A Wideband mm-Wave Watt-Level Spatial Power-Combined Power Amplifier With 26% PAE in SiGe BiCMOS Technology

Abstract

We present a wideband watt-level power amplifier (PA) for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Ka$ </tex-math></inline-formula> -band designed and implemented in the 0.25- <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:C BiCMOS technology. The core of the design is a chip with multiple custom PA unit cells (PA-cells), which are interfaced with a power combiner placed on a laminate. The power combiner is based on a principle of the recently proposed multichannel transition with spatial power combining functionality, where an array of strongly coupled microstrip lines (MLs) interface a single substrate integrated waveguide (SIW). The realized watt-level PA combining four differential cascode PA-cells achieves 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">$P_{{\text {sat}}}$ </tex-math></inline-formula> ) of 30.8 dBm with 26.7% power-added efficiency (PAE). The 64-QAM modulation tests confirm the competitive PA performance on multi-Gb/s communication signals. The obtained combination of the high PAE and high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P _{{\text {sat}}}$ </tex-math></inline-formula> over a wide frequency band (30%) is an advantageous property of the proposed solution with respect to the previously published designs. This high performance is the result of using the proposed architecture with low-loss (0.6 dB) and wideband (54%) parallel spatial power combiner. Moreover, the presented joint EM–circuit–thermal optimization allows achieving optimal system-level performance by taking into account various critical multiphysics effects occurring in the combined PA. This article describes the design and performance of the whole integrated structure and its individual components.