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 GHz is a “quiet” band Used 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 design had noise figure of 6-8 dB Want 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:

All components can also be characterized by an equivalent noise temperature:

Bk

PT se

BkG

PT oe

Noise Figure

Noise Figure (F) is another way of expressing noise Defined as the reduction in signal-to-noise ratio:

Can also be calculated from the equivalent noise temperature:

For a lossy component at To=290K, the noise figure is equal to the attenuation in the component:

1oo

ii

NS

NSF

oeo

e TFTT

TF )1(1

oT

TLF

GL )1(1

1

Noise in Systems

Most real systems are a series of individual components in cascade Can be represented by an equivalent network:

The noise figure and equivalent temperature of the cascade is:

The characteristics of the first component dominate the system In a low-noise system, the first amplifier stage is key

G1F1Te1

G2F2Te2

G1G2FcasTe,cas

21

3

1

21,

21

3

1

21

11

GG

T

G

TTT

GG

F

G

FFF ee

ecasecas

System Overview

Current System Design (J. Simoneau)

Amplifier to be replaced

Transmission Lines

T-lines are efficient conductors of RF energy and inefficient radiators

Come in balanced and unbalanced forms

Coaxial cable is a common form of unbalanced line

T-lines 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:

0

0

ZZ

ZZ

L

L

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.

CopperSubstrate

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-of-

circuit 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

Single-stub tuner

Quarter-wave transformer

Bias Tees

MMIC

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?