Advances in Analog and RF IC Design for Wireless Communication Systems

Gabriele Manganaro, Domine M W Leenaerts

• Publisher: Academic Press
• Year: 2013
• Print ISBN: 9780123983268
• eBook ISBN: 9780123983329
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Advances in Analog and RF IC Design for Wireless Communication Systems gives technical introductions to the latest and most significant topics in the area of circuit design of analog/RF ICs for wireless communication systems, emphasizing wireless infrastructure rather than handsets. The book ranges from very high performance circuits for complex wireless infrastructure systems to selected highly integrated systems for handsets and mobile devices. Coverage includes power amplifiers, low-noise amplifiers, modulators, analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), and even single-chip radios. This book offers a quick grasp of emerging research topics in RF integrated circuit design and their potential applications, with brief introductions to key topics followed by references to specialist papers for further reading. All of the chapters, compiled by editors well known in their field, have been authored by renowned experts in the subject. Each includes a complete introduction, followed by the relevant most significant and recent results on the topic at hand. This book gives researchers in industry and universities a quick grasp of the most important developments in analog and RF integrated circuit design. - Emerging research topics in RF IC design and its potential application - Case studies and practical implementation examples - Covers fundamental building blocks of a cellular base station system and satellite infrastructure - Insights from the experts on the design and the technology trade-offs, the challenges and open questions they often face - References to specialist papers for further reading

Chapter 1

Wireless Infrastructure

Gabriele Manganaro^a and Domine Leenaerts^b, ^aAnalog Devices, Boston, USA, ^bNXP Semiconductors, Eindhoven, The Netherlands

Introduction

Wireless communication is today one of the most important ways to transport voice, video, and data using radio-frequency (RF) or microwaves. In fact, since 2002, more phone calls are made via a wireless link rather than a wired link. Even more striking, according to recent statistics on a global scale, today there are already more mobile phone subscriptions than people with access to electricity or access to safe drinking water. The modern mobile handheld terminal, the smartphone, is a clear example of it; it transports voice via a GSM, or W-CDMA cellular communication pipe and data/video can be transported via the WLAN connectivity pipe. Microwaves are typically used for satellite links to broadcast television, to enable internet for remote areas, and for private networks.

In a wireless infrastructure, wireless devices can communicate with each other or communicate with a wired network. In a cellular wireless infrastructure the communication goes first through an access point, called the base station. The mobile handheld device communicates via the base station (BTS) with another mobile device or can access the wired network. Communication takes place in the RF cellular frequency bands from 700 MHz up to 3 GHz with the upcoming LTE-A operating in even higher frequency bands between 3 and 4 GHz. Base stations communicate between themselves via a wired (optical) or again wireless link. The wireless link is very important and is referred to as the microwave backhaul of the base station. The communication happens at various microwave frequencies in the 13–40 GHz range. As base stations do have a fixed geographical position, the communication between base stations is a so-called point-to-point communication, the antennas needed for the microwave backhaul are pointed to each other (i.e. line-of-sight setting).

A satellite (wireless) infrastructure operates in a similar way, where the satellite can be considered as the base station or the access point. At the other end one finds the indoor-unit or set-top-box which is connected to the outdoor unit, the transceiver, and the dish. Most often the wireless downlink communication happens in the 10.7–12.75 GHz Ku-band, but the 18.2–22.0 GHz Ka-band is becoming popular too. Uplink communication, that is the link from earth to satellite, takes place in the 13 GHz or 30 GHz frequency bands.

1.1 The cellular infrastructure

Mobile data traffic is expected to increase 18-fold over the next five years to 11 Exabytes per month by 2016 as a result of an ever-increasing demand for data throughput driven by widening spread of smartphones and, even faster, of tablet devices and other data-hungry mobile devices. In the meantime, wireless technologies like lte advanced are approaching the physical limits for achievable channel capacity because the spectrum is a limited resource. The consequence of all this is that further growth of the network capacity must come from new networks where for instance macro cells are overlaid by small cells and offload of mobile networks might take place with seamlessly integrated WiFi access points.

