High-Efficiency Wireless Transmitters Employing RF Pulse-Width Modulation

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High-Efficiency Wireless Transmitters Employing RF Pulse-Width ModulationRanjit GharpureyThe growth in infrastructure for wireless systems such as cellular telephony and wireless local area networks (WLAN), and the widespread availability of communication devices, has had a profound impact on multiple aspects of modern life over the recent decades. Examples of this include commerce, entertainment, healthcare, navigation, safety and security, social-media, transportation and workspace productivity, in addition to basic person-to-person communication. In the foreseeable future, the emergence of applications driven by the "internet-of-things", wherein a significantly larger number of devices, such as household and industrial appliances, will require wireless connectivity, will place even greater demands on the wireless infrastructure. Power efficiency of communication links, and compatibility with technologies such as advanced semiconductor processes that enable miniaturization and low-cost deployment, will be critical to future proliferation of wireless systems. Efficiency is important in both mobile and stationary devices for minimizing energy wastage. With potentially billions of wireless communication devices being deployed over the coming years, the need for efficient operation is in fact, fundamental. Power efficiency is also critical in mobile devices since it directly impacts the available operating time of the device. The proposed research will investigate design techniques for significantly enhancing the efficiency of wireless communication transmitters through innovative architectures that leverage advanced Complementary Metal "Oxide" Semiconductor (CMOS) processes. The research will also include an investigation of transmitter architectures that can be easily reconfigured to operate in different end environments, and on techniques that reduce the spurious interference generated by transmitters, that can degrade the performance of other devices. A key part of the proposed research will be an investigation of Pulse-Width Modulation (PWM) signaling schemes, as applied to the problem of wireless transmitters. Techniques that reduce noise in the transmitter spectrum will be explored. To avoid the noise caused by quantization in the time-domain, analog-PWM techniques will be investigated. Techniques for efficient generation of PWM directly at the desired RF band without the need for frequency upconversion will be employed. This will help reduce the out-of-band spurs that can be a significant limitation in upconverted baseband PWM due to co-existence considerations. The use of phase-locked loop (PLL) based PWM generator, which allows for generation of high-speed analog PWM will be studied. The use of efficient class-D output stages to drive output loads over broad bandwidths with minimal reconfiguration will be investigated. Such transmitters can be an enabler for techniques such as channel-bonding, wherein data rates can be increased multiple-fold by combining data streams that are transmitted over multiple bands concurrently. A practical design to validate and verify the proposed circuit techniques will be implemented in a modern CMOS technology. A practical wireless system, such as 4G-LTE will be employed for this investigation. The work will form the core of the doctoral research of one graduate student researcher, who will gain expertise in theoretical, design-related and experimental aspects to the design of wireless transmitters.