A Ku-Band CMOS LNA with Symmetric Polarity-Selective Transformer for Efficient 180° Phase Shifting

We proposes a Ku-band CMOS low-noise amplifier (LNA) with an integrated 180° phase shift function, aimed at reducing the chip area of beamforming systems. The proposed LNA consists of two stages, with the final stage utilizing a differential structure featuring a polarity-selective transformer for the 180° phase shift. This functionality is achieved by altering the polarity induction direction of the transformer using a switch, enabling the 180° phase shift without additional chip area. The LNA was implemented in a $28-\text{nm}$ bulk CMOS process, achieving a compact core size of $0.6 \times 0.21 ~\text{mm}^{2}$. Measurement results show a phase error and gain error between the 0° and 180° phase shift modes of $<0.64^{\circ}$ and $<0.052 ~\text{dB}$, respectively, within the $9.5-12.6 \text{GHz}$ operating frequency range. Furthermore, the LNA demonstrates a minimum noise figure of 2.75 dB and a maximum gain of 23.2 dB, validating the effectiveness of the proposed design.