DESIGN OF AN ULTRA-WIDE-BAND CMOS LOW NOISE AMPLIFIER

A Thesis Submitted to the Department of Electrical and Electronic Engineering

Of AHSANULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY

By Md. Sadirul Islam, Student ID: 09.01.05.152 Farzana Ishtiaq, Student ID: 09.01.05.160 Afsana Akhtar, Student ID: 09.01.05.202 Shakib Aman, Student ID: 09.01.05.208

Tazreen Ahmed, Student ID: 09.01.05.028

In Partial Fulfillment of the Requirements for the Degree Of

Bachelor of Science in Electrical and Electronic Engineering July 2013

AHSANULLAH UNIVERSITY OF SCIENCE AND TECHNOLOGY Dhaka, Bangladesh

i

DECLARATION

This is to certify that this thesis is the outcome of the original work of the undersigned. No part of this work has been submitted elsewhere, partially and fully, for the award of any other degree or diploma. Materials of work found by other researcher are mentioned by references. Any material reproduced in this thesis has been properly acknowledged.

(Dr. Pran Kanai Saha) (Md. Sadirul Islam) Professor, Department of Electrical and Electronic Engineering BUET, Bangladesh

(Farzana Ishtiaq)

Signature of Supervisor

(Afsana Akhtar)

(Shakib Aman)

(Tazreen Ahmed)

Signature of Authors

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ACKNOWLEDGMENTS

We want to express our sincere gratitude to our supervisor, Professor Dr.

Pran Kanai Saha, for his continuous guidance and support throughout our

thesis at Ahsanullah University of Science And Technology. His wisdom and

kindness had been invaluable and made the whole thesis experience

enjoyable.

We specially thank Mr. Md. Sariful Islam (Lecturer, Dept. of EEE, AUST) for his

valuable suggestion and concise comments on some of the research papers of

the thesis. He has been very kind enough to extend his help at various phases

of this research.

This thesis would not have been possible without the guidance and the help of

several individuals who in one way or another contributed and extended their

valuable assistance in the preparation and completion of this thesis.

Last but not the least, to our family and the one above all of us, the

omnipresent God, for giving us the strength to complete this thesis within

given resource and time.

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ABSTRACT

The objective of this paper is to investigate a ultra-wideband (UWB) low noise

amplifier (LNA) by utilizing a simple inductively degenerated LNA with

resistive feedback into differential topology, which can improve the

bandwidth. The Proposed LNA has been simulated by using HSpice

considering BSIM3 model in 0.18 m RF CMOS technology. Based on those

technologies, this proposed UWB LNA obtained a flat gain 8dB bandwidth of

4.7GHz, the constant gain of 8dB, noise figure lower than 2.2dB, and the return

loss better than 30dB. HSpice simulation of the proposed LNA shows wider

bandwidth of 1.2GHz, low power consumption with gain of 8dB in the

frequency band of 4.2 GHz to 8.9GHz. Finally, LNA characterization exhibits

ultra-wide bandwidth characteristic and low noise margin. This proposed

LNA can be used in UWB and microwave communication system.

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Contents

Chapter 1 Introduction1

1.1: Ultra-wideband Technology.....................1

1.2: CMOS Technology.3

1.3: VLSI Technology3

1.4: Basic concept of Ultra-Wide-Band Technology4

1.5: Ultra-Wide-Band Technologies..6

1.5.1: Carrier Free Direct Sequence UWB Technology.6

1.5.2: Multi-Band OFDM (MB-OFDM) UWB Technology........6

1.6: Advantages of using Ultra-Wide-Band.6

1.7: Potential Applications of Ultra-Wide-Band.10

1.7.1: Communications and Sensors10

1.7.2: Position Location and Tracking.12

1.7.3: Radar Applications12

1.8: Ultra-Wide-Band Design Challenges12

1.9: Objective of this thesis..13

1.10: Organization of the thesis...13

Chapter 2 UWB Low Noise Amplifier (LNA)...14

2.1: Parameters in LNA Design.16

2.1.1: Noise Figure.16

2.1.2: Input Impedance Match.18

2.1.3: Gain.19

2.1.4: Linearity.20

2.2: Low Noise Amplifier (LNA) Topologies.22

2.2.1: Amplifier Distributed (DA).23

2.2.2: Common Gate (CG)24

2.2.3: Inductively Degenerated Common Source Topology (IDCS)...26

2.2.4: Cascode Topology..27

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2.2.5: Folded Cascode Topology...28

2.2.6: Cascade Topology29

2.2.7: Current Reuse Topology..29

2.2.8: Differential Topology.31

2.2.9: Novel Topology.32

2.3: Proposed Topology.32

Chapter 3 Architecture of UWB LNA and Simulation Results..33

3.1 Architecture of UWB LNA...36

3.1.1 Single Ended LNA.37

3.1.2 Full Differential LNA..41

3.1.3 Balun Circuit43

3.2 Final Simulation Results..44

Chapter 4 Conclusion..52

4.1 Summary of Contribution...52

4.2 Future Work52

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List of Figures

Fig 1.1: Ultra wideband Technology ..2

Fig 1.2: Block Diagram of UWB System.2

Fig 1.3: Illustration of the Definition of UWB frequency range..4

Fig 1.4: UWB spectral mask for indoor communication systems..5

Fig 2.1: (a) Block Diagram of LNA at receiving end14

(b) Signal processing.15

Fig 2.2: Combination of power amplifier circuit and LNA circuit..15

Fig 2.3: Equivalent small signal circuit...17

Fig 2.4: More hardware in the input matching network..19

Fig 2.5: Equivalent circuit with inductive source degeneration.19

Fig 2.6: CP1 and 3rd order intercept point20

Fig 2.7: Two-tones with the IDM3 product...21

Fig 2.8: Generalized structure of distributed LNA...23

Fig 2.9: Conventional CG- LNA and low noise techniques employing feedback ..24

Fig 2.10: (a) Common source configuration for Narrow band 26

(b) Inductive degenerated CS for UWB..26

Fig 2.11: Cascode configuration..27

Fig 2.12: Folded cascade configuration..28

Fig 2.13: Conventional current reuse configuration..30

Fig 2.14: Differential capacitive cross coupled configuration..31

Fig 2.15: Noise cancelling principle of differential topology.31

Fig 3.1: Block Diagram of LNA.33

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Fig 3.2: Common LNA Architectures: Resistive termination34

Fig 3.3: Common LNA Architectures: 1/gm termination34

Fig 3.4: Common LNA Architectures: Shunt-series feedback...35

Fig 3.5: Common LNA Architectures: Inductive degeneration35

Fig 3.6: Simplified Block Diagram of proposed LNA..36

Fig 3.7: LNA topology for UWB single ended LNA...37

Fig 3.8: LNA topology for UWB LNA Small-signal equivalent circuit of the input of LNA...38

Fig 3.9: S21of Single Ended LNA...39

Fig 3.10: S11of Single Ended LNA39

Fig 3.11: AC output Noise Figure of Single Ended LNA.40

Fig 3.12: Maximum Power Gain of Single Ended LNA...40

Fig 3.13: Full-Differential LNA.41

Fig 3.14: Balun Circuit...43

Fig 3.15: S21 (dB) of Differential LNA...44

Fig 3.16: S11 (dB) of Differential LNA...44

Fig3.17: Comparison between S21 and S11 ...45

Fig 3.18: AC output Noise figure of Differential LNA.46

Fig 3.19: Minimum AC output Noise figure of Differential LNA..46

Fig 3.20: S22 of Differential LNA..47

Fig 3.21: Comparison between S11 and S22 of Differential LNA...47

Fig 3.22: S12 of Differential LNA..48

Fig 3.23: Output Noise of Differential LNA...48

Fig 3.24: Input Noise (dB) of Differential LNA...49

Fig 3.25: Comparison between input noise (dB) and output noise (dB)...49

Fig 3.27: Maximum Power Gain of Differential LNA..50

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List of Tables

Table 1.1: FCC allocations for each UWB category.5

Table3.1: Comparison of performance between Single ended LNA and Differential LNA........50

