Beyond Design - High-Speed Serial Link Design (SERDES)

The simplest method of transferring data through I/Os of ICs is to directly connect the data path from one IC to the next in parallel. But, since most data consists of more than one bit of information the parallel data path is multiple bits wide. This is fine for signal routing between ICs on a multilayer PCB over short distances. However, it has two inherent problems for high-speed data transfer over long distances.

Design Challenges - Designing With DDR

Long time signal integrity experts Rick Hartley and Barry Olney join the I-Connect007 Editorial Team for a discussion around DDR and the complications board designers inevitably face when they design for DDR.

Barry Olney's High Speed Simulation Primer

The I-Connect007 editorial team recently spoke with Barry Olney of iCD about simulation. Barry explains why simulation tools can have such a steep learning curve, and why many design engineers are still not using simulation on complex high-speed designs. Barry also highlights common mistakes that design engineers make using simulation tools, and he offers a variety of tips and techniques for anyone dealing with simulation challenges.

Beyond Design: Dampening Plane Resonance with Termination

Plane pairs form a radial transmission line that propagates electromagnetic energy within a plane cavity emanating from a feed point, within the plane, outward in all directions. And, like all transmission lines, will reflect if not terminated. In this month's column, I will look at how to dampen plane resonance with RC termination to match the plane's characteristic impedance.

Beyond Design: Stackup Configurations to Mitigate Crosstalk

Crosstalk is dependent on the signal trace separation, the trace to plane(s) separation, parallel segment length, the transmission line load and the technology employed. But, crosstalk also varies depending on the physical stackup configuration. In this month's column, I will delve into the properties of microstrip and stripline crosstalk and how to mitigate the concern.

Beyond Design: Stackup Planning - 3 decades of Innovation

The multilayer PCB is the most critical component of an electronics assembly. If it fails-your system fails! The PCB is so fundamental, that we often forget that it is a component and like all components, must be chosen based on specifications in order to achieve the best possible performance of the product.

Beyond Design: Simulation Slashes Iterations

The majority of high-speed digital designs take two to three iterations to develop into a working product. However, these days the product life cycle is very short and therefore time to market is of the essence. An aggressive timeline can mean that a re-spin is not possible. However, high-speed digital multilayer boards can be designed to work "Right First Time", with little additional effort, providing you follow a tried and proven process .

Beyond Design: Routing Strategies for HSD

As the typical PCB design becomes more complex, so do the techniques and strategies required, not only to complete the design but to create a functioning product that performs to specification. Every situation is different-requiring unique tradeoffs.

Beyond Design: Fringing Fields

A parallel plate capacitor (or a planar pair) has two conductors separated by a dielectric layer. Most of the energy, in the structure, is concentrated directly between the plates. However, some of the energy spills over into the area outside the plates. The electric field lines associated with this effect are called fringing fields.

Beyond Design: Stackup Planning Pt6 - Impedance Variables

Interconnect Impedance is a trade-off between trace width, trace (copper) thickness, dielectric thickness and dielectric constant. Then if you also need to include differential impedance, the trace clearance also comes into play. One should weigh up all the pros and cons of changing each variable and make an informed decision rather than just handing it over to the fab shop to adjust.

Beyond Design: The Wavelength of Electromagnetic Energy

The speed of light is the one universal physical constant that we are yet to break. At a lightning 299,792,458 m/s, it is the maximum speed at which mass-less particles of light, electromagnetic energy and gravitational waves travel in a vacuum. In this month's column, I will look at how the wavelength of electromagnetic energy relates to the multilayer PCB.

Beyond Design: Alternative Series Termination Techniques

Terminations are used to eliminate impedance mismatch and hence reflections in order to avoid crosstalk and electromagnetic radiation. It is necessary when the round trip propagation time of the signal is equal to or greater than the transition time of the driver. In this month's column, I will elaborate on two particular cases of series termination.

Beyond Design: Split planes - Reprise

At high frequencies, the return current follows the path of least inductance, which is directly below the signal trace, but that path is broken by the split. In this case, the return current has to find an alternative path back to the source, creating a larger loop area. In this month's column, I will review the two common solutions, to this issue, plus introduce a third optimal solution.

Beyond Design: The Impact of Rise Time on Bandwidth

In digital electronics the term bandwidth is use to describe the signal spectrum since square waves are made up of numerous sine waves (harmonics), of the fundamental frequency. The shorter the rise time in the time domain-the higher the bandwidth in the frequency domain and the more closely the waveform resembles an ideal square wave.

Beyond Design: Predicting and Measuring Impedance

In order to control the impedance of high-speed signal interconnects, one first needs to predict the impedance. A precision field solver is arguably the most accurate way to calculate the  impedance. Then once the board is fabricated, the transmission lines need to be physically measured, with a TDR, to determine the actual impedance to qualify the board.

Beyond Design: Transmission Line Termination

In an ideal world, the energy emanating from an IC output driver would travel through the PCB transmission line and be totally absorbed by the load. However, if energy is not completely absorbed, then the residual will be reflected back along the interconnect. In this month's column, I will look at how to effectively terminate transmission lines.

Beyond Design: Impact of PDN Impedance on EMI

Impedance is defined in both the time and the frequency domains. In the time domain, we need to consider the impact of the interconnect impedance on the propagation of electromagnetic energy. However, in the frequency domain, the AC impedance needs to be kept below an acceptable level to prevent excessive radiation.

Beyond Design: Interconnect Impedance

Arguably, the most critical factor in high-speed PCB design is the impedance of the interconnect. Energy is never lost but rather transforms into other forms of energy. Specifically, in the case of an unmatched transmission line, energy can be transferred into heat, coupled into adjacent elements, reflected or radiated.

