Radiofrequency interferece filters design based on complementary split rings resonators

Abstract

Low frequency analog and digital electronic circuits are susceptible to radiofre- quency interference (RFI). This disturbance is produced when the coupled RF signal is recti¯ed by the non-linear behavior of the semiconductors used in the small signal analog input stages of the electronic system. These circuits present an AM demodulation e®ect produced by nonlinear- ity of internal transistors, generating parasitic signals in the low-frequency range and undesired o®set voltage. In this paper, an alternative to the current standard EMI ¯lters is presented by combining the conventional printed circuit board layout with complementary split ring resonators (CSRRs), in order to reduce the output o®set impact due to RFI. An operational ampli¯er circuit has been designed with a 4-stage CSRR ¯lter, electromagnetically simulated and experimentally tested. Two prototypes have been implemented, with and without CSRRs in order to compare the ¯lter properties in standard FR4 substrate. The resonance frequency of the CSRRs has been designed in the vicinity of 2.4 GHz in order to prevent susceptibility in the ISM band. Electro- magnetic and electrical equivalent circuit model simulations are also provided and compared with experimental results. Measurement data show an e®ective rejection of the undesired RF demod- ulation without a®ecting the signal integrity out of the ¯lter band, and therefore a signi¯cant reduction concerning output o®set voltage impact in terms of RFI amplitude with no-extra cost in terms of the device area or manufacturing process.