High Speed with Signal Integrity eBook

HIGH SPEED WITH SIGNAL INTEGRITY EBOOK

AUGUST 2022

Double Density Cool Edge a high-speed, space-saving hybrid connector solution

Featuring a compact design with two rows of contacts, the 0.80mm pitch board-to-board connectors are highly configurable and accommodate both high-speed and low-speed signal and power.

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HIGH SPEED WITH SIGNAL INTEGRITY EBOOK

2022 High Speed with Signal Integrity , Connector Supplier’s newest eBook, focuses on the challenges and advances that impact the fast-paced world of data transmission. Experts from 11 leading connector suppliers cover connectivity solutions for signal distortion due to impedance mismatch, crosstalk, attenuation, reflection, and switching; the challenges of maintaining signal integrity in harsh environments; and the various cable options and other innovations available to maximize performance. This eBook also features a selection of more than 24 relevant connectivity products designed for high-speed applications across a range of markets and environments. Contributors include Amphenol Communications Solutions, Axon’ Cable , COAX Connectors, ept, Fischer Connectors, Greenconn, ICC (Interstate Connecting Components), IMS Connector Systems, I-PEX, Mouser, Nicomatic, Omnetics Connector Corporation, Phoenix Contact, and Smiths Interconnect. Please enjoy this edition, the second of three 2022 eBooks. Our next eBook, Smart Connectivity, Connected Infrastructure, and the Internet of Things, will be available in November 2022. Connected devices are part of all areas of life, from consumer gadgets to industry technology to medical equipment, transportation, and more. This collection will explore the role of interconnects throughout the world of connected technology. In the meantime, please subscribe to our weekly e-newsletters , follow us on LinkedIn, Twitter, and Facebook , and check out our eBook archives for more applicable, expert-informed connectivity content.

John Bishop

Managing Director

Managing Editor Amy Goetzman

Associate Managing Editor AJ Born

Creative Director Raine Arzola

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41 HYPERBOLOID CONTACT TECHNOLOGY AND RUGGED MATERIALS PROTECT SIGNAL INTEGRITY IN DATA DRIVEN APPLICATIONS SMITHS INTERCONNECT 38 FEA SIMULATION AIDS SIGNAL INTEGRITY IN HIGH-SPEED CONNECTOR DESIGNS GREENCONN

7 SIGNAL INTEGRITY IS KEY TO TODAY’S HIGH- SPEED CONNECTIVITY DESIGNS EPT 11 10 KEY STRATEGIES TO ENSURE SIGNAL INTEGRITY AT HIGH DATA SPEEDS FISCHER CONNECTORS DESIGNING FOR HIGH SPEED WITH SIGNAL INTEGRITY

MAKING THE MOST OF HIGH SPEED WITH SPECIFIC CONNECTIVITY SOLUTIONS

CHALLENGES THAT IMPACT HIGH SPEED/ SIGNAL INTEGRITY

46 REPLACING PRINTED WIRING WITH ENGINEERED CABLE SOLUTIONS FOR HIGH- SPEED APPLICATIONS AMPHENOL COMMUNICATIONS SOLUTIONS 51 GETTING THE RIGHT SPEED WITH BOARD-TO- BOARD CONNECTION PHOENIX CONTACT 54 FIVE CONSIDERATIONS WHEN SPECIFYING RF COAXIAL CONNECTORS FOR HIGH SPEED WITH SIGNAL INTEGRITY APPLICATIONS COAX CONNECTORS LTD 58 PRODUCT BRIEFS FEATURED SUPPLIERS PRESENT A VARIETY OF PRODUCTS DESIGNED FOR THE UNIQUE CONNECTIVITY NEEDS OF APPLICATIONS THAT REQUIRE HIGH SPEEDS AND SIGNAL INTEGRITY.

21 DESIGNING HIGH-SPEED SIGNAL INTERCONNECTS FOR CHALLENGING ENVIRONMENTS IMS CONNECTOR SYSTEMS 26 HOW TO DESIGN OPTICAL FIBER CABLES FOR INTERCONNECT SOLUTIONS IN HARSH ENVIRONMENTS AXON’ CABLE 32 IMPROVING SI PERFORMANCE WITH PADDLE CARD TECHNOLOGY FOR MICRO-COAXIAL CABLE HARNESSES I-PEX INC. INNOVATIONS THAT IMPROVE HIGH-SPEED CONNECTIVITY PERFORMANCE 17 MAINTAINING SIGNAL INTEGRITY IN THE ERA OF SWAP OMNETICS CONNECTOR CORPORATION

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CONTRIBUTORS

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DESIGNING FOR HIGH SPEED WITH SIGNAL INTEGRITY

SIGNAL INTEGRITY IS KEY TO TODAY’S HIGH-SPEED CONNECTIVITY DESIGNS

JOSHUA JACOBI, DIRECTOR OF SALES AND MARKETING, EPT MARKETING TEAM, EPT

DEFENDING AGAINST SIGNAL LOSS The types of materials present near the signal path are critical to the success of a high-speed signal. It is important to avoid cross-sectional changes in the contact material and to use material with high conductivity. The dielectric constant of a plastic material also affects signal transmission. The typical standard for phase matching throughout an interconnecting system is 85-100 ohms. Because electronic components can act both as an interference sink and as a source of interference, the proximity of sensitive components increases the risk of mutual interference. A high-speed signal can be lost through insertion loss as well as return loss. Insertion loss is the deviation(s) within the impedance curve, resulting in signal reflections. This describes the loss of a signal along the