Beyond Design: Lumped Element to Distributed System

As the frequency and rise time increase, the PCB trace behaves as a distributed system with parasitic inductance and capacitance characterized by delay and scattered reflections. The behavior we are now concerned about, occurs in the frequency domain. In this month's column, I will discuss the difference between the lumped element model and the distributed system.

Beyond Design: The Frequency Domain

Perhaps one of the most fundamental steps in the process of gaining proficiency in high-speed digital design is learning to think in the frequency domain. For most of us, the vast majority of our early experience with electrical circuits and signals remains within the context of voltages and currents that are either static or dynamic with respect to time.

Beyond Design: 100th 'Beyond Design' Column

Well believe it or not, this is my 100^th Beyond Design column. When I was first approached to write a regular column, I thought that I may be able to convert my course on Advanced Design for SMT, which I had been presenting throughout Australia and New Zealand since 1994, into a number of segments. However, I never envisaged reaching the one hundred mark.

Beyond Design: Curse of the Golden Board

At low frequencies, the inductance of transmission line paths can be ignored. However, as the frequency increases, we soon realize that the multilayer PCB is not an ideal environment to transfer high-speed data. Here parasitic capacitance and inductance plague the most basic of designs. Inductance in particular, impacts on virtually all signal and power integrity issues.

Beyond Design: Stackup Planning Part 5

Traditional stackup structures which use a combination of signal and power/ground planes. But to achieve the next level in stackup design, one needs to not only consider the placement of signal and plane layers, in the stackup, but to visualize the electromagnetic fields that propagate the signals through the substrate.

Beyond Design: The Key to Product Reliability

With today's rapid product development cycles and time-to-market pressures, PCB designers are pushed to their limit. This situation leaves many developers with the question of how to ensure that their high-speed digital design performs to expectations.

Beyond Design: High-Speed PCB Design Constraints

The key methodology is to understand the underling high-speed design issues and then translate these into corresponding design constraints that will be adhered to during the entire design process. It is best to develop these high-speed design constraints based on pre-layout simulation.

Beyond Design: Transmission Line Modeling

To ensure the prototype has first pass success, designers need to perform accurate board level simulation, throughout the entire design process. However the challenge is: how do you quickly perform the simulation if all the models, for the board are not available and if the simulation setup time is prohibitive? Enter the I/O Buffer Information Specification (IBIS).

Beyond Design: The Proximity Effect

The skin effect and the proximity effect are manifestations of the same principle: that magnetic lines of flux cannot penetrate a good conductor. The frequency at which both effects begin to occur is the same. In this month's column I will focus on the proximity effect.

Beyond Design: Not All Substrates are Created Equal

PCB substrates are all around us in every gadget we use. Be it a computer, a smart phone or a simple child's toy. However, each product has a specific performance requirement and as such may need a distinct type of substrate to comply with the product's specifications particularly for high-speed designs.

Beyond Design: The Ten Fundamental Rules of HSD Pts 1- 5

This is a compilation of all Ten Fundamental Rules of High-Speed Design including parts 1-5 in flipbook format. Establish Design Constraints, Control the Impedance, Floor Plan the Placement based on Connectivity, Define the Power Delivery Planes and Paths, Optimize the Power Distribution Networks. Route the Board Prioritizing Critical Signals, Analyze the Return Current Paths, Run the Post Layout Simulation, Eliminate Crosstalk, Assess Electromagnetic Compliancy.

Beyond Design: The Ten Fundamental Rules of HSD Pt 5

The final part, of the ten fundamental rules of high-speed PCB design, focuses on board level simulation encompassing signal integrity, crosstalk and electromagnetic compliancy. In Part 1, of this series of columns, I mentioned that there is always room for one more rule at the top. And, that this rule may be the foundation of earlier rules. The Zeroth Rules is revealed.

Beyond Design: The Ten Fundamental Rules of HSD Pt 4

Part 4 deals with the routing of critical signals and return path discontinuities. Needless to say, matched delay/length, differential pairs and other critical signals should be routed first before less important low-speed and static signals are completed. It is imperative to maintain this priority.

  Design007 Magazine - November 2018                                                 #96

Beyond Design: The Ten Fundamental Rules of HSD Pt 3

Continuing on from my previous columns-the 10 fundamental rules of high-speed PCB design Parts 1 and 2-in this month's column, I will elaborate on power distribution networks (PDNs) and defining power planes and paths.

Design007 Magazine - October 2018                                                   #95

Beyond Design: The Ten Fundamental Rules of HSD Pt 2

In last month's column, I introduced the ten fundamental rules of high-speed PCB design. This month, I will elaborate on the importance of controlling the impedance and floor planning the placement based on connectivity.

Design007 Magazine - September 2018                                                   #94

Beyond Design: The Ten Fundamental Rules of HSD Pt 1

In this month's column, I reflect on the ten most important considerations to embrace to achieve a successful high-speed PCB design that performs reliably to expectations. I will elaborate further on these ten points over the next few columns.

Design007 Magazine - August 2018                                                   #93

Beyond Design: It's a Material World

Over the years, a huge range of materials have been developed for multilayer PCB fabrication. We live in a material world and selecting the best material for an application is often a daunting task. In this month's column, I will look at how to quickly sort through the vast array of choices to make an informed decision.

Design007 Magazine - July 2018                                                   #92

Beyond Design: Crosstalk Margins

What is an acceptable level of crosstalk? That depends on the technology being used and has changed quite dramatically over the years. The trend is towards lower core voltages, which conserves power. But, reducing the core voltage also reduces the noise margin. In this month's column, I will delve into the threshold of acceptable crosstalk and how to mitigate its impact on high-speed designs.

