rf system design and simulation using gan 12 & 13 march...

Presented by

Bhupinder Singh

RF system design and simulation using GaN12 & 13 March 2015

Finetuning Academy (www.finetuningrf.com)

Learning Objectives RF System design – Basics, Simulation using ADS – Advanced Techniques

Using Non-Linear Models to design the PA Circuit

Design Constraints for different Modulation Schemes like QPSK, QAM, OFDM

Design of RF Power Amplifier using GaN HEMT in Pulsed / CW mode

Design of RF Power Amplifier using GaN HEMT in Doherty configuration

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Course Description

This 2-Day workshop addresses the following key areas: Overview of RF System design, RF system simulation using ADS, GaN HEMT based PA simulation using non-linear models in ADS, PA circuit design in CW / Pulse mode, Doherty PA Configuration using GaN devices


• Schedule

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Topics, Mar-12, Thursday Time

Power Amplifier - Efficiency and Linearity enhancement

Techniques900-1030

Tea Break 1030-1045

Power Amplifier - Efficiency and Linearity enhancement

Techniques1045-1115

GaN Power amplifier design with Simulation examples (CW

Mode, Broadband)1115-1300

Lunch Break 1300-1345

GaN Power amplifier design with Simulation examples (Doherty

Configuration)1345-1500

Tea Break 1500-1515

GaN based PA design, Die version, in Ku-band 1515-1630

Interactive Session 1630-1700

Topics, Mar-13, Friday Time

RF System design - Introduction 900-1030

Tea Break 1030-1045

RF System design and Simulations using ADS 1045-1300

Lunch Break 1300-1345


Tea Break 1500-1515


Interactive Session 1630-1700


• Bhupinder Singh received his Master’s Degree in Microwave System Design from IIT Kanpur, Kanpur India. He has 23 years of RF system / subsystem design, development and testing for Govt, Military, and Cellular and VSAT industry. He is currently Director-Technical at RF Specialities. He was a scientist at Aeronautical Development Establishment from 1991-2001. Previously he was RF Design Lead at HFCL, DMC-STRATEX, Blackbay, Technical Head-Telecom R&D at Astra MWP, Eminent Systems. He is an advanced user of Simulation tools like ADS, MWO, ALTIUM and ACAD. He is skilled at using Spectrum Analyzer, NW Analyzer, Vector Signal Analyzers, signal generators. RF Specialities (RFS) is one of the leading companies in the development, design, servicing and maintenance of RF Equipment in India. Boasting of a state-of-the-art RF laboratory and backed with experienced & well-trained manpower, it provides unique and cost-effective solutions in the shortest turn-around time for the satellite, broadcasting, telecom and military industry.

4

Speaker


• Module-1: RF Power Amplifier▫ PA Fundamentals

▫ GaN Technology – Properties

▫ PA Design Steps, Device Selection and Model

▫ Simulated Load Pull

▫ PA Measurement

▫ One Tone and Two Tone IMD

▫ ACPR WCDMA (PAR 6dB)

5


• Module-2: RF Power Amplifier Efficiency Enhancement Techniques▫ Doherty PA – Conventional and Modified

▫ Envelope Elimination and Restoration

▫ BIAS Adaption

6


• Module-3: RF Power Amplifier Linearization Techniques▫ PA Characterization

▫ Digital Communication System

▫ Feedforward Linearizer

▫ Digital Pre-distortion

▫ Adaptive Digital Pre-distortion

▫ Adaptive Digital Pre-distortion at IF

▫ Adaptive Digital Pre-distortion at Baseband

7


• Topic 4: RF System Design▫ Analog Transceiver Parameters

▫ Noise Figure

▫ Noise Figure of Cascade

▫ Equivalent Noise Temperature

▫ 1-db Compression

▫ Dynamic Range

▫ IMD

▫ Digital Modulated System

▫ BER

▫ QAM System – Primary Noise and Distortion Elements

▫ Effect of Source Phase Noise

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• Q and A Session

• Quiz to assess how much information participants learned

• Survey participants to see if they found the training beneficial

Assessment and Evaluation

9

Presented by

Bhupinder Singh

MODIFIED DPA USING GaN TRANSISTOR


INTRODUCTION

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• Power Amplifiers for Efficiency and Power Output

