IMPROVEMENT IN LINEARITY OFLOW NOISE AMPLIFIER

GUIDE: Prof. F.A .Talukdar

Asst. Prof. R.H.Laskar ECE Department

NIT Silchar

By Ram Kumar

Outline

• Motivation• Introduction• Background• Basic LNA Design• Problem Formulation• Proposed Work• Reference

MotivationNumerous co-existing wireless standardsand wireless equipment

RF Receiver

• Antenna receives the entire band of signals• Stringent requirements on the receiver front-end• BPF filters the out of band channels• LNA receives the entire in-band signals• In-band channel interference problems in LNA – Intermodulation

BPF1 BPF2LNA

LO

Mixer BPF3 IF Amp

RF front end

LOW NOISE AMPLIFIER• First gain stage in receiver– Amplify weak signal

• Significant impact on noise performance– Dominate input-referred noise of front end

• Impedance matching– Efficient power transfer– Better noise performance– Stable circuit

LNA

subsequentLNAfrontend G

NFNFNF

1

LNA Design Consideration

• Noise performance• Power transfer• Impedance matching• Power consumption• Linearity

Intermodulation• Intermodulation is one of the major causes of distortion in RF

systems• When two signals with different frequencies are applied to a

non-linear system, the output in general exhibits some components that are not harmonics of the input frequencies . This is called inter-modulation

• The 3rd order inter-modulation product are the interferers at (2ω1 ± ω2), and (2ω2 ± ω1) which can appear very close to those at ω1 and ω2 (when ω1-ω2 is small) and cannot be removed by a low pass filter.

IIP3• A point at which the amplitude of

fundamental and the 3rd intermodulation meet called iip3.

Background

Existing Linearization Techniques• Optimum Biasing• Negative Feedback• Derivative superposition

Optimum Biasing

Current

IIP3=

gm3=0 results in very high IIP3

id = gm1vgs +gm2vgs2

+gm3vgs3+….

Optimum Biasing

Drawbacks– High IIP3 obtained over a narrow region– Process variations degrade IIP3– Limited voltage gain due to restricted input transconductance (gm1)– Poor NF

Negative Feedback

• Linearity improvement at the expense of circuit gain• Feedback techniques not suitable at RF frequencies

Derivative Superposition (DS) Method

problem of narrow range with optimum biasing technique.

gm3 negative in strong inversion and positive in weak inversion

Wide range of bias values with small gm3 and hence IIP3 improvement obtained

Drawbacks

• Weak inversion transistor connected in parallel degrades NF Second order non-linearity effect on IIP3• Auxiliary transistor affects both linearity and input match leading to increased design steps

Circuit Diagram of inductive source Degeneration LNA

S11 (Reflection Parameter)

Noise Figure

S21

IIP3

Problem Formulation

• Increase the iip3 without sacrificing noise figure.

• For high iip3 vgs-vt should be high but it reduces gain.

• Increase the iip3 without sacrificing the gain.

Proposed work• IM3 components in the drain current of the main

transistor has the required information of its nonlinearity

Auxiliary circuit is used to tune the magnitude and phase of IM3 components

Proposed work

• Making an auxiliary circuit without degradation in noise figure.

• Improve output matching circuit. • Improve biasing to increase Vgs-Vt.• Making layout.

References• V. Aparin, G. Brown, and L. E. Larson, “Linearization of CMOS LNAs via

optimum gate biasing,” in Proc. IEEE Int. Circuits Syst. Symp.,Vancouver, BC, Canada, May 2004, vol. 4, pp. 748–751.

• C. Xin and E. Sánchez-Sinencio, “A linearization technique for RF low noise amplifier,” in Proc. IEEE Int. Circuits Syst. Symp., Vancouver, BC, Canada, May 2004, vol. IV, pp. 313–316.

• T. Lee and Y. Cheng, “High-frequency characterization and modeling of distortion behavior of MOSFETS for RF IC design,” IEEE J. Solid-State Circuits, vol. 39, no. 9, pp. 1407–1414, Sep. 2004.

• T. Lee, The Design of CMOS Radio-Frequency Integrated Circuits, Cambridge University Press, 1998.

• Choi, K., T. Mukherjee, and J. Paramesh, A linearity-enhanced wideband low-noise amplifier," IEEE RF Integrated Circuits Symp. Dig., 127{130, June 2010.

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