Read the signal integrity analysis of high speed connectors

With the rapid development of electronic communication technology, integrated circuit packaging and interconnection board, the signal transmission bandwidth requirements is increasing. At the same time, the rate of transmission of interconnected channels is getting faster and faster, and the decision time window of logic gates is getting smaller and smaller. Therefore, the development of information technology directly leads to the integration of integrated circuit packages, transmission lines and connections in the interconnect channel, from the beginning of the "lumped parameter model" to the "distributed parameter model". Compared to the package of integrated circuits, the transmission lines and connectors on the printed circuit board, due to the relatively large geometric size, are more likely to enter the "distributed parameter model", ie the high-speed signal interconnection channel. PCB interconnects, connectors, and components placed on them form the main components of an electronic device interconnect system. Signals are spread through the printed board interconnects and connectors to other printed boards, forming the entire back. Board system. As key parts of the overall connector interconnection system, improve the system transmission rate has become a bottleneck, therefore, developed to meet the high-speed transmission connector performance, high speed interconnect system is to enhance the performance of the main section of the hand, but also to solve the high-speed information system A key factor in the interconnection problem.

High-speed connectors the early 1990s, under the strong promotion of information technology for connecting high-speed digital signal transmission and start developing. At present, the transmission rate of high-speed connectors abroad has reached 10 Gbps, and is developing to 40 Gbps . As early as 2005, FCI, the world's leading connector manufacturer, cooperated with Lucent Bell Labs to successfully achieve signal transmission at up to 25 Gbps using FCI's high-speed connector AirMaxVS and Bell Labs' signal transmission architecture. The performance of the high speed connector.

Driven by information technology equipment, digital information equipment in the fields of communications, railway transportation, aerospace, medical equipment, high-end weapons, etc. will place higher demands on the performance of high-speed connector products, such as high density, modularity, High reliability, multi-functionality, etc., to meet the needs of various applications such as modularization, integration, environmental resistance and anti-interference of system transmission. In the past, the most important considerations in the development of electrical connectors were mechanical properties such as insertion force and foot flatness. Second, consider the electrical characteristics of the connector, such as insulation resistance, rated current, contact resistance, and so on. However, with the advent of the high-speed communication era, the performance requirements of the electrical connector are more engraved, and the transmission line effect caused by the high-speed transmission cannot be ignored. Solving the signal integrity problem of the high-speed connector becomes a key factor in the connector design.

Research status at home and abroad

At present, connectors have become the second pillar industry of electronic components. According to statistics from the latest connector authoritative research institute Bishop & Associates, sales of connectors in China market in 2013 have reached US$13.6 billion, accounting for global market share. 24%, China has become the largest sales market for connectors. The development and application of high-speed connectors began in developed countries in Europe and America. The international large-scale connector manufacturers led by Molex, Tyco, FCI and other companies rely on technology and scale advantages. Has always mastered the cutting-edge technology of the connector manufacturing industry, especially in the field of communication and military applications that require high transmission speed, environmental resistance, high reliability, low crosstalk and low noise. International companies have obvious advantages. And the profitability of connector products in this field is relatively high.

As customer demand for higher and higher transmission speed, suppliers overseas connections on the basis of its original products, the introduction of new design techniques to optimize and fine tune its product process, the circuit board connection techniques such as soft interference (The hole in the board can be made smaller); custom plastic is used to compensate for signal tilt. It is recommended to ream the board. To meet system performance and reliability requirements, system designers carefully balance the relationship between transmission speed, power, and package density. With the growth of large data processing and transmission in interconnected systems, the requirements for transmission speed are constantly being promoted. The data transmission rate of foreign high-speed communication systems has been changed from the original 6.25Gbps to 12.5Gbps , and it is popularized to 25Gbps . In the future, the data transmission rate will be increased to 40 Gbps, 100Gbps or even 1T bps , and the high-speed connectors that match it will also be connected. Will definitely get faster development.

The development of semiconductor technology has prompted connector manufacturers to design and develop higher speed products. The backplane connector market has experienced a period of rapid growth in the new century, and these connectors are prepared to meet the competition of next-generation applications. There are mainly vendors in this field: Amphenol TCS, FCI, Molex, Tyco, all of which can supply 25Gbps connectors. There are currently few areas of mass production that require such high transmission speeds, but this high-performance connector gives room for future system updates and is attractive to system designers.

High-speed backplane connectors are a critical part of the new system hardware and, once selected at the beginning of the system design, may not be replaced with other connectors. Since the frequency of 10Gbps operation above, when the different internal structure of the connector portion, the transmission performance is not large like. In view of this, foreign equipment manufacturers have reached an agreement with their main connector suppliers to require connector suppliers to share intellectual property in design and production, with sufficient consistency in design and production to ensure interface interchangeability and high-speed transmission. Compatibility. This practice of requiring connector manufacturers to share connector technology is rare in history, creating a historical precedent, and is likely to be the development trend of the connector industry in the future. The development of materials and product structure technologies has broadened the bandwidth of cable assemblies and increased the speed of cable assemblies. Using passive and active signal conditioning technology, copper cable can provide a cost-effective solution with speeds greater than 10 Gbps and up to 24 m. Through nearly 20 years of product development, we have formed high-speed connector manufacturers based on Tyco, Amphenol, Molex, FCI, ENRI, etc., through technological innovations such as basic theory and material research and development, such as HM. The popularization of high-end high-speed connectors such as 2mm, ZD, ExaMax, LRM, etc., as shown in the figure below, the connector signal transmission rate is gradually increased from 2.5Gbps to 12.5Gbps, and then climbs to 25Gbps or even 40Gbps.

