Rakshith Venkatesh

14/27/2009

What is an RF Low Noise Amplifier?The low-noise amplifier (LNA) is a special type of

amplifier used in the receiver side of communication systems to amplify very weak signals captured by an antenna.

RF means high frequency (hundreds of MHz to GHz).The job of the LNA is to boost the incoming signal power

while adding as little noise and distortion as possible to this received signal.

For example, the 5GHz frequency band is the used for wireless communication. IEEE 802.11 wireless standard uses this frequency band.

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About this project:

The main intension is to design a low power RF amplifier without sacrificing the amplifier gain and its Noise-Figure (SNR_in/SNR_out).

Cascode Design

Low Power Design

Technology 90nm 90nm

Frequency 5.5GHz 5GHz

Gain >13dB > 12dB

Power Dissipation

>8mW < 4mW

Noise Figure

~2-3dB < 4dB

S12 <-25dB < -25dB

Typical values of conventional

design and my objective

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Design StepsThe bias current (0.13mA/um) is selected and then the ‘W’ of the transistors

based on this. The supply voltage is decided based on the number of stages stacked and the gain needed. Start off with the ‘Vdd’ specified for the technology.

The MOSETs are biased and we must ensure that all the transistors are operating in the saturation region (Vds > Vgs – Vth). Gate biasing voltage is calculated using the transfer characteristics of the stage.

Impedance matching at the input stage of the amplifier is done so that the input impedance is equal to 50Ohm, the series resistance of the RF signal source.

Output impedance matching is done assuming the device is terminated at 50Ohm. In other words the load resistance is 50.

The simulation is run using ‘HSPICE’ and the parameters like S21(gain), S11, S22, S12, NF, NFmin and power dissipation are calculated.

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Conventional Design of an LNA

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Ref: ‘60-GHz PA and LNA in 90-nm RF-CMOS’, Yao T et.al, Radio Frequency Integrated Circuits Symposium, 2006, IEEE, 4 pp.

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Circuit Diagram of the LNA in this work

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S21 or Gain of the designed LNA

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S12 or Reverse Isolation

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S11 plot

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S22 plot

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NF with Nfmin = 3.5dB

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Power Calculation

The bias current of the circuit is 3.2 mA and the power supply voltage is 1.5 V.

Hence, Power Dissipation = Bias Current . Vdd

= 4.8mW

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Comparison with low power designsParameter Paper[1] Paper[2] This work

Technology (nm) 250 90 90

Voltage Supply (V) 2 1.2 1.5

Frequency (GHz) 2.4 5.5 5.0

Gain (dB) 14.7 15.4 13

Noise Figure(dB) 2.5 2.7 5.6

Power (mW) 1.97 20.6 4.8

S12 (dB) -28 -32 -45.86

S11 (dB) -20 -14 -10.3

S22 (dB) -22 -8.8 -14.5

[1] ‘Design of a New Low-Power 2.4 GHz CMOS LNA’, Ickjin Kwon and Hyungcheol ShinJournal of the Korean Physical Society, Vol. 40, No. 1, January 2002, pp. 47[2] ‘Low-power 5 GHz LNA and VCO in 90 nm RF CMOS’ , D. Linten et.al, VLSI Circuits 2004, Digest of Technical Papers. 2004 Symposium, 17-19 June 2004, 372- 375.

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Comparison with normal designsParameter Paper[3] Paper[4] This Work

Technology(nm) 90 90 90

Voltage Supply (V) 1.2 1.2 1.5

Frequency (GHz) 5.5 3.1 to 5.9 5.0

Gain (dB) 13.3 13.5 13

NF (dB) 2.9 2.8 – 3.8 5.6

Power (mW) 9.72 5.4 4.8

S12 (dB) -28 <-57 -45.86

S11 (dB) -14.4 ~ - 15 -10.3

S22 (dB) -19 NA -14.5

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[3] ‘A 5-GHz Fully Integrated ESD-Protected Low-Noise Amplifier in 90-nm RF CMOS’, IEEE journal of solid state circuits, Dimitri Linten et.al, VOL. 40 No. 7 JULY 2005.[4] ‘A 90-nm CMOS Two-Stage Low-Noise Amplifier for 3-5-GHz Ultra-Wideband Radio’ , Radio Frequency Integrated Circuits Symposium 2008, p489 – 492.

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Conclusion and Future workThe current re-use technique will enable bias current sharing

between two amplifier stages.This in turn reduces the power dissipated in the circuit and

hence the energy consumption.Noise matching at the input port can be improved to get a

better NF.LNA for 60 GHz and above with low power design.The transistor stages are stacked in the work here, we can find

the optimum number of transistor stages that can be stacked for a constant power supply ‘Vdd’ and find gain and power consumption values for each increase in the stage.

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Referenceshttp://bwrc.eecs.berkeley.edu/Research/RF/projects/60GHz/ma

tching/ImpMatch.html for impedance matching.

Introduction to LNA Design, queen’s learning wiki. http://bmf.ece.queensu.ca/mediawiki/index.php/Introduction_to_LNA_Design

RF Microelectronics by B Razavi, Prentice Hall Communications Engineering and Emerging Technologies Series.

Radio Frequency Electronics by Jon B Hagen, Cambridge University Press.

‘60-GHz PA and LNA in 90-nm RF-CMOS’, Yao T et.al, Radio Frequency Integrated Circuits Symposium, 2006, IEEE, 4 pp.

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