Table3.2: Performance of LNA51

Table3.3: Comparison with other LNA from the bibliography.51

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List of Abbreviations

BPSK Binary Phase Shift Keying

CGLNA Common-Gate Low-Noise Amplifier

CSLNA Common-Source Low-Noise Amplifier

CCC Capacitive Cross-Couple

CDMA Code Division Multiple Access

DS Direct Sequence

EVDO Enhanced Voice-Data Only

EIRP Effective Isotropic Radiated Power

FH Frequency Hopping

FCC Federal Communications Commission

IP3 3rd Order Intercept Point

IMD3 3rd Order Intermodulation

IDCS Inductively Degenerated Common Source

IIP3 3rd Order Input Power Level

LPI Low Probability of Intercept

LPD Low Probability of Detection

LOS Line Of Sight

MBOFDM Multi-Band Offset Frequency Division Modulation

MMIC Microwave Monolithic Integrated Circuit

NLOS Non-Line Of Sight

OFDM Offset Frequency Division Modulation

OIP3 3rd Order Output Power Level

x

PG Processing Gain

PDA Personal Digital Assistant

PSD Power Spectral Density

SNR Signal To Noise Ratio

SpO2 Oxygen Saturation Sensor

SFDR Spurious Free Dynamic Range

UWB Ultra-wideband

VSWR Voltage Standing Wave Ratio

WWAN Wireless Wide Area Network

WLAN Wireless Local Area Network

WPAN Wireless Personal Area Network

WBAN Wireless Body Area Network

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Chapter 1

Introduction

The late 20th and early 21st century can be referred to as the wireless era, in which we

witnessed the rapid growth of wireless communication technologies. It is not uncommon

nowadays for an average home to have several digital cameras, portable music players,

cellular phones and external hard drives. As the number of device increase, so does the

number of wires connecting these devices together. It is usually frustrating to see a mess of

cables around the home or office desk and can also be inconvenient to have to carry these

cables when travelling.

One could see how wireless technologies could erase the life of user by removing some or

all of these wires. The current wireless data technologies can be divided into 3 categories:

WWAN (Wireless Wide Area Network),

WLAN (Wireless Local Area Network)

WPAN (Wireless Personal Area Network).

WWAN includes direct satellite link, CDMA based EVDO and WIMAX that covers regions of

several miles wide. WLAN system is Wi-Fi (802.11a/b/g). Wi-Fi has the potential for high

data rates. WPAN has a coverage range of a few feet. Two notable examples of WPAN are

infra-red and Bluetooth communication.

Among all these wireless technologies, Ultra-Wideband (UWB) is the most promising

technology for next generation WPANs, especially because of its low cost, low power and

high data rates for applications.

1.1 Ultra-wideband Technology

The recent surge in the demand for low power portable wireless electronics that can offer

extremely high data rates has resulted in much active research in Ultra-wideband (UWB)

systems. UWB is widely recognized as a promising technology for high data rate, short-

range applications with precise time resolution and high energy efficiency. Ultra wideband

(also known as UWB or as digital pulse wireless) is a wireless technology for transmitting

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large amounts of digital data over a wide spectrum of frequency bands with very low

power for a short distance.

Figure 1.1: Ultra wideband Technology

All these benefits originate from the wideband current technology, UWB can offer data

rates up to 480 Mbps and its operational frequency spectrum is between 3.1 and 10.6GHz.

However, the wideband operation of UWB systems imposes many design challenges that

have not been explored before in the traditional narrowband ones.

A basic UWB system has a signal pulse generator which generates a Gaussian pulse to

transmit the encoded signal. The pulses are amplified and transmitted via antenna to the

receiver. When receiving antenna receives the transmitted signal, LNA amplify the signal

before it continues on into the receiver.

Figure 1.2: Block Diagram of UWB System.[1]

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Here LNA is the subsystem and in this thesis our focus is the LNA design. We will discuss

about LNA in chapter 2 and LNA design in chapter 3.

1.2 CMOS Technology

Complementary metaloxidesemiconductor (CMOS) is a technology for constructing

integrated circuits. In CMOS technology, both N-type and P-type transistors are used to

realize logic functions.

CMOS was originally not considered a good technology for analog and RF applications

[Compared to Silicon-Germanium (SiGe) and Gallium-Arsenide (GaAs)]. However, the rapid

growth of the digital industry due to the continuous scaling of the CMOS technology has

motivated designers to create analog and RF CMOS circuits that can be integrated easily

with digital circuitry. The speed of CMOS is more than adequate for a common wireless

system which has a maximum operating frequency at 10 GHz. Despite the inferior

performance of RF CMOS circuits compared to SiGe and GaAs counterparts, the feasibility

of integrating analog/digital/RF circuits on chip, the potential low cost and low power

consumption and the dominance of CMOS in digital circuitry has provided reasonable

motives to adopt CMOS over other technologies.

1.3 VLSI Technology

Very-large-scale integration (VLSI) is design/manufacturing of extremely small, complex

circuitry using modified semiconductor material. It may contain millions of transistors,

each a few mm in size which is called Integrated circuit (IC).It is the process of creating

integrated circuits by combining thousands of transistor-based circuits into on a single chip

and has wide range of applications mostly based on electronic logic devices. As a side effect

of advances in the world of computers, there has been a dramatic proliferation of tools that

can be used to design VLSI circuits. CMOS having the ability to allow a high density of logic

functions on a chip, it became the most used technology to be implemented in VLSI chips.

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1.4 Basic concept of Ultra-Wide-Band Technology

Ultra-Wideband Communications was first employed by Guglielmo Marconi in 1901 to

transmit Morse code sequences across Atlantic Ocean using spark gap radio transmitters.

Approximately fifty years after Marconi, UWB technology was applied to impulse radars in

military applications and this technology was restricted to military from 1960s to 1990s.

However, ultra-wideband is now ready for commercial applications because of recent

advancements in microprocessors stemming from the rapid development of semiconductor

technology.

Federal Communications Commission (FCC) in the United States defined UWB signal as any

emitting signal that has a fractional bandwidth greater than or equal to 0.20 or has a

bandwidth greater than or equal to 500MHz. The fractional bandwidth is calculated as 2

( fH - fL)/( fH + fL) and can be expressed as:

Bf= B

100% =

100%

Where B is the absolute frequency bandwidth, fc is the center frequency, fH is the upper -10

dB corner frequency and fL is the lower -10 dB corner frequency as shown in the figure.

Figure 1.3: Illustration of the Definition of UWB frequency range.

The early applications of UWB technology were primarily radar related, driven by the

promise of fine-range resolution that comes with large bandwidth. But the recent 3.1-

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10.6GHz allocation extends the UWB use to a larger application area for which the specific

frequency ranges are reported in the table 1.4.1 FCC allocations for each UWB category.

Table 1.1: FCC allocations for each UWB category

Class/Application Frequency Band for operation

Communication and measurement systems 3.1 to 10.6 GHz (different out-of-band

emission Limits for indoor and outdoor

devices)

Imaging : ground penetrating radar, wall,

medical imaging

960 MHz or 3.1 to 10.6 GHz

Imaging: through wall 960 MHz or 1.99 to 10.6 GHz

Imaging: surveillance 1.99 to 10.6 GHz

UWB operational frequency bands, authorized by the FCC are, below 960 MHz, 3.1-10.6

GHz and 22-29 GHz. The FCC has mandated that UWB radio transmissions can legally

operate in the range 3.1 to 10.6 GHz, with the power spectral density (PSD) satisfying a

specific spectral mask assigned by FCC. Figure illustrates the UWB spectral mask for indoor

communications. According to the spectral mask the allowed effective isotropic radiated

power (EIRP) is below 41.3 dBm /MHz .

Figure 1.4: UWB spectral mask for indoor communication systems.

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1.5 Ultra-Wide-Band Technologies

UWB communications transmit in which it does not interfere with conventional

narrowband and carrier wave used in the same frequency band.

