Impedance Calculations and Control in Altium Designer

Impedance in your traces becomes a critical parameter to consider during high speed or high frequency design. An impedance mismatch between a signal source, load, and the trace that connects them cause problems like ringing, noise coupling, and EMI. Instead of using a homemade tool to work out the impedance of each trace in your PCB, Altium Designer incorporates PCB impedance calculations as part of your design rules. You’ll be able to manage the impedance throughout your board based on the stackup you need for your next PCB.

ALTIUM DESIGNER

A unified, heavily rules-driven PCB stackup impedance calculator and design platform.

Starting out working with high speed devices forces you to relearn everything you thought you knew about PCB design. Impedance mismatches are something of an afterthought in low speed devices, and all you worry about is getting your signals from point A to point B. But as your PCBs become more advanced, your components switch faster, and you incorporate more layers into your stackup, impedance mismatch can ruin your device.

The impedance of the traces in your PCB depends on their geometry, material, and arrangement. Their configuration within the board also affects the impedance seen by signals in your traces. Edge-coupled, embedded, and offset trace arrangements all have variations in their impedance values, and you’ll need design software that can account for the impedance of these different geometries.

A number of equations are used to define and calculate various design parameters in PCBs, just like any other area of engineering. These equations must account for everything from the substrate dielectric properties to the thickness of layers and geometry of your traces. No one has time to memorize every single impedance formula for traces in a PCB. Instead, great design software will allow you to incorporate these calculations as part of your design rules.

Controlling Impedance with the Right Stackup

Your stackup plays an important role in determining the impedance seen by your signals. Neighboring signals act like groups of capacitors and inductors that are coupled by the PCB substrate, and these parasitic elements affect the impedance seen by your signals. However, if you can get your stackup just right, you can control the impedance seen by signals in your traces.

Getting your stackup just right means that you need software that lets you fully customize your layer stack, right down to selecting the appropriate dielectric constant for your board layers. A stackup manager that links to material library helps greatly as you can choose from common board materials when planning your stackup. Combined with the numerous other built-in tools, you can select for the right ground plane thickness, dielectric constant, copper foil layout, and define the best trace arrangement for your board.

How Design Rules Help Control Impedance

Your design rules aren’t there to constrain creativity, and they’re meant for more than just checking component placement for the PCB stack-up. Certain features like vias and traces have important geometric rules that should be followed in order to ensure your signals don’t degrade. PCB design software with powerful rules checking engine helps you avoid design errors that can hamper signal integrity. You can rest assured that your device works properly as designed once it leaves the production line.

Impedance mismatch between components and traces, via placement, trace length matching and spacing, copper foil and circuit board thickness, and many other design parameters should be customizable in your PCB, allowing you to control the impedance seen by your signals. Following these specifications means that your PCB software needs to include an impedance calculation tool that is incorporated as part of your design rule.

• Controlling impedance requires advanced design rule checking and routing tools that are only available in the best PCB design software.Learn more about controlled impedance routing.
• Impedance controlled design requires specifying tight tolerances on your layer, trace arrangement, and trace geometry. Great PCB design software makes all of this easy.

  Learn more about design rules for trace routing and layout.

• If you must terminate certain elements in your PCB, there are a number of standard termination methods that you should use, depending on your design Learn more about termination methods for your high speed/high frequency PCBs.

Rules and constraints editing in Altium Designer

Impedance Calculations as Part of Your Design Rules

If you start searching for impedance calculators on the internet, you’ll find plenty of options that can help you get an idea of the appropriate trace geometry and layer stack that help you manage impedance. Unfortunately, these calculators will never interface with your design rules, and you’ll have to check the impedance of every single trace manually. Keeping a trace impedance calculator around can be useful for planning your board design, but they make verification unwieldy.

Instead, your printed circuit board design software should include trace impedance calculation as part of your design rules. These calculations need to take into account the material properties of the layers in your stackup, the geometry of your traces, and their arrangement on the board. Since different trace impedance calculations include different approximations, you’ll need the ability to customize the equation used to define the impedance of your traces, depending on your application.

