Air Gap Corrections in Clamped Stripline in Plane Permittivity Extraction
Air gap corrections eliminate systematic two to six percent dielectric underestimation in clamped stripline tests, preventing finished board impedance failures.
Series Capacitance
Circuit Configuration
Capacitive elements connected end-to-end along a single conductor path divide the applied voltage and reduce the total effective capacitance of the branch. In printed circuit board designs, series capacitance is often introduced intentionally using surface-mount DC-blocking capacitors or occurs unintentionally through gaps and split ground planes. This electrical arrangement prevents DC currents from flowing while allowing high-frequency AC signals to pass through.
Signal Propagation
Unintentional series gaps can block low-frequency return currents and distort high-speed signal pulses. In contrast, intentional capacitors are used to isolate different DC voltage domains, such as between a transmitter and receiver on a high-speed bus. The physical size of the capacitor and its pad layout must be carefully optimized to avoid creating impedance discontinuities.
Layout Optimization
Designers must minimize the pad and trace discontinuity associated with mounting these components to prevent signal reflections. Placing the capacitor close to the connector or receiver helps to contain the impedance mismatch and maintain high signal quality. By carefully selecting the component footprint and routing path, engineers can incorporate this capacitive coupling without degrading the high-speed channels of the board.
This structural approach ensures that high-speed communication lines remain electrically isolated and protected from damage caused by different ground potentials.