Despite the single named used for the ultra wideband (UWB) transmissions, there are two

very different technologies being developed:

Carrier free direct sequence ultra wideband technology

MBOFDM, Multi-Band OFDM ultra wideband technology

1.5.1 Carrier Free Direct Sequence UWB Technology

Direct sequence (DS) format for ultra wideband is often referred to as an impulse,

baseband or zero carrier technology. DS based UWB increases system performance over

traditional impulse based UWB by using direct sequence spread technology, while

maintaining a very simple system structure. This form of UWB technology transmits a

series of low power Gaussian shaped pulses which are coherently received at the receiver.

Each of the DS UWB pulses has an extremely short duration typically between 10 and 1000

picoseconds. As a result it is shorter than the duration of a single bit of the data to be

transmitted.

1.5.2 Multi-Band OFDM (MB-OFDM) UWB Technology

This form of ultra wideband technology uses a wide band or multiband orthogonal

frequency division multiplex (MBOFDM) signal that is effectively a 500 MHz wide OFDM

signal. This is 500 MHz signal is then hopped in frequency to enable it to occupy a

sufficiently high bandwidth.

1.6 Advantages of using Ultra-Wide-Band

The main advantages of UWB technology are high data rates, low cost and low power. This

means that many types of devices in the home and business environments, such as laptops,

mobile phones, TVs, DVDs, memory sticks, digital cameras and MP3 players could be

networked wirelessly at a data rate that would effectively be impossible using classical

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radio technology. This is because of UWB's very large data rate at very low power and at

low cost.

Some forms of UWB allow distances to be measured accurately. The nature of the short-

duration pulses used in UWB technology offers several advantages over narrowband

communications systems.

1. Large channel capacity

Main advantage of UWB technology is perceived from the channel capacity. Channel

capacity is the theoretical maximum possible number of bits per second of information

which may be conveyed through one or more links in an area. According to the Shannon

Hartley theorem channel capacity can be expressed as:

C= B log2 (1+SNR)

Where C represents the channel capacity in bits per second, B is the channel bandwidth in

Hz and SNR is the signal-to-noise ratio.

Thus channel capacity increases linearly with increasing channel's bandwidth to the

maximum value available, or by increasing the signal power exponentially where

bandwidth is fixed.[2] By virtue of the large bandwidths inherent in UWB systems, large

channel capacities could be achieved in principle without invoking higher-order

modulations requiring a very high SNR. Ideally, the receiver signal detector should match

the transmitted signal in bandwidth, signal shape and time. A mismatch results in loss of

margin for the UWB radio link. Several gigahertz of bandwidth available for UWB signals, a

data rate of gigabits per second (Gbps) can be expected.

2. Ability to Work with Low Signal to Noise Ratios

The Hartley-Shannon formula for maximum capacity also indicates that the channel

capacity is only logarithmically dependent on signal-to-noise ratio (SNR). Therefore, UWB

communications systems are capable of working in harsh communication channels with

low SNRs and still offer a large channel capacity as a result of their large BW.

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3. Ability to Share the Frequency Spectrum

The FCCs requirement of 41.3dBm/MHz, 5 equal to 75 nano watts/MHz for UWB systems,

puts them in the category of unintentional radiators, such as TVs and computer monitors.

Such power restriction allows UWB systems to reside below the noise floor of a typical

narrow band receiver and enables UWB signals to coexist with current radio services with

minimal or no interference. However, this all depends on the type of modulation used for

data transfer in a UWB system.

4. Low Probability of Intercept (LPI) and Low Probability of Detection (LPD)

Because of low average transmission power, UWB communications systems have an

inherent immunity to detection and intercept. The extremely narrow pulse-width and low

duty cycle because the UWB signals to be spread thinly over a wide bandwidth resulting in

extremely low power spectral densities over GHz bandwidths. With such low transmission

power, the eavesdropper has to be very close to the transmitter (about 1 meter) to be able

to detect the transmitted information. In addition, UWB pulses are time modulated with

codes unique to each transmitter/receiver pair. The time modulation of extremely narrow

pulses adds more security to UWB transmission, because detecting picoseconds pulses

without knowing when they will arrive is next to impossible. Therefore, UWB systems hold

significant promise of achieving highly secure, low probability of intercept and detection

communications that is a critical need for military operations.

5. Resistance to Jamming

Unlike the well-defined narrowband frequency spectrum, the UWB spectrum covers a vast

range of frequencies from near DC to several gigahertz and offers high processing gain for

UWB signals. Processing gain (PG) is a measure of a radio system's resistance to jamming

and is defined as the ratio of the RF bandwidth to the information bandwidth of a signal:

PG = RF Bandwidth

Information Bandwidth

The frequency diversity caused by high processing gain makes UWB signals relatively

resistant to intentional and unintentional jamming, because no jammer can jam every

frequency in the UWB spectrum at once. Therefore, if some of the frequencies are jammed,

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there is still a large range of frequencies that remains untouched. However, this resistance

to jamming is only in comparison to narrowband and wideband systems.

6. Multipath Propagation Performance

The phenomenon known as multipath is unavoidable in wireless communications

channels. It is caused by multiple reflections of the transmitted signal from various surfaces

such as buildings, trees, and people. The straight line between a transmitter and a receiver

is the line of sight (LOS); the reflected signals from surfaces are non-line of sight (NLOS).

The effect of multipath is rather severe for narrowband signals; it can cause signal

degradation up to 40 dB due to the out-of-phase addition of LOS and NLOS continuous

waveforms. On the other hand, the very short duration of UWB pulses makes them less

sensitive to the multipath effect. Because the transmission duration of a UWB pulse is

shorter than a nanosecond in most cases, the reflected pulse has an extremely short

window of opportunity to collide with the LOS pulse and cause signal-degradation.

7. Superior Penetration Properties

Unlike narrowband technology, UWB systems can penetrate effectively through different

materials. The low frequencies included in the broad range of the UWB frequency spectrum

have long wavelengths, which allows UWB signals to penetrate a variety of materials,

including walls. This property makes UWB technology viable for through-the-wall

communications and ground-penetrating radars. However, the material penetration

capability of UWB signals is useful only when they are allowed to occupy the low-frequency

portion of the radio spectrum.

8. Simple Transceiver Architecture

UWB transmission is carrier-less, meaning that data is not modulated on a continuous

waveform with a specific carrier frequency, as in narrowband and wideband technologies.

Carrier-less transmission requires fewer RF components than carrier-based transmission.

For this reason UWB transceiver architecture is significantly simpler and thus cheaper to

build.

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1.7 Potential Applications of Ultra-Wide-Band

There have been tremendous research efforts to apply ultra wide band (UWB) technology

to the military and government sectors. Some of them are already accomplished and some

are intended for future.

UWB technology can enable a wide variety of applications in wireless communications,

networking, radar imaging, and localizing systems. The potential applications UWB are

categorized into three parts:

Communications and sensors

Position location and tracking

Radar applications

1.7.1 Communications and Sensors

For wireless communication the use of UWB technology offers significant potential for the

deployment of 3 communication systems:

Low Data Rate for Sensor Network:

Under the low-rate operation mode, UWB technology could be beneficial and potentially

useful in sensor, positioning and identification networks. A sensor network comprises a

large number of nodes spread over a geographical area to be monitored. Depending on the

specific application, the sensor nodes can be static or mobile. With its unique properties of

low complexity, low cost and extremely low power spectral density (PSD), UWB technology

is well suited to sensor networks. The innovative communication method of UWB at low

data rate gives numerous benefits to different sectors. For instance, the wireless

connection of computer peripherals such as mouse, monitor, keyboard, joystick and printer

can utilize UWB technology. UWB allows the operation of multiples devices without

interference at the same time in the same space. It can be used as a communication link in a

sensor network. It can also create a security bubble around a specific area to ensure

security. It is the best candidate to support a variety of WBAN applications. A network of

UWB sensors such as electrocardiogram (ECG), oxygen saturation sensor (SpO2) and

electromyography (EMG) can be used to develop a proactive and a smart healthcare

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system. This can benefit the patient in chronic condition and provides long term health

monitoring. In UWB system, the transmitter is often kept simpler and most of the

complexity is shifted towards receiver, which permits extremely low energy consumption

and thus extends battery life.

