Low Noise Amplifier Design

1
Low Noise Amplifier Design

• Session 8

2
Introduction of Noise

• High Frequency Noise
• Thermal (Johnson or Nyquist) noise
• Thermal vibration of bound charges.
• Shot noise
• Random fluctuations of charge carriers.
• Low Frequency Noise
• Flicker (1/f) noise
• Noise power varies inversely with frequency.

LNA cares high frequency noise only!
3
Noise Factor and Noise Figure of Amplifier
Si Input signal power So Output signal
power Ni Standard input thermal noise No Total
output noise power ?N Amplifier excess noise
power G Amplifier power gain
Noise factor
Noise figure
(NikT0B-174dBm/HzBandwidth(dBHz) _at_ TT0290K)
4
Noise Figure of a Two-Port Networks
Noise Parameters (4 values) Fmin Minimum noise
factor _at_ ?S ?min rn Rn/Z0 Normalized noise
resistance GminGmin?qmin Minimum-noise source
reflection coefficient _at_ F Fmin
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Noise Parameters of the Transistor
GaAs FET ATF-10136 Noise Parameters
Bias dependent
Frequency dependent
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Noise Parameters from Linear Model
Touchstone-format S-parameters with noise data
! SIEMENS Discrete RF Semiconductors ! BFP420 !
Si NPN RF SIEGET Grounded Emitter Transistor in
SOT343 ! VCE 1 V IC 1.5 mA ! Common
Emitter S-Parameters
February 1998 GHz S MA R 50 ! f
S11 S21 S12
S22 ! GHz MAG ANG MAG ANG MAG
ANG MAG ANG 0.010 0.9253 -0.9 5.283
179.7 0.0013 94.7 0.9962 -0.5 0.100
0.9234 -7.4 5.274 174.7 0.0117 85.7
0.9935 -4.1 1.000 0.8120 -72.4 4.363 126.8
0.0972 48.1 0.8140 -37.3 2.000 0.6826
-129.4 3.080 88.7 0.1318 21.7 0.5819
-60.9 3.000 0.6464 -171.6 2.264 61.1 0.1373
6.7 0.4292 -76.2 4.000 0.6509 155.6
1.748 38.1 0.1339 -2.2 0.3584 -96.2 5.000
0.6888 132.5 1.389 18.6 0.1269 -7.3
0.3011 -115.3 6.000 0.7115 116.0 1.148 1.5
0.1241 -7.7 0.3095 -142.2
! ! f Fmin Gammaopt rn/50 ! GHz
dB MAG ANG - 0.450 0.71 0.32 21
0.35 0.900 0.76 0.51 34 0.27 1.800
1.07 0.36 78 0.20 2.400 1.17 0.36
97 0.19 3.000 1.43 0.37 132 0.12
4.000 1.70 0.41 -173 0.09 ! ! SIEMENS AG
Semiconductor Group, Munich
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Noise Parameters from Nonlinear Model
Nonlinear Transistor Model
Determine Biasing Circuits
Small Signal Analysis
Noise measurements
Optimum Noise Figure Match GMN Minimum Noise
Figure NFMin Noise Resistance RN
?????????????,???????!
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Constant Noise Figure Circles of Transistor

• Let F Fi ? Fmin
• GS- CFi rFi
• ?GS-Plane??????,????constant noise figure circle

??
??
where
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Constant Noise Figure Circles of Transistor
NFmin-3dB
rn??,???Gmin?NF?????
NFmin-2dB
NFmin-1dB
NFmin
Gmin
GS-Plane
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Noise Circles v.s. Available Gain Circles
Trade-off is needed!
NF
Gmin
GA
??NF and GA ????VSWR1
GS-Plane
GMS
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Inductor Series Feedback Method
BFP420 (IC1.5mA, VCE1V) _at_ f2GHz
Stabilizing load
Emitter feedback inductor
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Inductor Series Feedback Method
GMS
Gmin
LE 0 nH
LE 0.8 nH
LE 2.4 nH
??LE???GMS?Gmin??,?????????????input
matching???????????