A SiGe Common-Collector-Common-Base Linear Power Amplifier with 17–28-GHz P1dB 3-dB Bandwidth and Enhanced Large-Signal Stability

This paper presents a broadband SiGe common-collector-common-base (CC-CB) two-stage linear PA with enhanced large-signal stability. Through driving-point admittance analysis, the conventional SiGe cascode PA topology, equipped with a common-emitter device, is shown to be prone to large-signal instability, rendering it unsuitable for broadband PA designs. To address this, the adoption of a CC stage is explained in detail. In addition, a stacked distributed balun is proposed for broadband output matching, accounting for the constraints of limited substrate resistivity. The proposed PA achieves a $P_{\text {sat }}$ of 19.3 to 23.3 dBm, with a $P A E_{\text {sat }}$ of 10.4 to $28.6 \%$ over 17 to 30 GHz. The $P_{1 \mathrm{~dB}} 3-\mathrm{dB}$ bandwidth ranges from 17 to 28 GHz, with a $P A E_{1 \mathrm{~dB}}$ of 11.0 to $22.1 \%$. The PA supports 400-MBd 32-APSK/64-QAM signals. For 64-QAM signals, it achieves $14.7-18.9 \mathrm{dBm} / 6.0-15.7 \% P_{\text {avg }} /$ PAE at an $E V M_{\text {rms }}$ level of -25 dB, from 18 to 28 GHz.