A macro cell base station delivers the best performance and coverage, but is very expensive to roll out. The cell radius of a macro base station is around 1–25 km and can handle more than 256 users. The average transmitted power is more than 10 W; peak power is more than 100 W. A macro base station consists of one or more reasonable-sized cabinets plus a big tower, which means that in very populated areas acquiring a site to install the macro base station might be difficult and very expensive.

The small cell can densify the macro cell network in urban areas with a lower total cost of ownership. Small cells, a collection of pico and micro cells, typically have a cell size between 200 m and 1 km and can handle up to 256 users. The average transmit power is around 5 W. However, a high-performance backhaul is mandatory for optimal performance. This backhaul can be wired or wireless. The macro cells and small cells together should deliver a high-quality (e.g. best coverage and capacity) user experience for voice and data.

The addition of WiFi access points should improve the capacity in high-traffic areas and “hot spots” and is mainly data centric.

The backhaul is a key element for high-performance cellular networks. The majority of the microwave, wireless, links use the spectrum between 6 and 38 GHz and offer capacities up to 400 Mbps with 56 MHz channel bandwidth and 256 QAM constellation. The main challenge in the microwave backhaul is the required line-of-sight (LOS) and strict alignment between the two end points. The requirement of LOS can be relaxed by the introduction of beam forming techniques and/or advanced MIMO techniques.

1.2 The satellite infrastructure

The microwave satellite market is a mass market with over 80 million outdoor units in 2012. The majority of the outdoor units are for satellite TV reception in the Ku-band. This is a mainly one-way communication pipe with the satellite. A smaller market is the two-way communication pipe for applications like credit card data, internet in remote areas, maritime communication, and private networks (e.g. CNN). This very-small-aperture-terminal (VSAT) communication uses data rates up to 4 Mbps. The name VSAT depicts the size of the antenna, a dish antenna that is smaller than 3 m.

The low-noise block (LNB) outdoor unit is the receiver converting the received satellite signals in the Ku-band down to the L-band (950–2100 MHz). The LNB is connected via a coax cable to the set-top-box in the house, where the costumer can select the TV channel. The set-top-box will power the LNB via the coax cable. Consequently, as the set-top-box can only deliver a certain amount of power, the power consumption of the LNB is a critical design parameter.

1.3 Challenges

Wireless infrastructure, be it cellular or satellite, is a more professional market segment rather than consumer market segment. Consequently, the market is traditionally driven by performance demand rather than by cost. A typical RF card in a base station or a low-noise block down converter unit in a satellite receiver is mainly based on discrete III–V compound technology components. They deliver the required performance, while the associated cost and power consumption is a lesser issue. But this landscape is changing. Mobile phone operators see their energy bills exploding while they are expanding the capacity of their cellular infrastructure. And as the expansion is taking place in dense areas like shopping malls, the installed access point should be small in size too. If satellite communication should become available in developing areas such as India and South America, a price reduction would be needed.

Consequently, there is a need to move away from III–V compound technologies toward silicon-based solutions, which inherently can provide cost reduction and power dissipation reduction, similar to what has been observed in mobile handheld devices in the past. However, the required performance, more easily delivered by GaAs-like technologies, should not be compromised. This is a challenge for silicon-based technologies where the active devices inherently have poorer performance. The RF radio especially will face challenges from this technology change.

This book will address the various issues related to the transition from III–V compound technology toward silicon-based solutions for RF radios in wireless infrastructure.

On the other hand, the data converters (ADCs and DACs) in the same signal chain have already seen a substantial shift from a mix of BiCMOS and CMOS designs to a near monopoly of CMOS data converters in the most recent designs. Some of the driving forces behind this technology shift follow.

