Improved Circuit Board Filters Employing SMT Capacitors

The bandwidth of circuit board filters employing surface-mount capacitors is limited by the magnetic field coupling between the input and output of the filter. Most of this coupling is due to the magnetic field that wraps the body of the capacitor and is generally attributed to the "self inductance" of the capacitor. This magnetic field coupling can be effectively eliminated by mounting geometries that create an opposing magnetic field. To-date this project has demonstrated several practical mounting structures that significantly increase the bandwidth of circuit board filters without adding to the cost or significantly increasing the required board area. The current objective is to develop a design procedure for quickly determining the optimum design without extensive modeling.

Publications

1. A. McDowell and T. Hubing, “Optimization of Shunt Capacitor Filters for Reduction of Common Mode Current in Motor Drives,” Clemson Vehicular Electronics Laboratory Technical Report - CVEL-12-036, Apr. 21, 2012.
2. A. McDowell and T. Hubing, “Parasitic Inductance Cancellation for Surface Mount Shunt Capacitor Filters,” IEEE Transactions on Electromagnetic Compatibility, vol. 56, no. 1, Feb. 2014, pp. 74-82.
3. A. McDowell and T. Hubing, “A Compact Implementation of Parasitic Inductance Cancellation for Shunt Capacitor Filters on Multilayer PCBs,” IEEE Trans. on Electromagnetic Compatibility, vol. 57, no. 2, Apr. 2015, pp. 257-263.