What is the best way to design a PCB for mixed-signal applications?

If you are working on a project that involves both analog and digital signals, you might be wondering how to design a PCB that can handle both types of signals without compromising performance, reliability, or cost. In this article, you will learn some of the best practices and tips for designing a PCB for mixed-signal applications, such as choosing the right components, layout, grounding, and shielding.

1 Components selection

One of the first steps in designing a PCB for mixed-signal applications is to select the appropriate components for your circuit. You should consider the specifications, compatibility, and quality of the components, as well as their availability and cost. For example, you should choose resistors and capacitors that have low tolerance, low noise, and low temperature coefficient for analog signals, and high-speed, low-power, and low-skew devices for digital signals. You should also avoid using components that can introduce interference, such as relays, switches, or LEDs, near sensitive analog circuits.

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2 Layout strategy

Another important step in designing a PCB for mixed-signal applications is to plan your layout strategy carefully. You should separate the analog and digital sections of your PCB as much as possible, and use different power and ground planes for each section. You should also place the components that convert between analog and digital signals, such as ADCs, DACs, or op-amps, near the boundary of the two sections, and use short and direct traces to connect them. You should avoid crossing analog and digital traces, or running them parallel to each other, as this can cause crosstalk, noise, or signal degradation.

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Larry Lowe

Retired I&E Engineer at Braskem
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Be sure to separate high and low voltage. Use a “faraday” cage around the low voltage signals. This can be done with a grounded shield.

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Anton Mamaev

leading designer of electronic equipment (BIS LLC)
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Datasheets, application notes and other stuff from IC manufacturers often contain useful tips and layout examples. They can help you avoid some problems.

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3 Grounding technique

A good grounding technique is essential for designing a PCB for mixed-signal applications, as it can reduce the noise and interference that can affect your signals. You should use a star or a tree topology for your ground connections, and connect the analog and digital grounds at a single point, preferably near the power supply. You should also use wide and thick traces or planes for your ground connections, and avoid creating ground loops or stubs, as these can create unwanted currents or voltages. You should also use decoupling capacitors and ferrite beads to filter out high-frequency noise from your power and ground lines.

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Zachariah Peterson

Owner, NWES | PCB Design for RF, Mil-Aero, Data Center, AI/ML | That guy in the Altium videos
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This is terrible advice and a recipe for EMC failure. Unless you're operating at only audio frequencies (no digital at all), don't start using a tree or star or whatever other grounding strategy. Use a plane layer for ground and put it next to your digital layer. You can route low-frequency analog as differential traces using differential buffers and eventually take that into your ADC or MCU, and that will handle return current control at the low kHz range and under.

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4 Shielding method

Finally, you should consider using a shielding method to protect your PCB from external sources of noise or interference, such as electromagnetic fields, radio waves, or static electricity. You can use a metal enclosure, a copper foil, or a conductive coating to cover your PCB, and connect it to the ground. You can also use shielded cables, connectors, or sockets to connect your PCB to other devices or components. You should also avoid placing your PCB near sources of noise or interference, such as motors, transformers, or speakers.

By following these best practices and tips, you can design a PCB for mixed-signal applications that can deliver high-quality performance, reliability, and cost-effectiveness. You can also use software tools, such as schematic capture, simulation, or layout editors, to help you design and test your PCB before fabrication.

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Zachariah Peterson

Owner, NWES | PCB Design for RF, Mil-Aero, Data Center, AI/ML | That guy in the Altium videos
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Shielding is usually needed when you already have screwed up the PCB so bad that it is failing EMC and you've refused to learn the correct design approach to fix the problem. Following linkedin's AI generated PCB design articles will help you create a board that is so noisy it requires shielding to pass EMI.

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5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Zachariah Peterson

Owner, NWES | PCB Design for RF, Mil-Aero, Data Center, AI/ML | That guy in the Altium videos
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If you want to design a mixed-signal PCB correctly, do the exact opposite of what this article tells you to do. With the number of times all this info has been repeatedly debunked, I'm kind of surprised that the correct information has not made its way into the dataset.

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Anton Mamaev

leading designer of electronic equipment (BIS LLC)
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Books on EMC tell a lot of useful information. A device made with good electromagnetic compatibility usually already takes into account mixed signal problems.

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What is the best way to design a PCB for mixed-signal applications?

1

2

3

4

5

1 Components selection

2 Layout strategy

3 Grounding technique

4 Shielding method

5 Here’s what else to consider

Electronic Engineering

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What is the best way to design a PCB for mixed-signal applications?

1

2

3

4

5

1 Components selection

2 Layout strategy

3 Grounding technique

4 Shielding method

5 Here’s what else to consider

Electronic Engineering

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