Stories with Tag Signal Integrity

• PCBs, copper pours, ground planes, and you

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  Posted: 2025-01-30 04:33:25

  Verbose tl;dr

  This post discusses the nuances of ground planes and copper pours in PCB design, emphasizing that they are not automatically equivalent. While both involve areas of copper, a ground plane is a specifically designated layer for current return paths, offering predictable impedance and reducing EMI. Copper pours, on the other hand, can be connected to any net and are often used for thermal management or simple connectivity. Blindly connecting pours to ground without understanding their impact can negatively affect signal integrity, creating unintended ground loops and compromising circuit performance. The author advises careful consideration of the desired function (grounding vs. thermal relief) before connecting a copper pour, potentially using distinct nets for each purpose and strategically stitching them together only where necessary.

  This comprehensive discourse, entitled "PCBs, copper pours, ground planes, and you," delves into the intricacies of printed circuit board (PCB) design, focusing specifically on the often-misunderstood concept of ground planes and their relationship to copper pours. The author meticulously dismantles the common misconception that simply flooding areas of a PCB with copper and connecting it to ground constitutes a proper ground plane, elucidating the significant differences between a true ground plane and a mere copper pour.

  The article commences with a foundational explanation of signal propagation in PCBs, emphasizing the role of return currents and their preferred paths. It underscores the importance of providing low-impedance return paths for signals to minimize noise and ensure signal integrity. The author then introduces the concept of a ground plane as an ideal, low-impedance return path that effectively distributes return currents evenly across its surface. This uniform distribution, the author argues, is key to mitigating electromagnetic interference (EMI) and maintaining signal quality.

  A significant portion of the article is devoted to contrasting true ground planes, typically found on multi-layer PCBs and characterized by a continuous sheet of copper on an inner layer, with copper pours on outer layers, often erroneously referred to as ground planes. The author meticulously details how the presence of discontinuities, such as traces and components, in these outer layer copper pours significantly alters their behavior and impedes their ability to function as effective ground planes. These discontinuities introduce impedance variations and can lead to the formation of ground loops, potentially exacerbating noise issues rather than mitigating them.

  Furthermore, the author explores the impact of the shape and size of copper pours on their effectiveness, emphasizing the importance of minimizing sharp corners and narrow necks that can concentrate current flow and increase impedance. The discussion extends to the topic of thermal relief connections for components soldered to copper pours, explaining their purpose in facilitating soldering while acknowledging their potential to introduce impedance discontinuities.

  The article also touches upon the nuances of using copper pours for other purposes, such as power distribution, and highlights the challenges associated with mixing power and ground pours on the same layer. The author advocates for careful consideration of the potential for noise coupling and the importance of separating power and ground planes, particularly in high-speed designs.

  Finally, the author concludes with practical recommendations for designing effective ground planes and utilizing copper pours strategically. This includes advice on choosing the appropriate layer for ground planes, optimizing the shape and size of copper pours, and utilizing techniques such as stitching vias to improve the performance of copper pours and mitigate the effects of discontinuities. The overarching message is that a thorough understanding of the principles governing signal propagation and return currents is essential for designing robust and reliable PCBs, and that the seemingly simple act of adding copper to a PCB requires careful planning and execution.

  • PCB Design
  • Ground Planes
  • Copper Pours
  • Electronics
  • Hardware
  • electrical engineering
  • Signal Integrity
  • EMI
  • EMC
  • Printed Circuit Boards
  • PCB Manufacturing
  • circuit design

  Summary of Comments ( 57 )
  https://news.ycombinator.com/item?id=42874885

  Verbose tl;dr

  Hacker News users generally praised the article for its clarity and practical advice on PCB design, particularly regarding ground planes. Several commenters shared their own experiences and anecdotes reinforcing the author's points about the importance of proper grounding for signal integrity and noise reduction. Some discussed specific techniques like using stitching vias and the benefits of a solid ground plane. A few users mentioned the software they use for PCB design and simulation, referencing tools like KiCad and LTspice. Others debated the nuances of ground plane design in different frequency regimes, highlighting the complexities involved in high-speed circuits. One commenter appreciated the author's focus on practical advice over theoretical explanations, emphasizing the value of the article for hobbyists and beginners.