High Data Rate:

The unique applications of UWB systems in different scenarios have initially drawn much

attention, since many applications of UWB spans around existing market needs for high

data rate applications. Demand for high density multimedia applications is increasing,

which needs innovative methods to better utilize the available bandwidth. UWB system has

the property to fill the available bandwidth as demand increases. The problem of designing

receiver and robustness against jamming are main challenges for high-rate applications.

The large high-resolution video screens can benefit from UWB. These devices stream video

content wirelessly from video source to a wall-mounted screen. Various high data rata

applications include internet access and multimedia services, wireless peripheral

interfaces and location based services. Regardless of the environment, very high data rate

applications (>1 Gbps) have to be provided. The use of very large bandwidth at lower

spectral efficiency has designated UWB system as a suitable candidate for high internet

access and multimedia applications. Standardized wireless interconnection is highly

desirable to replace cables and propriety plugs. The interconnectivity of various numbers

of devices such as laptops and mobile phones is increasingly important for battery-

powered devices.

Home Network Applications:

Home network application is a crucial factor to make pervasive home network

environment. The wireless connectivity of different home electronic systems removes

wiring clutter in living room. This is particularly important when we consider the bit rate

needed for high definition television that is in excess of 30 Mbps over a distance of at least

few meters. In IEEE 1394, an attempt has been made to integrate entertainment, consumer

electronics and computing within a home environment. It provides isochronous mode

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where data delivery is guaranteed with constant transmission speed. It is important for

real time applications such as video broadcasts.

1.7.2 Position Location and Tracking

Position location and tracking have wide range of benefits such as locating patient in case

of critical condition, hikers injured in remote area, tracking cars, and managing a variety of

goods in a big shopping mall. For active RF tracking and positioning applications, the short-

pulse UWB techniques offer distinct advantages in precision time-of-flight measurement,

multipath immunity for leading edge detection, and low prime power requirements for

extended-operation RF identification. The reason of supporting human-space intervention

is to identify the persons and the objects the user aims at, and identifying the target task of

the user. Knowing where a person is, we can figure out near to what or who this person is

and finally make a hypothesis what the user is aiming at. This human-space intervention

could improve quality of life when used in a WBAN. In a WBAN, a number of intelligent

sensors are used to gather patients data and forwards it to a PDA which is further

forwarded to a remote server. In case of critical condition such as arrhythmic disturbances,

the correct identification of patients location could assist medical experts in treatment.

1.7.3 Radar Applications

Short-pulse UWB techniques have several radar applications such as higher range

measurement accuracy and range resolution, enhanced target recognition, increased

immunity to co-located radar transmissions, increased detection probability for certain

classes of targets and ability to detect very slowly moving or stationary targets. UWB is a

leading technology candidate for micro air vehicles (MAV) applications. The nature of

creating millions of ultra-wideband pulses per second has the capability of high

penetration in a wide range of materials such as building materials, concrete block, plastic

and wood.

1.8 Ultra-Wide-Band Design Challenges

Designing UWB systems have several challenges, some of which have not been reached

before in traditional narrowband systems. One particular design techniques have evolved

to handle narrowband signals extremely efficiently, but these techniques do not apply UWB

13

systems. Furthermore, since the entire system power consumption is no longer dominated

by the radiation power, achieving low power consumption in the LNA and mixer is

extremely important.

The requirement for maximum total power consumption set by the 802.15.3a specification

at 110 Mb/s and 200 Mb/s is 100 mW and 250 mW, respectively. Which implies that, in

case of designing a UWB transceiver, a power save mode must be supported. To meet these

constraints, a transceiver must either target the lowest power for all data rates or use an

architecture that scales power with data rate. It is also advantageous to have an

architecture that scales power consumption under optimal channel conditions.

Another challenge is narrowband jammers. Due to the wide operational band of UWB,

interferences from existing radio systems are unavoidable. The FCC spectral mask for UWB

EIRP is -41.3 dBm/MHz, Which is low enough to not cause interference to other wireless

system sharing the same bandwidth. However, this does not guarantee that in-band

narrowband transmitters do not saturate UWB receivers. This presents a serious challenge

for UWB since other systems operating in the same band usually have much higher

transmitted powers. For example, the transmitted power of cellular radios can be up to +30

dBm, which are several orders of magnitude higher than UWB transmitters are permitted.

1.9 Objective of this thesis

The objective of this thesis is to design a ultra-wideband (UWB) low noise amplifier (LNA)

with minimum noise figure, Maximum Signal Voltage gain transfer, minimum power

dissipation

1.10 Organization of this thesis

This thesis begins with an overview of UWB signals and systems followed by a discussion

about UWB LNA and then proceeds this research in two sections: a simple single ended

inductively degenerated LNA with resistive shunt feedback and a fully differential LNA

based on the single ended LNA proposed before. Both sections analyze the performance of

the LNA and systems in detail, and numerous measurements accompany the design choices

to show the improvements and tradeoffs. The final chapter concludes and discusses

exciting new research directions that expand this body of work.

14

Chapter 2

UWB Low Noise Amplifier

Low Noise Amplifier (LNA) is an electronic amplifier, located close to the detection device

which can reduce the losses in the feedline. It is placed at the front of a radio receiver

circuit. The receivers front end is dominated by the first few stages. The effect of noise

from these stages of the receiver chain is reduced by the gain of LNA, while the noise is

injected directly into the receiver signal. So for a LNA, to boost the desired signal power is

necessary. Its main function is to amplify extremely low signals without adding noise, thus

preserving the required Signal-to-Noise Ratio (SNR) of the system at extremely low power

levels.[3] Additionally, for large signal levels, the LNA amplifies the received signal without

introducing any distortions, which eliminates channel interference.

Figure 2.1: (a) Block Diagram of LNA at receiving end

15

Figure 2.1: (b) Signal processing.

A good LNA has-

1. A low NF (like 1 db)

2. A large enough gain (like 20 db)

3. A large enough intermodulation (IP3) and compression point (P1 db)

Criteria are- 1.Operating bandwidth

2. Gain flatness

3. Stability

4. Input-output voltage standing wave ratio (VSWR)

Figure 2.2: Combination of power amplifier circuit and LNA circuit.

16

2.1 Parameters in LNA Design

For any communication system LNAs are basic building blocks. There are 4 important

parameters are in LNA design:

1. Noise figure

2. Input impedance match

3. Gain

4. Linearity

2.1.1 Noise Figure

The ratio between the total output noise power due to all noise sources and the output

noise power generated by the source internal resistance is known as noise figure (NF).[4]

Measuring noise figure in low noise elements become particularly important to the

development of next generation communications system. This application note examines

the process of making practical noise figure measurements of low noise amplifiers. Keeping

a low NF is a crucial process when designing the LNA.

According to Friis for n-stage network equation is:

NFt = 1+ (NF1-1) + (NF2-1)/Ap1 + (NF3-1)/Ap2Ap3 +..+ (NFn-1)/Ap1 Ap(n-1)

Where, Ap =gain of the stage

Overall NF is dominated by NF1.

We can discard the noise contribution of the later stages on overall noise figure

calculation[5], which means we could only focus on the noise situation, which is given

below:

17

Figure 2.3: Equivalent small signal circuit.

It contains current noise in drain ), current noise in gate ,

resistance from Rg and Lg

). The noise figure of such LNA can be expressed as:

.. (1)

Where,

.. (2)

Here,

= Gate noise in the channel

= Thermal noise in the channel

gm1/gdo1 ( =1 in long channel devices)

QL= 1/ 0RsCgs1 = Quality factor of input match network

Cgs1= WLCox

c=0.395 (even consider the short-channel effect [6])

0=work frequency

r=resonance frequency gm1/Cgs1

18

From (1) and (2) we get that,

The value of QL.opt = 3.5 5.5

Finally F reaches its minimun value and that is[7]:

The channel bandwidth,

.(3)

2.1.2 Input Impedance Match

It is mainly conjugate pair of load and source impedances. The input impedance of the

amplifier (Zin) which is now tuned to the source impedance (Z0) using two inductors LS and

Lg. From figure 2.3 input impedance of LNA is expressed as:

Zin=sLg+RLg+Rg+Z1

Where,

Z1= sLs+1/sCgs1+ TLs

We can adjust Ls to make the input impedance that equals Rs (50) when working

frequency is close to 0 ,which means Zin=Re(Zin) = TLs=Rs ; (neglecting RLg & Rg)[8]

Ls =Rs/ T

& Lgs=1/ 02Cgs1-Ls

Ls does not affect the real part of Zin.

