A Compact 48–63 GHz 3-dB Transformer-Based Quadrature Coupler With Arbitrary Transformer Coupling Coefficient in 22-nm CMOS FDSOI

This letter presents a novel 3-dB transformer-based quadrature coupler (TFQC) that is based on lumped inductors connected between the coupler ports. Compared to previously reported 3-dB TFQCs that strictly require a coupling coefficient (k) of 0.707, the proposed coupler can be designed with any arbitrary k for the transformer (TF), offering a much-expanded design space and scalability across frequency and different technologies. In addition, the required TF’s inductance of the proposed coupler is reduced compared to previous TFQC designs, allowing for a further size reduction. To validate the theory of the proposed coupler, a 48–63 GHz prototype is implemented in a 22-nm CMOS FDSOI technology, occupying an area of 0.017 mm2 with an average insertion loss (IL) of 1.81 dB.