Transmission Line (TL) Effects



Transmission line (TL) effects are one of the most common causes of noise problems in high-speed DSP systems. When do traces become TLs and how do TLs affect the system performance? A rule-of-thumb is that traces become TLs when the signals on those traces have a rise-time (Tr) less than twice the propagation delay (Tp). For example, if a delay from the source to the load is 2nS, then any of the signals with a rise-time less than 4nS becomes a TL. In this case, termination is required to guarantee minimum overshoots and undershoots caused by reflections. Excessive TL reflections can cause electromagnetic interference and random logic or DSP false-triggering. As a result of these effects, the design may fail to get the FCC certification or to fully function under all operating conditions such as at high temperatures or over-voltage conditions.


Transmission Line Propagation Delay Characteristic Impedance Multiple Load Signal Trace 
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  1. 1.
    Hall S, et al (2000) High Speed Digital System Design. John Wiley & Sons, New York.Google Scholar
  2. 2.
    Texas Instruments Inc (2003) OMAP5912 Applications Processor Data Manual.
  3. 3.
    Mentor Graphics (2004) Hyperlynx Signal Integrity Simulation software.

Copyright information

© Springer US 2010

Authors and Affiliations

  1. 1.Texas Instruments IncorporatedStaffordUSA

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