19

To get more degrees in the design, we can add additional hardware to the input impedance

matching network. It is possible for more area on the chip.[9]

Figure 2.4: More hardware in the input matching network.

2.1.3 Gain

LNA must have high gain for the processing of signal into post circuit. High gain LNA is

designed for application by manufacturer. If the LNA doesn't have high gain, the signal will

be affected in by noise in LNA circuit itself. So high gain of LNA is a important parameter of

LNA. An inductive load is used to maximize amplifier gain and linearity. The power gain is

given by when LNA is matched at input and output.

Figure 2.5: Equivalent circuit with inductive source degeneration.

20

From this equivalent circuit,we can express the transconductance (Gm1) of the first stage

(common source):

T/2 0Rs

For a certain technology we considered that gm= nCox(W/L)(VGS-VTS),all parameters are

fixed except channel bandwidth. For large gain,we can increase W for the weak signal.

According to equation (3), increased width could elevate noise figure and introduce to

more noise to LNA.

2.1.4 Linearity

Linearity is an important parameter of LNA. There are many ways to describe the linearity

of LNA. High linearity is necessary for low adjacent channel leakage power. For linearity,

third order (IP3) intercept point is the commonly used method. The IIP3 is plotted

graphically by plotting the output power verses the input power both on dB scales. Here

two curves are drawn:

1. One for the linearly amplified signal at an input tone frequency

2. Another for a non-linear product

Figure 2.6: CP1 and 3rd order intercept point.

21

From the figure 2.6, it shows 1 dB compression point (P1 dB) and 3rd order intercept point

(IP3). IP3 is a figure of merit for linearity. For the derivation of IP3, two-tone test is

typically used. IP3 is an important parameter for system designers to estimate the spurious

free dynamic range (SFDR).

The P1 dB is defined as the point where the gain has dropped by 1 dB on the logarithmic

scale of gain as a function of input power. The point where the curves of the fundamental

signal and third order distortion product signal intercept, is known as IP3.The input power

level is known as IIP3 and the output power is known as OIP3.Figure 2.6 shows the output

power vs. input power of the fundamental frequency and the 3rd order intermodulation

(IMD3) product.[10]

The method of measuring two-tone IP3, begins by applying two sinusoids to the circuits

input at frequencies f1 and f2. The frequencies at which the IMD3 products appear for the

signals:

2f1 f2

2f2 f1

Where,

2f1 = 2nd harmonic of f1

2f2 = 2nd harmonic of f2

Figure 2.7: Two-tones with the IDM3 product.[11]

22

IP3 can be calculated by two equations:

OIP3=P1st+(P1st-P3rd)/2 dBm

IIP3=OPI3-G dBm

Where,

P1st = Power of the fundamental in dbm

P3rd= Power of the 3rd order intermodutlation product in dbm[12]

To increase the current density or current draw of the LNA is the easiest way to improve

the IP3 performance.

2.2 Low Noise Amplifier (LNA) Topologies

There are various types of LNA topologies. The two well-known topology structure found

are common source (CS) topology and common gate topology (CG). There are various other

possible topologies, such as:

1. Distributed Amplifier (DA) topology

2. Common Gate (CG) Topology

3. Inductively degenerated common source topology (IDCS)

4. Cascode Topology

5. Folded Cascode Topology

6. Cascade Topology

7. Current reuse topology

8. Differential topology

9. Novel topology

23

2.2.1 Amplifier Distributed (DA)

Distributed amplifiers are widely used in wideband LNA design. This type of structure

which utilizes several stages of common-source amplifiers is well-known for large power

and area consumption (0.8mm2 in and 1.4mm2 in ). It combines the parasitic gate-source

capacitance with on-chip inductors to build transmission lines which have intrinsic

broadband frequency response that goes all the way down to DC.

Figure 2.8: Generalized structure of distributed LNA.[10]

Features of DA topology are:

The capability of designing on-chip T-lines, and high-Q inductors

Integrated circuits incorporating on-chip T-lines

In frequency domain, the transistors parasitic capacitances are absorbed

into the constants of the T-line

Until the cut-off frequency of the line itself is reached, the circuits bandwidth

remains approximately constant

Capable of providing a wideband input/output matching

Advantages of DA topology are:

Very broad band performance

Good Input/output matching

Power combining characteristics

Partially isolated port for dc bias injection[13]

24

Drawbacks of DA topology are:

Large silicon area, which is due to the presence of several on-chip inductors

and/or transmission lines

High power consumption that is related to the number of stages

required to enhance the gain

2.2.2 Common Gate (CG)

The conventional common-gate low-noise amplifier (CGLNA) exhibits a relatively high

noise figure (NF) at low operating frequencies relative to the MOSFET fT, which has limited

its adoption even though its superior linearity, input matching, and stability compared to

the inductively degenerated (CS-LNA). The design of a low-power inductorless LNA using a

capacitive cross-coupled (CCC) gm -boosting and a positive feedback schemes is described

that improves the NF and retains the advantages of the CGLNA. The LNA designed in 0.13

mum CMOS shows more than 15 dB input return loss, maximum gain of 18.2 dB, NF of 2.86

dB, and the third-order input intercept point (IIP3) is 2 dB while dissipating 1.8 mA from

1.2 V supply.

Figure 2.9: Conventional CG- LNA and low noise techniques employing feedback. [10]

25

Features of CG topology are:

It is a parallel resonance as opposed to the series resonance of the

inductor-degenerated LNA

Low Q (quality factor)

Wider bandwidth

Advantages of CG topology are:

Wide operation BW

Accurate ranging

Extremely high-speed data communication

Drawbacks of CG topology are:

Number of on-chip inductors

Becomes more troublesome when designing a balanced or differential LNA

Large group-delay variation due to several resonances in the input-

matching network

It requires moderate to large silicon area and introduces a high insertion-

loss that degrades the amplifier NF and gain

26

2.2.3 Inductively Degenerated Common Source Topology (IDCS)

The inductive source degeneration design is widely used in ultra-wideband low noise

amplifier (3.1-10.6 GHz band). It is a widely used topology in narrow-band RF applications.

The cascode device decouples the input and output matching.

Figure 2.10: (a) Conventional inductively degenerated common source

configuration for narrow band applications. [10]

(b) Inductive degenerated CS for UWB.

Features of IDCS topology are:

Increases the voltage gain of the LNA & the output impedance

Additional cascode device provides large active load to improve voltage

gain at high frequency

Advantages of IDCS topology are:

High gain, low noise, high linearity over a wide frequency range

Doesnt use any off-chip components, it can be easily integrated as one

part of a complete low-voltage transceiver

Drawback of IDCS topology is:

Comparatively large in size.

27

2.2.4 Cascode Topology

The cascode is a two-stage amplifier composed of a transconductance amplifier followed by

a current buffer. Compared to a single amplifier stage, this combination may have one or

more of the following characteristics: higher input-output isolation, higher input

impedance, high output impedance, higher gain or higher bandwidth. In modern circuits,

the cascode is often constructed from two transistors (BJTs or FETs), with one operating as

a common emitter or common source and the other as a common base or common gate.

The cascode improves input-output isolation (or reverse transmission) as there is no direct

coupling from the output to input.

Figure 2.11: Cascode configuration. [10]

Features of Cascode topology are:

Increases the voltage gain of the LNA & the output impedance

Additional cascode device provides large active load to improve voltage

gain at high frequency

Advantages of Cascode topology are:

High gain, low noise, high linearity over a wide frequency range

Doesnt use any off-chip components, it can be easily integrated as one

part of a complete low-voltage transceiver

Drawback of Cascode topology is:

Comparatively large in size

28

2.2.5 Folded Cascode Topology

The basic folded cascode consists of three fundamental circuit elements: a common-base

transistor, an associated emitter resistor and a voltage reference, which is connected to the

base of the cascode transistor. The input of such a stage is in the form of a current, which is

applied to the emitter of the common-base transistor. The output is also in the form of a

current, available at the collector of the common-base transistor.