Design007 Magazine - June 2018                                                   #91

Beyond Design: DDR3/4 Fly-by Termination and Routing

DDR3/4 fly-by topology is similar to daisy chain or multi-drop topology, but has very short stubs, to each memory device in the chain, to reduce the reflections. If you are employing high-frequency DDR4, then the bandwidth of the channel needs to be as high as possible. However with today's extremely fast edge rates, the sequencing of the stubs and the end termination, and the associate load, can make a measurable difference in signal quality.

Design007 Magazine - May 2018                                                   #90

Beyond Design: Common Mode Radiation 

Electromagnetic radiation can occur as either differential mode or common mode. Differential mode is typically equal and opposite and therefore any radiating fields will cancel. Conversely, common mode radiation is identical. It does not cancel but rather reinforces.  Unfortunately, differential mode propagation can be converted to common mode. In this month's column, I will explore the symptoms of common mode radiation.

Design007 Magazine - April 2018                                                   #89

Beyond Design: HyperLynx DRC Review 

There is an old saying, "You get what you pay for." However, free software usually comes at a price: the results might be inaccurate, the software might be time-consuming to set up and use, and the tool might overlook issues that require a revision to mitigate. But HyperLynx DRC Free Edition is the exception to the rule. It provides analysis tools that complement any PCB layout tool that can export ODB++ or IPC-2581B formats.  

Design007 Magazine - March 2018                                                 #88

Beyond Design: AC/DC are not only a Rock Band 

SERDES serial links are used to provide high-speed, high-bandwidth data transmission over differential signals and also minimize the number of IO pins and interconnects. And although it saves the PCB designer routing numerous parallel traces, implementing high-speed serial links can be challenging. Any small discontinuities in the physical geometries, along the transmission path, can significantly degrade the signal.

Design007 Magazine - February 2018                                              #87

Beyond Design: The Target Impedance Approach to PDN Design

Today's high performance processors employ low DC voltages with high transient currents and high clock frequencies in order to minimize the power consumption and hence the amount of heat dissipated. The goal of robust PDN Planning is to design a stable power source, taking the above into account, for all the required on-board power supplies. In this month's column, I will look at the target impedance approach to PDN design.

Design007 Magazine - January 2018                                                #86

Beyond Design: Ground Bounce

Ground bounce is the voltage produced between two points in the power delivery path. It is fundamentally related to the total inductance of the current path and shared return paths and the instantaneous surge current delivered by the power supply. Once again, we find that inductance is the covert enemy of the high-speed PCB designer. In this month's column, I will look at supply bounce and how to minimise the impact on high-speed digital circuits.

The PCB Design Magazine - December 2017                                    #85

Beyond Design: Signal Flight Time Variance in Multilayer PCBs

A transmission line does not carry the digital signal itself but rather, guides electromagnetic energy. Signals travel at the same speed, given the same medium. However, the outer layer-microstrip traces-are embedded in a melange of dielectric material, solder mask (if present) and air. This lowers the effective dielectric constant and increases the propagation speed compared to that of stripline-inner layer-traces.

The PCB Design Magazine - November 2017                                     #84

Beyond Design: Next Gen PCBs

As PCB transmission frequencies increase, the current mainstream PCB technology is reaching its performance threshold. However, recently substrate integrated waveguides structures have emerged as a viable alternative and are ideally suited to the high-speed transmission. In this month's column, I will review the substrate integrated waveguide and its incorporation with the microstrip transmission line.

The PCB Design Magazine - October 2017                                     #83

Beyond Design: When Do Traces Become Transmission Lines

At low frequencies, traces  on a PCB behave simply as lossless lumped elements. But as the frequency increases, the copper trace and adjacent dielectric become a transmission line, the skin effect forces current into the outer regions of the conductor and frequency dependant losses impact on the quality of the signal. The PCB trace now behaves as a distributed system with parasitic inductance and capacitance.

The PCB Design Magazine - September 2017                                       #82

Beyond Design: Plane Cavity Resonance

Plane pairs, in multilayer PCBs, are essentially unterminated transmission lines-just not the usual traces or cables we may be accustomed to.  But as with signal traces, if the transmission line is mismatched or unterminated, there will be standing waves-ringing.  The bigger the mismatch, the bigger the standing waves and the more the impedance will be location dependent.

The PCB Design Magazine - August 2017                                       #81

Beyond Design: When Legacy Products No Longer Perform

It is a common quandary that established products, that have worked flawlessly for years, suddenly stop performing reliably due to a new batch of ICs, that has been used in the latest production run. The cause of this problem is rise time shrinkage. Over the years, as logic drivers have continued to switch faster and faster, problems with ringing, crosstalk and electromagnetic emissions (EMI) have become progressively worse.

The PCB Design Magazine - July 2017                                          #80

Beyond Design: Transmission Line Losses

Pragmatic effects, such as frequency dependent losses, come into play at clock frequencies above 1GHz and are of particular concern for fast rise time signals such as multi-gigabit serial links. This frequency dependence causes rise time degradation and reduces the upper bandwidth of the signal resulting in reduced channel data transfer. In this month's column I will look at the impact of transmission line losses on signal integrity.

The PCB Design Magazine - June 2017                                          #79

Beyond Design: FPGA PCB Design Challenges

The primary issue with FPGA-PCB integration is generating optimal FPGA pin assignments that do not add vias and signal layers to a PCB stackup. Engineers generally do not consider FPGA pin assignments that expedite the PCB layout. Hundreds of logical signals need to be mapped to the physical pin-out, of the device, and also harmonize with the routing requirements whilst maintaining the electrical integrity of the design.

The PCB Design Magazine - May 2017                                           #78

Beyond Design: The Dark Side - Return of the Signal

As signal traces come into close proximity, of an aggressor signal, part of that signal is unintentionally electromagnetically coupled into the victim trace as noise. I have mentioned before that current flow is a round trip-the current must return back to the source to complete the loop. So what about crosstalk in the return path, of the reference planes, as the current weaves its way back through the expansive wasteland of copper?