  The Hacker News post "PCBs, copper pours, ground planes, and you" has generated a lively discussion with several insightful comments. Many of the commenters express appreciation for the author's clear and concise explanation of grounding techniques, particularly for those without a deep background in electronics.

  One recurring theme is the importance of the article's emphasis on practical considerations and real-world examples. Several commenters share their own experiences and anecdotes about troubleshooting grounding issues, highlighting the value of the author's advice. One user mentions how the article helped them understand why a particular grounding approach failed in a past project.

  Another point of discussion centers on the nuances of ground plane design. Commenters delve into specific techniques for optimizing ground planes, such as using vias to connect different layers and avoiding isolated "islands" of copper. They also discuss the trade-offs between different grounding strategies, considering factors like signal integrity, electromagnetic compatibility (EMC), and manufacturing cost. One commenter specifically praises the article's explanation of how ground planes can help reduce noise and improve signal quality.

  Some comments focus on the educational value of the article. Several users mention how the article serves as a good introduction to grounding principles for beginners, while others point out that even experienced engineers can benefit from the practical tips and insights. One commenter suggests using the article as a teaching resource for electronics courses.

  Several commenters also discuss the software tools and techniques used for PCB design, referencing specific software packages and highlighting their respective strengths and weaknesses. They also touch upon the importance of simulation and testing in verifying the effectiveness of grounding strategies.

  A few comments also delve into more advanced topics related to grounding, such as the effects of high-frequency signals and the challenges of grounding in mixed-signal designs. One commenter raises a specific question about the impact of ground plane impedance on signal integrity, prompting a further discussion among other users.

  Overall, the comments on the Hacker News post reflect a general appreciation for the article's clarity and practical focus. The discussion provides further context and insights into the complexities of grounding in PCB design, demonstrating the importance of careful planning and execution.

• Proper decoupling capacitor practices, and why you should leave 100nF behind

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  Posted: 2025-01-26 16:00:50

  Verbose tl;dr

  The article argues against blindly using 100nF decoupling capacitors, advocating for a more nuanced approach based on the specific circuit's needs. It explains that decoupling capacitors counteract the inductance of power supply traces, providing a local reservoir of charge for instantaneous current demands. The optimal capacitance value depends on the frequency and magnitude of these demands. While 100nF might be adequate for lower-frequency circuits, higher-speed designs often require a combination of capacitor values targeting different frequency ranges. The article emphasizes using a variety of capacitor sizes, including smaller, high-frequency capacitors placed close to the power pins of integrated circuits to effectively suppress high-frequency noise and ensure stable operation. Ultimately, effective decoupling requires understanding the circuit's characteristics and choosing capacitor values accordingly, rather than relying on a "one-size-fits-all" solution.

  The blog post "Proper Decoupling Capacitor Practices, and Why You Should Leave 100nF Behind" argues that while the traditional practice of using 100nF (0.1µF) capacitors for decoupling integrated circuits (ICs) has been a long-standing rule of thumb, it's no longer the optimal solution in many modern digital circuit designs. The author contends that a deeper understanding of the underlying principles of decoupling and the specific needs of contemporary ICs calls for a more nuanced approach.

  The core function of a decoupling capacitor is to provide a localized source of current for the IC, mitigating voltage fluctuations caused by rapid changes in current demand during switching operations. These fluctuations, often referred to as noise or ripple, can disrupt the proper functioning of the IC and other components in the circuit. Traditionally, 100nF capacitors were considered adequate for this task. However, with the advent of faster switching speeds and higher clock frequencies in modern digital circuits, the frequency content of this noise has shifted upwards. The author explains that the impedance of a capacitor decreases with increasing frequency. Therefore, a capacitor that presents a low impedance at lower frequencies (like a 100nF capacitor) may exhibit a significantly higher impedance at the higher frequencies characteristic of today's high-speed digital systems. This higher impedance renders the capacitor less effective at filtering out high-frequency noise.