The bar is higher than ever for high-speed performance, and PCB components have the potential to be either a great asset or an Achilles’ heel, especially if signal integrity is not given the foremost consideration while testing the design. What was previously only a problem for high- frequency applications is now encountered by hardware developers across the digital sphere due to the demanding nature of high data rates, some even exceeding 20+ Gb/s. Even in low-end applications, demand is increasing for smaller, faster, and more capable electrical components while less and less space is available on the rapidly shrinking real estate on today’s PCBs. Basic design requirements are always in play: how much space is available on the module, floating capability, the desired connection technology, the number of pins and the pin assignment, as well as overall performance requirements. The most pressing challenge is to manage these requirements successfully while avoiding the looming threat of signal loss during module operation. If the present signal paths are dampened or lost, the multitude of additional design factors can become entirely irrelevant as the components lose their ability to transmit data. For a module to work at peak operational capability, defending against signal loss must be at the forefront of design.

Optimization of the ept Colibri connectors from 10+ Gb/s to 16+ Gb/s. Graphic: ept GmbH

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signal’s path, presented as the ratio of outgoing to incoming signal. With a high insertion loss, a signal can no longer be clearly identified by the receiver and therefore a limit value of -3 db is typically set. Insertion loss is made up of different components: coupling losses, dielectric losses, reflection losses, line losses, and radiation losses. Coupling losses occur at the contact point between the male and female connectors. Reliable contacting with appropriate tolerances when plugged in is crucial to reducing signal transmission losses. The ohmic contact resistance should also be kept as low as possible through a large contact area and a high contact force at the contact point. Foreign materials on the connector surface, such as particles produced by abrasion, can increase the contact resistance. High-quality connectors are provided with at least a superficial layer of gold to prevent this from occurring. Apart from the insertion loss, the return loss must also be considered. Return loss is the portion of the reflected signal in the inserted signal. Given a connector’s impedance profile, there is little room for a system designer to further influence the return loss. The best way to do this is with the rise time or the pinout. The rise time describes the

time in which the signal lies between two defined amplitude values (typically between 10% and 90%). The lower the rise time, the greater the bandwidth and the closer the impedance is to that of the rest of the system. Another critical source of signal interference is crosstalk, or the undesired influence of a differential signal by another signal on a different line. The capacitive and the inductive coupling can be considered separately. Near-end crosstalk (NEXT) occurs when the signal transmission of a pair interferes with the signal transmission of a parallel pair, which mainly occurs through induction. The higher the frequency, generally the more interference will affect the second pair. If the absolute value in decibels is high, there is a high level of crosstalk attenuation, so only a small influence can be measured in the disturbed pair. At a value of -20 dB, 1% of the signal is crosstalk. At a value of -40 db, on the other hand, only 0.01%. In contrast to near end crosstalk, far end crosstalk (FEXT) occurs over the entire length of a line. Interference with the signal from a neighboring pair is therefore measured at the end of the transmission link and is usually lower because the interfering signal is attenuated along the line.

Crosstalk can be reduced by layouts in the pinout by placing two potentially influencing contact pairs away from each other with ground contacts. A contact design with the shortest possible signal The effect of near and far crosstalk on signal transmission. Graphic: ept GmbH.

Dependence of the impedance on the rise time. Graphic: ept GmbH.

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paths also reduces the influence of crosstalk.

As mentioned previously, a connector can be influenced by other components of the assembly and also have an electromagnetic effect on surrounding components. With the coupling inductance LK, the connector can be described in both functions – as source and sink. The coupling inductance is to be regarded as an EMC parameter since the connector can be easily described by considering the electrical conditions. This applies to interference immunity as well as interference emission. The coupling inductance is not a measure that applies equally to the entire connector because it can be influenced by the signal assignment on the connector and the connector geometry. Example: As a case-specific example, a maximum coupling inductance of 47 picohenry (pH) was determined for an HDMI signal at a voltage of 4.4 kV. Comparatively, coupling inductance values are between 1 and 4 pH. with the shielded connector.

Of course, data transmission within a PCB system must not be disrupted, falsified, or prevented, which is why protection from electromagnetic interference is a topic of great concern for signal integrity in high-speed systems. Electromagnetic interference can be comparable to crosstalk; the only difference is that the source of interference is not within the individual signal paths in the connector but is produced externally. High-speed data transmissions are particularly susceptible to interference from unwanted electromagnetic effects; even a small impulse can falsify a useful signal and prevent the receiver from clearly interpreting the digital information.

Simulation of an unshielded (above) and a shielded (below) connector. Graphic: ept GmbH.

A shielded connector can offer two positive properties for the user: it is less likely to act as a source of interference while also, due to the presence of shielding, is less likely to be an interference sink for signals. By using shielded connectors, components can be closer to sources

Dependence of the impedance on the rise time. Graphic: ept GmbH.

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of interference. A higher performance class is also made possible for the prescribed burst and surge tests of the electrical device.

Example of a 0.8 mm connector in its unshielded (left) and shielded (right) versions. Graphic: ept GmbH.

Distribution of current flow through a shield plate. Graphic: ept GmbH.

The risk of signal loss increases as the need for high-speed connectivity surges. The higher the frequency of the signal, the more difficult it is for the recipient to understand the sender. The goal when developing new high-speed connectors is to minimize this interference within the transmission path. Careful consideration of materials, the possibility of EMC shielding, insertion loss, return loss, and crosstalk is essential to optimizing high- speed design potential.