VITA high speed connector

ZD high speed connector

LRM high speed connector

Signal integrity design, which has a complete theoretical analysis, such as "field and microwave technology", "high-speed signal transmission", "signal integrity of high-speed digital systems and transmit radio administer" Gained; with a variety of High-speed signal simulation analysis software, such as Keysight's ADS; and complete signal integrity test platforms such as signal generators, spectrum analyzers, vector network analyzers, oscilloscopes, time domain impedance testers, and bit error rate analyzers. , and other supporting analysis software.

Professional high-speed connector manufacturers are mainly aerospace electronics, China Aviation Optical, Sichuan Huafeng, relevant research centers all Beijing University of Aeronautics and Astronautics, Beijing University of Posts and Telecommunications, Shanghai Jiaotong University. As in recent years supporting the needs of military weapons models, domestic major connector manufacturers through imitation or improve foreign-related high-speed transmission connector products, have developed a VITA46, LRM, JVPX, J599,1394 high-speed transmission connector, However, the transmission of this type of connector generally does not exceed 6.25Gbps. In addition, some manufacturers have begun to develop connector products with higher transmission rates in line with the needs of users, and have achieved certain results.

Overall, domestic connector development started late, in terms of the basic theory, raw materials, machinery processing, product testing lagged behind developed countries in Europe and America. In addition, due to the inconsistency in the demand for high-speed connectors in various electronic, aerospace, marine, and aerospace systems in China, and the neglect of exchanges and cooperation between various high-speed connector manufacturers, domestic high-speed products are incompatible with each other, and the level of product development is not good. Qi, seriously hindered the development of high-speed products, compared with the development level of foreign high-speed connectors, the development of domestic high-speed connectors mainly have the following shortcomings:

(1) In the research of signal integrity theory, domestic research institutes (such as Xi'an University of Electronic Science and Technology, Shanghai Jiaotong University, Southeast University, National University of Defense Technology, University of Science and Technology of China, Nanjing University of Aeronautics and Astronautics, Southwest Jiaotong University, Chinese Academy of Sciences) Graduate school, etc.) is more in-depth, but mainly stays in theoretical research and computer simulation analysis, and the real engineering is less practical. Domestic Huawei, ZTE and other communication equipment vendors also established their own independent signal integrity research departments, which have a relatively complete signal integrity test platform, but basically there is no report on the above signal integrity issues. The development and supporting units of major domestic weapon models (such as Aerospace Science and Technology, Aerospace Science and Technology, China Light and Power Group, China Shipbuilding Heavy Industry, Weapon Group, etc.) have reached an organic collection in theory and engineering practice, but are subject to various factors. The degree of theoretical application has yet to be deepened.

(2) in terms of the development of raw materials, domestic materials manufacturers high-speed production of material for a connector (e.g., PPS, LCP, TPX, Rogers, etc.) substantially not meet the actual requirements, poor performance stability, and even unable to produce some materials . The materials for domestic high-speed connectors are basically dependent on imports, which poses a serious hidden danger to the localization and popularization of high-speed connectors.

(3) In terms of parts processing and manufacturing, due to the structural characteristics of high-speed connectors, many parts require extremely high dimensional accuracy. Domestic processing equipment, molds and process methods are still unable to meet the requirements, which limits to some extent. Increased transmission performance of high speed connectors.

(4) In terms of precision assembly of products, compared with foreign automated integrated assembly, the domestic manual or manual plus semi-automatic assembly method is basically adopted, the assembly consistency is poor, the efficiency is low, and the consistency of the connector is artificial. The factors are larger.

(5) In terms of product testing and verification, there is currently no uniform high-speed connector specification in China. The connector test specifications, methods and indicators of various manufacturers are different from each other. The technical level of the high-speed signal integrity test platform is uneven, which seriously lags behind product development.

In recent years, the domestic major connector manufacturers and university research institutes began to realize these problems, start importance to study signal integrity problems of high-speed connectors, and achieved some results. Beijing University of Posts and Telecommunications Laboratory electrical contact in a good technical background communications, high-speed signal integrity problems letters connector launched a series of studies, research master Ye Xiaolan HDMI signal integrity of high speed connectors and optimized, Ho Ching The performance of high frequency electrical connectors was investigated. Li Xunbo from the University of Electronic Science and Technology of China analyzed the loss of SFP and obtained the mathematical fitting relationship between loss and frequency.