The PCB Design Magazine - April 2017                                          #77

Beyond Design: Return Path Discontinuities

Simultaneous switching noise is a major problem in high-speed systems. But, the underlying issue is really the management of transmission line return currents that flow on the nearby reference planes, causing the planes to bounce. High-speed design is not as simple as sending a signal over an interconnect. But rather, one should also consider the interaction of the PDN and how and where the return current flows.

The PCB Design Magazine - March 2017                                         #76

Beyond Design: Microstrip Coplanar Waveguides

Coplanar Waveguides (CPW) have been used for many years in RF and microwave design as they reduce radiation loss, at extremely high frequencies. And now, as edge rates continue to rise, they are coming back into vogue. Today's high-speed, fast rise time serial interfaces are prone to excess loss, in the transmission lines, which is a major cause of signal integrity issues.

The PCB Design Magazine - February 2017                                       #75

Beyond Design: New Functionality Improves Productivity

Productivity features not only save time-to-market but also curb frustration. One of the main details lacking in today's PCB design software is the flow of impedance control from design capture through to board fabrication. If the impedance, of all the required technologies, is determined up-front at the time of capture, the engineer's intent should be preserved and flow through to downstream tools.

The PCB Design Magazine - January 2017                                       #74

Beyond Design: PDN - Decoupling Capacitor Placement

The impact of lower core voltages and faster edge rates has pushed the frequency content of typical digital signals into the gigahertz range. Consequently, the performance of decoupling capacitors, that are required to complement the Power Distribution Network (PDN) and curb signal induced fluctuations, must also be extended up into this range. This month, I look at effective decap placement.

The PCB Design Magazine - December 2016                                       #73

Beyond Design: Marketing in the Maturing EDA Industry

In this month's column, Barry Olney explains how Electronics Design Automation (EDA) sales and marketing techniques have evolved as EDA has matured, and traces the drop in tool cost over time, along with the increase in tool capability. The latest EDA offerings provide highly productive tools for the ever increasing number of global users, at an affordable price point. Really, it has never been better!

The PCB Design Magazine - November 2016                                       #72

Beyond Design: Uncommon Sense - Differential Pairs

It is remarkable that with all of today's high performance systems, in which very complicated electromagnetic effects play a dominant role, many of us still hold misconceptions about the fundamental nature of how signals interact with interconnects. In this month's column, I will look at the contemporary ways of addressing an old issue (Deja View - as I call it) and go beyond the design of PCBs.

The PCB Design Magazine - October 2016                                       #71

Beyond Design: Rock Steady Design

How do we ensure that our high-speed digital design performs to expectations, is stable given all possible diverse environments and is reliable over the products projected life cycle? One word: Impedance! For very little extra effort, your design can have improved performance and reliability giving you greater confidence in your products performance for the projected lifetime.

The PCB Design Magazine - September 2016                                       #70

Beyond Design: How to Handle the Dreaded Danglers Pt2

In Part 1 of this series, I deliberated on how dangling via stubs distort signals passing through an interconnect and also decrease the usable bandwidth of the signal. The conventional solution, to this problem, is to back-drill (or control depth drill) the vias to bore out the via stub barrels, so that the via stubs are reduced in length if not completely removed. This month I will look into all the possible solutions to alleviate this issue.

The PCB Design Magazine - August 2016                                        #69

Beyond Design: How to Handle the Dreaded Danglers Pt1

Dangling via stubs can distort signals passing through an interconnect and also decrease the usable bandwidth of the signal. A via stub acts as a transmission line antenna, and has a resonant frequency determined by the quarter wavelength of the structure. At this frequency, the transmitted signal is greatly attenuated-by up to 3dB. This month, I look at the issues created by via stubs and how to resolve them.

The PCB Design Magazine - July 2016                                          #68

Beyond Design: The Rise of the Independent Engineer

With the changing demographics, the old timers - the master PCB designers - are about to retire and hand-over the exacting job of PCB design to the Gen-X and Ys. These generations will tackle the most demanding designs without possessing the experience that we veterans benefit from. Apart from a demanding regime of training, what can these guys do to become a successful independent engineer?

The PCB Design Magazine - June 2016                                          #67

Beyond Design: Mastering "Black Magic"

The Dr. Howard Johnson, the world's foremost authority on Signal Integrity, has recently released his High-Speed Digital Design (HSDD) Collection. This includes, professionally recorded seminars that he presented, for over 20 years, at Oxford University and worldwide and is arguably the most practical and enlightening course on high-speed - black magic - ever delivered. This month I review the Collection.

The PCB Design Magazine - May 2016                                           #66

Beyond Design: Artificial Intelligence in EDA Tools

The keynote speaker at the Apex Design Forum, in Las Vegas this year, was Dean Parker, a manager at Google X. Parker specializes in Artificial Intelligence (AI). He said that EDA tool vendors need to trash all their old 1990s code and start over-this time with artificial intelligence. But, how could AI influence the PCB design process. This month, I will take a look at the endless possibilities.

The PCB Design Magazine - April 2016                                          #65

Beyond Design: DDR3/4 Fly-by vs T-topology Routing

DDR3/4 Fly-by topology supports higher frequency operation, reduces simultaneous switching noise, reduces the quantity and length of stubs and consequently improves signal integrity. And, for a PCB designer - eases routing of memory devices dramatically. However, strict attention should be paid to the signal propagation, on each layer, ensuring the total flight time of the critical signals match, regardless of length.