A prerequisite for effective shielding is to use a material with high conductivity. The number of contact points can be decisive for successful shielding. The interference current induced in the shield of the connector in turn generates a magnetic field that can affect the signal contacts. The higher the current, the stronger the magnetic field. The current flow is divided by multiple contacting of the shielding plate and the magnetic field is thus reduced.

Visit ept to learn more.

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10 KEY STRATEGIES TO ENSURE SIGNAL INTEGRITY AT HIGH DATA SPEEDS

MOHAMMAD AZADIFAR IEEE SENIOR MEMBER AND SIGNAL INTEGRITY ENGINEER FISCHER CONNECTORS

Design complexity and demand for bandwidth are increasing as more sensors are connected to systems and more data need to be transmitted quickly, reliably, and securely. The priority is to ensure that a signal sent from A to B is not distorted. Ensuring signal integrity is critical for engineers who design data-heavy applications that rely on constant streams of accurate data, such as for the Internet of Things, Industry 4.0, and interconnected ecosystems. Above all, at high bit rates and over long distances, effects such as noise, distortion, insertion/return losses, and crosstalk may degrade electrical signals to the point where errors occur and a device or system fails.

For seamless connectivity, connector performance should be seen as just one part of the equation. Other key factors that determine data transmission success include the quality and performance of the cable itself, the interface between the connector cabling and connected devices, and the quality of the transmitter and receiver. Balanced cabling performance is defined by multiple parameters. The most relevant are attenuation (insertion loss), reflection (return loss), near-end crosstalk (NEXT), and far-end crosstalk (FEXT). In fact, every single decision in the design of a cable-connector assembly can ultimately affect signal integrity.

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Ten key design challenges must be overcome to optimize products for high-speed data transmission: 1. TRANSMISSION LINE The loss of the cable connection affects signal transmission. The higher the signal frequencies, the stronger the loss. As the maximum required frequency (fMAX) of a signal goes high compared to the distance that it needs to travel, simplified lumped circuit models need to be replaced with their high-frequency counterparts, such as transmission line formulation or even full wave Maxwell’s equations. The DC connectivity of metallic surfaces can no longer guarantee high- speed connectivity. 2. SIGNAL DEGRADATION Reflection and attenuation are the two main mechanisms of signal degradation. Degradation can occur at the intersection of the transmitter

and connector. If the input impedance of the transmitter is different from the input impedance of the connector, part of the input energy will reflect towards the transmitter. Some of the remaining energy will be lost in the connector due to metallic or dielectric loss, and the wave will reach the other side of the connector. While reflection is the most important mechanism of loss of signal at the connector, attenuation is the main mechanism of loss in the cable. Apart from these two effects, noise and crosstalk by other pairs can also cause problems. 3. IMPEDANCE MATCHING To optimize impedance matching (ratio of V/I or E/H), factors such as diameter of contact, distance between contacts, contact form factor, and type of materials for all components should be considered. The design of a connector can affect NEXT and FEXT performances, and the connector must also be optimized against these constraints.

Signal degradation due to attenuation and impedance mismatch: a) on the transmitter side, b) on the cable and receiver side.

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coupling from one channel to the other one within a cable. To minimize crosstalk, both the location of pins and the attribution of signals to the pin layout are critical. 5. VECTOR NETWORK ANALYZER (VNA) Data protocols provide the normative values of data transmission parameters (insertion loss, return loss, crosstalk, noise) to ensure the compatibility of the various components of a system – transmitter, receiver, cable, connector – so that they can function together appropriately. Typical protocols include Ethernet, USB, SDI, DP, and HDMI. Once a design has been optimized for a defined protocol, a physical connector- cable assembly prototype needs to be tested to validate the full characterization using a Vector Network Analyzer (VNA). This measures the wave parameters of the reflection and transmission at electrical connections of components as a function of frequency, the so-called scattering parameters, or S-parameters. Typical devices to be tested do not have coaxial interfaces, which are necessary to perform the measurement, so test fixtures often need to be inserted between an instrument’s coaxial interface and the device under test (DUT), such as a PCB, package, connector, or cable. To connect the cable-connector assembly to the VNA device, one needs to design a high-speed precision PCB based on the required bandwidth.

The differences between a connector without and with a design optimized for impedance matching.

4. CROSSTALK It is important to ascertain whether, and to what intensity, waves running in parallel channels interact with each other and cause interferences (crosstalk). One of the parameters for cable- connector assembly to achieve the usual bit error rate (BER) of 1e-12 tolerated in the physical layer, is the level of NEXT and FEXT crosstalk, i.e., the field

Comparison of two crosstalks with different ways of attributing signals in the same connector.

Examples of PCB fixtures for VNA measurement.

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8. DE-EMBEDDING The effect of PCB fixtures must be removed from measurement results using de-embedding. It is recommended to implement the IEEE 370-2020 standard to ensure an optimal PCB manufacturing and de-embedding process. 9. SERDES SIMULATION The overall speed of a communication system on the physical layer depends on the physical layer’s architecture and the specifications of the

6. GEOMETRICAL OPTIMIZATION Any geometrical entities can potentially improve or disturb the flow of energy from one side of a connector to the other side. Hence, every high- speed related design must be cross-optimized for all aspects of mechanical, electrical, signal- integrity, and EMI/EMC performances. The main influential parameters to consider are connector design, cable length, cable performance (loss), and the controlled and repeatable cable assembly and potting processes above 1 Gb/s.

