Trace Impedance Calculations as Design Rules in Altium Designer
If you’re designing a high speed, high frequency or mixed signal board, you’ll need to pay careful attention the impedance of your traces while routing. Impedance mismatch between sources and loads can lead to signal problems that compromise data integrity and lead to noise in your board. Who wants to work out the impedance of every trace configuration by hand? Instead of using paper and pencil, you can take advantage of the rules-driven environment in Altium Designer to ensure your traces are routed with the right impedance.
TOPICS IN THIS SOLUTION
A unified, rules-driven PCB design program that includes an PCB impedance calculator.
There is a saying among the high speed design community: there are those have signal integrity problems and those that will soon have signal integrity problems. Once TTL was introduced, switching between logic states became fast enough that everyone needed to take steps to ensure signal integrity in their traces. Impedance mismatch between traces used to be tolerable as only longer traces acted as transmission lines and those that did act as transmission lines could be easily terminated with a resistor and/or capacitor.
Nowadays, as components include higher pin counts, are routed through multiple layers in the stackup, and trace density has increased, ensuring your traces have a defined impedance is critical to ensuring your signals remain clean and transmission line effects can be avoided. Using the right multi-layer stackup and maintaining the right trace geometry are critical to maintaining signal integrity throughout your device.
Working with the right PCB design software will help ensure that you can maintain signal integrity throughout your PCB without manually defining the geometry of every single trace in your device. Altium Designer includes a trace width impedance calculator as part of your design rules, making impedance controlled routing quick and easy.
Trace impedance depends on a number of variables, including material properties, the geometry of the trace, and its arrangement with respect to its reference plane arrangement. Microstrip, stripline, and offset trace arrangements all produce different impedance values, and your design software should give you tools to account for any impedance calculation for these different arrangements.
Third party impedance calculators that you might find on the internet can help you get an idea of the best trace geometry, arrangement, and layer stack that help you control impedance in your board. However, these calculators will never interface directly with your PCB layout software as part of your design rules. You’ll still be stuck checking the impedance of every trace on your board, even if you use automated or interactive routing.
Controlling Impedance With Your Design Rules
While you can’t change the laws of physics or modify the real equations that define impedance of your traces and vias, the right design software lets you control how your board is routed based on desired impedance values. When your software is built on the back of single rules-driven design engine, trace impedance calculations can be included as an integral part of your routing tools, ensuring your trace impedance will always take a desired value.
Your design rules are meant for more than just checking routing parameters, component placement, and connections between components. They make it easy to verify your design as you layout your board, and you can immediately see if your design needs to be changed. This helps you avoid design errors that can ruin signal integrity, ensuring your device works properly as soon as it leaves the production line.
- The best PCB design software integrates interactive routing with trace impedance calculations, making controlled impedance routing easy. Learn more about controlled impedance routing.
- Your layer stackup plays an important role in your impedance calculations and in controlling the impedance in your board. Learn more about how your PCB layer stack affects impedance.
- An autorouter can be a useful tool that saves you time and energy when routing your board. Any autorouter needs to interface directly with your design rules when laying traces. Learn more about using an autorouter for PCB layout.
Defining trace impedance as a design rule in Altium Designer
Design verification is quick and easy when your PCB design software includes a trace width impedance calculator as part of your design rules. These calculations need to take into account the layer stackup arrangement, trace geometry, location of reference planes, and the arrangement of traces on the board. You’ll need the ability to customize the equation used to define the impedance of your traces.
Once you’ve used an interactive routing tool to place your traces, a great signal integrity package allows you to diagnose crosstalk between neighboring traces and inform your design going forward. You can quickly check for any problems resulting from crosstalk or minor impedance mismatches among traces when you use the right signal integrity package within your PCB design software.
Signal Integrity Verification
Incorporating impedance calculations as part of your design process doesn’t require an iterative process. When your design software is built on a single rules-based engine, the required trace impedance is determined automatically. The software determines the required trace width and tolerances automatically, and the required impedance, spacing, and geometry are immediately verified as soon as you layout a trace.
Once you’ve defined your required impedance and its tolerances, and once you’ve laid out your traces, you can use a great signal integrity package to check that your signals are free of ringing or cross talk. Altium Designer allows you to run simulations with different proposed termination methods and compare the results side-by-side. You can easily determine which termination scheme has the greatest benefit on signal integrity.
- Signal integrity simulations are also critical for high speed design. The right simulation package makes it easy to assess all aspects of signal integrity. Learn more about the best signal integrity package for high speed design.
- A trace width impedance calculator will naturally interface with interactive routing tools in your PCB design software. Learn more about interactive routing in your PCB design software.
- Even though most people worry about trace geometry, they also need to worry about their stackup and trace arrangement with respect to a reference plane. Learn more about how your layer stackup affects trace impedance.
Signal integrity simulation in Altium Designer
Ensuring signal integrity with the right design tools is easiest when you have access to design tools that can be used to control impedance on all of your signal nets. When your desired impedance and tolerance are encoded as design rules and constraints, you won’t have to go back and check your design at each step of the process. You need a design package that gives you these standard features in a single program.
Layout, component management, and simulation tools are most useful when they are placed in an integrated environment that enforces a consistent workflow and interfaces with your design rules. An integrated environment means that all your design features operate using a single data structure and are accessible in a single interface. Only Altium Designer enforces this type of workflow for PCB design, allowing you to reclaim your productivity and design with confidence.
Altium Designer’s Unified Design and Layout Environment
Rules checking features in your design software were created to ensure that your design and layout choices will meet critical design standards, ensure signal integrity, and meet impedance tolerances. When you work in a unified design environment, your rules checking features form the foundation of your design, simulation, and management tools, and all within a single program.
PCB design no longer requires separating multiple features into multiple design tools, and you shouldn’t have to purchase critical tools for modern PCB design as add-ons. Everyone else in the PCB design industry still separates your critical design, simulation, and management tools into separate programs. Altium Designer knows that your workflow is more productive when you have access to the tools you need in a single environment.
- A rules-driven design engine forms the core of Altium Designer. This unique software architecture enforces a consistent language for all of your design tools, helping to prevent data errors that are common in other design programs.Learn more about unified, rules-driven design in Altium Designer.
- If you want to control the impedance of your traces, you need a design rules editor that interfaces directly with your layer stack manager. This lets you customize your design rules and constraints for any application.Learn more about your layer stack and impedance control in Altium Designer.
- No one can anticipate every possible signal integrity problem. The best way to check your signal integrity is to use a signal integrity simulation package that is integrated with the rest of your design features.Learn more about analyzing signal integrity in Altium Designer.
The days of cobbling together multiple verification tools and switching between design features in different programs are over. You can take full control over impedance in your board when accurate impedance calculations are integrated directly into your design rules and layout features. If you’re tired of working with design software that separates your design tools into different programs, you need to work with the only unified PCB design package on the market.
If working in a rules-driven environment sounds like a difficult challenge, you can rest assured that Altium will stand by your side and give you the resources you need to succeed. Altium Designer users can access the AltiumLive forum, podcasts delivered professional designers, a thorough knowledge base, and design webinars. Altium provides the support you need to reach success.
The best design, verification, and simulation features are included as standard features in Altium Designer. You won’t have to search the internet for a trace width impedance calculator to control impedance and prevent signal integrity problems. Unlike other design packages, Altium Designer includes these tools and many more in a single software package. Avoid the guesswork and get the perfect trace geometry in every design with Altium Designer.