Figure 2.12: Folded cascade configuration. [10]

Features of Folded Cascode topology are:

Composed of one NMOS transistor & one PMOS transistor

Requires a large supply voltage

Total transconductance is increased with the same current consumption

Advantages of Folded Cascode topology are:

Possesses exclusive advantages in terms of amplifier linearity noise figure,

and bias stability

One single transistor exists in each DC path which increases the voltage

swing and consequently improves the circuit linearity and power gain

Drawback of Folded Cascode topology is:

The inherently low gain is one of the major concerns as the current

consumption is limited

29

2.2.6 Cascade Topology

A cascade amplifier or topology is any diode constructed from a series of amplifiers. It is

basically a differential amplifier with one input grounded and the side with the real input

has no load. It can also be seen as a common collector (emitter follower) followed by a

common base. Since the input side has no load there is no gain on that side and the Miller

effect does not come into play.

Features of Cascade topology are:

Found in multi section or multi stage circuit topology

Two or more stages connected to achieve the high gain

Advantages of Cascade topology are:

Two or more LNA blocks of CS and CG can be connected in cascade to get

desired gain

Drawbacks of Cascade topology are:

Supply voltage requirement is more in cascade topology

Consumes large silicon area as compared to cascode topology

2.2.7 Current Reuse Topology

Low power low voltage operation is found to be the bottleneck of future CMOS system

implementations. To comply with these constrains, a current reuse configuration is here

reported to design UWB Low Noise Amplifiers (LNA).

30

Figure 2.13: Conventional current reuse configuration. [10]

Features of Current Reuse topology are:

Reduce the power consumption of LNA

Preserve high gain

The power consumption, noise and the IIP3 can be improved

Advantages of Current Reuse topology are:

Suitable configuration for LNA implementation because of its low DC

power consumption, high and flat gain, low NF and high reverse

isolation

Can be used with any circuit configuration like cascode, CS,CG and

feedback topologies or even with multi stage cascaded structures to

reduce the DC power consumption

Drawbacks of Current Reuse topology are:

Since the second stage of the traditional current-reused LNA topology

requires a DC bias as well as biasing resistor, they will result in extra

noise and signal leakage

High input and output impedances, thus requiring external impedance

matching networks

31

2.2.8 Differential Topology

Differential topology considers the properties and structures that require only a smooth

structure on a manifold to be defined. Smooth manifolds are 'softer' than manifolds with

extra geometric structures, which can act as obstructions to certain types of equivalences

and deformations that exist in differential topology.

Figure 2.14: Differential capacitive cross coupled configuration.

Figure 2.15: Noise cancelling principle of differential topology. [10]

Features of Differential topology are:

Can Highly diminish the 2nd order nonlinearity

Shunt series triple resonance peaking technique is adopted to achieve

wideband flat gain

32

Advantages of Differential topology are:

Provide the input matching and low noise figure, but the power gain of

6.1-8.5dB (or 5.2-8.2dB) is insufficient to suppress the noise of the

subsequent components

Input matching, high power gain, and low noise figure under the

wideband condition

Better immunity to environmental noise, improved linearity, low power

consumption

Drawbacks of Differential topology are:

Not suitable for low-power applications

Single-stage LNAs consume low power but their output bandwidth

cannot provide the flat-high-gain response

2.2.9 Novel Topology

Few novel topologies are also possible other than the topologies discussed above. Novel

topology is nothing but the combination of above basic topology with either bandwidth

extension techniques or noise cancelling techniques. Even in few papers topology is

invented to optimize BW, gain and NF simultaneously at the cost of other parameters.

2.3 Proposed Topology

After taking all the benefits and drawbacks of different topologies, Inductively Degenerated

Common Source (IDCS) and Cascode topology is chosen for higher gain, better input

impedence matching and Differential LNA is chosen for linearity and stability along with

reverse isolation and immunity to noise. Easement of designing as well as further

improvement of the device is also given priority.

33

Chapter 3

Architecture of proposed UWB LNA and Simulation

Results

For the UWB receiver using direct-conversion architecture, Low Noise Amplifier (LNA) is

an important system block. It is the first gain stage after antenna in the receive path, so the

LNA noise figure is critical since it directly adds to the total noise figure of whole system. It

is also expected for LNA to have good gain, linearity and stability. Furthermore, good

reverse isolation is desirable for LNA to reduce the amount of LO signal that leaks from the

mixer back to antenna.

Figure 3.1: Block Diagram of LNA

Based on the way input matching is provided LNA can be classified into four

architectures [13] : Resistive termination, 1/gm termination, shunt-series feedback and

inductive degeneration.

34

Resistive termination technique is a straightforward matching method which uses a

resistor at the input port to provide a termination of 50 impedance. It suffers from poor

noise performance due to the deleterious effect of real resistor at input port.

Figure 3.2: Common LNA Architectures: Resistive termination

The 1/gm termination method uses the source of common gate stage as the termination

point and the impedance is set by the 1/gm of the transistor in the common gate stage. It is

more suitable for bipolar transistor than CMOS to achieve low noise figure performance.

Figure 3.3: Common LNA Architectures: 1/gm termination

35

Shunt-series feedback uses shunt series feedback to set the input and output impedances of

the system. The bias point of the input is fixed with the output voltage. This method can

increase the power dissipation compared to others with similar noise performance.

Figure 3.4: Common LNA Architectures: Shunt-series feedback

The inductive source degeneration method employs inductor at source terminal to

generate a real term for the input impedance.

Figure 3.5: Common LNA Architectures: Inductive degeneration

This method often works with cascode transistor and has been widely used for LNA design

due to its good noise performance, reverse isolation and high feasible gain.

In this paper, an inductively degenerated LNA with resistive shunt feedback is adopted to

achieve wide bandwidth and good noise performance.

36

3.1 Architecture of the proposed LNA

Figure 3.6 shows the simplified block diagram of the proposed LNA architecture, where

two simple inductively degenerated LNA with resistive shunt feedback is paired to make a

Differential LNA to get higher linearity, better input matching, higher power gain and lower

noise figure for wide band application.

Figure 3.6: Simplified Block Diagram of proposed LNA

37

3.1.1 Single Ended LNA

As shown in Fig. 3.5, this LNA employs cascode transistor (M1 and M2) to reduce miller

effect of gate-drain capacitor (Cgd) and enhance gain. Inductor Ls is for simultaneous noise

and input matching; inductor Lg is for the impedance matching between the source

resistance Rs and the input of the LNA.

Figure 3.7: LNA topology for UWB single ended LNA [13]

Capacitor Cgs in Fig. 3.3 represents the gate-source capacitance of the input transistor M1.

Resistor Rf is a shunt feedback resistor added to the conventional cascode narrowband

LNA. The capacitor Cf is for ac signal coupling purpose. The inductor Lload is a shunt peaking

inductor at the output port. The large amplitude range of signals, received in antenna in

wireless communications systems, requires variable gain stages to enhance the signal to

the noise ratio (SNR). The variable gain feature is realized by including an additional n-type

MOSFET in parallel with the cascode device in the traditional cascode LNA.

38

Figure 3.8: LNA topology for UWB LNA Small-signal equivalent circuit of the input of LNA

While in high-gain mode, the original cascode device steers current signal to LC load and

the additional NMOS bypasses the signal directly to VDD to lower the gain in low gain mode.

Note that in Fig.3.5, Ms1 is used to bypass the signal in lower gain mode. As shown in the

small-signal equivalent circuit (Fig. 3.6) for input part of this LNA, a series combination of

reactive elements is chosen to have a serial resonance at the frequencies of interest. The

symbol t means the cutoff frequency of transistor M1. The -3-dB bandwidth of a typical

RLC resonant circuit is inversely proportional to its Q-factor (BW-3db=0/QWB), where QWB

is approximately determined by following equation.

