A Compact, Wideband Complex Cascode Power Amplifier With LC Neutralization for VSWR-Resilient Operation in High-Density Phased Arrays

This article proposes a design methodology for achieving intrinsic performance resilience in power amplifiers (PAs) against antenna impedance variations inherent to modern phased-array systems through the improvement of the PA output matching (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S\!_{22}$</tex-math> </inline-formula>). This goal, however, presents a challenge for conventional cascode PAs due to their inherently high output impedance and often entails a direct tradeoff with PA output power and efficiency. To address this, a complex L-C neutralized cascode topology is developed to align the conjugate-match condition with the optimal load-pull impedance, thereby enabling a low output reflection coefficient without compromising the PA’s large-signal performance. In addition, the PA’s linearity is enhanced using a technique analogous to that of a multi-gate transistor (MGTR); in particular, the bias control is applied via the back gate of the SOI devices, leaving the primary RF signal path unperturbed. Fabricated in the Globalfoundries 22FDX+ technology, the PA delivers a linear power of 15.4dBm with a peak power-added efficiency (PAE) of 34% into a 50-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $</tex-math> </inline-formula> load. When subjected to voltage standing wave ratio (VSWR) circles up to 4:1, across the 37–43-GHz frequency range and using a single bias setting, the power gain deviation remained below 1.5dB relative to the 50-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $</tex-math> </inline-formula> case, while the degradation in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {OP}_{\mathrm {1\text {dB}}}$</tex-math> </inline-formula> was limited to less than 3 dB. The corresponding drop in PAE<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}_{\text {OP1 {dB}}}$</tex-math> </inline-formula> was held to less than 11%. The PA’s performance was also assessed using a 64-QAM modulated signal. Across the 39–43-GHz band, even under 4:1 VSWR conditions, the measured error vector magnitude (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {EVM}_{\mathrm {rms}}$</tex-math> </inline-formula>) remained below −24.5dB. Concurrently, the average output power (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {avg}}$</tex-math> </inline-formula>) and average PAE (PAE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">avg</sub>) consistently exceeded 6.8dBm and 9%, respectively.