The Fischer MiniMax™ Series with nine contacts is an example of a connector that has been specifically designed to achieve high-speed data transfer using a single protocol (USB 3.2).

transmitter and receiver. In many applications a special configuration of a communication link may deviate from specifications in the standards. System-level serializer/deserializer SerDes) simulations are used to measure the data transmission rate of a cable-connector assembly. The simulations can be visually represented in an eye diagram, in which a superimposition of bits create an “eye” shape that provides insight into the system and crucial connection parameters at a glance. The diagram shows whether signal transmission is taking place at the required speed and how susceptible is it to interference.

7. IMPEDANCE MEASUREMENT After ensuring mastery of the transverse electromagnetic (TEM) mode of propagation by observing the longitudinal field distribution, it is essential to make sure that pin diameters and their distributions are designed properly to achieve the right impedance. The design of a connector can affect NEXT and FEXT performances, and the connector must be optimized against these constraints as well. For impedance measurement, one can use a time domain reflectometry (TDR) device.

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SerDes simulation of MiniMax link at 5 Gb/s: a) eye diagram illustrates minimum eye opening for USB 3.2 Gen 1, b) bathtub timing curve and jitter calculations at receiver ports.

10. LINK OPTIMIZATION There are numerous situations in which the channel eye diagram is closed. The eye can be opened by including signal conditioning techniques such as continuous time linear equalization (CTLE), decision feedback equalization (DFE), or other methods. To optimize products for high-speed data transmission and prevent signal distortion, engineers should design for signal integrity

from the outset. By taking a holistic approach to connectivity (from transmitter to receiver), the common pitfalls outlined above can be avoided. It is also necessary to thoroughly test the associated connection technology at both component and system level.

Visit Fischer Connectors, Data Transmission to learn more.

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CHALLENGES THAT IMPACT HIGH SPEED/ SIGNAL INTEGRITY

MAINTAINING SIGNAL INTEGRITY IN THE ERA OF SWAP TRAVIS NEUMANN, SPECIAL PROJECT MANAGER, OMNETICS CONNECTOR CORPORATION

SWaP (Size, Weight, and Power) is a major challenge for designers tasked with the development of modern-day electrical and computer equipment. A shift from analog to digital electronics has brought new and improved capabilities in smaller package sizes. What once required a computer, camera, fax machine, and phone can now be done on a single device. To accomplish this pairing down of size and components, more electronic signals now fit into a reduced form factor. New chip and board materials have lowered operating voltages and current demands, thereby increasing battery life for portable devices. Those same processes and materials also brought a better understanding of impedance, and how something as seemingly simple as wire spacing inside a board or cable can have a dramatic effect on the quality of signals, especially those running at high speeds. Additionally, to combat attenuation, connectors developed in the past two decades are able to push data and power using flat pins. Flat conductors have less field effect on neighboring conductors, improving signal integrity and performance. Follow that up with appropriate shielding around the exterior through use of conductive foil wrap or braid and it creates a compact solution that maintains performance across a wide array of environments.

From field radios to portable surveillance systems, each device is responsible for distributing power and signals accordingly. These devices include GPS and night-vision aids, as well as Wi-Fi hotspots capable of transmitting real-time battlefield intelligence in some of the harshest environments on the planet. Equipment used in the field has many specific considerations such as damage resistance and environmental factors, and signal requirements are primary during the design process. Users want small lightweight solutions that deliver in these tough environments, and it is necessary to examine how these variables will affect size, weight, and power. SIZE The size of connectors can be determined from customer preference, use case, or both. Connectors based on MIL-DTL-83513 and MIL- DTL-32139 specifications can be customized to different form factors which meet specialized requirements. Options exist to reduce the overall size of the connector, with one great option being hybrids. Hybrid connectors utilize several large contacts for power delivery with smaller contacts to carry signal and come in any number of form factors.

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Hybrid connector

Hybrid circular connectors utilizing metal latches rather than traditional hardware are found in many high-reliability applications. For example, in a removable UAV wing, hybrid circular connectors provide rapid field setup and power/ signal delivery to vital components, such as servos and sensors. Their small size and circular shape pass through the wing spars without risk of getting caught or stuck in an unreachable location. Hybrid circular connectors also appear in a multitude of soldier-worn applications. Chargers, tablets, radios, and many other electronic devices promote health and safety and provide situational awareness. Hybrids provide data transfer through USB, Ethernet, or HDMI, while including additional power lines in packages smaller than the industry standard form factor. WEIGHT Weight requirements are determined by application and environment; the latter plays a critical role in the end solution. Weight is a key requirement in soldier-worn applications, and can have significant impact in equipment used in aeronautics, especially in space, as well.

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The introduction of cube satellites (CubeSats) in the late 1990s and early 2000s sparked a driving effort to reduce the overall size and weight of the craft while improving capability. Gone are the days of single, large, ultra-expensive satellites. Constellations of these nanosatellites that utilize small, ruggedized connectors are being launched regularly. Requirements for CubeSats may have a weight budget for plated plastic connectors only. Where EMI may be less of an obstacle, connector assemblies without metal housings keep the form factor to an absolute minimum. In other space applications, the need for an aluminum or stainless housing with gold plating is a necessity for shielding cosmic radiation.

