A 2.5-to-18GHz Reconfigurable LNA With 1.38-to-1.97dB NF Using Switchable Diplexer and Low-Noise Oriented Input

An ultra-broadband reconfigurable low-noise amplifier (LNA) is presented in this paper. A design strategy is proposed that consists of low-noise oriented input, switchable diplexer, gain smoothing output, and a high-isolation single-pole-double-through (SPDT) switch. The low-noise-oriented stages employ source degeneration inductors, RC feedbacks, and middle inductors with special optimizations to attain low noise and sufficient gain, while the flatness is ignored. The diplexer is frequency reconfigurable to provide band overlap and alleviate gain smoothing requirements of followed stages. Gains are flattened by two separate amplifying stages. The SPDT switch combines the two paths and avoids possible oscillations. The prototype in GaAs pHEMT shows 2.5-to-18-GHz bandwidth (i.e. 2.5-to-8 GHz and 6-to-18 GHz), 1.38–1.53/1.64–1.97 noise figure, 21.5-dB average gain, and <2.5-dB overall gain fluctuations.