• BJTs, GaAsFETs, VDMOS, LDMOS, GaN

• Controlled source and switched mode PA

• Modes of Operation for controlled source PAs : A, B, AB, C


PA FUNDAMENTALS

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ASSUMPTIONS • Load is purely resistive • All harmonics shorted • Constant trans

conductance (𝒈𝒎 ) • Knee voltage is small

compared with drain voltage


PA FUNDAMENTALS

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Class-A

𝐼𝐷𝐶= 𝐼𝐷𝑄 =𝑣𝑑𝑠,𝑚𝑎𝑥

𝑅=

𝑉𝐷𝐷

𝑅

𝑃𝑑𝑐 = 𝑉𝐷𝐷𝐼𝐷𝐶 = 𝑉𝐷𝐷2

𝑅

𝑃𝑜,𝑚𝑎𝑥= 𝑣𝑑𝑠,𝑚𝑎𝑥2

2𝑅 =

𝑉𝐷𝐷2

2𝑅

η = 𝑃𝑜,𝑚𝑎𝑥

𝑃𝑑𝑐 =

1

2 = 50%

𝑉𝑑𝑠,𝑚𝑎𝑥= 2𝑉𝐷𝐷

𝐼𝑑𝑠,𝑚𝑎𝑥= 2𝐼𝐷𝑄 = 2𝑉𝐷𝐷

𝑅

𝑃𝑚𝑎𝑥= 𝑃𝑜,𝑚𝑎𝑥

𝑉𝑑𝑠,𝑚𝑎𝑥𝐼𝑑𝑠,𝑚𝑎𝑥= 1

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Class-B

𝐼𝐷𝐶= 𝐼𝑑𝑠,𝑚𝑎𝑥

π ; 𝐼1=

𝐼𝑑𝑠,𝑚𝑎𝑥

2

𝑃𝑑𝑐 = 𝑉𝐷𝐷𝐼𝐷𝐶 = 𝑉𝐷𝐷𝐼𝑑𝑠,𝑚𝑎𝑥

π

𝑃𝑜 = 𝑉𝐷𝐷

2𝐼1 =

𝑉𝐷𝐷

2 𝐼𝑑𝑠,𝑚𝑎𝑥

2

η = 𝑃𝑜,𝑚𝑎𝑥

𝑃𝑑𝑐 =

𝜋

4 = 78.5%

𝑃𝑚𝑎𝑥= 𝑃𝑜,𝑚𝑎𝑥

𝑉𝑑𝑠,𝑚𝑎𝑥𝐼𝑑𝑠,𝑚𝑎𝑥= 1

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PA FUNDAMENTALS

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PA FUNDAMENTALS

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Class C


PA FUNDAMENTALS

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𝛟 is the current conduction angle (CCA)


PA FUNDAMENTALS

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PA FUNDAMENTALS

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Optimum load at fundamental frequency is given by

opt

Finetuning Academy (www.finetuningrf.com) 10


SEMICONDUCTOR PROPERTIES

13


SEMICONDUCTOR PROPERTIES

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Design steps for PA realization


PA DEVICE SELECTION

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PA DEVICE SELECTION

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PA MODEL

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SIMULATED LOAD PULL

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SIMULATED LOAD PULL

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SIMULATED LOAD PULL

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PA MEASUREMENT

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• One tone measurement : AM-AM and AM-PM distortion

• Two tone measurement : IMD (typically 30dbc for constant envelope modulation)

• ACPR, EVM, CCDF are metrics for Digitally modulated signal


Two Tone IMD Measurement

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One Tone Measurement

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ACPR WCDMA (PAR 6db)