exposure. Recent technology also allows for plating of plastics to enhance electrical properties, with overall weight of the connector being relatively unaffected by the addition of nickel plating. More ruggedized lightweight connectors with metal shells are fabricated using aluminum alloys and plated for additional corrosion protection. This allows the protection and durability of metal without the risk associated with a “plastic” only connector. Small lightweight ruggedized connectors have physics working to their advantage. Form factors, weight, and engineered materials combine to create solutions that are nearly insusceptible to damage from shock and vibration that occurs during launch. POWER Power needs, followed by quantity of signals, are typically addressed first when designing miniature ruggedized connectors. Power should be considered in terms of voltage and current. In most cases digital signaling working voltage is low, and generally not an issue. Power demand may dictate a larger wire gauge than the 26 and 30AWG found in micro- and nano-sized offerings. These deliver 3 A or 1 A of current respectively. Designers sticking with a traditional connector may end up spreading power across multiple contacts, which can ultimately affect the overall size and weight of the solution. Mentioned earlier, hybrid solutions are an option for designs to provide specific power contacts and additional signal lines in a reduced size to keep the overall form factor at a minimum. Unmanned

Latching PPS connectors

SWaP has become a priority in many applications. In recent years, a number of connector manufacturers have started offering different form factors without a metal shell in alternate configurations to save size and weight while delivering much needed power. In these cases, weight is decreased by eliminating the metal housing, and using advanced polymers able to withstand the environment. Materials such as polyimide, PEEK, and Ultem, to name a few, are used in environments where resistance to chemicals and temperature is needed for extended

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robotics and aerospace systems provide a great example of hybrid and SWaP in connectors. Power requirements have evolved from 30 A to over 300 A or more in heavy lift type applications over the past decade, with some adding signal to provide telemetry, pulse wave modulation (PWM), or other data transfer.

contacts to prevent breakdown of the connectors. High voltage and current demands may create electrical noise inside the connector and require additional shielding. Shielding adds both size and weight to the overall solution through use of conductive braid, conductive shrink tubes, wraps, or ground terminations. In many cases, shielding is critical for maintaining device performance. With modern applications regularly demanding small portable form factors to get the job done, fitting a factory’s worth of computing power into a package with reduced size and weight can be a real challenge. Fusion of solutions utilizing proven designs and alternate materials can be a great asset when it comes to reducing size, weight, and power demands. Designers open to use of materials both in and outside of traditional specifications will find themselves with more solutions in their toolbox to address challenging environments.

UAV power connector with additional signal pins

Voltage can also present challenges in terms of power and signal delivery and affect overall size and weight. Voltages above those found in the MIL- DTL-83513 or MIL-DTL-32139 base specification will require additional contact-to-contact spacing and insulation methods such as individually shielded

Visit Omnetics Connector Corporation to learn more.

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DESIGNING HIGH-SPEED SIGNAL INTERCONNECTS FOR CHALLENGING ENVIRONMENTS RICHARD FIACCO, MANAGER-BUSINESS DEVELOPMENT NORTH AMERICA, IMS CONNECTOR SYSTEMS CHRISTOPHER GIEBEL, RF ENGINEERING LOEFFINGEN, GERMANY, IMS CONNECTOR SYSTEMS

can make small adjustments to improve the performance of a design even within tight parameters. Software such as CST Studio Suite or Ansys HFSS simulation can be used to evaluate the RF performance of a connector within a design. Material (insulators and

If you are up to a challenge, try designing a connector targeted to handle high-speed signals, while minimizing crosstalk and passive intermodulation, keeping impedance consistent, and ensuring that insertion loss/return loss

is under control while working at millimeter wave frequencies. Then add in the need to address materials, housing, and contacts for use in challenging environmental conditions. The first step is to define the market/industry and environment the connector will be used in. Are any industry standards required

THE FIRST STEP IS TO DEFINE THE

contact materials) selections can improve performance, along with plating materials and thicknesses, which

MARKET/INDUSTRY AND ENVIRONMENTS IN WHICH THE CONNECTOR WILL BE USED.

will vary due to frequency requirements. Once materials are chosen, a stress and strength analysis must be performed to ensure the components will hold up to the expected mating cycles.

for the components or the final product? These factors will determine specification and influence final system performance, but designers

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Test data on electric field (E-Field) analysis of the swept contact in a high-speed data connector. This shows the strength of the E-Field that surrounds the contact.

E-Field through the contact to board

MCAH Series Jack, mounted to circuit board

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In addition, keep in mind that the connector is only one part of a system which includes a circuit board, cable, and another connector and board at the other end. Consider that the component you are designing may have an impact on signal timing throughout your system. Any imperfections in materials or assembly within the connector will affect signal quality and timing.

can occur from a device or cable that is too close to the assembly.

The next issue which affects most cellular, high- speed systems is passive intermodulation, also referred to as passive intermod or PIM. This internal distortion is found in passive components (such as RF connectors and cable). When two or

Crosstalk of electromagnetic fields on circuit board

Once you have designed your connectors and assemblies, be aware that high-speed signals will most likely need isolation shielding on the cable and possibly within the connector to address alien crosstalk (no, not the Star Trek kind!). Alien crosstalk refers to the external interference that

more signals are within a component, these signals can interfere with one another, creating additional orders of signals that can degrade signal speed and quality. (If this is an issue, review the IEC Standard 62037 for PIM testing.)

