{"id":17834,"date":"2017-06-16T08:00:15","date_gmt":"2017-06-16T15:00:15","guid":{"rendered":"http:\/\/www.autodesk.com\/products\/eagle\/blog\/?p=1210"},"modified":"2023-09-25T13:37:21","modified_gmt":"2023-09-25T20:37:21","slug":"high-speed-pcb-design","status":"publish","type":"post","link":"https:\/\/www.autodesk.com\/products\/fusion-360\/blog\/high-speed-pcb-design\/","title":{"rendered":"What Is High Speed PCB Design?"},"content":{"rendered":"

What Is High Speed PCB Design? An Introduction For the Complete Beginner<\/h1>\n\n\n

Is this the world of PCB design<\/a> that you know? The one where you spend most of your time selecting the right components, getting them all placed on your board layout, wiring everything up with traces, and sending your files off to your manufacturer? At this stage, you\u2019re probably designing standard boards, and if someone were to mention signal integrity<\/a>, crosstalk, or reflections, you\u2019d likely feel lost. For good reason, those aren\u2019t the kind of problems that you solve in your day-to-day work.<\/span><\/p>\n\n\n\n

But sooner or later you might have a high speed PCB project slapped down on your desk. And when this happens, you better strap on your boots, because you’ll be wading through some really deep information. The truth is, there are engineers out there with doctorates that devote their entire lives to studying high-speed PCB design, like <\/span>Lee Ritchey at Speeding Edge Circuits<\/span><\/a>. We are by no means trying to cover everything there is to know about high-speed design. Rather, what you\u2019ll find within is a very basic explanation of high-speed design, written for someone that just develops regular circuit boards and wants to know what\u2019s beyond the horizon.<\/span><\/p>\n\n\n

So What Is High Speed PCB Design?<\/h2>\n\n\n

To put it simply, high speed PCB design is any design where the integrity of your signals starts to be affected by the physical characteristics of your circuit board, like your layout, packaging, layer stackup, interconnections, etc\u2026 If you start designing boards and run into problems like delays, attenuation, crosstalk, reflections, or emissions, then congratulations! You\u2019ve found yourself in the world of high speed PCB design.<\/span><\/p>\n\n\n\n

What makes high speed design so unique is the amount of attention paid to these issues. You might be used to designing a simple board where most of your focused time is on component placement and routing. But with a high speed design, it becomes more important to consider exactly where you are placing your traces, what width they\u2019re going to be, how close they are to other signals, and what kind of components they are connected. And when you have to make considerations of this sort, then your PCB design<\/a> process will take on a whole new level.<\/span><\/p>\n\n\n\n

Now let\u2019s back up for a moment. We know that a good indication of a high speed design is when you\u2019re dealing with signal integrity issues, but what exactly does that mean? We need to understand signals in a nutshell.<\/span><\/p>\n\n\n

Signals & Signal Integrity In a Nutshell<\/h2>\n\n\n

Whatever kind of design you\u2019re working on, it\u2019s going to be sending some kind of signal down your lengths of copper traces to a final destination. This <\/span>signal can be either analog or digital<\/span><\/a>, to review, here\u2019s the difference:<\/span><\/p>\n\n\n

Digital Signals<\/h3>\n\n\n

A digital signal is commonly referred to as a square wave or clock signal, and it\u2019s what you\u2019ll find in every digital system known to man. Unlike analog signals, which can have values all over the place, a signal provides a much simpler representation of values, consisting of a high point and low point, or 1 and 0, or on and off. If you saw a digital signal\u2019s waveform on a graph, it would look like this:<\/span><\/p>\n\n\n\n

\"digital-square-wave\"\/
A simple digital signal waveform, notice the define high and low points to designate on and off points in a circuit. (Image source<\/a>)<\/em><\/figcaption><\/figure>\n\n\n

Analog Signals<\/h3>\n\n\n

On the other side of the spectrum are analog signals, which can have a set range of positive and negative values. Unlike digital signals which are just a series of on and off points, analog signals can have a varying degree of results based on their signal strength and frequency. Looking at an analog signal\u2019s waveform on a graph will look like this:<\/span><\/p>\n\n\n\n

\"analog-signal-waveform\"\/
An analog signal waveform which can be all over the place based on its strength (Amplitude) and frequency (Time). (Image source<\/a>)<\/em><\/figcaption><\/figure>\n\n\n\n

Now here\u2019s the real issue with these signals, digital or analog – they are prone to interference, and this is where Signal Integrity (SI) comes into play. When a signal is affected by its environment, then issues arise. For example, let\u2019s say that you have a net that\u2019s transmitting some signal, which contains data, from point A to point B on your PCB layout. We can say that point A is the transmitter, and point B is the receiver of this signal. Between point A and point B, there are a ton of things that can interfere with the integrity of your signal, like:<\/span><\/p>\n\n\n\n