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Presented by

Bhupinder Singh

PA EFFICIENCY ENHANCEMENT TECHNIQUES


• Modern Communication systems demand high PAR

• High Efficiency

• Multiband –Multi standard operation

• Better linearity

• DOHERTY POWER AMPLIFIER

• ENVELOPE ELIMINATION AND RESTORTION

• BIAS ADAPTION

Introduction

27


DOHERTY PA


ENVELOPE ELIMINATION AND RESTORTION


BIAS ADAPTION


• Ideal efficiency value 78.5% at maximum power output

• Efficiency decreases as the input drive level is reduced

• η= Pi/4*p ; p is the reduction in input voltage drive

• Increase the load resistance by same factor p its possible to return to ideal efficiency value of 78.5%

Ideal Class B Amplifier

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• Active load pull concept, dynamically alters the load resistance for maximum efficiency

• Extends high efficiency operation to lower power levels

• 𝑍1=𝑅𝐿*(1 +𝐼2

𝐼1 )

Conventional Doherty PA

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• Three distinct operating regions are defined for DPA

• Low Drive region: Carrier amp conducting Peaking amp OFF

• Load Modulation Region: Carrier saturated Peaking turning ON

• Peak Power Region: Carrier and Peaking amplifiers saturated


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34


Theory of operation

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𝐈′𝐋


Theory of operation

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• 𝐼3 = 𝐼1𝑅1

𝑅3 ----(1)

• 𝐼3 = 𝑅2

𝑅2+𝑅3𝐼′𝐿 ; 𝐼2 =

𝑅3

𝑅2+𝑅3𝐼′𝐿

• 𝐼′𝐿 = 𝐼2 + 𝐼3 = 𝐼3(𝐼2

𝐼3+1) =

𝐼3

𝛽 ; where β is the current division ratio


Theory of operation

37

impedance seen at the output of the Carrier amplifier is

• 𝑅3 = 𝐼3+𝐼2

𝐼3

𝑍12

𝑅𝐿 =

𝑍12

𝛽𝑅𝐿 (2)

And the impedance seen at the output of the Peaking amplifier is

• 𝑅2 = 𝐼3+𝐼2

𝐼2

𝑍12

𝑅𝐿 =

𝑍12

(1−𝛽)𝑅𝐿 (3)


Theory of operation

38

• Case-1 (Symmetric Doherty)

current and power division ratios of α=β=0.5

𝑅1= 𝑅2=𝑅3=𝑍2=2𝑍1

2

𝑅𝐿 in Peak Power Region

• for 𝑍1=35 𝛀 and 𝑅𝐿=50 𝛀

• 𝑅1= 𝑅2=𝑅3=𝑍2 = 50 𝛀

• In low power region

𝑅1=𝑍22

𝑍12 𝑅𝐿=100 𝛀 (6db back-off)


Theory of operation

39

• Case-2 (Asymmetric Doherty)

current and power division ratios of α=β=0.25

𝑅1= 𝑍2=𝑅3=3𝑅2; in Peak Power Region

for 𝑍1=15 𝛀 and 𝑅𝐿=50 𝛀

• 𝑅1=𝑍2=18 𝛀; 𝑅2=𝑅3/3=6 𝛀

• In low power region

𝑅1=𝑍22

𝛃𝑅3=72𝛀 (12db back-off)


Limitations of Conventional DPA

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• In the low power region, the assumption of Peaking Amplifier being open is difficult to achieve

• The power splitter and combiner at the input and output of the DPA are inherently narrowband due to the presence of lambda by four transformers

• The Peaking and Carrier amplifiers are to be designed using wideband matching techniques


Modified DPA

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• Simple modifications to improve operating BW of Conventional DPA

• 30% operating BW centered around 1450MHz till 6db back-off

• Cree CGH40045 GaN transistor for Carrier (Class AB) and Peaking Amplifier (Class C)

• Symmetric DPA structure

• Better than 30% efficiency over full BW and 6-db Back-off range


Modified DPA

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• The Carrier and Peaking amplifier were designed over a broad range of frequencies 1.2GHz-1.8GHz. ADS simulations were carried out to check and optimize the performance of Carrier and Peaking amplifier over this frequency range

• Replacing the 50 ohms impedance inverter at the output of Carrier amplifier by a 70 Ohms impedance inverter, inserting another 70 ohms impedance inverter at the Peaking amplifier output and removing the 35 ohms Impedance transformer at the load. The load is now directly connected at the junction of two 70 Ohms impedance inverters.


