In today’s electronic engineering landscape, the demand for high-speed design has never been higher. With interfaces like USB-C, WIFI, DDR, MIPI, and others becoming cornerstones of tomorrow’s products, designers need to have an understanding of what high-speed signals are and the challenges they pose.
In this series we will delve into some of the important considerations required to make these designs successful.
Welcome back to our series on High Speed PCB design. In the previous article, we explored some common mistakes in high speed routing. In this article, we will discuss simulation of high speed designs, specifically what tools are available and what simulation techniques they offer.
Choosing the Right Tool for The Job
Simulation can be a great tool to help check over the design before fabricating a prototype. Several software packages cater to different aspects of high-speed design testing, each offering unique capabilities that address specific challenges in this field.
One of the leading tools for high-speed design is HyperLynx. It provides an accessible yet powerful solution for high-speed PCB analysis. HyperLynx offers automated workflows for signal integrity, power integrity, and EMI analysis, making it suitable for engineers who may not be experts in those areas. Its ease of use and integration with PCB layout tools make it an attractive option for small to medium-sized teams focused on rapid design cycles.
Keysight’s Advanced Design System (ADS) provides comprehensive simulation capabilities, including time-domain reflectometry (TDR), eye diagram analysis, and S-parameter analysis. These features are essential for assessing signal integrity, detecting reflections, and optimizing impedance matching. ADS is particularly favored in RF and microwave designs but is also widely used for high-speed digital applications.
Another popular software package is Ansys HFSS, known for its high-frequency electromagnetic simulation capabilities. HFSS is invaluable for analyzing signal integrity in complex 3D structures, such as vias, connectors, and package transitions. It excels in providing detailed insight into crosstalk, EMI, and power integrity. HFSS is often used in conjunction with Ansys SIwave, which focuses on PCB and IC package analysis, offering end-to-end high-speed design validation. Together, these tools provide a holistic approach to managing the electrical performance of high-speed designs.
Cadence Sigrity is another prominent player in the high-speed design software space, offering a range of tools for signal integrity and power integrity analysis. Sigrity’s strengths lie in its ability to perform comprehensive signal and power analysis on complex PCB designs. It integrates well with Cadence’s Allegro PCB design suite, allowing seamless data exchange between layout and simulation environments.
Examples of Porticos projects utilizing PCB layouts.
Signal Integrity Analysis
There are a few different methods to analyze signal integrity.
Transient simulations capture the time-varying behavior of signals, useful for observing waveform quality, reflections, and overshoot.
Eye diagrams are often generated from these simulations. An eye diagram is a powerful visualization tool used in high-speed digital and communication system analysis to assess the quality of a transmitted signal. It is generated by overlaying multiple bits of a signal on a single plot, forming an image that resembles an open eye. The clarity of the eye pattern provides insights into signal integrity issues such as jitter, noise, and timing errors. A well-defined eye opening indicates a clean signal with minimal distortion, while a closed or distorted eye suggests potential problems that could lead to data errors. Below is an example of an eye diagram. It can be an invaluable tool to analyze signal integrity before the design is fabricated.
Frequency-Domain (S-Parameter) Simulations analyze how signals behave over a range of frequencies. It helps assess insertion loss, return loss, and crosstalk in interconnects, connectors, and transmission lines. This can be especially useful in tracking down noise sources and testing out mitigation strategies.
Finally, Time-Domain Reflectometry simulates how a pulse reflects along a transmission line, helping to identify impedance mismatches and discontinuities.
Power Integrity Analysis
When it comes to high speed importance, power integrity is critical for many high speed circuits to ensure good performance. Luckily there are simulation techniques to help analyze this.
DC Drop Analysis Examines voltage drops across the power distribution network (PDN) to ensure that all components receive stable voltage. This can help catch power bottlenecks like too few vias on a power supply output or a thermal relief connection that’s not thick enough.
Conversely, AC analysis evaluates the power plane’s ability to supply stable power at high frequencies, considering the impact of decoupling capacitors and the overall PDN impedance.
Electro-Magnetic Interference (EMI) Simulations
When it comes to EMI, there are typically 2 main simulation types: radiated and conducted emissions analysis.
Radiated emissions analysis predicts the levels of EMI that a design might emit, helping to ensure compliance with regulatory standards like FCC or CE.
Conducted emissions analysis assesses noise that may propagate through power or signal lines, which could affect the performance of nearby circuits or systems. Unlike other design constraints, these performance characteristics are strictly regulated by governments around the world. Meeting EMC guidelines is critical to the successful launch of a product.
Oftentimes, EMI issues are challenging to fix. Testing is typically done at an external lab because the equipment is large and expensive and fixes often involve changing things like power or signal routing which are tied into the layout.
Conclusion
Selecting the right testing software for high-speed design depends on the specific needs of the project and the expertise of the engineering team. Tools like ADS and HFSS provide deep, specialized analysis, while solutions like Sigrity and HyperLynx offer comprehensive and integrated workflows. By leveraging these tools, engineers can identify and address potential SI, PI, and EMI issues.
While simulation is a good tool it’s important to remember that there is no substitute for the real thing. Even a well setup simulation will not be able to account for every possible factor in the design. That said, simulation can be a good way to identify problems ahead of time, test out possible solutions, and ultimately deliver a successful product.
Do you need help developing simulations for your PCB implementation? Remember that Porticos has a team of engineers to help you with your design and implementation. Get in touch to learn more.