Accurate Impedance Calculations

Working with software that includes impedance calculations as part of your design rules allows you to automatically check that the impedance in your traces is properly controlled. You won’t have to manually check every single trace. Instead, you can specify the calculation you need for your trace arrangement and substrate, and you can automatically check that your arrangement provides the impedance value you need.

Instead of writing down calculation results from an external calculator and manually defining each thickness or trace geometry, your PCB design software should integrate these capabilities into your design rules and automatically check your impedance values during design. You’ll see a major productivity boost as this critical yet simple verification step is automated. Your design rules should make it easy to set the appropriate constraints for your trace impedance.

• Your stackup affects your trace impedance, and you can take advantage of this to control impedance throughout your board.Learn more about your layer stackup and how it affects trace impedance.
• Controlling impedance is just one aspect of high speed design that helps ensure signal integrity throughout your board.Learn more about maintaining signal integrity in high speed design.
• Making sure your signals remain clean takes the right analysis and error checking tools in your PCB design software.

  Learn more about error checking features in your PCB design software.

Defining impedance calculations for your layer stack in Altium Designer

Unifying Signal Integrity Tools in a Rules-Driven Environment

When you need to control the impedance of single-ended or differential traces in your PCB, you’ll have to use a number of design tools that each focus on a different aspect of your final PCB. Working with design software that separates tools into different windows and enforces different workflows reduces your productivity, making it difficult to address what should be simple design issues.

Your design tools, design rules, component models, and simulation packages should be placed in an integrated environment with a consistent workflow. Tools in this environment are designed to pass data between each other in a consistent format, reducing errors in communication between design tools. Features in this environment are all accessible from a single program, and new features can be easily added to your design software as extensions.

The Unified Design Environment in Altium Designer

Design rules checking features in your PCB design software need to be integrated with the rest of your design tools, helping ensure your device will work exactly as designed. This type of unique communication between design tools is only possible when you work in a fully unified design environment. Altium Designer is the only PCB design software package that runs on a heavily rules-driven design engine, and all your design verification features interface with your design tools in a single interface.

The rest of the PCB design industry still separates your critical design, management, and verification features into separate programs with different workflows. Instead of working in a tired design paradigm, it’s time to take the plunge into a unified design environment. It’s time to try Altium Designer.

• At the core of Altium Designer is a rules-driven design engine. This unique architecture means that all your design tools communicate using the same language, which prevents data errors that are common in other design programs.Learn more about the rules-driven design engine in Altium Designer.
• Your layer stackup manager is critical for controlling impedance throughout your board. Your layer stack manager should allow you to customize your board arrangement and define the impedance required for your application.Learn more about customizing your layer stack for impedance control in Altium Designer.
• Signal analysis tools allows you to diagnose and solve signal problems that aren’t anticipated in your design rules. The best way to check your signal integrity is to use a simulation package that is integrated with the rest of your design features.Learn more about signal integrity analysis in Altium Designer.

If you’re tired of working with separated design tools in different programs and interfaces, you need to work with a unified design platform. This design paradigm integrates all your design tools into a single interface. Only a unified PCB design environment gives you full control over impedance in your board by integrating your design rules and accurate impedance calculations. These important features ensure that your next high speed device won’t fall victim to signal problems like noise coupling, ringing, signal reflection, or EMI.

Instead of scouring the internet every time you need help, you can get access to all the design support you need directly from Altium. Everyone that uses Altium Designer can access the AltiumLive forum, podcasts with professional designers, a thorough knowledge base, and webinars provided by industry experts. Altium doesn’t leave you to design alone and provides with all the support you need.

The best design, rules checking, and simulation features will ensure that your next PCB will work as designed and will not fall victim to signal integrity problems. Only Altium Designer gives you access to all these tools and many more in a single software package. These tools work together as part of a single platform that is governed by a rules-driven engine. Instead of guessing at best trace geometry for your next PCB, Altium Designer can help you get it right the first time.