Design of Compact Bidirectional Amplifier Utilizing Transformers-Stacking Technique

Extremely high cost and form factors have become the most important reason limiting the promotion of large-scale phased-array systems for fifth-generation communication and K-/Ka-band satellite communication (SATCOM). This article presents a novel topology of ultracompact bidirectional amplifiers utilizing transformers-stacking techniques for low-cost large-scale phased arrays. In contrast to conventional bidirectional amplifier structures, this article proposes a more scalable bidirectional topology, which utilizes a magnetic self-canceling technique to stack the low-noise amplifier (LNA) into the power amplifier (PA) completely, realizing the function of the bidirectional amplifier with negligible performance penalty. In order to verify the proposed technique, the first bidirectional amplifier whose LNA mode and PA mode can work in different bands is implemented in a 45-nm CMOS SOI process for the K-/Ka-band SATCOM system. This design achieves 18.3-dBm peak saturated output power ( $P_{\text {sat}}$ ) and 15.9-dBm peak 1-dB compression output power ( $\rm {OP}_{1\,\text {dB}}$ ) in the Ka-band PA mode while maintaining a minimum noise figure (NF) of 2.46 dB in the K-band LNA mode. Furthermore, a notch filter is integrated into the three-winding transformer-based transmit/receive switches (TRSWs) to suppress the sidelobe of TX and avoid performance deterioration of the RX. Benefiting from the integration of a build-in-self notch filter, the proposed design has good gain suppression (>45 dB) to block the interferer from other TX chips in the LNA mode. The core size of this proposed design is only 0.14 mm2, which is only 20%–50% of the size occupied in conventional works.