Cat 6 PCB debugging technology

1. Implementation criteria and definition of important indicators

The implementation standards of category 6 modules are EIA/TIA 568B. 2-1. The most important parameters are insertion loss, ripple loss, and near-end crosstalk.

Insertion Loss Insert Loss): Because the transmission channel impedance exists, it will increase the attenuation of the signal's high-frequency component as the signal frequency increases. The attenuation is not only related to the signal frequency, it is also related to the transmission distance. As the length increases, the signal attenuation also increases. Measured by the number of signals lost along the transmission channel per unit length, it indicates the ratio of the signal strength from the source sending end to the receiving end.

Return Loss (Return Loss): As the impedance in the product changes, local vibrations will occur, resulting in signal reflection. A part of the energy reflected to the sending end will produce noise, resulting in signal distortion and reduced transmission performance. If the full-duplex gigabit network is used, the reflected signal is mistaken for the received signal, causing fluctuation of useful signals and confusion. The less the reflected energy, the better the impedance consistency of the channel line. The more complete the transmission signal, the less noise the channel has. Calculation Formula of Return Loss RL: Return Loss = transmit signal ÷ reflection signal.

In the design, ensuring the full line Consistency of the impedance and cooperating with the six types of 100 ohm impedance cables is the way to solve the return loss parameter failure.

For example, the interlayer distance of the PCB line is uneven, the cross section of the copper conductor of the transmission line is changed, and the conductor in the module does not match the conductor of the six types of cables.

Signal Attenuation)

Return Loss (Return Loss): As the impedance in the product changes, local vibrations will occur, resulting in signal reflection. A part of the energy reflected to the sending end will produce noise, resulting in signal distortion and reduced transmission performance. If the full-duplex gigabit network is used, the reflected signal is mistaken for the received signal, causing fluctuation of useful signals and confusion. The less the reflected energy, the better the impedance consistency of the channel line. The more complete the transmission signal, the less noise the channel has. Calculation Formula of Return Loss RL: Return Loss = transmit signal ÷ reflection signal.

In the design, ensuring the full line Consistency of the impedance and cooperating with the six types of 100 ohm impedance cables is the way to solve the return loss parameter failure.

For example, the interlayer distance of the PCB line is uneven, the cross section of the copper conductor of the transmission line is changed, and the conductor in the module does not match the conductor of the six types of cables.

Return Loss)

Near-end crosstalk NEXT): NEXT refers to signal coupling between one line and the other line in a pair of transmission lines, that is, the signal received by another adjacent line when one line pair sends a signal. This type of crosstalk signal is mainly caused by the coupling of neighboring pairs by Capacitance or inductance.

How to Reduce the signal coupled by Capacitance or inductance, or offset or weaken the interference signal by means of compensation, so that it cannot generate a standing wave is the main way to solve this parameter failure.

Near-end crosstalk)

2. core technologies and failure mechanisms

The following content is mainly based on the explanation of the PCB trial process of cat6 modules of a Korean company, which is of great reference significance. In the trial phase of the module, we use theory as a guide and use computer-aided design as the basis to quickly achieve the expected results.

In the PCB design of the six types of modules in China, we mainly use the theory of diagonal line compensation as the basis for a large number of trials, which can also achieve the expected results. The following theories are used as a reference.

3.1 Signal leakage caused by module and plug

Signal interference occurs between each other on the link. To prevent signal interference, the conductor in the balanced link is twisted to achieve balanced transmission. Although the twisting structure may change the phase between signals, it also increases the signal attenuation on the line. This structure is called the unshielded structure (UTP ). 4 pairs of balanced twisted pair wires have different twist distances for this purpose.

The end of the cable uses modular connectors, namely the information module, to form a connection between the connector and the connector, and form a balanced structure between the conductors in the interconnection zone, that is, the permanent link of the six types of systems. In the permanent link, signal interference occurs on the balanced line, that is, crosstalk, which solves the problem of crosstalk. It is the core technology used to manufacture connectors for high-speed communication.

Loss of contact between contact terminals is also caused by attenuation and reflection loss. This loss is a problem that causes obstacles and faults during high-speed signal transmission. By solving these problems, it is the core technology used to manufacture connectors for high-speed communication.

3.2 Module and plug generation signal leakage explanation

In the connection line between the module and the plug, each pair of connection terminals in the plug is also a balanced line.

Balance the loss of signal leakage and impedance generated by the conductor in the line.

The biggest obstacle to communication is signal leakage.

The solution to the leakage problem can be found by studying the E and H fields, or from the method of reverse attenuation. This is the core technology of high-speed communication connector manufacturing.

3.3 E and H

The signal interference on the Balance line, that is, electromagnetic field interference, can be described through the distribution of E and H fields.

The main parameter of the electronic communication line test is the relevant measurement under the frequency sweep. When audio or data packets are attached to the frequency signal for transmission, the higher the transmission speed requirement, the faster the frequency.

Using computer simulation technology, this part is viewed using some special instruments, failure model 3-1.

-1 electromagnetic field mutual interference model on parallel lines

3.4 signal leakage solution

The most basic method to explain the problem of outlet signal leakage is to collect signals and send them back in the signal Concentration Area Based on the signal leakage simulation diagram of the inductance and capacitor. A table is a simulation map that simulates the leakage signals at the IDC terminal in reverse coupling mode.

The number of data received at the IDC terminal is returned to solve the problem of leakage.

In the design, the design of coupling capacitance is a key parameter, which is related to the length of the coupling line, the distance between lines, the width, and the arrangement of compensation lines.

Figure 3-2 Figure 3-3

Considering that four pairs of lines are used to transmit signals at the same time in the six categories of systems, Comprehensive Remote String winding and Integrated Remote String winding are inevitable. Considering all the influences, computer simulation is performed to design a compensation line. It is a computer simulation and line design process for the design of cat6 circuit boards.

Figure 3-4

3.5 trial production of six types of modules in China

Six Types of module processes are generally carried out by domestic counterparts. After determining the main loop, the design of the Compensation Loop is carried out, and a large number of program design and sample preparation are carried out, after the baseline of the compensation line and PCB interlayer structure are basically determined, the subsequent work will mainly improve the performance through technological improvement.

The main adjustment parameters include:

① Interlayer gap parameters; Copper Foil Thickness parameters; 8 Main Transmission Line Layout parameters, 8 main transmission line width, relative distance;

② Use diagonal compensation to adjust the compensation for each line and other lines, including the compensation line location distribution, compensation line length and width, and compensation line gap;

③ Adjust the process parameters of the PCB processing plant.