First of all, starting from 0.18 μm and even more with finer-lithography CMOS processes, the transition frequency, f_T, of MOS devices has become very competitive with the one of many of the bipolar devices available with some of the mainstream BiCMOS processes and for a comparable price. Moreover, both the active and passive device matching have been steadily improving with CMOS scaling. Combining that with the far greater level of integration achievable in CMOS makes nanometer-scale CMOS processes far more attractive than BiCMOS alternatives in designs with moderate resolution (10–16 bits) and a high sample rate (100 MSPS–1 GSPS and beyond) that are needed for wireless infrastructure.

One of the many design challenges associated with this process technology shift is represented by the lower and lower power supply usable with scaled CMOS processes. Specifically, 3.3 V and 5 V analog supplies, which were common for older BiCMOS data converters, have been replaced with 3.3 V, 2.4 V, 1.8 V, and, more recently, 1 V and even 0.9 V analog supplies in deep nanometer CMOS data converters as 40 nm or 28 nm. This has inevitably led to formidable design challenges due to lowering voltage headroom and the ability to design analog circuits with a sufficiently low noise power spectral density with rapidly shrinking usable signal power.

The greater adoption of CMOS processes for high-performance data converters for wireless infrastructure has also fueled another trend. Scaled CMOS processes have enabled dramatic improvements in terms of both cost- and power-effective digital signal processing functionality. Therefore it is very common in present-day wireless infrastructure data converters that a good deal of the digital post-processing in the receive path is integrated on the same die with the ADC and, conversely, that the digital pre-processing in the transmit path is integrated on the same die with the DAC. Such digital functions include, for example, digital down conversion, filtering, channel separation in the case of the receive path; and consist, for example, of digital up conversion, interpolation, filtering, etc., in the case of the transmit path.

Furthermore, this on-chip availability of efficient digital functionality has also enabled the practical implementation of on-chip calibration and nonlinear correction schemes for some of the cited analog-domain shortcomings. So, in a way, the source of some of the analog design grief introduced by nanometer processes can also be tackled by means of the rich digital processing power introduced by Moore’s law by a broad new slew of techniques loosely categorized as “digitally assisted analog (and RF) design.”

Furthermore, the increasing demand for larger data throughput, combined with the increasing availability of computational DSP power fueled by Moore’s law, has driven the demand from BTS manufacturers for wider and wider bandwidth signal chains able to process co-existing and different communication standards (not only GSM channels, but also LTE, WCDMA, etc.). Without doubt, that has made the RF front-end and the data converters the “performance bottleneck” of this class of radio systems. Along with that, the power, functionality, and cost advantages of DSPs have fueled the quest for the “holy grail” of radios, known as “software radio” and consisting of a signal chain where the RF and analog front-end are increasingly smaller and where the analog-to-digital conversion and the digital-to-analog conversion boundaries move closer and closer to the antenna, allowing more of the (de-)modulation/filtering/processing of the communication channels to be efficiently and reliably performed in the digital domain. Indeed one of the chief challenges of this quest lies in the fact that moving the boundary between the physical analog medium and the digital one toward higher frequency or wider bandwidth is paid for by dramatic increases in power consumption to perform the conversion.

It is mainly because of this reason that for a given set of communication specifications and development and implementation costs a balanced choice for the borderline between analog and digital leads to sensitive signal-chain trade-offs. In many commercial cell phone BTSs this boundary lies presently between the tens and hundreds of MHz and where the ADC samples the lowest intermediate frequency (IF) stage of a heterodyne scheme or where the DAC directly synthesizes the signals at one of the IF frequencies, or possibly at RF.

Another critical design challenge originates from the need, mentioned above, to develop a BTS that is physically small in size: going from a unit similar in size to a small refrigerator to one similar to a desktop PC or possibly slightly bigger than a laptop. To reduce physical size, higher integration is certainly one lever, but most importantly heat removal is a very important challenge. Heating sinks, fans, and other sizeable devices for heat removal and management need to be eliminated. That means the electronics need to dissipate less heat and need to be able to operate in a much hotter ambient temperature. Clearly the previously cited power consumption challenge originating from increasing communication performance demands is further aggravated by these much more challenging operating environment conditions. Not only circuit design technology and silicon reliability are challenged. Electrical, thermal, and mechanical aspects of package technology, assembly and manufacturing, printed circuit boards, to cite a few, come into play and trade-offs between all these aspects take center stage in the design development process.

