧ inductance

C1, C2‧‧‧ capacitor

RL1, RL2‧‧‧ curve

IL1, IL2‧‧‧ curve

RL1a, RL2a‧‧‧ curve

1 is a schematic diagram of a test system according to an embodiment of the present invention; FIG. 2 is a schematic diagram of a cable equivalent circuit according to an embodiment of the present invention; and FIG. 3 is a circuit equivalent circuit of a cable according to an embodiment of the present invention; FIG. 4 is a comparison diagram of a return loss of a cable equivalent circuit and a physical cable of a comparative example according to an embodiment of the present invention; and FIG. 5 is a cable equivalent circuit according to an embodiment of the present invention; A comparison diagram of the insertion loss of a physical cable of a comparative example; and FIG. 6 is a comparison diagram of the reflection loss of a cable equivalent circuit and a physical cable of a comparative example.

The spirit and scope of the present disclosure will be apparent from the following description of the preferred embodiments of the present disclosure. Modifications do not depart from the spirit and scope of the disclosure.

The terms “first”, “second”, etc. used in this document are not specifically intended to refer to the order or order, nor are they used to limit the case. They are only used to distinguish between components or operations described in the same technical terms. .

The term "coupled" as used herein may mean that two or more elements are in direct physical or electrical contact with each other, or indirectly in physical or electrical contact with each other, and "coupled" may also mean two or more. The component elements operate or act on each other.

One embodiment of the invention is a test system. For narrative It is clear that the following test system of the network device is taken as an example, but the invention is not limited thereto.

1 is a schematic diagram of a test system 100 in accordance with an embodiment of the present invention. In the present embodiment, the test system 100 includes a test device 110, a device under test 120, and a cable equivalent circuit 130. The test device 110 is coupled to the device 120 via the cable equivalent circuit 130. That is, the cable equivalent circuit 130 is coupled between the test device 110 and the device under test 120.

In the present embodiment, the test device 110 and the device under test 120 can be implemented, for example, by a computer, router, switch, or other suitable device. The cable equivalent circuit 130 can be implemented, for example, with a physical circuit (eg, a filter).

It is noted that the connection relationship and implementation manner of the test device 110, the device under test 120, and the cable equivalent circuit 130 are not limited to those disclosed in the embodiment, and the connection relationship is sufficient for the test system 100 to implement the following technical contents. Both implementations and implementations are applicable to the present invention.

In the present embodiment, the test device 110 can be used to provide a test signal to the device under test 120 via the cable equivalent circuit 130. The device under test 120 can be used to receive the test signal through the cable equivalent circuit 130, and corresponding to the test signal, provide a response signal to the test device 110 through the cable equivalent circuit 130, thereby completing the test operation.

The cable equivalent circuit 130 can be used to simulate the characteristics of a physical cable (eg, insertion loss and return loss). By replacing the physical cable with the cable equivalent circuit 130, the inconvenience in testing, the test cost can be reduced, and the efficiency of the test operation can be improved.

The following paragraphs will illustrate the specific details of the cable equivalent circuit 130. FIG. 2 is a schematic diagram of a cable equivalent circuit 130 according to an embodiment of the present invention.

In the present embodiment, the cable equivalent circuit 130 includes a low pass filter 132, a resistive element RO1, a resistive element RO2, a resistive element RO3, and a resistive element RO4. The low pass filter 132 of the present case can be a conventional low pass filter. Low-pass filters are commonly used in electronic circuits to allow low-frequency signals with frequencies below a trade-off threshold to pass and to attenuate or block high-frequency signals at frequencies above the cut-off threshold. In the present embodiment, the low pass filter 132 is, for example, a differential low-pass filter, but the invention is not limited thereto. The differential low pass filter herein can be a conventional differential low pass filter. The differential low-pass filter typically has two inputs (ie, differential inputs) and two outputs (ie, differential outputs), and a differential low-pass filter can be used to attenuate or block differential low-pass filtering through the differential inputs. High frequency differential signal. The differential signal is, for example, two signals having the same amplitude and opposite phase. The signal receiving end compares, for example, the voltage difference between the two signals to determine whether the signal transmitting end sends a logic 0 or a logic 1.

