Digitally Assisted, Fully Integrated, Wideband Transmitters for High-Speed Millimeter-Wave Wireless Communication Links

Over the past decades, there has been a massive increase in RF telecommunication technologies and systems. These systems have been developed aiming at very different applications, such as ultra-low-power communications like RFID and NFC, systems for broadband ubiquitous connectivity like the different standards for WiFi or the successive generations of cellular networks. These developments have taken place in parallel to—and driven by—the advances in CMOS technologies, which have allowed the development of high-performance, low-power, and highly integrated systems at a competitive price, making them suitable for the mass market. This chapter reviews the semiconductor technologies that allow RFIC design at mm-wave frequencies, and it also outlines the main applications of mm-waves.

In this chapter, considerations for the system-level study of a transceiver for multi-Gbps mm-wave communications will be presented. These considerations will be applied to the analysis of a transceiver that will satisfy the demands of future backhaul and fronthaul wireless links in the E-band. Starting from a set of given link specifications, a link budget analysis will be performed in order to assess the required output power at the transmitter. Additionally, the choice of an architecture that addresses the trade-off between performance and design complexity will be justified, describing its main features and deriving the specifications for each block in the transmitter.

This chapter will discuss the main impairments that affect the performance of wideband, high-speed mmW transceivers. Each impairment will be first introduced theoretically, and then its effect on a wideband mmW transceiver will be analyzed at system level. Numerical examples correspond to a reference E-band wideband transceiver, implemented using an FPGA for the baseband processing, commercial off-the-shelf DACs and baseband components, and specifically designed BiCMOS integrated circuits for the IF and mmW front-end blocks.

Wideband mmW communication systems suffer from a series of imperfections that can greatly jeopardize the signal quality. One of the most detrimental effects is the frequency-selective I/Q imbalance, which is present in most wideband mmW transceivers. This chapter analyzes the frequency-selective I/Q imbalance in detail, explaining its mathematical fundamentals and outlining methods to detect and compensate for it.

The design of millimeter-wave circuits involves understanding and dealing with new challenges, which make every design step crucial for a successful design. For instance, the high frequency of operation makes almost every layout connection behave as a transmission line, and therefore, they need to be adequately modeled and sized. In addition, transistors work close to their maximum operating frequency and voltages, and thus adequate transistor layout and biasing are a must, not to mention the fact that some components like transmission lines or transformers are not readily available in the design kits, and some other available components are not adequately modeled upto millimeter-wave frequencies. This means that the classical lower frequency design methodology consisting of sequential schematic simulation, layout implementation, and parasitic extraction is no longer valid, as the parasitics and electromagnetic behavior of every component and connection need to be taken into account from the very beginning. This chapter will outline the design methodology to be followed for successful, time- and resource-efficient design of millimeter-wave integrated circuits.

This chapter deals with the design of up-conversion mixers for application in mmW transmitters. First, the operation principles, figures of merit and common implementations for mmW mixers are presented. Then, the principles of I/Q modulation are reviewed, and some common architectures are discussed. Afterwards, design examples of a 16-21-GHz I/Q upconverter and an E-band upconverter are given. These circuits are basic building blocks of double-conversion wideband mmW transmitters, and they are designed to meet the requirements of the wideband BiCMOS integrated transmitter described throughout this book.

The power amplifier is usually the last active element in an RF transmitter front-end, and usually one of the most critical blocks. It is the main contributor to the front-end power consumption, and its linearity determines the overall performance of the communication link. This chapter will discuss considerations for the design of wideband mmW PAs, applying the concepts to the design of an E-band power amplifier for multi-Gbps spectrally efficient communication links. First, the most representative performance metrics will be described, and different design approaches and architectures for mmW PAs will be reviewed. Then, the design of the Eband PA will be presented, validating its performance with measurement results.

This chapter deals with integrated mmW power detectors. First, motivations for their use, figures of merit, and common implementations are reviewed. Then, a design example of an integrated mmW wideband detector is presented and validated with measurement results. It is integrated at the output of an E-band power amplifier and it can be used for built-in integrated self-test (BIST) purposes or as a first step towards an integrated self-healing system.

In previous chapters of this book, design considerations and examples of different building blocks (I/Q up-converters, mixers, power amplifiers, power detectors, etc.) of mmW wideband transmitters for multi-Gbps and spectrally efficient communications have been given, as well as different methods to evaluate and compensate for the front-end imperfections in order to maximize the performance of the communication link. In this chapter, design considerations for the mmW transmitter itself will be provided, which consist of a combination of the aforementioned blocks. As in previous chapters, such considerations will be explained using an example: a wideband and high-linearity E-band transmitter [1], which is integrated using a state-of-the-art 55-nm BiCMOS process from STMicroelectronics  [2].