The PCB Design Magazine - March 2016                                         #64

Beyond Design: The Need for Speed - Strategies for Design Efficiency

Years of experience with the one EDA tool obviously develops efficiency whether the tool be high-end feature packed or basic entry-level. And, one becomes accustomed to the intricacies of all the good and bad 'features' of their PCB design tool. However, there comes a time where one should consider a change for the better. This month, I will look at productivity issues that impede the PCB design process.

The PCB Design Magazine - February 2016                                       #63

Beyond Design: Faster Than a Speeding Bullet

The speed of a computer does not depend intrinsically on the speed of electrons, but rather on the speed of energy transfer between electronic components. Electron flow, in a multilayer PCB, is extremely slow - about 10mm per second - so how does the signal travel so fast, how fast does it actually transfer information and what are the limitations?  

The PCB Design Magazine - January 2016                                       #62

Beyond Design: Plane Crazy Part 2

In the recent, four part, Stackup Planning series of columns I described the best configurations for various stackup requirements but I did not have the opportunity to delve into the use of planar capacitance to reduce the AC impedance at frequencies above 1GHz. In this column, I will flesh out this topic, and consider the effects of plane resonance on the Power Distribution Network (PDN).

The PCB Design Magazine - December 2015                                        #61

Beyond Design: Plane Crazy Part 1

A PDN must provide a low inductance, low impedance path between all ICs. In order to reduce the inductance, we must also minimize the loop area enclosed by the current flow. Obviously, the most practical way to achieve this is to use power and ground planes. In this two part column, I will look at the alternatives to planes, why planes are used for high-speed design and the best combination for your application.

The PCB Design Magazine - November 2015                                           #60

Beyond Design: Why Autorouters Don't Work - The Mindset!

Ask any group of PCB Designers what they think of autorouters and the majority will say that they don't use them because they don't work. I have been battling this mindset for over twenty years now and it still persists today, even with the dramatic advances in routing technology. But, even the most primitive autorouter may have some useful features. It's all about changing that mindset of the designer and having a crack at it.

The PCB Design Magazine - October 2015                                           #59

Beyond Design: Stackup Planning Part 4

In the final part of the Stackup Planning series I will look at 10 plus layer counts. The methodology I have set out, in previous columns, can be used to construct higher layer count boards. In general, these boards contain more planes and therefore the issues associated with split power planes can usually be avoided. Also, ten plus layers require very thin dielectrics, in order to reduce the total board thickness.

The PCB Design Magazine - September 2015                                           #58

Beyond Design: Top Gear - PADS Professional Road Test

We hear all the hype about new EDA tools but how do they actually perform on your design? This month Barry Olney road tests Mentor Graphics' new PADS Professional and puts it through a rigorous performance evaluation - let's see how the Xpedition technology actually performs integrated into the PADS tools.

The PCB Design Magazine - August 2015                                            #57

Beyond Design: Stackup Planning Part 3

This month I will look at higher layer count stackups as the four and six layer configurations are not the best choice. Each signal layer should be adjacent to, and closely coupled to, an uninterrupted reference plane, which creates a clear return path and eliminates broadside crosstalk. As the layer count increases, these rules become easier to implement but decisions regarding return current paths become more challenging.

The PCB Design Magazine - July 2015                                               #56

Beyond Design: Stackup Planning Part 2

In Part 1 of the Stackup Planner series, I looked at how the stackup is built, the materials used in construction and the lamination process. And, I set out some basic rules to follow for high-speed design. It is important keep return paths, crosstalk and EMI in mind during the design process. Part 2 follows on from this with definitions of basic stackups starting with four and six layers....

The PCB Design Magazine - June 2015                                               #55

Beyond Design: Stackup Planning Part 1

The PCB substrate that physically supports the components, links them together, via high-speed interconnects and also distributes high current power to the ICs, is the most critical component of the electronics assembly. The PCB is so fundamental, that we often forget that it is a component and like all components, must be selected based on specifications in order to achieve the best possible performance.......

The PCB Design Magazine - May 2015                                               #54

Beyond Design: Controlled Impedance Design

For perfect transfer of energy, the impedance of the driver must match the transmission line. A good transmission line is one that has constant impedance along the entire length of the line, so that there are no mismatches resulting in reflections. But unfortunately, drivers do not have the exact impedance to match the line so terminations are used to balance the impedance, match the line and minimize reflections.......

The PCB Design Magazine - April 2015                                              #53

Beyond Design: Learning the Curve

Currently, power integrity is just entering the mainstream market phase of the technology adoption life cycle. The early market is dominated by innovators and visionaries who will pay top dollar for new technology, allowing complex and expensive competitive tools to thrive. However, the mainstream market waits for the technology to be proven before jumping in. More about the PDN learning curve ........

The PCB Design Magazine - March 2015                                              #52

Beyond Design: Split Planes in Multilayer PCBs

Creating split planes in multilayer PCBs at first seems like a good idea. These days' processors require more than six or seven different high current power sources. And, keeping sensitive analog circuitry isolated from those nasty, fast, digital switching signals seems like a priority in designing a noise free environment for your product - or is it?

The Electronic Specifier Design Magazine - March 2015                           #51

Beyond Co-design

Better software features highly in driving up productivity and reliability. As designs become more complex and time-to-market schedules become more demanding, engineers must take advantage of pre-layout simulation, and simultaneous process design in order to beat the competition. Electronic Specifier Design  - Pan-European edition.

The PCB Design Magazine - February 2015                                           #50

Beyond Design: Effects of Surface Roughness on High-speed PCBs

Below 1GHz, the effect of copper surface roughness on dielectric loss in negligible. However, as frequency increases, the skin effect drives the current into the surface of the copper dramatically increasing loss. The effective resistance of the copper increases relative to the additional distance over which the current must transverse the surface contours.

