Suppression of conducted noise coupling in a board with digital and RF circuits by a ferrite film plated on an interposer

This paper presents evaluation results of conducted noise suppression effect of a ferrite film directly plated on an interposer substrate in the long-term evolution (LTE) communication band. A test board for evaluations has an IC with digital and RF circuits which is designed for investigations of electromagnetic noise coupling at the IC chip level. Firstly, we have confirmed effectiveness of a ferrite film onto an interposer in suppression of conducted noise from a digital circuit to a board by simulations. Then, we have verified that the ferrite film reduces conducted noise coupling to the RF circuit, occurring inside the board, by measurements of In-phase/Quadrature (I/Q) signals and high frequency voltages of power supply lines.