The Design Of CMOS Low Noise Amplifier With Active Inductor

In recent years,motivated by the growing market of Radio Frequency communications systems, much effort has been devoted to the implementation of Radio Frequency integrated circuits(RFIC) in a CMOS technology.Compared to other processes,CMOS process has advantages of low cost,low power and easy facility in being integrated with other systems.With the advance of deep-submicrometer CMOS process,the characteristic size is decreasing and thereby cutoff frequency is increasing,the performance of CMOS RFIC is impeoved quickly.Low noise amplifier(LNA) is the key circuit in the RF front end.Conventional design objectives for LNAs are to minimize the amplifier's noise figure(NF) ,to provide good reasonable gain with good linearity and to provide good input matching to the antenna or to the filter. In order to achieve good performance, a high quality(Q) factor inductor,which also helps to reject out of band signals and noise, is desired.Nevertheless,the Q factor of CMOS on-chip spiral inductors cannot meet the above requirement due to the associated parasitic capacitance and resistance losses that arise from the substrate and metal lines.Additional processing steps may enhance Q factor ,but introduce extra cost and complex circuit is introduced.On the other hand,the huge size of spiral inductor leading to large chip area and high costs.These drawbacks of CMOS spiral inductor, such as low Q factor,large integrated area and inductance value cannot be electronically tuned,can be overcome by utilising an active inductor.CMOS transistor-only active inductor can obtain high Q factor with reasonably design which can operate up to the cutoff frequency of the transitors in theory.This paper focus on the issues of LNA in RF receiver front-end.The fundamentals of LNA and some common structure as well as their merits and demerits given out. The paper also gives a detailed analysis of the LNA with source inductor degeneration, which are currently the most widely used. Based on the analysis, an LNA with active inductor load is presented.