The PCB Design Magazine - January 2015                                           #49

Beyond Design: Electromagnetic Susceptibility (EMS)

As PCB Designers, we are concerned with electromagnetic emissions, as every product we design must pass the FCC/CISPR compliancy, but what about susceptibility to external sources? Noise sources range from medium to high frequency, RF and microwave radiation and can be generated by nearly any electrical appliance or device.

The PCB Design Magazine - December 2014                                            #48

Beyond Design: Signal Integrity - Part 3 of 3

Where most designers go wrong and how to avoid the common pit-falls. Digital designs become less forgiving as edge rates and frequencies increase. What used to work, in the past, may not now and a different approach to layout may be necessary. Also, there may be many issues that aren't at first apparent but affect the reliable performance of the product.

The PCB Design Magazine - November 2014                                            #47

Beyond Design: Signal Integrity - Part 2 of 3

In last month's column, I looked at how advanced IC fabrication techniques have created havoc with signal quality and radiated emissions. Part 2, of Signal Integrity, will cover the effects of crosstalk, timing and skew on signal quality.

The PCB Design Magazine - October 2014                                            #46

Beyond Design: Signal Integrity - Part 1 of 3

As system performance increases, the PCB designer's challenges become more complex. The impact of lower core voltages, high frequencies
and faster edge rates has forced us into the high-speed digital domain. But in reality, these issues can be overcome by experience and good design techniques.

Dataweek Magazine - October 2014                                            #45

Concurrent Design Cuts Development Costs and Time

As The traditional PCB design process is to execute each stage of the design in sequence. But, as designs become more complex and time-to-market schedules become more demanding, one must take advantage of pre-layout simulation, and simultaneous process design in order to beat the competition. Dataweek Magazine - South African edition.

The PCB Design Magazine - August 2014                                            #44

Beyond Design: Material Selection for Digital Design

Materials used for the fabrication of the multilayer PCB absorb high frequencies and reduce edge rates and that loss, in the transmission lines, is a major cause of signal integrity issues. But we are not all designing cutting-edge boards, and sometimes we tend to over-specify requirements that can lead to inflated production costs.

The PCB Design Magazine - July 2014                                               #43

Beyond Design: Concurrent Design

With the traditional PCB design process, the designer executes each stage of the design in sequence. But, as designs become more complex and time-to-market schedules become more demanding, we must take advantage of pre-layout simulation, and simultaneous process design in order to beat the competition.

The PCB Design Magazine - June 2014                                               #42

Beyond Design: Surface Finishes for High-Speed Design

Electroless nickel immersion gold (ENIG) finish has traditionally been the best fine pitch (flat) surface and lead-free option for SMT boards over recent years. But unfortunately, nickel is a poor conductor with only 1/3 the conductivity of copper. Also, nickel has a ferromagnetic property that can adversely affect electromagnetic fields in the high-frequency domain.

The PCB Design Magazine - May 2014                                                #41

Beyond Design: Transmission Lines

From barbed wire to high-speed interconnect. Long before Facebook and Twitter, there was a more primitive type of social network. It allowed distant communities to meet remotely to share music, spread news and to just gossip. The long-forgotten social revolution, and extremely basic technology, was built on barbed wire fences.

The PCB Design Magazine - April 2014                                               #40

Beyond Design: Mythbusting - There are no on-way trips

One of the greatest myths in PCB design is that we only have to route signal traces from pin-to-pin to make a complete connection. And, that ensuring these traces have matched delay is the only timing issue we need to consider. However, current is not a one way trip-it must complete the circuit back to the source in order to provide the round-trip current loop.

The PCB Design Magazine - March 2014                                              #39

Beyond Design: Matched Length does not equal Matched Delay

In previous columns, I have discussed matched length routing and how matched length does not necessarily mean matched delay. But, all design rules, specified by chip manufacturers regarding high-speed routing, specify matched length-not matched delay. In this month's column we'll take a look at the actual differences between the two.

The PCB Design Magazine - February 2014                                         #38

Beyond Design: Effective Routing of Multiple Loads

Different terminating strategies have advantages and disadvantages depending on the application, but in general, series termination is excellent for point-to-point routes, one load per net. In summary, series termination reduces ringing and ground bounce. But, what if there are a number of loads-how should these transmission lines be routed?

The PCB Design Magazine - January 2014                                         #37 

Beyond Design: PDN Planning and Capacitor Selection Part 2

In last month's column we looked closely at how to choose the right capacitor to lower the AC impedance of the PDN at a particular frequency. We also examined capacitor properties and types of capacitors that are readily available and touched on the target frequency approach for analyzing a PDN. This month we will continue on from there looking at the one capacitor value per decade and optimized value approaches.

The PCB Design Magazine - December 2013                                     #36

Beyond Design: PDN Planning and Capacitor Selection Part 1

In a previous column, I described the basics of planning for a low AC impedance, between the planes, in order to reduce supply noise and provide reliable performance. This column, spread over two parts,  will focus on capacitor selection and three alternative approaches to analyzing the Power Distribution Network.

The PCB Design Magazine - November 2013                                         #35

Beyond Design: Entanglement - The Holy Grail of High-speed Design

While high-speed SERDES serial communications seems to currently be at the cutting edge of technology, maybe it will shortly become an antiquated low-speed solution-even speed-of-light fiber optics may become obsolete. This month, we'll look at how quantum physics is transforming our world and how it could affect PCB design.

The PCB Design Magazine - October 2013                                         #34

Beyond Design: Impedance Matching - Terminations

The impedance of the trace is extremely important, as any mismatch along the transmission path will result in a reduction in signal quality and possibly the radiation of noise. By understanding the causes of these reflections and eliminating the source of the mismatch, a design can be engineered with reliable performance.