Where, Rfm=Rf/[1-Av] and Av represents the open-loop voltage gain of LNA. The key role of

the shunt-feedback resistor Rf is to reduce the Q-factor of the LNA input circuit. With low Q-

factor, LNA is capable of providing wide bandwidth (BW-3dB). Resistor Rf also helps in

flattening the gain over a wide bandwidth of frequencies with small noise figure

degradation.

39

Simulation Results of Single Ended LNA

Simulation results show that Single Ended LNA has S21 gain of 10dB with bandwidth 1GHz

between 8GHz and 9GHz with center Frequency 8.5GHz. Simulation results are shown in

Fig 3.9 to Fig 3.12.

Fig 3.9: S21of Single Ended LNA

Fig 3.10: S11of Single Ended LNA

40

Fig 3.11: AC output Noise Figure of Single Ended LNA

At the center frequency 8.5GHz Noise figure of the Single Ended LNA is 2dB. Maximum

Power gain of this LNA is 18.35dB at 7GHz, and 18dB at the center frequency.

Fig 3.12: Maximum Power Gain of Single Ended LNA

41

3.1.2 Differential LNA

LNA in our design, according to the specifications, is differential with variable gain mode.

Since the transceiver architecture is Zero-IF architecture, the output load is the capacitive

impedance seen by LNA when connected to the next mixer stage. A reasonable estimate of

the value of input capacitance of the mixer is 400 fF and is used in our design and

simulations in parallel with a 200 resistance. As shown in Fig. 3.4, a full-differential LNA

is designed based on the single-ended LNA in previous section.

Figure 3.13: Differential LNA [13]

The most important advantage of differential LNAs over single-end ones is that differential

LNA has much higher immunity to environmental noise. This is to make sure that an

adequate rejection of the noise and the interfering signals traveling through the common

substrate.

42

Design Procedure

The load inductor Lload= 2.664 nH is designed to resonate with the output capacitance (400

fF) and the parasitic drain capacitance of the cascode transistor at the center frequency of

the band. If we assume Cd,M2 200fF, then output resonance frequency is:

In order to reduce the Q-factor and improve the bandwidth of the output network, a small

resistor Load= 5 is added in series with the load inductor. The source input matching is

achieved by selecting the source degeneration inductor Ls= 0.17 nH to match the input

resistor 50 such that

The gate inductance Lg= 2.223 nH resonates with Cgs and parasitic source capacitance

(300 fF) of low-gain mode transistor at resonance frequency:

As mentioned earlier, the feedback resistance Rf= 1.14 k and Cf= 2 pF are chosen to

reduce the Q-factor of the input network and AC coupling respectively.

The bias resistance Rbias= 1.417 k is chosen high enough to minimize its noise power

contribution, which is given by:

43

While selecting the W/L ratio of the input transistors, trade-off between the noise power

contributed and the gain needs to be considered. The noise power of the n-channel

MOSFET is given by:

Whereas gain is:

If gm is increased to improve the gain, the noise contributed by the MOSFET increases

proportionally. The W/L ratio of the cascode transistor is selected such that the ratio of

gms of M1 and M2 is close to 550. Finally, the W/L of the low-gain mode transistor is

optimized to give the necessary gain in the low-gain mode.

3.1.3 Balun Circuit

A Balun is a device which converts unbalanced impedance to balanced and vice versa. A

Balun Circuit is used whenever a circuit design requires signals on two lines that are equal

in magnitude and 180 degrees out of phase. In our Design we have used Balun to create

differential input and achieve differential output.

Figure 3.14: Balun Circuit

44

3.2 Final Simulation Results

The Design was simulated with BSIM3 model provided for 0.18 m RF CMOS process. Some

of the important parameters for LNA such as S21, S11, S12, S22, Power gain and Noise Figure

are simulated in HSpice. Figures 3.13 to 3.24 show the corner simulations for each of

these parameters.

Fig 3.15: S21 (dB) of Differential LNA

Fig 3.16: S11 (dB) of Differential LNA

45

Fig3.17: Comparison between S21 and S11

Gain and input matching parameters (S21 and S11) are plotted in Fig 3.15 to Fig 3.17. S21 of

the proposed LNA is plotted in Fig 3.15. S21 is around 8dB from 4.8GHz to 9GHz. It can be

compared with S21 of the single ended LNA in Fig 3.10. S21 of Single ended LNA is 10dB

from 5.6GHz to 9GHz. Comparison shows that Differential LNA gets wider bandwidth but

lower gain.

Fig 3.16 shows S11 of the Differential LNA, which has a value of -30dB at 8.9GHz. Comparing

this plot with the S11 of single ended LNA of Fig 3.11, we get Single ended LNA has a S11 of -

12dB.

So, S21 and S11 of Fig 3.17 assure good input matching of the network.

46

Fig 3.18: AC output Noise figure of Differential LNA

Fig 3.18 shows the AC output noise figure and Fig 3.19 shows the stability factor of the

proposed LNA. AC output noise figure is less than 2.5dB.

Fig 3.19: Minimum AC output Noise figure of Differential LNA

47

Fig 3.20: S22 of Differential LNA

Fig 3.20 shows the S22 of the proposed LNA and the Comparison between S11 and S22 is

shown in Fig 3.21.

Fig 3.21: Comparison between S11 and S22 of Differential LNA

48

Fig 3.22: S12 of Differential LNA

Fig 3.22 shows the S12 of the LNA of this work. The output noise is shown in Fig 3.23.

Fig 3.23: Output Noise of Differential LNA

49

Fig 3.25: Input Noise (dB) of Differential LNA

The input Noise is shown in 3.25. Fig 3.26 shows the comparison between input noise and

output noise.

Fig 3.26: Comparison between input noise (dB) and output noise (dB)

50

Fig 3.24: Maximum Power Gain of Differential LNA

Maximum power gain of the proposed LNA is shown in Fig 3.24. At 7GHz we get the

maximum power gain with a value of 18.3dB. At center Frequency 8.9GHz Power Gain is

more than 18dB.

Comparison of performance between Single ended LNA and Differential LNA in this paper

is given in the table below.

Table3.1: Comparison of performance between Single ended LNA and Differential LNA

Parameter Single Ended Double Ended

Frequency 8.6GHz 8.9 GHz

Power Supply Voltage 1.8 V 1.8 V

Power Consumption 5.6 mW 2.7mW

S21 10 dB 8dB

S11 -12dB -30dB

Noise Figure 2dB 2.15dB

51

The performance of the proposed Differential LNA is summarized in the table below.

Table3.2: Performance of LNA

Figure Value

Maximum Gain 18 dB

BW-3dB 7.5-10.6GHz

Noise Figure < 2 dB

S11 -27 dB

S21 8 dB

Power Consumption 27mW

Bias Current 15mA

Comparison with other works in the reference is given in the table below.

Table3.3: Comparison with other LNA from the bibliography

Technology Bandwidth Gain NF Differential Input Match Power

[15] 0.5m 100 900 MHz

14.8 dB 3.3 dB no no 3.4 mA 3.3V

[11] 0.35m 50 900 MHz 11 dB 4.4 dB no yes 1.5 mA 3.3V

[14] 0.25m 2 1600 MHz 13.7 dB 2.5 dB no yes 14 mA 2.5V

[16] 0.18m .8 1 GHz 26 dB 4.1 dB yes yes 20 mA 1.8V

[17] 0.13m 100 930 MHz

13 dB 4 dB yes yes 0.6 mA 1.2V

This work

0.18 m 8.2-9.4GHz 18 dB < 2 dB yes yes 15mA 1.8V

52

Chapter 4

Conclusion

4.1 Summary of Contribution

A simple inductively degenerated single ended LNA proposed by [13] has been modified

to improve LNA gain, Bandwidth and Noise Figure. A differential topology of the single

ended LNA has also been implemented in this work. The aspect ratio of the MOS

transistor has been optimized in this work for increasing LNA gain. Resistance and

Inductance of the circuit has also been optimized for better matching of the circuit to

improve the reflection coefficient (S11). The circuit has been simulated in HSpice and

HSpice simulation results shows wider bandwidth of 8.2 9.4GHz and higher power gain

of 18dB, better matching performance with S11 around -30dB at 8.8GHz.

