EMC Question of the Week: August 5, 2019

Electric Fields Lines under a Microstrip Trace

The electric field strength between a digital circuit trace carrying a 3.3-volt signal and a 0-volt ground plane located just below the trace increases when the

  1. permittivity of the dielectric is increased
  2. transition time of the signal is decreased
  3. width of the trace is decreased
  4. height of the trace is decreased

Answer

The correct answer is "d". The strength (magnitude) of an electric field line is equal to the voltage difference between the two ends divided by the length of the line. Keeping the voltage the same, while decreasing the length of the field line, will increase its strength. The other three options presented here have little or no effect on the field strength.

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