Compact on-chip 90° and 180° splitters/combiners in silicon technology for 24 GHz applications

This paper presents two compact on-chip 180° and 90° power splitters/combiners based on a lattice-type LC-balun and a lumped-element quadrature coupler, respectively. The devices have been realized in a silicon-based technology using spiral inductors and Metal-Insulator-Metal (MIM) capacitors and dimensioned for the frequency range around 24 GHz. Combining branches into an interleaved transformer has enabled a very compact realization of the LC-balun and the quadrature coupler, consuming a minimal chip area of 0.018 mm². The 180° power splitter/combiner offers amplitude and phase imbalance of 0.6 dB and 10°, whilst the 90° circuit offers 2 dB and 0.6° at 24 GHz, respectively. Port matching better than 10 dB has been observed for both devices from 19 GHz to 28 GHz.