Monolithic feedback low noise X-band amplifiers using 0.5-μm GaAs MESFETs: comparative theoretical study and experimental characterization

Three different feedback low-noise-amplifier (LNA) circuit topologies for simultaneous noise and power matching are theoretically investigated and compared for the X-band application. The smallest minimum noise figure (NF_min) is shown to be achieved by the common source parallel feedback (CSPF) topology, while the common source series feedback (CSSF) topology exhibits the best overall performance. Experimentally, a CSSF three-stage LNA has been fabricated using 0.5-μm-gate GaAs MESFETs and systematically characterized. In this LNA circuit, an optimal series feedback for noise figure, gain, and stability is implemented via a proper choice of the short stub length. The size of the fabricated monolithic microwave integrated LNA chip is only 1 mm²/stage. The measured gain varies from 22.0 to 23.0 dB in the frequency range of 8 to 10 GHz, with good flatness. The input/output voltage standing wave ratios are less than 2 and 1.43, respectively. The noise figure of the three-stage LNA is less than 2.6 dB. These measured data are sufficient for practical applications and are also in good agreement with simulated results