In the present embodiment, the resistance values of the resistance elements RO1-RO4 are all equal to one element resistance value R1, and the low-pass filter 132 has a line resistance value R2. It is noted that the component resistance value R1 herein is particularly representative of the resistance value of the resistance elements RO1-RO4, which may be replaced by other names, such as a first resistance value or the like. On the other hand, the line resistance value R2 is specifically used to represent the resistance value of the low-pass filter 132 on the circuit, and may be replaced by other names, such as a second resistance value or the like. Therefore, the terminology of the component resistance value R1 and the line resistance value R2 is not intended to limit the case.

In the present embodiment, the low pass filter 132 includes a first input terminal, a second input terminal, a first output terminal, and a second output terminal. The low pass filter 132 has a reference potential, that is, a virtual ground VG. It is noted that the virtual ground VG here is only a reference potential when the differential low-pass filter receives the differential signal, and the virtual ground VG is usually the signal potential depending on the differential signal, and is not the actual ground potential in the ground or system. (usually 0V). The resistive element RO1 can be coupled between the first input of the low pass filter 132 and the ground potential. The resistive element RO2 can be coupled between the second input of the low pass filter 132 and the ground potential. The resistive element RO3 can be coupled between the first output of the low pass filter 132 and the ground potential. The resistive element RO4 can be coupled between the second output of the low pass filter 132 and the ground potential. On the other hand, the first input end and the second input end of the low pass filter 132 can be coupled to the test device 110, and the first output end and the second output end of the low pass filter 132 can be used to couple the receiving device 120. It is noted that the above-mentioned so-called ground potential refers in particular to the ground potential in the system. The ground potential in the system can be coupled to the actual ground or not to the actual ground but only a common reference potential in the system.

Through the above arrangement (ie, the resistance element RO1-RO4 electrically coupled to the ground potential is coupled to the end of the low-pass filter 132), when the cable equivalent circuit 130 receives the test signal from the test device 110, the cable The equivalent circuit 130 can generate two current paths P1, P2. In the current path P1, the current flows, for example, through the resistance element RO1 to the ground potential. In the current path P2, the current flows, for example, into the low pass filter 132 and through the virtual ground VG as a return path.

That is, if the cable equivalent circuit of a comparative example includes only the low pass filter 132, the cable equivalent circuit of this comparative example has only one current path (i.e., current path P2). However, in the present invention, the end point of the low-pass filter 132 in the cable equivalent circuit 130 is further coupled to the resistance elements RO1-RO4 electrically connected to the ground potential, so that another current path (ie, current) can be added. Path P1).

In this way, by adjusting the characteristics of the current paths P1, P2, that is, by adjusting the element resistance value R1 and/or the line resistance value R2, the circuit characteristics of the cable equivalent circuit 130 can be fine-tuned to make the cable Equivalent circuit 130 can simulate a physical cable more accurately.

In an embodiment, in order for the cable equivalent circuit 130 to meet the cable specification of ANST/TIA-568-C.2, the component resistance value R1 and the line resistance value R2 may conform to the following formula:

In another embodiment, in order for the cable equivalent circuit 130 to meet the cable specification requirements of ANST/TIA-568-C.2, the component resistance value R1 and the line resistance value R2 may conform to the following formula:

In yet another embodiment, to make the cable equivalent circuit 130 meet the cable specification requirements of ANST/TIA-568-C.2, the component resistance value R1 and the line resistance value R2 may conform to the following formula: .

In summary, in order to make the cable equivalent circuit 130 comply with the specification requirements of the cable types CAT 3, CAT 5e, CAT 6, and CAT 6A in ANST/TIA-568-C.2, the component resistance value R1 and the line resistance value. R2 can meet the following formula:

The following paragraphs provide specific circuit details of the cable equivalent circuit 130 in an embodiment of the present invention, however, the cable equivalent circuit 130 of the present invention is not limited thereto.