The PCB Design Magazine - September 2013                                       #33

Beyond Design: Material Selection for SERDES Design

Many challenges face the engineer and PCB designer working with new technologies. Materials used for the fabrication of the multilayer PCB absorb high frequencies and reduce edge rates thus putting the materials selection process under tighter scrutiny. This column will look at the factors that must be taken into account, in the selection process, and provides some options for PCB designers.

The PCB Design Magazine - August 2013                                          #32

Beyond Design: Practical Signal Integrity

"There are two types of designers: Those that have signal integrity problems and those that will." - Sun Microsystems.

If you are a digital designer, you will eventually have SI problems whether you like it or not. But all is not lost. If you learn to work with these issues, then you will soon become proficient with high-speed design.

The PCB Design Magazine - July 2013                                                #31

Beyond Design: Design for Profit

Design for Profit is gaining more recognition as it becomes clear that the cost reduction of printed circuit assemblies cannot be controlled by manufacturing engineers alone. The PCB designer now plays a critical role in cost reduction.

The PCB Design Magazine - June 2013                                              #30

Beyond Design: Skewed Again

Differential skew refers to the time difference between the two single-ended signals in a differential pair. Any mismatch in delay (skew) will result in changing part of the differential signal power into common-mode power. When skew needs to be adjusted, it is best done at either end of the differential pair. In this way, the coupling and signal quality of the remainder of the pair is maintained.

The PCB Design Magazine - May 2013                                                 #29

Beyond Design: Losing a Bit of Memory

No matter what type of memory you are designing with, the clock should always have the longest delay. This ensures that the other signals have time to settle before the clock arrives at the device and samples the bus.

The PCB Design Magazine - April 2013                                               #28

Beyond Design: Electromagnetic Fields, Part 2

In my last column, Electromagnetic Fields: Part 1, we looked at how magnetic fields revolve around the earth and how these fields are also present in a multilayer board. In Part 2, we will look at how electromagnetic fields influence transmission lines and how they can be applied in a BEM field solver.

The PCB Design Magazine - March 2013                                            #27

Beyond Design: Electromagnetic Fields, Part 1

Danish physicist Hans Christian Oersted discovered that electric currents create magnetic fields. He later found that a current-carrying wire created a circular magnetic field around that wire, and that this circular field was strongest closer to the wire. Traces in a multilayer PCB act in much the same way. A current loop produces a field similar to that of the Earth.

The PCB Design Magazine - February 2013                                         #26

Beyond Design: Post Mortem Simulation

Often we find that PCB simulation is engaged too late in the design cycle. This results in the simulation process becoming more a post-mortem to uncover what has gone wrong with the design and how it can be resurrected to work as intended.

The PCB Design Magazine - January 2013                                         #25

Beyond Design: Routing Techniques for Complex Designs

To err is human; to completely mess it up, use software. Autorouter software is essentially artificial intelligence (AI) software - although fairly basic - that makes certain decisions that mimic what designers do in the process of routing a board. Its capacity to do this, of course, varies by software developer, and is dependent upon algorithm complexity and how easy or difficult it is to control the router. 

The Electronics News - January 2013                                               #24

Multilayer PCB Simulation - Barry Olney

Faster edge rates cause reflections and signal quality problems. And, although the package and your clock speed have not changed a problem may exist for legacy designs. The enhancements in driver edge rates have a significant impact on signal quality, timing, crosstalk, and EMC. So whether you like it or not - you are now a high-speed designer.

The PCB Design Magazine - December 2012                                         #23

Beyond Design: Interactive Placement and Routing Strategies

PCB layout is a means to combine your artistic side and your creative skills with the power of automation. I always say that if a PCB design looks good, it will probably work well. However, neatness in routing often leads to unwanted crosstalk as trace segments are routed in parallel for long distances.

The PCB Design Magazine - November 2012                                        #22

Beyond Design: The Plain Truth About Plane Jumpers

Moats, islands, cut-outs in the ground plane, isolated power planes, floating ground regions are often used by PCB designers to reduce crosstalk, EMI. But a high-speed signal crossing a split in the plane causes problems along at least three dimensions, including signal quality, crosstalk, and EMI. The problem is the impedance discontinuity in the signal path crossing the split.

The PCB Magazine - September 2012                                             #21

Beyond Design: Critical Placement

Today's high-speed digital products use high frequencies and fast rise times that demand careful attention to PCB layout to ensure that the system works not only in the prototype phase, but also in mass production, and under all possible operating conditions.

The PCB Magazine - August 2012                                                #20

Beyond Design: Mixed Digital-Analog Technologies

Field programmable gate arrays (FPGAs) are becoming more complex, integrating functions such as processors, multi-gigabit SERDES transceivers and support for multiple I/O standards. However, designing power management and signal paths (including analog-to-digital converters, operational amplifiers and interface) around these FPGAs is no easy task.

The PCB Magazine - July 2012                                                        #19

Beyond Design: Pre-Layout Simulation

Today's high-speed processors, SERDES interfaces and decreased time-to-market requirements are pushing design teams toward more nimble development processes. But there is no point in completing a design on time if it does not work!  My motto is: 'Simulate twice - build once.'

The PCB Magazine - June 2012                                                   #18

Beyond Design: Design Rules & DFM for High-Speed Design

Requirements for PCB design can vary considerably from one design to the next. I specialize in high-speed design (HSD) but I am often asked to do a board that incorporates a switch-mode power supply. Or, there may be an analog section that needs to be laid out, so the design rules I use vary depending on the application. Where to Start?

The PCB Magazine - May 2012                                                      #17

Beyond Design: Power Distribution Network Planning

Fast rise times, low output-buffer impedance and the simultaneous switching of busses create high transient currents in the power and ground planes, degrading performance and reliability of the product. Inadequate power delivery can exhibit intermittent signal integrity issues.

