Analysis and Design of Slotline-Balun-Based Tri-Coil Input Matching and Output Power Combining for Broadband Power Amplifiers

This article presents the analysis and design of a slotline-based balun and power combiner for millimeter-wave (mm-Wave) broadband power amplifiers (PAs). By introducing transmission lines (Tlines) and a transformer with parasitic capacitors, an equivalent circuit model of slotline balun is proposed, for the first time, achieves consistency with its electromagnetic (EM) model over a wide frequency range. Based on this model, a slotline-balun-based tri-coil input matching network and output power combiner are developed. Besides, theoretical analyses and design guidelines for extracting the corresponding model parameters are provided. To verify the proposed model, a broadband PA was implemented in a 40-nm LP CMOS process with a core area of 0.24 mm2. Under a power consumption of 209mW, the prototype achieves a 3-dB bandwidth from 70.6 to 98.4GHz, a maximum power gain of 20.6 dB, a saturated output power ($P_{\mathrm {sat}}$) of 13.6 dBm, and a peak power-added efficiency (PAE) of 10.5%. Besides, a 32-Gb/s 16-QAM signal with an error vector magnitude (EVM) of −20.1 dB is demonstrated at a carrier frequency of 85 GHz.