Characterization of wideband decoupling power line with extremely low characteristic impedance for millimeter-wave CMOS circuits

A wideband decoupling power line for millimeter-wave circuits can be realized with a transmission line having an extremely low characteristic impedance, Z₀ → 0Ω. It is, however, very difficult to characterize such a line with the ordinary two-port S-parameter measurement. This paper presents an alternative measurement technique that uses transmission line stubs. The measurement results confirm that a power line impedance below 1Ω is successfully achieved over a very wide frequency range (> 80 GHz). A measurement-based method of finding the necessary length of such a low-impedance line for realizing good decoupling is also proposed.