The PCB Magazine - April 2012                                                     #16

Beyond Design: Stackup Planning and the Fabrication Process

Back in 1987, when I first started working on high-speed designs, the PCB stackup did not seem that important. But that was running at a maximum frequency of 166 MHz, which at the time seemed fast. Times have changed. Now, multi Gbps designs are becoming the norm and the stackup configuration, characteristic and differential impedance control are crucial to the performance and reliability of the product.

The PCB Magazine - March 2012                                                  #15

Intro to Board-Level Simulation and the PCB Design Process

High-speed digital multilayer boards can be designed to work right the first time, with little additional effort, providing you follow a tried and proven process that results in a reliable, manufacturable design that conforms to specifications and is produced on time and to budget.

The PCB Magazine - February 2012                              #14

Beyond Design: Plan B -  Post-Layout Simulation

Unfortunately, board-level simulation is engaged too often towards the end of the design cycle.  Ideally the simulation should be done during the design process to ensure design integrity. By following this year's series of columns on Board-Level Simulation and the Design Process, designers can be up-to-date on the best methodology to follow.

The PCB Magazine - January 2012                                              #13

Beyond Design: A New Slant on Matched-Length Routing

Serpentine traces are commonly used for matched length signals and supported by all popular EDA tools. It is therefore easier to follow tradition and use this pattern. It would be best using the serpentine pattern with at least 5x trace width spacing in a stripline configuration to reduce crosstalk and radiation. But, if real estate is at a premium then maybe it's time to give the old octal spiral a go.

The PCB Magazine - December 2011                                              #12

Beyond Design: Controlling the Beast

Crosstalk creates noise that erodes the noise margin. The degree of crosstalk is dependant of several factors including driver strength, transmission line length, how far the segments run closely in parallel and signal rise time. In the case of long line lengths, a series terminator slows the signal rise time and extinguishes reverse-coupled crosstalk at the near end, improving crosstalk considerably.

The PCB Magazine - November 2011                                           #11

Beyond Design: The Perfect Stackup - for High-Speed Design

Throughout the past 30 years, the concept of the perfect stackup has changed considerably. This is especially true in more recent years, where engineers and designers have had the opportunity to use simulation tools that act as another pair of eyes when it comes to understanding the intricacies of the effects of transmission lines on multilayer PCBs. This month we look at the perfect stackup for high-speed design.

The PCB Magazine - October 2011                                               #10

Beyond Design: Differential Pair Routing

Some argue that since the two halves of the differential pair carry equal and opposite signals, a good ground connection is not required as the return current flows in the opposite signal. Others say that beyond the fact that differential pairs transfer equal and opposite signals, there are no special requirements that need to be considered when using differential pairs. They should be treated as two single-ended signals.

The PCB Magazine - September 2011                                               #9

Beyond Design: Embedded Signal Routing

We hear all the time that one should avoid routing high-speed signals on the outer layers of a multilayer PCB. I myself preach this. Some say that this decreases radiation by up to 15 db. But, how much attenuation do we actually get from embedding the high-speed signals between the planes?

The PCB Magazine - August 2011                                                   #8

Beyond Design: The Dumping Ground

By definition, a ground plane in a PCB is a layer of copper that appears to most signals as an infinite ground potential. This month, we discuss best practices for selecting reference planes and routing pairs for high-speed designs on multilayer boards.

PCB007 online - August 2011                                                        #7

Beyond Design: Controlling Emissions and Improving EMC

This application note discusses electromagnetic compliancy (EMC) fundamentals and common approaches and methodologies to suppress unintentional noise.

The PCB Magazine - June 2011                                                        #6

PCB Design Techniques for DDR, DDR2 & DDR3, Part 2

To improve signal integrity and support higher frequency operations, the JEDEC committee defined a fly-by termination scheme used with the clocks, command and address bus signals of DDR3. Fly-by topology reduces simultaneous switching noise (SSN) by deliberately causing skew between the data and strobes at every chip/DRAM, requiring controllers to compensate for this skew by adjusting the timing per byte lane.

The PCB Magazine - May 2011                                                          #5

PCB Design Techniques for DDR, DDR2 & DDR3, Part 1

This application note details the tried and proven design rules and techniques for DDR PCB Design and looks at DDR, DDR2 and DDR3 design rules and critical constraints.

PCB007 online - May 2011                                                                #4

Ground Pours: To Pour or Not to Pour?

Copper ground pours are created by filling unused areas with copper and then connecting the copper fill with stitching vias to ground. Some PCB designers do this as a matter of habit. Also, many reference designs supplied by chip manufacturers use this ground pour technique so you may need to follow their recommendations if you want the design to work especially at high speeds--WRONG!

Application Note - Feb 2011                                                               #3

Multilayer PCB Stackup Planning

Planning the multilayer PCB stackup configuration is one of the most important aspects in achieving the best possible performance of a product. A poorly designed substrate, with inappropriately selected materials, can degrade the electrical performance of signal transmission increasing emissions and crosstalk and can also make the product more susceptible to external noise.

Application Note - Dec 2010                                                              #2

Generic Multilayer PCB Specification

This specification has been developed for the specifaction of fabrication of rigid SMT and Mixed Technology Multilayer Printed Circuit Boards (PCB's) of less than 12 inches [300 mm] square.

Printed Circuit Design Magazine - January 1996                                      #1

Design for EMC - Barry Olney

In order to accurately predict potential problem areas, minimize electromagnetic interference and susceptibility and verify their design, today's PCB designers not only need to plan for EMC but also must use software to analyse the physical layout. As clock speeds approach 50 MHz, signal integrity issues should be considered.

All trademarks are registered trademarks of their respective owners. The information provided on this blog is for informational purposes only. The author(s) make no representations about the suitability of the information contained on this site for any purpose. Information is provided here "as is" without warranty of any kind.