LOW NOISE AMPLIFIER DESIGN FOR RADIO TELESCOPE SYSTEM

VAHID KOUHDARAGH

UNIVERSITI TEKNOLOGI MALAYSIA

UNIVERSITY TECHNOLOGY OF MALAYSIA

LOW NOISE AMPLIFIER DESIGN FOR RADIO TELESCOPE SYSTEM

VAHID KOUHDARAGH

A project report submitted in partial fulfillment of the

requirements for the award of the degree of

Master of Science (Electronic and Telecommunication Engineering)

Faculty of Electrical

University Technology of Malaysia

NOVEMBER 2009

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Dedicated to my beloved family and country, Iran.

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ACKNOWLEDGEMENT

First and foremost, I would like to express my gratitude to God for His

abundant grace that I am able to be what I am today. I also wish to express my

sincere appreciation to my thesis supervisor, Dr. Sharifah Kamilah Bte Syed Yusof

for her precious guidance, encouragement, critics, advices, knowledge and

motivation. Without her support and interest, this thesis would not have been the

same as presented here.

I would love to express my thank you to all my fellow postgraduate students

who have been going through the thick and thins during the development of this

thesis. My sincere appreciation also goes to all my colleagues and friends who have

provided assistance at various occasions. Last but not least, a very special

appreciation goes to my family for their continuous supports, loves and cares.

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ABSTRACT

The purpose of this project is to design a low noise amplifier (LNA) for a

radio telescope. The LNA is an electronic amplifier used in communication systems

to amplify extremely weak signals captured by antennae. This thesis describes the

procedure of designing an LNA for 7 GHz frequency. Noise matching is an

important technique which was considered in the design process. The designed LNA

achieved a gain of 30 dB with 1 GHz bandwidth. The noise figure achieved was less

than 2.9 dB. Return-losses were improved by 6 dB with a new proposed optimization

method.

ABSTRAK

Objektif projek ini adalah untuk mencipta sebuah penguat suara rendah

(LNA) untuk teleskop radio. The LNA adalah penguat elektronik yang digunakan

dalam sistem komunikasi untuk menguatkan isyarat yang sangat lemah untuk

ditangkap oleh antena. Tesis ini menjelaskan seluruh prosedur dalam penciptaan

sebuah LNA selama 7 GHz frekuensi. Kebisingan yang berpadanan adalah teknik

penting yang dipertimbangkan dalam proses penciptaan. LNA yang dicipta dapat

mencapai gain 30 dB dengan 1 GHz bandwidth. Angka hingar yang diperolehi

adalah kurang daripada 2,9 dB. Kehilangan dapat diperbaiki sebanyak 6 dB dengan

kaedah yang dicadangkan.

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TABLE OF CONTENT

CHAPTER TITLE PAGE

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

TABLE OF CONTENT vi

LIST OF APPENDICES vii

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF ABBREVIATIONS xvi

LIST OF SYMBOLSLS / NOTAITIONS xvii

1 INTRODUCTION 1

1.1 Radio Telescope 1

1.2 LNA‟s Usage in Radio Telescope 2

1.3 Noise and Temperature 3

1.4 FET Modeling and Noise Parameter 4

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1.5 Reducing Receiver Front-End Noise 5

1.6 Problem Statement 6

1.7 Project Objectives 6

1.8 Scope of Study 7

2 LITERATURE REVIEW 8

2.1 LNA in Radio Telescope 9

2.2 The Ideal Amplifier and LNA 9

2.3 Investigation on Previous Studies 13

2.3.1 Dual MOSFET in LNA Design 13

2.3.2 2-Stage LNA by MOSFET 15

2.3.3 LNA Design with Chebyshev Filter 16

3 METHODOLOGY 20

3.1 Introduction 20

3.2 Noise, Noise Temperature and Noise Figure 23

3.3 Designing Process 24

3.4 Calculations and Designing Process 24

3.4.1 Biasing 24

3.4.2 Design Rules for Impedance Matching Networks 26

3.4.3 Design of Impedance Matching Networks 27

3.4.3.1 Input Matching Network for 7 GHz 27

3.4.3.2 Output Matching for 7 GHz 29

3.4.3.3 Intermediate Matching Network for 7 GHz 31

3.4.4 Improving Return Losses 32

3.5 Stability at 7 GHz for ATF-34143 33

3.6 Schematic of Circuit at Two Stages and component

Values 35

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3.7 Designing for 5 Stage 37

