Design of a Low-Noise 24 GHz Receiver Using MMICs Eric Tollefson, Rose-Hulman Institute of Technology Advisor: Dr.
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Transcript Design of a Low-Noise 24 GHz Receiver Using MMICs Eric Tollefson, Rose-Hulman Institute of Technology Advisor: Dr.
Design of a Low-Noise 24 GHz
Receiver Using MMICs
Eric Tollefson, Rose-Hulman Institute of Technology
Advisor: Dr. L. Wilson Pearson
Overview
Project
Description and Background
Introduction to Noise
System Overview
Microwave Components
Design
Results
Future Work
Acknowledgements
Project Background
23.6-24
Used
GHz is a “quiet” band
for passive sensing of water vapor
Making
measurements of manmade signals
present from 23.3-24.3 GHz
– 24.0-24.25 GHz is an ISM band
For
maximum sensitivity, the receiver must have
as little noise as possible
Previous
Want
design had noise figure of 6-8 dB
to redesign for a newer first-stage amplifier
with better noise performance
Introduction to Noise
Noise
is a natural phenomenon present everywhere
White noise has Gaussian distribution and equal power at
all frequencies
Often referred to as AWGN – Additive White Gaussian
Noise
A source can be modeled by a noisy resistor at
temperature Te:
Ps
Te
kB
All
components can also be characterized by an
equivalent noise temperature:
Po
Te
Gk B
Noise Figure
Noise Figure (F) is another way of expressing noise
Defined as the reduction in signal-to-noise ratio:
F
Can also be calculated from the equivalent noise temperature:
F 1
Si N i
1
So N o
Te
To
Te ( F 1) To
For a lossy component at To=290K, the noise figure is equal to the
attenuation in the component:
1
L
G
T
F 1 ( L 1)
To
Noise in Systems
Most real systems are a series of individual components in cascade
Can be represented by an equivalent network:
G1
F1
Te1
G2
F2
Te2
The noise figure and equivalent temperature of the cascade is:
F2 1 F3 1
Fcas F 1
G1
G1 G2
G1G2
Fcas
Te,cas
Te,cas
Te 2
Te3
T e1
G1 G1 G2
The characteristics of the first component dominate the system
In a low-noise system, the first amplifier stage is key
System Overview
Amplifier to be replaced
Current System Design (J. Simoneau)
Transmission Lines
T-lines
are efficient conductors of RF energy and
inefficient radiators
Come
in balanced and unbalanced forms
Coaxial
T-lines
cable is a common form of unbalanced line
have a characteristic impedance
– Normally must be matched to other components
– 50 Ω is the most common
Mismatches
at junctions create reflections
– Represented by Γ, the reflection coefficient:
Z L Z0
Z L Z0
Microstrip Construction
Microstrips are another form of transmission line
Circuit is created in copper over substrate and ground plane
Substrate is dielectric material, usually low-loss
Shape determines electrical characteristics
– Strip width determines characteristic impedance
– Open-ended stubs add reactance
– Stubs can also provide virtual short circuits to ground
– Combinations form filters, impedance transformers, etc.
Substrate
Copper
Fujitsu LNA MMIC
Monolithic
Microwave
Integrated Circuit
Fujitsu FMM5701X
– Wide bandwidth: 18-28 GHz
– High gain: 13.5 dB @ 24
GHz
– Low noise figure: 1.4 dB @
24 GHz
– Requires external matching
and bias circuitry
– Difficult to perform out-ofcircuit testing
520 μm
450 μm
Design of Matching Networks
For
maximum gain, amplifier input should be
conjugate matched (Γin= ΓL*)
For
optimum noise performance, amplifier input
must see a specified reflection coefficient (Γin=
Γopt)
Chose
to optimize for noise performance
– Used single-stub tuner to match 50 Ω to Γopt
– Used quarter-wave transformer to match amplifier
output to 50 Ω line
Design of DC Bias Tees
Amplifier
is powered by DC bias injected into RF
input and output pins
Must
design circuitry to provide RF isolation from
the DC source and block DC from the RF signal
path
– Used radial stubs to provide virtual RF short to ground
– Used λ/4 sections to transform short into open at
transmission line
– Will use coupled lines in future versions to block DC
from RF connections
Completed Design
Bias Tees
MMIC
Single-stub
tuner
Quarter-wave transformer
Results – S Parameters
Bias Conditions:
VDD=0 V
IDD=0 mA
VGG=-1 V
Results – S Parameters (cont.)
Bias Conditions:
VDD=5 V
IDD=72 mA
VGG=-1 V
Future Work
Troubleshoot
to obtain correctly working
prototype
Verify
that matching design is correct
Measure
noise figure and gain parameters
Integrate
into complete system
Measure
whole-system parameters for
comparison with previous design
Take
new noise measurements
Acknowledgements
Dr.
L. Wilson Pearson
Joel Simoneau
Chris Tompkins
Simoneau,
J. et al. “Noise Floor Measurements
in the Passive Sensor Band (23.6 to 24 GHz)”
Pozar, David. “Microwave Engineering 2nd Ed.”
John Wiley & Sons, 1998.
Questions?