Free Trials

Download a free trial to find out which Altium software best suits your needs

How to Buy

Contact your local sales office to get started on improving your design environment

Downloads

Download the latest in PCB design and EDA software

  • PCB DESIGN SOFTWARE
  • Altium Designer

    Complete Environment for Schematic + Layout

  • CircuitStudio

    Entry Level, Professional PCB Design Tool

  • CircuitMaker

    Community Based PCB Design Tool

  • NEXUS

    Agile PCB Design For Teams

  • CLOUD PLATFORM
  • Altium 365

    Connecting PCB Design to the Manufacturing Floor

  • COMPONENT MANAGEMENT
  • Altium Concord Pro

    Complete Solution for Library Management

  • Octopart

    Extensive, Easy-to-Use Component Database

  • PRODUCT EXTENSIONS
  • PDN Analyzer

    Natural and Effortless Power Distribution Network Analysis

  • See All Extensions
  • EMBEDDED
  • TASKING

    World-Renowned Technology for Embedded Systems Development

  • TRAININGS
  • Live Courses

    Learn best practices with instructional training available worldwide

  • On-Demand Courses

    Gain comprehensive knowledge without leaving your home or office

  • ONLINE VIEWER
  • Altium 365 Viewer

    View & Share electronic designs in your browser

  • Altium Designer 20

    The most powerful, modern and easy-to-use PCB design tool for professional use

    ALTIUMLIVE

    Annual PCB Design Summit

    • Forum

      Where Altium users and enthusiasts can interact with each other

    • Blog

      Our blog about things that interest us and hopefully you too

    • Ideas

      Submit ideas and vote for new features you want in Altium tools

    • Bug Crunch

      Help make the software better by submitting bugs and voting on what's important

    • Wall

      A stream of events on AltiumLive you follow by participating in or subscribing to

    • Beta Program

      Information about participating in our Beta program and getting early access to Altium tools

    All Resources

    Explore the latest content from blog posts to social media and technical white papers gathered together for your convenience

    Downloads

    Take a look at what download options are available to best suit your needs

    How to Buy

    Contact your local sales office to get started improving your design environment

    • Documentation

      The documentation area is where you can find extensive, versioned information about our software online, for free.

    • Training & Events

      View the schedule and register for training events all around the world and online

    • Design Content

      Browse our vast library of free design content including components, templates and reference designs

    • Webinars

      Attend a live webinar online or get instant access to our on demand series of webinars

    • Support

      Get your questions answered with our variety of direct support and self-service options

    • Technical Papers

      Stay up to date with the latest technology and industry trends with our complete collection of technical white papers.

    • Video Library

      Quick and to-the-point video tutorials to get you started with Altium Designer

    PCB Design Guidelines for Controlled Impedance Routing

    Altium Designer
    |  July 16, 2018

    Alaska with a cellphone reception on it. Polar impedance.

    In June 1831, Sir James Clark Ross discovered the North Magnetic Pole on the Boothia Peninsula in Northern Canada. While the term “discovery” seems to indicate that the North Magnetic Pole is static, the North and South Magnetic Poles, in fact, move continuously. The Earth’s magnetic field changes over time and as those changes occur, the positions of the poles also shift. Given the rate of movement at 55 km per year, we may have another meaning for “polar express.”

    When working through the travel of signals in your PCB, though, you might not have the time, money, or energy to worry through the investment of traveling from one polar tip to the other. Trace routing and trace width are important to keep in mind; however, the traces on your circuit board’s power plane can make keeping track of differential impedance difficult. Learning more about how to make the most of your PCB design software for traces and controlled impedance routing can help.

    Exploring Complex Impedance

    In terms of impedance, the concept of “polar” involves a different type of exploration. Complex impedance is an important tool for working with multi-component AC circuits. Instead of using sines and cosines to represent voltages and currents in those circuits, we can express impedance as a complex exponential or . Impedance works as the voltage/current ratio for a single complex exponential at a particular frequency.

    From there, we can express the impedance of individual circuit elements as pure or real imaginary numbers. With this, the purely imaginary reactive impedance of an ideal inductor is:

    Meanwhile, the purely imaginary reactive impedance of an ideal capacitor appears as:

    Moving to pure or imaginary numbers requires using a complex plane with resistance along the real axis. Here, the reactance values of the capacitor and an inductor become imaginary numbers. The imaginary impedance provides the reactive component of the impedance and allows us to evaluate changes in phase that occur due to the reactance.

    With series combinations of RL and RC components, we can add the component values as components of a vector. As complex numbers, those values have the same units as resistance. If we want to add two impedances, using complex numbers allows us to add the real and imaginary .

    Polar Form of Complex Impedance

    The polar form of complex expressions for RL and RC circuits appears as a two-dimensional coordinate system that illustrates the relationship between the amplitude and phase of the voltage and current. Each point on a plane is a given distance from a reference point and a given angle from a reference direction. The reference point functions as the pole, while the ray from the pole in the reference direction refers to the polar axis. The distance from the pole equals the radial coordinate or radius, while the angle represents the polar angle.

    In the polar form, the magnitude of the complex impedance equals the ratio of voltage amplitude to the current amplitude. The phase of the complex impedance equals the phase shift of the current ahead of the voltage. In equation form, impedance appears as:

    The magnitude represents the ratio of the voltage difference amplitude to the current amplitude. The argument Ɵ gives the phase difference between the voltage and current, while represents the imaginary unit. Using the polar form for complex impedance simplifies multiplication and division of impedance quantities.

    Screenshot of traces laid out in Altium

    Being able to plan your traces for controlled impedance routing is necessary

    PCB Impedance Control

    Our very brief discussion of complex impedance and the polar form of complex impedance underlines both the mathematical complexity involved with calculating impedance and tough problems that we encounter with impedance control in PCB design. With multi-layer high-frequency circuits consisting of numerous vias and branches acting as transmission lines, the problem becomes even tougher due to the potential for energy reflection between the source and the load. No matter the type or complexity of the circuit, maximum signal transfer only occurs if all impedances along the signal path match.

    Using best design practice in your circuit board can make it so that your traces are routed properly and impedance can be matched properly. To match the output impedance of the source, the trace impedance, and the input impedance of the load:

    • Match component impedance
    • Measure trace characteristics such as length, width, and thickness
    • Use microstrips to achieve the desired impedance

    Controlled Impedance Routing and Altium Designer®

    Altium allows you to analyze the signal integrity of your PCB design at the schematic capture stage. You can also define the supply nets and use the Tools menu to provide average track impedances and route lengths. Altium offers a straightforward solution for impedance matching the components within your design. With , you can also analyze the reflection on selected nets and experiment with different terminator values.

    To determine the routing impedance, you can use one of two formulas found in Altium . The first allows you to determine the characteristic impedance of a microstrip, while the second provides the characteristic impedance formula for a stripline. Both equations show the dielectric thicknesses, the routing width, and the dielectric constant of the dielectric material.

    Screenshot of Altium ’s  working through trace routing

    Trust your PCB design software to help map your traces efficiently and effectively

    Altium further simplifies this task with its Characteristic Impedance Width option. With this option, you can establish the Routing Width Design rule within the PCB Rules and Constraint Editor and then enter your required impedances. The Characteristics Impedance Width option automatically translates the required impedances into widths for each signal layer. Interactively controlled, Altium ’s impedance routing feature automatically adjusts the track width for the required impedance.

    To learn more about controlled impedance routing and component impedance matching for your high-speed PCB design, talk to an expert at Altium.

    About Author

    About Author

    PCB Design Tools for Electronics Design and DFM. Information for EDA Leaders.

    most recent articles

    Back to Home