3.8 New Method for Improving Return Losses 38

4 RESAULTs AND ANALYZING 41

4.1 Introduction 41

4.2 2-Stage Cascade LNA 41

4.3 5-Stage LNA 47

4.4 Previous Studies Analyzing 52

4.5 Conclusion 57

5 CONCLUSION AND DISCUSSION 58

REFERENCES 59

APPENDICES A-B 65-84

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A Process Flow Chart 65

B Gantt Chart Project 2 67

C Data Sheet 69

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LIST OF TABLES

TABLE NO. TITLE PAGE

3.1 Capacitor Values 37

3.2 Resistor Values 38

3.3 Inductor Values 38

4.1 2-Stage LNA Properties 47

4.2 5-Stage LNA Properties 50

4.3 Simulation Results After and Before 52

Optimization

4.4 Proposed Design in Comparison with 57

Other Related Studies

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 LNA‟s Position in Radio Telescope 3

1.2 Intrinsic Noise Equivalent Circuit of a FET 5

2.1 Block Diagram of a Radio Telescope 9

2.2 The Nullor Simple Schematic 10

2.3 Noise Cancelling Principle 12

2.4 Dual MOSFET Gate Schematic 14

2.5 2-Stage LNA by 4 Transistors 16

2.6 CMOS LNA with Chebyshev Filter 17

2.7 Miller Structure in LNA 19

3.1 The Flowchart of Designing a LNA 22

3.2 DC Biasing Network 25

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3.3 The Block Diagram of an Amplifier Circuit 25

3.4 Input Matching Network by Smith Chart 29

3.5 Output Matching Network by Smith Chart 31

3.6 Intermediate Matching Network by Smith Chart 33

3.7 Reflection Coefficients on a 2-Port Network 35

3.8 Schematic of Circuit at Two Stages 36

3.9 Two First Stages of 5 Stages Cascade 39

4.1 Noise Figure Performance (2-Stage LNA) 42

4.2 S-Parameters Performance (First Step) 43

4.3 S-Parameters Performance (Second Step) 44

4.4 Circuit of LNA After Adding Inductors and Capacitors 45

4.5 S11 and S12 Performance (Last Step) 45

4.6 S21 and S22 Performance (Last Step) 46

4.7 Stability Figure (mu_load) 46

4.8 5-Stage LNA‟s Circuit (Two First Stages) 48

4.9 Noise Figure Performance (5-Stage LNA) 48

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4.10 S- Parameters Performance for 5-Stage Cascade (First Step) 49

4.11 S-Parameters Performance for 5-Stage LNA (Last Step) 51

4.12 Stability Factor over Frequency (5-Stage LNA) 51

4.13 NF and Gain Performance (LNA with Dual Mosfet) 53

4.14 NF Performance over Frequency 54

4.15 S-Parameters Performance over Frequency (Common Gate) 54

4.16 NF and Gain Performance over Frequency (Chebyshev Filter) 55

4.17 Return Losses Performance over Frequency (Chebyshev Filter) 56

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LIST OF ABBREVIATIONS

LNA - Low Noise Amplifier

ADS - Advance Design System

NF - Noise Figure

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LIST OF SYMBOLSLS / NOTAITIONS

T - Total Noise Temperature

Gn - Available Power Gain of Nth Amplifier

K - Boltzmann‟s Constant (J/K)

- Operating Bandwidth (Hz)

Fmin - The Minimum Noise of Transistor

- Impedance of Source

- Impedance of Load

Vgs - Voltage of gate-source

Γ - Reflection Coefficient

Igss - Gate Leakage Current

Mu_load - Stability Coefficient

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CHAPTER 1

INTRODUCTION

1.1 Radio Telescope

A radio telescope is a form of directional radio antenna which is used in radio

astronomy. Radio waves reaching the ground can show objects or phenomena that

are difficult or impossible to detect in other wavelength ranges. Radio telescope

system involves the reflector, sub reflector, tertiary reflector, feed, cryogenics

subsystem, LNA, noise calibration system, frequency converters, digital

spectrometers, continuum signal processing, and monitor and control system. In this

thesis, the focus of the work would be on Low Noise Amplifier (LNA) design for

radio telescope system. [2]

1.2 LNA’s Usage in Radio Telescope

The LNA is a particular type of electronic amplifier which can be used in

communication systems and radio telescopes to amplify very weak signals which is

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captured by an antenna. In order to reduce the losses in the feed line, the LNA should

be located near to the antenna [1]. The ability of the receiver to detect a weak input

signal is fundamentally limited by the electrical noise which is present at its input.

Therefore proper design techniques should be considered to achieve the lowest

possible noise. LNAs are used in many systems where low-level signals must be

sensed and amplified [22]. Generally, the LNA is capable of decreasing most of the

incoming noise and amplifying a desired signal in a certain frequency range to

increase the signal to noise ratio (SNR) of the communication system and improve

the quality of received signal as well.

LNA‟s are used in conjunction with many radio frequency functions. The

signals which are coming from cosmic sources are originally unprocessed

information and should be analyzed in a proper manner. One of the most critical

building blocks in a radio telescope is LNA. This is because the incident signals from

cosmic sources are very weak in amplitude. Therefore, in order to analyze them they

should be amplified more than other signals [12].