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Prevent PIM within your connector and cable by doing the following: 1. Design out loose interfaces. Consider fully soldered connections. 2. Avoid use of any ferrous materials in the connector. Don’t use nickel in any platings. 3. Ensure that there are no stray metal flakes or oxidized metals within the cable or connector insulators. 4. During final assembly, ensure that the connector-to-cable or connector-to-board interface is tight. Once impedance is under control, insertion loss at a minimum, and PIM has been addressed in your designs, you still must consider crosstalk internal to the connector. To reduce crosstalk issues, shielding can be introduced between contacts if there is room. In addition, when working with a board connector, the main cause of impedance and crosstalk issues exists where the connector attaches to the board. When working on the cable connector, watch how the conductors of your cable mate to the contacts within the connector. Spacing must be controlled, and the method of termination — either crimp, solder, or insulation displacement — must be consistent. When working with a multi coax cable, in addition to dealing with the signal

HTP-High-speed Twisted Pair Multi-Gigabit Ethernet Connector Series from IMS features data transmission rates to 20 Gb/s; compact and modular design; and single, double, or quad versions. They can be watertight (upon request) and are designed for twisted pair cabling.

MCA-Mini Coax highspeed automotive connector from IMS features data transmission rates to 20 Gb/s, RF performance to 15 GHz, and single to 4 coax versions. It is significantly smaller than FAKRA series connectors. Through hole and SMT versions are available.

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Both HTP and MCAH have been designed for automotive use, including in EVs and autonomous driving systems. Space, weight, performance, and cost are the drivers. These connectors serve many other applications as well, such as commercial drones, autonomous farming equipment, and any application requiring high data rates and speed.

pins, you will need to address each individual shield within the confines of your connector.

into proven solutions! Discuss your application with experienced designers and engineers — they might already have a solution.

When designing these interconnects, use your imagination. Many “napkin sketches” have evolved

Visit IMS Connector Systems to learn more.

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HOW TO DESIGN OPTICAL FIBER CABLES FOR INTERCONNECT SOLUTIONS IN HARSH ENVIRONMENTS EMMANUEL BOURELLE, PRODUCT DESIGN ENGINEER, AXON’ CABLE BRUNO GIACOMINI, R&D PROJECT MANAGER, AXON’ CABLE STÉPHANE WATIER, INTERNATIONAL PROJECT MANAGER, AXON’ CABLE SANDRINE HERMANT, MARKETING PROJECT MANAGER, AXON’ CABLE

resist radiation, atomic oxygen, and outgassing.

26 For two decades, the need for ever-increasing capacity and speed to move data through our electronic devices has generated the deployment of millions of kilometers of optical fiber across the planet, thus enabling the creation of very high-speed networks. In telecommunications, the advantages linked to fiber optics, including high data rate and reliable transmission (EMI protection), have been known to engineers for a very long time. Today we consider technologies related to photonics to have reached maturity. However, for harsh environments, such as avionics and defense, key issues related to high temperatures, vibration, and shock must be considered to maximize the efficiency of optical technologies. In space, requirements are even more critical, as the photonic payload must also

Used in communication systems, navigation, sensing, and weapon systems, optical fiber technology is designed for: • Data transmission with high data rate up to 40 Gb/s • Optoelectronics devices such as transceivers for optical-to-electrical conversion • Modulation of a radio frequency signal and transmission over optical fiber (RF over fiber) • Power supply through a fiber optical cable (Power over fiber) • Optical sensor with optical fiber cable for sensing technology

Standard optical fiber cables can be used in internet networks for everyday applications, but the harsh environments of avionics and space require fiber optics with optimized design and materials. OPTICAL FIBER CABLES COMPATIBLE WITH RUGGED CONNECTORS Commonly, optical fiber cable structure is defined as pictured below.

• A strength member in aramid yarn or/and glass fiber • An external jacket in various materials such as fluoropolymers (ETFE, PTFE, PFA, FEP, etc.)

Several layers of protection surround a typical Axon’ optical fiber cable .

Axon’ optical fiber cable is designed to resist harsh environments.

For harsh environments, however, materials that comprise an optical fiber cable can be optimized as follows: • An optical fiber core/cladding in silica • A coating (also called the primary buffer) in various materials such as polyacrylate, polyimide, silicone • A buffer (also called the secondary buffer) in various materials such as fluoropolymers (ETFE, PTFE, PFA, FEP, etc.)

Optical fiber cables must be fully compatible with a wide range of standardized contacts or connectors including ARINC 801, MIL (e.g., MIL-PRF-29504), and ST, FC, and LC connectors. They also must endure operational constraints (stripping, shrinkage, crushing) and resist harsh environment conditions (temperature extremes, contaminant exposure, and radiation).

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MJ

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RELIABLE STRIPPING FOR HIGH QUALITY OPTICAL FIBER LINKS When assembling optical cables to connectors, the cable surface must remain clean at each stage of the process. During connector assembly, the glue must adhere to the entire surface to assure an effective retention of the connector-cable couple. Stripping plays a key role in the assembly process of connectors. This is particularly true for manual and automatic stripping of buffer and jacket, which must be reliable. As far as the buffer is concerned, stripping low- density extruded PTFE is a delicate operation because it can lead to the formation of filaments. Stripping silicone is also a key issue because the operation can bring dust particles to the cable surface. To avoid this problem, choose extruded ETFE as the buffer material to provide very clean cut and cable surfaces. ETFE material is chosen for the external jacket for the same reason.

fiber must be fully fixed to the connector to absorb severe constraints such as temperature changes and vibrations. To secure the area of connection, the process method begins by choosing a cable with very low shrinkage. The minimum shrinkage or elongation value defined in the ARINC 802 standard is 15 mm. But for harsh environments, some studies have shown that having a value down to 0.5 mm for a sample of 3.5 m length will be much more efficient. Limiting shrinkage/elongation also avoids the cost and the time-consuming process of thermal pre-conditioning, which benefits industrial manufacturing.

