Design of RF CMOS Low Noise Amplifiers Using a Current Based MOSFET Model

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Design of RF CMOS Low Noise Amplifiers Using a
Current Based MOSFET Model

• Virgínia Helena Varotto Baroncini
• Oscar da Costa Gouveia Filho

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OUTLINE

1. Introduction
2. MOSFET Model
3. High-Frequency Noise Model
4. LNA Analysis
5. LNA Design Example
6. Conclusion

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Introduction

• Submicrometer CMOS technology allows the
  integration of RF circuits.
• Low voltage and low power operation ? moderate
  inversion
• Model valid from weak to strong inversion

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MOSFET MODEL
IF forward current
IR reverse current
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Normalized currents
and
is the normalization current
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Operation Regions of the MOS transistor
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Small signal parameters
Transconductances
Capacitances
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High- Frequency Noise Model
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Channel Thermal Noise
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Induced Gate Noise
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(No Transcript)
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LNA Analysis
Cascode LNA with inductive source degeneration
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Impedance Matching
Z1 can be viewed as the parallel of a resistor R
with the capacitance Cgs
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Simplified small signal model for the LNA
matching is achieved simply by making the real
part of Zin equal to the source resistance and
its imaginary part equal to zero.
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Noise Figure
Definition
LNA small-signal model for noise calculations
The noise figure can be expressed as a function
of if
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Noise figure versus W/L for several inversion
levels at 2.5 GHz
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LNA Design Example
LNA Design Parameters
Resonance frequency 2,5 GHz
Supply voltage 2,5 V
Length 0,35 ?m
Source resistance 50 ?
Noise Figure lt 2dB
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1. Choice of the inversion level
Procedure
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2. Ls for impedance matching
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3. Transistor width for minimum noise figure
Noise figure versus W/L for several inversion
levels at 2.5 GHz
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4. Lg to satisfy the resonance frequency
5. Ld to adjust the gain and the output resonance
frequency
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LNA Design Results
W/L W ID Rs Ls Lg Ld
1500 525 ?m 4,1 mA 50 ? 0,7 nH 7,6 nH 2,5 nH
VDD
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Simulation results
Input impedance
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Noise Figure
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Conclusions

• The main advantage of this methodology is that is
  valid in all regions of the operation of the MOS
  transistors
• It is possible to move the operation point of RF
  devices from strong inversion to moderate
  inversion taking advantage of higher gm/ID ratio,
  without degrading the noise figure