Rakshith Venkatesh
4/27/2009
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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:
Typical values of
conventional
design and my
objective
 The main intension is to
design a low power RF
amplifier without sacrificing
the amplifier gain and its
Noise-Figure
(SNR_in/SNR_out).
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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
3
Design Steps
 The 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
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 designs
Parameter
Paper[1]
Paper[2]
This work
250
90
90
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
Technology (nm)
Voltage Supply (V)
[1] ‘Design of a New Low-Power 2.4 GHz CMOS LNA’, Ickjin Kwon and Hyungcheol Shin
Journal 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 designs
Parameter
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
[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 work
 The 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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References
 http://bwrc.eecs.berkeley.edu/Research/RF/projects/60GHz/mat




ching/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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