Example of 4-way fiber optic cable made by Axon’. Axon’ optical cables can be used without any pre-processing, whereas some competitor optical fiber cables need a thermal cycling of a few days before using.

Axon’ optical fiber cables terminated with Axon’ micro-D based optical connectors.

MECHANICAL RESISTANCE During the integration and routing phases in the equipment, the cables can be subjected to numerous constraints such as crushing, bending, torsion, shock, or kink. Beyond the installation recommendations, it is therefore very important to preserve not only the mechanical integrity (resistance of the structure) but also the optical

WHY A CABLE WITH LOW SHRINKAGE IS IMPORTANT The connection area between the connector and the fiber optic cable is a sensitive area, which if not made reliable, can cause degradation of the optical attenuation and breakage of the fiber. The optical

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performance of the cable. Attenuation should not be excessively increased at the wavelengths used.

results in terms of attenuation: A substantial crushing force of 500N leads only to a residual increase in attenuation of the order of 0.05 db (fiber optic cable type OM3 and @ 850 nm). Furthermore, some mechanical characteristics can be added, such as: • A bending radius of much less than 10 times the optical cable diameter • A tensile strength of much more than 200 N RADIATION RESISTANCE: A KEY ISSUE FOR SPACE APPLICATIONS In space, optical fibers are subjected to ionizing radiation that can cause damage. The high energy ions will break the chemical bonds of the glass that compose the optical fiber. Darkening of the optical fiber occurs due to micro or macro defects. However, optical fiber doped by fluorine is very resistant to radiation (at least until 200 MRad). Another extraterrestrial threat is atomic oxygen (ATOX) which erodes and damages materials including polymer insulated wires and cables. Protective solutions are achieved by wrapping, coating, or isolating wires in aluminum trays, but these solutions add mass to the system and decrease flexibility. Lightweight fiber optical cables that can resist ATOX are a real asset in this field. For space applications, another critical feature for cable materials is low outgassing. Outgassing materials release trapped gas, which can leave residue on instruments and surfaces. To evaluate outgassing, the key material parameters are measured for total mass loss (TML) and collected volatile condensable materials (CVCM). The rate of outgassing increases at higher temperatures

Micro and macro bending on an optical fiber generates leakage modes (sheath mode) and leads to an increase in attenuation performance. This is a well-known phenomenon.

Optical power loss due to macro-bending

Optical power loss due to micro-bending

These mechanical constraints will be combined with environmental constraints including temperature and vibrations, so the structure of the cable must be optimized to minimize their negative effects on optical performances. A way to improve the cable structure is to optimize the extrusion process as well as the adhesion between the different layers of materials. A good knowledge of the different materials used is a real advantage for the design.

In the end, a so-called “tight” structure meets the different requirements and obtains interesting

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With EMI protection and a high data rate (up to 40 Gb/s), optical fiber cables have many advantages for avionics, defense, and space applications. First, they must be optimized to resist mechanical and environmental constraints linked to the application. Processing methods (including stripping, shrinkage, crushing, and radiation resistance) should also protect the integrity of the cable design. Addressing other characteristics in a design will allow these cables to operate and ensure secure links in every type of environment.

because the vapor pressure and the rate of chemical reaction increase.

Lightweight, flexible, and easy-to-strip fiber optics protected by Radatox, a material developed by Axon’ that has a radiation resistance of at least 200 MRad (ECSS- Q-ST-70-06C). Axon’ fiber optical cables protected by Radatox are also characterized by their low outgassing in compliance with ECSS-Q-ST-70-02.

Visit Axon’ Cable to learn more.

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INNOVATIONS THAT IMPROVE HIGH-SPEED CONNECTIVITY PERFORMANCE

IMPROVING SI PERFORMANCE

WITH PADDLE CARD TECHNOLOGY FOR MICRO-COAXIAL CABLE HARNESSES HIROKI MASHIMA, PRODUCT MARKETING, I-PEX

Infrastructure telecommunication equipment, such as servers and switches, has become increasingly faster in the enterprise market. Therefore, signal integrity (SI) performance must be improved for each component used in these systems. Improvement of SI performance has a role in improving equipment performance. The challenge is that conventional PCB trace transmission has large insertion losses with limited transmission distance. Jumper harnesses that use cables to solve these problems are attracting attention as a possible solution. Figure 1 shows the conventional PCB trace transmission from ASIC to I/O. Figure 2 shows the jumper harness transmission from ASIC to I/O,

instead of PCB tracing as in Figure 1. This solution can reduce transmission loss by minimizing the PCB trace length using a low-profile connector, which can be placed under the heat sink (closer to ASIC), and with a directly terminated cable to an I/O connector. THE CHALLENGE The premise is that the transmission loss must be improved while lowering the connector height. The reason for lowering the connector size is that the connector needs to be placed under the heat sink to bring it closer to the ASIC (as shown in Fig. 2) to reduce transmission loss. Transmission speed is assumed to be 56 Gb/s PAM4 (frequency 14 GHz).

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Existing micro-coaxial connector products have no transmission quality problems up to around 13 GHz. However, resonance occurs around the target frequency of 17 GHz, resulting in deteriorated transmission quality.

Tables 1 and 2 show near-end crosstalk (NEXT) and far-end crosstalk (FEXT) for conventional products. The red circles indicate resonance points.