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Figure 1.1 LNA‟s Position in Radio Telescope [2]

1.3 Noise and Temperature

Generally, noise is something indistinguishable and undesirable. In

electronics fields however, it is something that always exist and have to be dealt with.

When an amplifier doesn‟t have any input signal, a tiny randomly oscillating output

signal can still be detected and is referred to as noise. Noise in electronic components

is made by random thermal oscillating of electrons so any device that operates over

absolute zero produces noise. [10].

In radio astronomy, noise is defined in terms of noise temperature. The noise

temperature of an antenna is the thermal temperature of a resistor whose terminals,

over a specific frequency bandwidth, have a mean available noise power due to

thermal agitation equivalent to the available power at the antenna‟s terminals. Using

temperature units permits direct comparison with celestial “source temperatures”

[12].

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Every object will produce electromagnetic waves if its temperature is above

absolute zero. The noise temperature of an antenna‟s radiation resistance will be

equal to the temperature of the particular source the antenna is “looking at” if the

angular extent of the source “fills” the antenna beam. This statement excludes non-

thermal mechanisms that generate electromagnetic waves such as synchrotron

radiation. In such cases, the noise temperature of the antenna‟s radiation resistance is

not equal to the thermal temperature of the source but instead would be equivalent to

the thermal temperature of an ideal blackbody emitting the same radiation at the

observing frequency. An ideal blackbody is defined as a perfect absorber and

radiator: it absorbs radiation at all frequencies and its own radiation is a function of

only temperature and frequency [12].

1.4 FET Modeling and Noise Parameter

The noise parameters of a FET can be calculated upon obtaining its

equivalent circuit noise model. Theoretically, the noise parameters depend on certain

parameters of the circuit model. The circuit model of the transistor is obtained by

iteratively fitting the model S-parameters to the actual measured S-parameters of the

device. There are various methods of doing this. Here, the chosen method is centered

on least-squares fitting of the simulated output of a circuit model to measured S-

parameters. After convergence, reliable values for various circuit elements such as

package capacitances and inductances are obtained. This method had been used for

manual calculation to obtain the value of NF and it is obvious that by using

sophisticated and strong software there is no worry about complicated calculations

[12]. Figure 1.2 shows intrinsic noise equivalent circuit of a FET.

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Figure 1.2 Intrinsic Noise Equivalent Circuit of a FET [12]

1.5 Reducing Receiver Front-End Noise

When radio signals reach Earth from thousands of light years away, they have

been really flagged and very weak. For detecting these signals, receiver front-ends

must have high gain and most importantly, very low noise amplifiers. Noise and gain

are important due to a particular property of amplifiers: first stage amplifier has the

most noise that typically dominates the noise of the stages after it. For a cascade of

amplifiers, the total noise temperature can be obtained by [12]:

T = + [ / + [ / ( )] + [ / ( )] +…. (1.1)

Where-

T = total noise temperature

Tn = noise temperature of nth amplifier

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Gn = available power gain of nth amplifier .

The solution to achieve low noise in an amplifier depends on the type of

transistor being used in the design. Gallium arsenide field-effect transistors (GaAs

FETs) and high electron mobility transistors (HEMTs) are the most familiar types of

transistors that have been used in LNAs for high frequencies. Technology has made

it probable for high frequency amplifiers to have excellent noise performance

without using cryogenic cooling. Although cryogenic cooling of receivers is usually

used to obtain low system noise temperatures in radio astronomy but the high cost of

procedure and maintenance are two main disadvantages of using cryogenic cooling.

Therefore, the application of cryogenic cooling is not considered in this work. There

are several limitations in the design of LNAs for high frequency applications. For

instance, a design for lowest noise may not lead to attain lowest return losses.

Therefore an optimized design is necessary to achieve the lowest noise and return

losses [12].

1.6 Problem Statement

Radio astronomy signals are very weak in amplitude. Therefore, in order to

analyze these signals an amplification of the signal is essential while the noise is

minimized. In order to solve this problem, LNA should be used in radio telescope

receivers. There are several limitations in design of LNAs for high frequency

application, for instance a design for lowest noise may not lead to attain lowest return

losses. Therefore an optimized design is necessary to achieve the lowest noise and

return losses [12].

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1.7 Project Objectives

The objective of this project is to design a LNA for radio telescope with high

gain and stability and low return losses and noise figure.

1.8 Scope of Study

This study is limited to the following scope of work in order to meet the specified

objectives:

(a) The LNA has been designed for 7 GHz frequency.

(b) LNA should have a gain more than 20 dB.

(c) NF should be less than 3.5 dB.

(d) The input and output return losses should be less than -10 dB.

(e) LNA should be unconditionally stable therefore the K factor should be more

than 1.

(f) The ADS has been used to simulate the circuit and to investigate the stability,

noise figure, gain and return losses.