Modified DPA

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Modified DPA

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• The relatively smaller impedance step (from 50 ohms to 100 ohms) at the output of Carrier amplifier improves the BW by a factor of 1.73.

• The power splitter at the input is a modification of Branch line hybrid where additional lambda by four sections are included to make it operate over octave band (1G-2G) without changing its size appreciably

• Offset delay lines were included at the output of the Carrier and the Peaking amplifier


Modified DPA

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Modified DPA

46


Modified DPA

47


DISCUSSION OF SIMULATION RESULTS

48

• Modified DPA delivers good efficiency over a broad BW

• Demonstrates Linearity improvement over Class AB amplifier

• Suffers from BW limitation of output combiner

• Further improvement possible by designing a wideband output combiner to covet the entire 0.8G to 2.7G cellular band


Result Discussion

49


Result Discussion

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Result Discussion

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Result Discussion

52

ACPR RESPONSE OF MODIFIED DPA


Result Discussion

53

ACPR RESPONSE OF CLASS AB PA

Presented by

Bhupinder Singh

POWER AMPLIFIER LINEARIZATION TECHNIQUES


PA CHARCTERIZATION

55

• PAs differ in values of coefficients 𝑎3 and 𝑎5 resulting in different looking AM-PM curves

• Coefficients 𝑎3 and 𝑎5 are higher for amplifier with higher AM-PM distortion


PA CHARACTERIZATION

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• Asymmetry in IMD • Due to time lag or phase shift as

measured in the envelope time domain, between the AM-AM and AM-PM response

• Phase change is mainly caused by C-V characteristics of gate source junction

• Reducing gate source capacitance will reduce AM-PM and hence IMD asymmetry


PA CHARACTERIZATION

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• AM-PM is significantly more in devices operating in Class AB mode where quiescent point is closer to region of maximum phase variation

• AM-PM is greatly reduced in GaN devices because of higher power density and smaller gate periphery


DIGITAL COMMUNICATION SYSTEM

58

• Peak power substantially higher than Average power

• Peaks are very infrequent • Time trajectory driven by distinct

“beat” or symbol clock • Two time domains: first shows

individual RF carrier variations and the second shows carrier modulation(Envelope Domain)

• Amplitude or Phase Distortion results in spectral spreading of signal



59

• As the PA distorts, alleviates distortion by driving PA harder

• No more headroom for improvement near saturation

• Signal emerging from pre-distorter will be highly distorted like uncompensated PA necessitating the use of high speed digital circuitry

• PD is a passive device having no gain



60



61


FEEDFORWARD LINEARIZER

62


FEEDFORWARD LINEARIZER

63


DIGITAL PREDISTORTION

64


ADAPTIVE DIGITAL PREDISTORTION

65


ADAPTIVE DIGITAL PREDISTORTION AT IF

66

Quad ModO

C

IPre Distorter O

C

I

BPFMicro ControllerF1,F2

Adaptation Algorithm

I.I^2

PA

Input


ADAPTIVE DIGITAL PREDISTORTION AT BASEBAND

67


ADAPTIVE DIGITAL PREDISTORTION AT BASEBAND

68


ADAPTIVE DIGITAL PREDISTORTION(ADPD)

69

ADPD Implementation issues • Input signal delay to compensate processing delays • Correction signal to contain multiple harmonics of baseband signal • Places stringent requirement on data converters • Digital correcting circuitry more complicated than the digital circuitry

generating the baseband signal

Presented by

Bhupinder Singh

RF SYSTEM DESIGN


ANALOG TRANSCEIVER PARAMETERS

71

a. Sensitivity (Noise floor, NF) b. Non Linear Distortion(2-Tone IMD) c. AM-AM and AM-PM distortion (1-Tone

