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More about decoupling and bypass capacitors, power-supply rails, models, and their interactions (Part 5.5)

Editor’s Note: In 2007, we published a four-part series on bypass capacitors and decoupling that was very popular with the design audience (links below). Now, one of the authors of Part 4 , Kendall Castor-Perry, extends the series with six more sections which explore interactions between supply and capacitor, capacitor materials, and simulation models. This very practical extension blends theory and measurements, and its lessons not only will improve your knowledge but help you minimize problems, some of which can be very subtle and difficult to diagnose and solve.

For various reasons, they are presented to you as linked pdf files, one per week, with the corresponding section links added in successive weeks:

  • Part 5.1 : “The regulators interaction with capacitors”: The interaction between the power-supply regulator and the decoupling (bypass) capacitor is explained. In addition, the overall impedance seen by the IC, including capacitors, PCB traces, and voltage regulator is assessed; click here
  • Part 5.2 : “Ring the changes, change the rings”: Ringing and other voltage transient effects examined with a small test-current step, as well as effect of capacitor dielectric, click here
  • Part 5.3 : “Some gain, some pain”: How coupling affects, and bleeds through, to op amp output; click here
  • Part 5.4 : “Don’t get into a macromuddle”: Inaccurate op-amp simulation macromodels can lead to misleading results on the effect of bypass capacitors in decoupling applications, click here
  • Part 5.5 : “When Harry regulator met Sally op amp”: Examine the signal chain from op amp to load, and the interaction of load current, power supply, and amplifier output, click here
  • Part 5.6 : “Steering in the right direction”: Validated simulations and macromodels provide an approach to proper selection of bypass decoupling capacitors in op-amp and other circuits.

You can read the previous parts by clicking on the corresponding link:

  • Part 1 : “Choosing and Using Bypass Capacitors,” click here
  • Part 2 : “Choosing and Using Bypass Capacitors,” click here
  • Part 3 : “Choosing and Using Bypass Capacitors,”click here
  • Part 4 : “Know the sometimes-surprising interactions in modelling a capacitor-bypass network,” click here

About the author
Kendall Castor-Perry has been practicing the electronic arts for over three decades, having designed industrial instrumentation, communications systems and audio circuits. He spends much of his time helping people to solve complex signal-path problems with both empathy and rigor.

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