Analysis and design of a wideband lumped-element quadrature directional coupler for complementary metal-oxide semiconductor implementation

This study proposes a new wide band quadrature coupler structure using a lumped-element technique. The theoretical operating conditions of the proposed structure are also analysed. The operating bandwidth is extended and the phase shift difference error is reduced by introducing two matching frequency points. When the designed centre frequency is 6 GHz, a theoretical calculation shows that the operating bandwidth is 2 GHz and the phase shift error ranges from -5.9 to 1.76°. A coupler with 6 GHz centre frequency is also designed in a 0.13 μm CMOS process and simulated using Cadence Spectre. The active area of the coupler is 560 μm × 640 μm. The post-layout simulation shows that the operating bandwidth has strong tolerance to the process variations.