1.4 This book

This book aims to provide an overview of the main and most current technical topics in radio-frequency and analog/mixed-signal IC design for wireless infrastructure. The chapters are contributed by some of the most well-respected professionals in this field both from industry as well as academia.

The chapter authored by H. Darabi provides a broad overview of the architectures and system trade-offs involved in the overall design of CMOS transceivers. Following that, the individual chapters dive into covering the challenges and the design techniques associated with all the main functional blocks in modern commercial cellular base station systems. Following an order that somewhat mirrors the cascade of stages between the antenna and the DSP, we begin with a chapter on the design of low-noise, high-linearity amplifiers (LNAs) authored by D. Leenaerts as well as another chapter on RF power amplifiers written by M. Acar et al.

That is followed by a chapter on frequency synthesizers/PLLs contributed by S. Levantino and C. Samori describing low phase noise oscillators used in down and up conversion. And, of course, coupled with that is a chapter on mixers and modulators by W. Redman-white. The special case of low noise down-converters for satellite communication systems is covered in a chapter by P. Philippe et al. The latter concludes the part of this book on what is commonly considered as the true radio-frequency electronics of this class of infrastructure radios.

The many classes of analog-to-digital and digital-to-analog converters found in base stations are discussed in the chapters that follow. R. Schreier and H. Shibata authored a chapter on emerging continuous time band-pass DS ADCs for communication applications. A more established ADC architecture in this arena is the pipelined ADC. That is the topic of the following chapter by M. Elliott and B. Murmann. Another ADC architecture that is gradually emerging as a viable option is the SAR ADC. Interleaving multiple lower-sampling-rate ADCs allows the building of overall higher-sampling frequency converters as described in the chapter by K. Doris et al. that follows.

Finally a chapter by G. Engel and G. Manganaro describes the other side of converters, namely modern high-performance digital-to-analog converters for the transmit path.

Last but not least, the chapter on time-to-digital conversion for digital frequency synthesizers describes an emerging breakthrough alternative to some of the other approaches in frequency synthesis as well as domain conversion. This chapter is authored by M. Perrott and concludes the volume.

Conclusive Remarks

Concluding this introduction, the two editors of this volume would like to acknowledge and thank the many authors of this book, who, on rather short notice and on a fast-paced schedule, have graciously managed to contribute a comprehensive and cohesive set of outstanding chapters on very critical topics for a very rapidly evolving and highly competitive space. Given the fast pace of innovation and the breadth of this field there is no doubt that reading this material will both answer questions and trigger new ones. In fact, the contents are very much on the tipping point of today’s state...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Chapter 1. Wireless Infrastructure
• Chapter 2. CMOS Transceivers for Modern Cellular Terminals
• Chapter 3. Low-Noise Amplifiers for Cellular Wireless Infrastructure
• Chapter 4. High-Efficiency Power Amplifiers for Wireless Infrastructure
• Chapter 5. Digital Fractional-N Frequency Synthesis
• Chapter 6. Mixers and Modulators in Wireless Systems
• Chapter 7. Integrated Satellite Low Noise Block Down-converter
• Chapter 8. Bandpass ΔΣ ADCs for Wireless Receivers
• Chapter 9. High-Performance Pipelined ADCs for Wireless Infrastructure Systems
• Chapter 10. Interleaving of Successive-Approximation Register ADCs in Deep Sub-Micron CMOS Technology
• Chapter 11. High-Performance Digital-to-Analog Converters for Wireless Infrastructure
• Chapter 12. Time-to-Digital Conversion for Digital Frequency Synthesizers
• Index