Fig. 3 is a circuit diagram of a cable equivalent circuit 130 according to an embodiment of the present invention. As previously mentioned, the cable equivalent circuit 130 includes a low pass filter 132 and resistive elements RO1-R04. Resistive elements RO1-R04 are separately coupled between the first input terminal of the low pass filter 132 and the ground potential, between the second input terminal and the ground potential, between the first output terminal and the ground potential, and Between the two outputs and the ground potential.

In this embodiment, the cable equivalent circuit 130 is coupled to the test device 110 through the resistors RS1 and RS2, and coupled to the device 120 via the resistors RS3 and RS4.

In the present embodiment, the low pass filter 132 includes resistors RI1, RI2, RI3, RI4, RI5, RI6, RI7, RI8, capacitors C1, C2, and inductors L1, L2. The resistors RI1-RI8, the capacitors C1, C2, and the inductors L1, L2 each have a first end and a second end. In the present embodiment, the aforementioned line resistance value of the low pass filter 132 may be the resistance value of any of the resistors RI1 - RI4. On the other hand, in an embodiment, the resistance values of the resistors RI1 - RI4 are identical to each other.

According to an embodiment of the invention, the first end of the resistor RI1 is coupled to the first input end of the low pass filter 132, the first end of the resistor RI2 is coupled to the second input end of the low pass filter 132, and the second end of the resistor RI3 One end is coupled to the first output end of the low pass filter 132, and the first end of the resistor RI4 is coupled to the second output end of the low pass filter 132.

The first end and the second end of the inductor L1 are respectively oppositely coupled to the second end of the resistor RI1 and the second end of the resistor RI3. The first end and the second end of the inductor L2 are respectively oppositely coupled to the second end of the resistor RI2 and the second end of the resistor RI4.

The resistor RI5 is connected in parallel with the inductor L1. That is, the first end and the second end of the resistor RI5 are separately coupled to the second end of the resistor RI1 and the second end of the resistor RI3. The resistor RI6 is connected in parallel with the inductor L2, that is, the first end and the second end of the resistor RI6 are separately coupled to the second end of the resistor RI2 and the second end of the resistor RI4.

The first end of the inductor C1 is coupled to the second end of the resistor RI1, the first end of the resistor RI5, and the first end of the inductor L1. The second end of the inductor C1 is coupled to the first end of the resistor RI7. The second end of the resistor RI7 is coupled to the second end of the resistor RI2, the first end of the resistor RI6, and the first end of the inductor L2.

The first end of the inductor C2 is coupled to the second end of the resistor RI3, the second end of the resistor RI5, and the second end of the inductor L1. The second end of the inductor C2 is coupled to the first end of the resistor RI8. The second end of the resistor RI8 is coupled to the second end of the resistor RI4, the second end of the resistor RI6, and the second end of the inductor L2.

The low pass filter 132 can be realized by the above-described circuit elements and the connection relationship between the circuit elements. However, it is noted that the circuit elements in the low-pass filter 132 and the connection relationship between the circuit elements are not limited to those disclosed in the above embodiments, and the circuit structure of the low-pass filter 132 in the above technical content of the present invention is sufficient. Both can be used in the present invention.

The following paragraphs will be combined with Figures 4 and 5 to provide a comparison of the circuit characteristics of the cable equivalent circuit 130 and the physical cable in an embodiment of the present invention. Fig. 4 is a graph showing a comparison of reflection loss of a cable equivalent circuit 130 and a physical cable of a comparative example according to an embodiment of the present invention. Fig. 5 is a comparison diagram showing the insertion loss of the cable equivalent circuit 130 and the physical cable of a comparative example according to an embodiment of the present invention.

