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

    With RF Circuit Impedance in Mind Your Designs Won't Look Bird-Brained

    Altium Designer
    |  March 30, 2018

    Bird comprised of circuit boards

    Several years ago, scientists compared the aerodynamic characteristics of several bird species with different species of bats. Feathered bird wings become inactive during the upstroke and maintain lift. Every downstroke increases thrust, lift, and flight speed. In contrast, bats have membranous wings that produce lift during the upstroke. Regardless of their methods, birds and bats overcome weight and drag to achieve flight efficiency.

    Two different wing designs and two different flight methods produce the lift-to-weight and lift-to-drag ratios needed for flight. Each amount of wing, body, and induced drag produces an energy cost. Certain characteristics—such as body shape—impact the energy costs for bats. Because wing actions generate less lift, bats fly slower and at shorter distances than birds.

    Similarly, a PCB, regardless of its design, will have to work toward its energy needs. There are several characteristics which may lead to impedance within a circuit that a board may maintain, and it is your job to understand what may cause these drags and keep your design from lifting up and flying high.

    Don’t Let Resistance, Reactance and Impedance Drag You Down

    Energy costs in PCB design increase because of the effect of resistance, reactance, and impedance. Resistance opposes a steady electric current. Resistive power results in an energy cost.

    Reactance measures the opposition to AC electricity caused by a capacitance or an inductance with reactive power storing energy in electrical and magnetic fields. While a perfect resistance does not vary with frequency, the impact of changing frequencies on a capacitor or an inductor causes reactance to change with frequency.

    At this point, the impact of the relationships between reactance, impedance, and frequency on PCB design become more apparent. The impedance of a capacitor has an inverse proportional relationship to capacitance while the impedance of an inductor has a direct relationship with inductance.

    RF Circuit Impedance: My, What Large Ears You Have!

    The very part that makes a bat special—protruding ears—increases the parasitic drag that reduces energy. Impedance—if not treated correctly—has a dramatic impact on circuit performance. You can impact impedance by working with the thickness and width of trace conductors, the thickness of the dielectric substrate, and the dielectric constant of the substrate impact impedance.

    Sudden changes in trace direction can cause changes in impedance. Dielectric constant can change across the length or width of a PCB. Changes in frequency and temperature also cause the dielectric constant to change. Each variance affects the characteristic impedance of an RF circuit.

    Close-up of circuit
    You’ll need to keep careful track of the sources for impedance in your circuit.

    Treating impedance correctly involves several key points. 50-Ω impedance represents the sweet spot for efficient signal transfer. If you achieve a characteristic impedance of 50-Ω in your circuit design, RF signal power transfers efficiently from the source to the load. Few signal reflections occur.

    In high-frequency circuits, mismatched impedances between the source and the load harm performance. Reflections and standing waves in high-frequency lines blend with desired signals and distort both amplitude and phase.

    As the distance from source to load increases, standing waves also cause impedance to ebb and flow. Varying values of impedance can exist because of trace design or the materials used in the trace. If the variances increase, the changes in impedance can lower signal gain, generate noise, or cause random errors.

    Say Hello to Controlled Impedance

    Judging the flight performance of a bird or bat becomes a matter of perspective. Birds may need to migrate farther and cannot afford to have energy costs take away from speed or endurance. Bats may fly slower but use other tools to locate food.

    Digital circuits deliver desired performance because of short transition times and high-clock rates. Devices and appliances have better capabilities because of the faster, sequential transfer of signals. Constantly increasing signal switching speeds requires another look at controlling the impedance of the transmission lines/PCB traces.

    Because of those factors, PCB designs require strict values and tolerances for traces. You should use good PCB design techniques to achieve a 50 Ω impedance at transmission line junctions, component connections, and terminators. Matching the impedances throughout the circuit yields a desired low voltage standing wave ratio (VSWR). Circuits with a low VSWR transfer the maximum amount of power from the source to the load.

     Collage of different circuit boards
    Ensure that your designs are working as intended by following design best practices.

    I use careful planning to achieve matched impedances within complex RF circuit designs that have broad operating frequencies. Good PCB design software enables me to work with these complex designs with ease by giving me the tools necessary to succeed and having an intuitive interface in which to use them.

    A strong choice for software, Altium Designer® has tools like a Signal Integrity analysis engine which allows you to match component impedances and use routing to control impedances. As well as use the software to select the signal and plane layer order, the thickness of the copper and dielectric, and the dielectric constant.

    If you’d like to consult more about circuit impedance, consider talking to an expert at Altium to learn more.

    About Author

    About Author

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

    most recent articles

    Back to Home