A 3.1–10.6 GHz UWB LNA Based on Self Cascode Technique for Improved Bandwidth and High Gain

Abstract

In this work, we present a self cascode based ultra-wide band (UWB) low noise amplifier (LNA) with improved bandwidth and gain for 3.1–10.6 GHz wireless applications. The self cascode (SC) or split-length compensation technique is employed to improve the bandwidth and gain of the proposed LNA. The improvement in the bandwidth of SC based structure is around 1.22 GHz as compared to simple one. The significant enhancement in the characteristics of the introduced circuit is found without extra passive components. The SC based CS–CG structure in the proposed LNA uses the same DC current for operating first stage transistors. In the designed UWB LNA, a common source (CS) stage is used in the second stage to enhance the overall gain in the high frequency regime. With a standard 90 nm CMOS technology, the presented UWB LNA results in a gain $\hbox {S}_{21}$ of $20.10 \pm 1.65\,\hbox {dB}$ across the 3.1–10.6 GHz frequency range, and dissipating 11.52 mW power from a 1 V supply voltage. However, input reflection, $\hbox {S}_{11}$, lies below $-\,10$ dB from 4.9–9.1 GHz frequency. Moreover, the output reflection ($\hbox {S}_{22}$) and reverse isolation ($\hbox {S}_{12}$), is below $-\,10$ and $-\,48$ dB, respectively for the ultra-wide band region. Apart from this, the minimum noise figure ($\hbox {NF}_{min}$) value of the proposed UWB LNA exists in the range of 2.1–3 dB for 3.1–10.6 GHz frequency range with a a small variation of $\pm \,0.45\,\hbox {dB}$ in its $\hbox {NF}_{min}$ characteristics. Linearity of the designed LNA is analysed in terms of third order input intercept point (IIP3) whose value is $-\,4.22$ dBm, when a two tone signal is applied at 6 GHz with a spacing of 10 MHz. The other important benefits of the proposed circuit are its group-delay variation and gain variation of $\pm \,115\,\hbox {ps}$ and $\pm \,1.65\,\hbox {dB}$, respectively.