Analysis and Design of a Gain-Enhanced 1–20-GHz LNA With Output-Stage Transformer Feedback

A gain-enhanced technique with output-stage transformer feedback (OSTF) for the low-noise amplifiers is proposed in this brief. The transformer is realized by a pair of magnetically coupled microstrip lines between the drain and source stages, one of which acts as a series-peaking inductor and the other as a source degenerate inductor. By adjusting the length and gap of the magnetically coupled microstrip lines, the tuning of the gain in high frequency is realized. To verify the proposed OSTF gain-enhanced scheme, two LNAs with the same structure are designed, with one having OSTF and the other not. The gain-enhanced wideband LNA with OSTF is fabricated in 0.15-
$\mu \text{m}$
GaAs pseudomorphic high-electron mobility transistor process. The total chip area, including input and output testing pads, is 1.24 mm 2. The simulated results show excellent performance with a maximum gain improvement of 3-dB at 20 GHz. The measured results show that the gain-enhanced LNA has an average gain of 22.6 dB and a noise figure below 2 dB from 1 to 20 GHz, which are in good agreement with simulated ones.