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Analog Fundamentals: High-Speed PCB Design

-September 17, 2013

What is a high-speed Printed Circuit Board (PCB)? What effects bandwidth in my PCB design? These are a few of the FAQs we get asked by designers about creating high-speed PCB designs.

Since PCB layout significantly influences circuit performance, design time and design cost, having good schematics and paying close attention to the layout process are critical to ensuring circuits perform as expected. Paying close attention to details is important. After trial and error, many designers find out the hard way that what might look good on the drawing board does not always deliver the anticipated circuit performance. That’s why it’s important for designers to understand key PCB design fundamentals, including component placement, signal routing, power supply bypassing and monitoring parasitics. 

In the PCB design layout process, one advantage of representing circuit functionality first as a schematic is that you and other designers can better understand the circuit. By organizing schematics as clearly as possible, you can help with layout, troubleshooting, debug and ultimately, reduce cost and time to market. 

For example, here’s a perfectly good schematic. It has the two basic, necessary functions. It shows the actual circuits (you can count the number of components). Each shows the connection and somewhere in the background they generate a NetList. As an alternative, here is exactly the same circuit, slightly rearranged. Note that the components here are bigger and easier to read. The functionality becomes apparent. It’s your choice which one better serves your purpose.

 

Figure 1: Schematic                   

Figure 2: Alternative

In Figure 1 and 2, the schematics have two basic functions: showing the actual circuit connection, which is important, and the generation of the NetList for layout. By examining the schematics, it is easier to find ways to make the circuit more effective.

It’s not possible in this post to cover all you need to know about designing a high-speed PCB. Each application is unique. But feel free to ask me questions here or connect with me on EngineerZone at RReeder. The good news is that there are lots of resources on high-speed PCB design fundamentals. My ADI colleague, Zoltan Frasch, will give an online technical tutorial on “PCB Fundamentals; High Speed and RF Design Considerations,” at ADI’s Design Conference on Sept. 25: http://bit.ly/12hyUqd

Moving forward, I will be blogging on other analog fundamentals intended for both newcomers to analog design and those who need a refresher.

Please let me know what analog fundamentals you’d like to hear about.

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