Wide Range Linearity Improvement Technique for Linear Wideband LNA

Abstract

This paper proposes a wideband linearity improvement technique for the CS-CG cascode structure in the Low-Noise Amplifier (LNA), in which the linearity of both CS and CG stages are improved simultaneously. At relatively low frequencies, the noise and nonlinearity contributions mainly come from the CS stage and a post-distortion method is adopted to eliminate the third-order harmonic. As the frequency increases, the nonlinearity and noise contribution of the CG stage becomes more severe due to its parasitic capacitances. A transformer feedback structure is proposed to increase the gain and reduce the noise, thereby improving the linearity of the CG stage. The linearization technique is applied to an ultra-wideband (UWB) cascode LNA to evaluate effectiveness. The designed LNA achieves a S11 of less than -10dB in a wide frequency range of 2.1-7.6GHz and a gain of more than 10dB with a peak of 11.7dB. Over this range, a minimum NF of 3.4dB and a relatively high IIP3 of greater than 10dBm with a 15.7dBm peak are achieved. The results indicate that the proposed technique effectively improves the linearity of the cascode LNA in a wide range of frequencies. At the same time, NF and gain performance are also improved.