Ultra compact multi-mode filter with novel rat-race inductor

A monolithic integrated filter with mode conversion and impedance transformation for GSM 900 is presented. Hereby, a so called rat-race inductor is utilized, replacing up to six conventional inductors and one transformer, resulting in a reduction in chip size by approximately 50 %. The rat-race inductor is handled theoretically and 3D-EM based simulations are carried out, verifying the proposed structures and expected results. A first wafer run is to be fabricated on Infineon Technologies P7MI semiconductor process. The insertion loss of the filter is as low as 2.3 dB accompanied by a phase imbalance of less than 5° and an amplitude imbalance of less than 0.5 dB.