An Efficient, Broadband SiGe HBT Non-Uniform Distributed Power Amplifier Leveraging a Compact, Two-Section λ/4 Output Impedance Transformer

An efficient, broadband SiGe HBT cascode nonuniform distributed power amplifier (NDPA) is presented for low-cost, fully integrated Si-based phased arrays. Optimum load impedances at each SiGe HBT cascode in a four-stage NDPA core are obtained by scaling the characteristic impedance (Z(0)) of the collector transmission lines (TLs) and tapering the SiGe HBT emitter area simultaneously. A novel compact, lumped-element two-section lambda/4 output impedance transformer (OIT) is proposed to lower the NDPA load impedance (Z(L)) from 50 to 25 St over more than one decade bandwidth (BW). Each lambda/4 impedance transformer is realized by four cascaded CLC pi-networks integrated into a single three-turn symmetric inductor in order to achieve compact size, high passive efficiency, and high LC cutoff frequency (f(c)). The systematic design approach of a lumpedelement lambda/4 impedance transformer with an arbitrary Z(0) is described in detail. The prototype NDPA was fabricated in 0.13-mu m SiGe HBT BiCMOS technology. The proposed SiGe HBT cascode NDPA supports both high linearity (HL) and high gain (HG) modes, each suited to a specific application. The NDPA attains a peak power gain of 10.3/12.5 dB, a saturated output power (P-out) of 21.3/21.5 dBm, and a power added efficiency (PAE) of 12.2%/12.5%-21.6%/22.0% for HL/HG modes, with a 3-dB BW from 1.5 to 24.0 GHz. The NDPA delivers 13.0-dBm average P-out with a PAE of 10.0% at 6-Gbit/s data rate 64 QAM modulation.

Automated summary

An efficient broadband SiGe HBT cascode nonuniform distributed power amplifier (NDPA) is proposed for low-cost, fully integrated Si-based phased arrays. The amplifier achieves optimum load impedances through scaling the characteristic impedance of the transmission lines and tapering the emitter area. A compact lumped-element output impedance transformer is designed to lower the load impedance and increase the bandwidth. The experimental results demonstrate the excellent performance of the amplifier in high linearity and high gain modes.