A 5–25.7-GHz CMOS LNA With Weakly Coupled Transformer for X-/Ku-/Ka-Band SATCOM Receivers

This letter presents a low-noise amplifier (LNA) for multiband satellite communication (SATCOM) applications, featuring a wide effective bandwidth (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{BW}_{\text {eff}}$</tex-math> </inline-formula>). Based on a feedback cascode structure, the design methodology to achieve wideband input matching in a multistage LNA is presented. A compact input matching network consisting of a parallel capacitor and a weakly coupled transformer is introduced to generate three distinct peaks in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S\!_{11}$</tex-math> </inline-formula>, effectively covering the 3-dB bandwidth (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{BW}_{3\,\text {dB}}$</tex-math> </inline-formula>) of the LNA. The fabricated LNA demonstrates a peak gain of 21.2 dB with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{BW}_{3 \,\text {dB}}$</tex-math> </inline-formula> from 5 to 25.7 GHz while consuming 16 mW. The noise figure (NF) remains within the range of 2.6–3.8 dB. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S\!_{11}$</tex-math> </inline-formula> and <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> are better than –10 dB across 5.2–28 GHz. To the best of the authors’ knowledge, the FoMs of this work are one of the best results reported for CMOS LNAs with such a wide bandwidth.