  The article emphasizes that the optimal decoupling strategy involves using a combination of capacitors with different values, effectively creating a "ladder" of capacitance. This approach leverages the unique impedance characteristics of different capacitor types across a wider frequency range. Specifically, the author advocates for including smaller value capacitors, such as 10pF or 100pF, placed physically closer to the IC's power pins. These smaller capacitors, while having lower overall capacitance, exhibit lower impedance at higher frequencies, effectively suppressing the high-frequency noise that the larger 100nF capacitor might miss. Larger capacitors, like the traditional 100nF and even larger values in the microfarad range, remain important for handling lower frequency noise and providing bulk capacitance for transient current demands.

  The author further delves into the practical considerations of capacitor selection, such as Equivalent Series Resistance (ESR) and Equivalent Series Inductance (ESL). These parasitic elements can significantly impact the capacitor's performance at higher frequencies. Lower ESR and ESL values are generally desirable for effective decoupling. The physical placement of the capacitors is also highlighted as crucial, emphasizing the importance of minimizing the inductance of the connection between the capacitor and the IC's power pins. Short and wide traces are recommended to minimize this inductance.

  In conclusion, the post advocates for a shift away from the blind application of the 100nF decoupling capacitor rule. Instead, it encourages a more deliberate and informed approach based on understanding the frequency characteristics of the noise being suppressed and the impedance properties of different capacitor values. The author champions a multi-capacitor decoupling strategy utilizing a range of capacitor values, including smaller capacitors placed very close to the IC's power pins, to effectively address the broader spectrum of noise present in modern high-speed digital circuits. This, they argue, ensures more robust and reliable circuit operation.

  • Decoupling Capacitors
  • Electronics
  • Hardware Design
  • PCB Design
  • circuit design
  • Capacitance
  • Noise Reduction
  • Signal Integrity
  • Embedded Systems
  • 100nF Capacitor
  • best practices
  • Hardware Engineering

  Summary of Comments ( 68 )
  https://news.ycombinator.com/item?id=42830948

  Verbose tl;dr

  Hacker News users discussing the article about decoupling capacitors generally agree with the author's premise that blindly using 100nF capacitors is insufficient. Several commenters share their own experiences and best practices, emphasizing the importance of considering the specific frequency range of noise and choosing capacitors accordingly. Some suggest using a combination of capacitor values to target different frequency bands, while others recommend simulating the circuit to determine the optimal values. There's also discussion around the importance of capacitor placement and the use of ferrite beads for additional filtering. Several users highlight the practical limitations of ideal circuit design and the need to balance performance with cost and complexity. Finally, some commenters point out the article's minor inaccuracies or offer alternative explanations for certain phenomena.

  The Hacker News thread linked has several comments discussing the original blog post about decoupling capacitors. Many of the comments delve into the nuances and practical considerations not fully explored in the blog post itself.

  A significant point of discussion revolves around the practicality of the author's advice. One commenter points out that while striving for ideal decoupling is theoretically sound, real-world constraints often necessitate compromises. They mention that factors like board space, component availability, and cost can influence decisions, sometimes making the "perfect" solution impractical. This leads to a discussion about the "good enough" approach, where engineers aim for adequate decoupling rather than striving for theoretical perfection.

  Another commenter raises the issue of the author's focus on digital circuits. They argue that the recommendations might not be universally applicable, particularly for analog circuits where noise considerations are significantly different. They suggest that applying the author's advice indiscriminately could lead to suboptimal results in analog designs.

  Several commenters discuss the importance of considering the entire signal path. They emphasize that decoupling capacitors are only one part of the puzzle and that proper layout, grounding, and component selection all play crucial roles in minimizing noise and ensuring signal integrity. One comment specifically highlights the importance of minimizing the inductance between the decoupling capacitor and the component it's serving, emphasizing the importance of placing the capacitor as close as possible.

  There's a thread discussing the use of ferrite beads in conjunction with decoupling capacitors. Commenters debate the effectiveness of ferrite beads, with some arguing for their use in specific situations while others express skepticism about their benefits. This leads to a discussion about the importance of understanding the impedance characteristics of different components and how they interact within a circuit.

  Finally, some commenters offer additional resources and further reading on the topic of decoupling capacitors, providing links to application notes, articles, and textbooks. This suggests a general interest in the topic and a willingness to explore it in more depth. The shared resources indicate that the discussion sparked a desire for continued learning and a deeper understanding of the complexities of decoupling in electronic circuits.