Table 2: Far-end Crosstalk

Table 1: Near-end Crosstalk

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The resonance frequency that occurs is dependent on the length of the ground return path. If the wavelength “λ” is long, the resonance frequency occurs in the low frequency band. Conversely, if the wavelength “λ” is short, the resonance frequency occurs in the high frequency band. Figure 3 shows the structure of the mating condition of the plug and receptacle of conventional micro- coaxial connector products. Due to the structure of the connector, the ground path cannot be easily set. Cable and terminal ground paths are connected by ground fingers. The area in green indicates the resonance area.

appearance of a micro-coaxial harness with paddle card. Mating contacts (pads) are configured on the paddle card.

Figure 4: Existing micro- coaxial product

Figure 5: Paddle card product

Figure 6 shows the structure of the mating condition of the plug and receptacle of the paddle card product. It is possible to set up many ground paths through the paddle card (FPC), giving it greater design flexibility.

The area in green indicates the resonance area.

Figure 3: Cross-section of existing product

THE COUNTERMEASURES By replacing the existing plug connector with a paddle card (FPC), the ground path can be easily installed. This leads to a stronger ground path and a shorter resonance area. WHAT IS A PADDLE CARD? A paddle card can be mated with a mating connector, and PCB or FPC can be designed for the plug circuit. Paddle cards are easy to add to ground structures, improving ground return. Impedance matching is simplified, and signal integrity is improved at higher frequencies.

Figure 6: Cross-section of paddle card product

By using a paddle card, the signal line width can be adjusted to specific requirements and the characteristic impedance can be easily matched.

Figure 7 shows a micro-coaxial cable connected to a paddle card. The connection method between the paddle card and the cable is achieved by soldering. The width of the paddle card terminal must be wide for mating contact with the receptacle. The terminals can be narrower at non-contact areas to support characteristic impedance control.

Figure 4 shows the appearance of a conventional micro-coaxial harness. Figure 5 shows the

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Figure 7: Paddle card product

CABLINE®-CA II Connector (0.4 mm pitch)

CABLINE®-VS II Connector (0.5 mm pitch) CABLINE-CA and CABLINE-VS II Connectors are I-PEX Enterprise Solutions for 56 Gb/s PAM4. They can be placed under the heatsink, closer to the CPU to reduce transmission loss.

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THE EFFECT Transmission characteristics, simulation conditions • Analytical software: Ansys HFSS 19.0 • Frequency: 0-40 GHz • Cable: Micro-coaxial cable, AWG #36, 42.5 ohm • Cable length: 254 mm (10 inches) • Connector with both ends • Pin assignment: GSSGSSGSSG (G: Ground, S: Signal) • Improved characteristic impedance • Existing product was 73 ohm-94 ohm • However, the paddle card product has improved to 84-93 ohm. Table 3 shows a comparison of the characteristic impedance of conventional and improved product using a paddle card.

• Improved NEXT and FEXT Paddle card products can shift the resonance frequency. As shown in the table below, the resonance frequency has been shifted from 17 GHz to 33 GHz. Thus, transmission up to the 25 GHz band is now possible. Tables 4 and 5 show results for NEXT and FEXT. These are comparisons between existing product and improved product with a paddle card. The red circles indicate resonance points.

Table 4: Near End Crosstalk

Table 3: Characteristic impedance

Table 5: Far-end Crosstalk

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This confirms that SI performance has been improved by changing from the existing product to a paddle card. In a layout where internal space is limited, such as server and switch, a paddle card with high SI performance, combined with a low connector height, is an effective solution.

• Improved insertion loss and return loss/ insertion loss and return loss also improved by improving characteristic impedance Tables 6 and 7 show results for insertion loss and return loss. These are comparisons between existing product and the improved product with a paddle card.

Visit I-PEX to learn more.

Table 6: Insertion Loss

Table 7: Return Loss

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FEA SIMULATION AIDS SIGNAL INTEGRITY IN HIGH-SPEED CONNECTOR DESIGNS CHEN GOLDBERG, GENERAL MANAGER, GREENCONN

The rapid development of high-speed signal software and hardware across all industries has created a higher level of frequency and bandwidth. Accordingly, the overall performance requirements for connector components are also more stringent. At the same time, the miniaturization of device and package forms, interconnects, and other devices within a system present additional design challenges. All these facts have a significant impact on signal transmission integrity. THE BASIC THEORY OF SIGNAL INTEGRITY OF HIGH-SPEED CONNECTORS As the overall structure of most devices and equipment become significantly smaller and operate at higher frequencies, signal integrity issues are arising and require special attention. Characteristic impedance, insertion loss, return loss, and crosstalk — among which impedance and crosstalk have the greatest impact on the signal integrity of a connector — must all be monitored at the testing level to ensure optimal device performance. Scattering parameters (S-parameters) are often used in signal integrity as a standard format to describe the broadband high-frequency behavior of interconnects. S-parameters are a format

for describing how a standard waveform of an interconnect or component scatters away during the DUT (Device Under Test) process.

Standard Waveform Input DUT Scattering. In this graphic, Transmission Waveform S21 represents the insertion loss, while Reflection Waveform S11 represents the return loss.

THE KEY FACTORS AFFECTING THE SIGNAL INTEGRITY OF HIGH-SPEED CONNECTORS Generally, the main factors affecting the signal integrity of high-speed connectors are design space, transmission rate, and signal loss. Different PCB layout designs are closely related to these factors, which have a critical impact on the overall signal integrity. Under different PCB layout designs, the high-frequency characteristics presented by the connector will be affected.

At present, the standard high-speed connector has a complete structure and specification to follow.

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