A Compact Transformer with Built-in Inductors for Matching Networks in K-Band CMOS Power Amplifiers

This paper proposes a compact transformer architecture called the Transformer with Built in Inductors (TBI) for impedance matching networks in K band CMOS power amplifiers (PAs). The TBI integrates the required series inductance directly into the transformer winding, eliminating the need for external metal routing. As a result, it reduces layout footprint and simplifies design without significantly degrading RF performance. To validate the concept, two 2 stage, 3 stack CMOS PAs were designed and simulated in a 65nm process—one using a conventional transformer and the other using the TBI. Simulation results show that the TBI based PA achieves a saturated output power (Psat) of 25.8dBm, an output 1 dB compression point (OP1dB) of 24.56dBm, a peak power added efficiency (PAE) of 37.6%, and a gain of 27.04dB, while reducing transformer area by approximately 36%. These results demonstrate that the proposed TBI structure offers comparable RF performance to conventional designs with a substantially smaller footprint.