Wireless LAN Radios

Preface ix

Acronyms xi

CHAPTER 1 802.11 Flavors and System Requirements 1

1.1 Definition 1

1.2 WLAN Market Trends 3

1.3 History of 802.11 6

1.4 802.11: b, a, or g? 8

1.5 802.11b Standard 10

1.6 802.11a Channel Allocation 13

1.7 802.11a and 802.11g: OFDM Mapping 14

1.7.1 Multipath Fading 14

1.8 802.11a/g: Data Rates 21

1.9 802.11a/g OFDM Packet Construction 24

1.10 802.11 System Requirements 24

1.10.1 Receiver Sensitivity 24

1.10.2 Transmitter Error Vector Magnitude 26

1.10.3 Transmitter Spectral Mask 28

1.11 Vector Signal Analysis 33

CHAPTER 2 Radio Receiver and Transmitter Architectures 43

2.1 Architectures 43

2.1.1 Superheterodyne Receiver 44

2.1.1.1 Choice of Intermediate Frequency in Superheterodyne Receiver 47

2.1.2 Low IF Receiver 51

2.1.3 Direct-Conversion Receiver 55

2.1.4 Receiver Architectures: Summary 59

2.1.5 Superheterodyne Transmitter 60

2.1.6 Low IF Transmitter 64

2.1.7 Direct-Conversion Transmitter 64

2.1.8 Polar Modulators 66

2.2 Process Choices: CMOS versus SiGe BiCMOS 67

CHAPTER 3 Analog Impairments and Issues 73

3.1 Receiver Sensitivity and Noise Figure 73

3.2 Receiver DC Offsets and LO Leakage 75

3.3 Receiver Flicker Noise 79

3.4 Receiver Interferers and Intermodulation Distortion 83

3.4.1 IP3, IP2, and P1dB 83

3.4.2 Tools for Analyzing Modulated Signal Distortion 96

3.5 Receiver Image Rejection 102

3.5.1 Superheterodyne Receiver 102

3.5.2 Low IF Architecture 104

3.5.3 Direct-Conversion Receiver 106

3.6 Quadrature Balance and Relation to Image Rejection 107

3.7 Quadrature Balance and Relation to EVM 109

3.8 Other Transmitter (Modulator) Impairments 116

3.9 Peak-to-Average Ratio and Relation to Linearity and Efficiency 121

3.10 Local Oscillator Pulling in PLL 124

3.11 Phase Noise in PLL 126

3.12 Far-Out Phase Noise 130

3.13 Effect of Phase Noise on OFDM Systems 131

3.14 Effect of Frequency Errors on OFDM 132

3.15 Summary of Analog/RF Impairments 135

CHAPTER 4 Some Key Radio Building Blocks 137

4.1 Low Noise Amplifier 137

4.2 Mixer and its Local Oscillator Buffers 142

4.3 Power Amplifier 148

4.4 Fully Integrated VCO 153

4.5 Multifrequency (Stacked) Mixer 157

4.6 Open-Loop Transconductance Linearization Circuit 158

CHAPTER 5 Calibration Techniques 161

5.1 VCO Calibration 163

5.2 Automatic Frequency Control 165

5.3 Quadrature Error and Local Oscillator Feedthrough Calibration 172

5.4 Bias Current Calibrations (R Calibration) 175

5.5 Filter Time-Constant Calibration (RC Calibration) 176

5.6 Other Calibrations 177

CHAPTER 6 Case Studies 179

6.1 Case Study 1: A CMOS 802.11a Transceiver 179

6.1.1 Architecture and Circuit Implementation 179

6.1.2 Receiver 181

6.1.3 Transmitter 183

6.1.4 Phase-Locked Loop 186

6.2 Case Study 2: High Performance WLAN Transmitter Utilizing Quadrature and LOFT Calibration 189

CHAPTER 7 Brief Discussion Of 802.11n and Concluding Remarks 197

7.1 Need for 802.11n 197

7.2 802.11a/b/g/n MIMO Transceiver 202

7.2.1 Architecture and Circuit Implementation 203

7.2.1.1 Receiver 203

7.2.1.2 Transmitter 205

7.2.1.3 PLL and LO Generation 207

7.2.1.4 Calibration Techniques 209

7.2.2 Packaging Issues 211

7.2.3 Measurement Results 211

7.2.4 MIMO Case Study Conclusion 216

7.3 Concluding Remarks 217

References 221

Annotated Bibliography 223

Index 233

About the Author 241