gm Based CMOS LNA Linearization Techniques – A Comparison

Author Name(s): Sumeet R. Wawarkar, Rupali Tawri, Mayank B. Thacker, Dipak Dahigaokar
Author Email: wawarkarsr@rknec.edu

Abstract

This paper proposes gm based CMOS LNA linearization techniques. A common source Cascode LNA with source degeneration is used as a base circuit operating on 0.8 to 2.5 GHz frequency range using TSMC 180nm technology and 1.8V supply. Linearization techniques i)Harmonic Termination, ii) Derivative Superposition, iii) complementary DS and iv) Post distortion are discussed and implemented on casode LNA. Comparison of results shows that IIP3 is improved by 17.8 dBm for Harmonic Termination, 10.7 dBm for Derivative Superposition, 8.5 dBm for Complementary DS and 20.2 dBm for Post Distortion technique.

Keywords LNA, Linearization Techniques, Harmonic Termination, Derivative Superposition, Complementary DS, Post Distortion.

Introduction

The 21st Century communication technology has been predominantly wireless in nature and has resulted in numerous standards spanned over closely spaced frequencies governing different applications [1]. An LNA is an important block in a wireless receiver and critical for enabling robust performance in obstructed environments. The image signal is produced in the non-linear devices because of the cross terms. This image signal dominates the minimum detectable signal at the receiver of the system. In such a situation, minimum detectable signal performance cannot be improved by bringing down Noise Figure of the system. The low-noise amplifier (LNA) has to provide high linearity preventing the interfering inter-modulation tones from corrupting the carrier signal. Improvise in linearity must not be at the cost of gain or NF. This requires the use of linearization techniques without much cost [1]. The organization of the paper is as follows. Section II reports the Common source Cascode LNA and its implementation. Section III discusses the linearization techniques used in this paper with the simulation results and section IV concludes the paper.

 

Conclusion

In this paper, a comparison of different gm based LNA linearization techniques along with simulation results has been presented. The conventional Inductive source degeneration cascade common source LNA does not provide a significant linearity at RF frequency. Linearization techniques are applied to the cascode circuit and significant improvement of linearity is observed. HB analysis when performed at different frequencies having equal powers and close frequency spacing, gives largest inter-modulations. The measured results with applied linearization techniques show that the techniques can improve linearity performance with small Noise Figure and little gain loss. When the results are examined, it is seen, post distortion method has a slight increase in noise figure than the other methods and it is highest increase in Harmonic Termination technique. A relatively good gain is seen in Derivative superposition technique. Minimum gain is nearly same for all other three techniques which is around 13.5 dB.

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