A Compact, Highly Linear Ku-Band SiGe HBT Flip-Chip Power Amplifier Module Using a Shared Single Center-Tap Four-Way Transformer Balun With a Double-Tapped Second-Harmonic Trap

초록

This article presents a compact, highly linear Ku-band SiGe heterojunction bipolar transistor (HBT) power amplifier (PA) module suited to low Earth orbit (LEO) satellite communication (SATCOM). For an output stage design, a tightly packed fully differential common emitter (CE) topology is chosen for superior linearity and linear power density to its cascode counterpart. A novel four-way transformer (TF) balun with a shared single center-tap (SSCT) is proposed, where two differential inputs are located on the same side, which greatly simplifies signal routings to the output stage for compact, efficient power combining and inherently forms dual common (CM) nodes for linearity enhancement. For the first time, the impact of a 2nd-harmonic emitter inductance (<FOR VERIFICATION> Le,2nd) on the PA large signal performance is investigated theoretically. Its adverse effect is mitigated by an optimized Cu pillar (CuP) bump array layout in flip chip (FC) configuration. Also, a double-tapped 2nd-harmonic trap is newly proposed, which is implemented by leveraging the dual-CM nodes of the proposed SSCT TF balun and CuP bump array. This novel IC-to-package co-design improves the PA linearity without on-chip inductors. A PA prototype is fabricated in 0.13-μ m SiGe HBT BiCMOS, with an active area of 0.24 mm2. It attains peak output power (POUT) and power added efficiency (PAE) of 24.2 dBm and 32.8% at 11.7 GHz, respectively, demonstrating the highest power density among any Si-based Ku-band PAs. The PA supports linear amplification of 250-MHz bandwidth (BW) 64/256 amplitude phase shift keying (APSK) Direct Video Broadcasting-Second Generation Satellite Extension (DVB-S2X) modulated signals at linear POUT (Pavg) of 18.3/16.4 dBm and average PAE (PAE_avg) of 17.8%/13.4%. By incorporating active device-passive network-package into the PA design, it successfully supports 400-MHz DVB-S2X 256 APSK signal at the Ku band and it would be suitable for low-cost, highly integrated transmit beamformer ICs (BFICs) for LEO SATCOM. © 2025 Elsevier B.V., All rights reserved.

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