An Efficient, Broadband SiGe HBT Non-Uniform Distributed Power Amplifier Leveraging a Compact, Two-Section <i>λ</i>/4 Output Impedance Transformer
Inchan Ju, Seokchul Lee, John D. Cressler
Abstract
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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Z_{0}$ </tex-math></inline-formula> ) of the collector transmission lines (TLs) and tapering the SiGe HBT emitter area simultaneously. A novel compact, lumped-element two-section <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /4 output impedance transformer (OIT) is proposed to lower the NDPA load impedance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Z_{L}$ </tex-math></inline-formula> ) from 50 to 25 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> over more than one decade bandwidth (BW). Each <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /4 impedance transformer is realized by four cascaded <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLC</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -networks integrated into a single three-turn symmetric inductor in order to achieve compact size, high passive efficiency, and high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> cutoff frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{c}$ </tex-math></inline-formula> ). The systematic design approach of a lumped-element <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /4 impedance transformer with an arbitrary <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Z_{0}$ </tex-math></inline-formula> is described in detail. The prototype NDPA was fabricated in 0.13- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> 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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {out}}$ </tex-math></inline-formula> ) 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {out}}$ </tex-math></inline-formula> with a PAE of 10.0% at 6-Gbit/s data rate 64 QAM modulation.