In Fig. 4, the curve RL1 represents the tendency of the reflection loss of the cable equivalent circuit 130 in one embodiment of the present invention to correspond to the frequency, and the curve RL2 represents the tendency of the reflection loss of the physical cable in the comparative example to correspond to the frequency. In Fig. 5, the curve IL1 represents the tendency of the insertion loss of the cable equivalent circuit 130 in Fig. 4 to correspond to the frequency, and the curve IL2 represents the tendency of the insertion loss of the physical cable of the comparative example in Fig. 4 to correspond to the frequency.

As shown in Figures 4 and 5, the trend of curve RL1 is similar to curve RL2, and the trend of curve IL1 is similar to curve IL2, so cable equivalent circuit 130 can be used to simulate a physical cable.

In contrast, Fig. 6 is a comparison diagram of the reflection loss of a cable equivalent circuit and a physical cable of a comparative example. The curve RL1a represents the tendency of the reflection loss of the cable equivalent circuit in this comparative example to correspond to the frequency, and the curve RL2b represents the tendency of the reflection loss of the physical cable to correspond to the frequency. As shown in the figure, in this comparative example, the cable equivalent circuit and the reflection loss of a physical cable are The trend should be significantly different in frequency. Therefore, the characteristics of the cable equivalent circuit 130 of the present case are more in line with the physical cable than the cable equivalent circuit in the comparative example.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present case. Anyone skilled in the art can make various changes and refinements without departing from the spirit and scope of the present case. The scope defined in the patent application is subject to change.

130‧‧‧ Cable equivalent circuit

132‧‧‧ low pass filter

RO1-RO4‧‧‧resistive components

VG‧‧‧Virtually

P1, P2‧‧‧ current path

Claims (9)

A cable equivalent circuit includes: a low pass filter including a first input end and a second input end, the low pass filter having a line resistance value, wherein the low pass filter is a differential low pass filter a first resistive element coupled between the first input end of the low pass filter and a ground potential, the resistance value of the first resistive element is equal to an element resistance value; and a second resistive element, The second input end of the low pass filter is coupled to the ground potential, and the resistance value of the second resistive element is equal to the element resistance value. The cable equivalent circuit of claim 1, wherein the low pass filter further comprises a first output end and a second output end, the cable equivalent circuit further comprising: a third resistive element coupled Between the first output end of the low-pass filter and the ground potential, the resistance value of the third resistance element is equal to the resistance value of the element; and a fourth resistance element coupled to the low-pass filter Between the second output terminal and the ground potential, the resistance value of the fourth resistance element is equal to the resistance value of the element. The cable equivalent circuit of claim 1, wherein the low pass filter further comprises a first output, the cable equivalent circuit further comprising: A second resistance element is coupled between the first output end of the low pass filter and the ground potential, and the resistance value of the second resistance element is equal to the element resistance value. The cable equivalent circuit of claim 3, wherein the low pass filter is a differential low pass filter, and the low pass filter further includes a second input end and a second output end, the cable The equivalent circuit further includes: a third resistive element coupled between the second input end of the low pass filter and the ground potential, the resistance value of the third resistive element is equal to the resistance value of the component; The fourth resistive component is coupled between the second output end of the low pass filter and the ground potential, and the resistance value of the fourth resistive component is equal to the component resistance value. The cable equivalent circuit according to any one of claims 1 to 4, wherein the resistance value of the element is R1, and the line resistance value is R2, then R1 and R2 are in accordance with the following formula: The cable equivalent circuit of claim 5, wherein R1 and R2 are in accordance with the following formula: . The cable equivalent circuit of claim 5, wherein R1 and R2 are in accordance with the following formula: The cable equivalent circuit of claim 5, wherein R1 and R2 are in accordance with the following formula: A test system comprising: a cable equivalent circuit comprising: a low pass filter comprising a first input and a first output, the low pass filter having a line resistance value; and a first resistance element Between the first input end of the low pass filter and the ground potential, the resistance value of the first resistive element is equal to a component resistance value; a test device coupled to the low pass filter An input terminal is configured to provide a test signal to the low pass filter; and a device to be tested is coupled to the first output end of the low pass filter for receiving the test signal through the low pass filter, And providing a response signal to the test device through the low pass filter.