Abstract
In this brief, a 0.1 to 23 GHz low-noise amplifier (LNA) employing a frequency-dependent feedback loop (FDFL) is presented. As predicted theoretically, the optimized FDFL enhances the bandwidth and the gain flatness in desired frequency band through purposely designing the feedback characteristics from negative to positive corresponding to the frequency. Based on the theoretical analysis of bandwidth enhancement, noise characteristic, and linearity of FDFL, an ultra-broadband LNA, utilizing the proposed technique, is designed and verified experimentally by a three-stage LNA chip implemented using a 0.15-μm GaAs pseudomorphic high electron-mobility transistor process. Measurement results show that the LNA obtains an average gain of 27.4 dB and noise figure of 2.7 to 4 dB in a frequency band from 0.1 to 23 GHz, with a compact chip area of only 1.36 mm 2 , including input/output testing pads.