4.2 Future Work

LNA in this paper can be extended to operate in other band groups of UWB standard

either by tuning the inductances and capacitances or placing the different matching

circuitry for each band in parallel. Combinations of these methods can also be used to

achieve the same. The simulations on layout are not available at the time of publishing

this paper due to certain limitations in the design kit, which have not been completely

resolved, can be solved in future.

The Noise Figure of the LNA can significantly be improved if a noise cancelling technique

is applied. In the future, noise canceling methods should be investigated while trying to

maintain the other performance measures at almost the same level.

Another issue to be addressed is that the input return loss is relatively high. This is

because the input matching network was not optimized for input return loss, as it was

designed to optimize gain, noise figure and power dissipation instead. However, this

53

problem could likely be solved by trading off increased power consumption for a better

input return loss.

At the circuit level, managing the tradeoff between supply voltage, clock speed, and

power consumption has been widely explored for digital circuits. However, analog

designers are faced with a few challenges without answers as transistors continue to

scale: creating new architectures to support low voltage operation and/or operating at

the optimal supply voltage. Instead of blindly following voltage scaling for digital

circuits, it is important to revisit and analyze tradeoffs made when important techniques

and architectures such as cascoding and op-amps cannot be used. Ultimately, to survive

with voltage scaling, analog designers must think in sub-systems of simple circuits that

functionally provide the same (or better!) performance as compared to well-known,

monolithic analog circuits.

In summary, the UWB LNA has room for improvement. However, it is important to pay

attention to the overall performance (the figure of merit) in order to decide whether a

particular modification is acceptable.

HSpice netlists

Single ended LNA .temp 27 .options post .param Vdd=1.8 .global gnd lload nvdd 1 2.664nH lg nin+ 7 2.223nH ls 4 gnd 0.17nH rload 1 2 5 rf 2 5 1.14K rbias 6 nvbias 1.417K cf 5 6 2pF c1 7 6 300fF c2 2 nvout 400fF Ms nvdd nvm 6 cmosn l=0.18u w=100u M2 2 nvdd 3 cmosn l=0.18u w=100u M1 3 6 4 cmosn l=0.18u w=100u vbias nvbias gnd dc=0.8v vm nvm gnd dc=0.8v vdd nvdd gnd dc=1.8v *vin nin+ gnd dc ac 500mv 0 .ac lin 50 3G 15G P1 nin+ gnd port=1 z0=50 dc = 0 P2 nvout gnd port=2 z0=50 .lin noisecalc=1 sparcalc=1 .print ac s11(db) s12(db) s21(db) s22(db) .print ac nf(db) nfmin(db) .print g_max .probe .end

Differential LNA .temp 27 .options post .param Vdd=1.8 .global gnd .subckt balun 1 2 3 4 E1 5 2 1 0 0.5 V1 3 5 F1 1 0 V1 -0.5 R1 1 0 1T E2 6 4 1 0 0.5 V2 2 7 F2 1 0 V2 -0.5 R2 7 6 1u .ends balun *part 1 lload1 nvdd 1 2.664nH lg1 nin+ 7 2.223nH ls1 4 gnd 0.17nH rload1 1 2 5 rf1 2 5 1.14K rbias1 6 nvbias 1.417K cf1 5 6 2pF c1 7 6 300fF c2 2 nvout1 400fF Ms1 nvdd nvm 6 cmosn l=0.18u w=100u M2 2 nvdd 3 cmosn l=0.18u w=100u M1 3 6 4 cmosn l=0.18u w=100u *part 2 lload2 nvdd 8 2.664nH lg2 nin- 14 2.223nH ls2 11 gnd 0.17nH rload2 8 9 5 rf2 12 9 1.14K rbias2 13 nvbias 1.417K

cf2 12 13 2pF c3 14 13 300fF c4 9 nvout2 400fF Ms2 nvdd nvm 13 cmosn l=0.18u w=100u M4 9 nvdd 10 cmosn l=0.18u w=100u M3 10 13 11 cmosn l=0.18u w=100u vbias nvbias gnd dc=0.8v vdd nvdd gnd dc=1.8v *vin nin gnd dc ac 500mv 0 xdi d c nin+ nin- balun xdo dd cd nvout1 nvout2 balun .ac lin 50 3G 12G P1 d gnd port=1 z0=50 dc = 0 P2 dd gnd port=2 z0=50 .print ac s11(db) s12(db) s21(db) s22(db) .print ac nf(db) nfmin(db) .print noise inoise(db) onoise(db) .print ac g_max .lin noisecalc=1 sparcalc=1

.end

Bibliography

[1] Ultra-Wideband Communications: Fundamentals and Applications By Faranak Nekoogar

[2] Ultra-Wideband Communications Systems: Multiband OFDM Approach By W. Pam

Siriwongpairat, K. J. Ray Liu

[3] Nejati, H.; Ragheb, T.; Nieuwoudt, A.; Massoud, Y., Modeling and Design of Ultrawideband

Low Noise Amplifiers with Generalized Impedance Matching Networks, ISCAS 2007. IEEE,

p.2622-2625, (2007)

[4] Nejati, H.; Ragheb, T.; Massoud, Y., Analytical Modeling of Common-Gate Low Noise

Amplifiers, ISCAS.2008, IEEE, p.888

[5] T. H. Lee, The Design of CMOS Radio-Frequency Integrated Circuits (second edition),

Publishing House of Electronics Industry, 2006

[6] Jiwei Chen, Bingxue Shi, Analysis and optimization of the impact of channel resistance on

CMOS LNA noise performance, Microelectronics Journal 33, p. 1027-1031, (2002)

[7] B. Chi, Z. Yu, B. Shi, Analysis and Design of CMOS RF Integrated Circuits, Tsinghua Press,

2006

[8] Massoud, Y.; Nieuwoudt, A.; Ragheb, T., Variability-Aware Synthesis for Wideband Low

Noise Amplifiers, ISCAS 2007, IEEE, p.3219-3222

[9] Design Considerations And Performance Requirements For High Speed Driver Amplifiers.

By: Nils Nazoa, Consultant Engineer (LA Techniques Ltd)

[10] Sunny Gyamlani, Sameena Zafar, Jigisa Sureja, Jigar Chaudhari, Comparative Study of

various LNA topologiesUsed for CMOS LNA Design,

[11] F. Bruccoleri, et al., Noise cancelling in wideband CMOS LNAs, IEEE ISSCC Dig. Tech.

Papers, pp. 406-407, 2002.

[12] C. Kim, M. Kang, P. T. Anh, H. Kim, and S. Lee, An ultra-wideband CMOS low noise

amplifier for 3-5 GHz UWB system, IEEE Journal of Solid-State Circuits, Vol.40, No. 2, Feb.

2005.

[13] C. Garuda, X. Cui, P.-C. Lin, S. J. Doo, P. Zhang, and M. Ismail, A 3-5 GHz Fully Differential

CMOS LNA with Dual-gain Mode for Wireless UWB Applications, 48th Midwest Symposium on

Circuits and Systems, Aug. 2005

[14] F. Bruccoleri, et al., Generating All Two-MOS-Transistor Amplifiers leads to new wide-

band LNAs, IEEE J. Solid-State Circuits, vol. 36, pp. 1032-1040, July 2001.

[15] J. Janssens, et al., A 10-mW Inductorless, Broadband CMOS Low Noise Amplifier for

900MHz Wireless Communications, Proc. of IEEE CICC, pp. 75-78, May 1998.

[16] Adiseno, et al., A 1.8-V Wide-band CMOS LNA for Multiband Multistandard Front-end

Receiver, Proc. of IEEE ESSCIRC, pp. 141-144,Sept. 2003.

[17] Stanley B. T. Wang, Ali M. Niknejad, and Robert W. Brodersen, A Sub-mW 960-MHz

Ultra-Wideband CMOS LNA, Berkeley Wireless Research Center, Dept. of EECS, UC Berkeley,

Berkeley, CA 94704, USA

[18] Microelectronic Circuits, by Prof. H. Rashid, pp. 554 580