Measurement)


Noise Figure

72

• Sources of receiver noise 1. Noise picked by antenna (Ta=290K) 2. Noise generated by the receiver . Thermal Noise -thermal agitation of bound charges

𝑽𝒏 = 𝟒𝒌𝑻𝑩𝑹 . 𝟏 𝒇 Noise present from 1Hz to 1MHz

. Available Noise Power= K𝑻𝒂B ; K=1.38∗ 𝟏𝟎−𝟐𝟑 (J/K) . Noise Power Density=K𝑻𝒂 (W/Hz)=-174dbm/Hz @RT


Noise Figure (Contd.)

73

SNR = 𝑾𝒂𝒏𝒕𝒆𝒅 𝑺𝒊𝒈𝒏𝒂𝒍 𝑷𝒐𝒘𝒆𝒓

𝑼𝒏𝒘𝒂𝒏𝒕𝒆𝒅 𝑵𝒐𝒊𝒔𝒆 𝑷𝒐𝒘𝒆𝒓

Noise Factor=𝑺𝑵𝑹 𝒂𝒕 𝑰𝒏𝒑𝒖𝒕

𝑺𝑵𝑹 𝒂𝒕 𝑶𝒖𝒕𝒑𝒖𝒕 for a linear 2-port N/W

=𝑺𝒊

𝑵𝒊

𝑺𝟎𝑵𝒐

=𝑵𝒐

𝑮 ∗𝑵𝒊

NF=10*log𝟏𝟎 𝑭


Noise Figure of Cascade

74


Equivalent Noise Temperature

𝑻𝒆= 𝑭 − 𝟏 ∗ 𝑻𝑶 ; hence

𝑭 =𝑻𝒆

𝑻𝒐+ 𝟏

75

Note: Overall system noise temperature including antenna is


1-db Compression

76

Input signal power in dbm that produces 1-db compression in gain is 𝑷𝒊𝒏,𝟏𝒅𝒃=𝑷𝒐𝒖𝒕,𝟏𝒅𝒃 - 𝑮 + 𝟏𝒅𝒃 Minimum Detectable Signal (MDS) is defined as 3 db above the noise floor, given by 𝑴𝑫𝑺 = 𝑲𝑻𝒂𝐁 + 𝟑 𝐝𝐛


Dynamic Range

77

Dynamic range is defined as the range between 1-db compression point and minimum detectable signal (MDS).


Intermodulation Distortion

78


Intermodulation Distortion (Contd.)

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80

Third order Intercept Point (TOI) . Figure of merit for intermodulation product suppression . High Intercept Point means higher suppression of undesired intermodulation



81

TOI of cascade



82

Example

Ans +9.1dbm


DIGITALLY MODULATED SYSTEM

83

• CCDF ACCDF curve shows how much time the signal spends at or above a given power level



84

ORIGIN OF CCDF CURVES



85

• CCDF specify the power characteristics of the signal that will be mixed, amplified and decoded in communication systems.

• Useful tool for baseband DSP Engineer to convey the signal characteristics to RF Engineer



86

• Pulse shaping can significantly effect CCDF curve

• A higher roll off factor (α) will result in lower Pk to Av power ratio compared with a lower roll off factor in a digital system



87

• Compression effect displayed by CCDF curve

• Cause could be Nonlinearities of PA, Mixer or pre amplifier



88

• EVM is the scalar distance between two phasor end points (magnitude of the difference vector)

• Usually expressed as the percent of the peak signal level, usually defined by the constellation’s corner states.


WHAT IS BER?


WHAT IS RESIDUAL BER?


QAM MODULATION


SYSTEM DIAGRAM


RECEIVE PROBLEMS


PRIMARY NOISE AND DISTORTION ELEMENTS


PRIMARY BER INFLUENCES


EFFECT OF SOURCE PHASE NOISE


• Email: [email protected]

• Phone: +91 80 23432021 / +91 93435 10805

Contact information

101

mailto:[email protected]

rf system design and simulation using gan 12 & 13 march...

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