Thesis (Ph. D.)--History, Technology and Society, Georgia Institute of Technology, 2006. / Dr. Susan Smulyan, Committee Member ; Dr. John Tone, Committee Member ; Dr. Larry Foster, Committee Member ; Dr. Steve Usselman, Committee Member ; Dr. John Krige, Committee Chair.

Portable communication systems require, in part, high-efficiency radio frequency power amplifiers (RF PA) if battery lifetime is to be conserved. Conventional amplifier classifications and definitions are presented in a unified and concise format. The Bipolar Junction Transistor (BJT) and Metal-Semiconductor Field Effect Transistor (MESFET) are evaluated as active devices in high-efficiency RF PA designs. Two amplifier classes (class CE and class F) meet the system requirements of an 850 MHz operating frequency, a power output of 3 W, a battery supply voltage of 9 Vdc, and a sinusoidal-type signal to be amplified. Both classes are evaluated through recent research literature and simulated using the PSpice® computer simulation program. Class CE and class F are found to provide efficiencies exceeding 80 percent under the given system constraints.</p. / Master of Science

Energy-efficient radio frequency (RF) power amplifiers (PAs) are critical and paramount to achieve longer battery life in state-of-the-art portable systems because they typically determine and dominate the power consumption of such devices. In this dissertation, a high-efficiency, linear RF PA with a dynamically adaptive supply and bias current control for code division multiple access (CDMA) and wideband CDMA (WCDMA) is conceived, simulated, and experimentally demonstrated with a discrete PCB-level design and in integrated circuit (IC) form. The PA efficiency is improved by dynamically adjusting both its supply voltage and bias current, there by minimizing its quiescent power dissipation. The PA supply voltage is derived from the battery by a noninverting, synchronous buck-boost switching regulator because of its flexible functionality and high efficiency. Adjusting the PA supply voltage and bias current by tracking the output power, instead of following the complete envelope in large baseband bandwidth wireless applications, is achieved by a converter with a lower switching frequency and consequently higher light-load efficiency, which translates to prolonged battery life. A discrete PCB-level prototype of the proposed system with 915 MHz center frequency, CDMA IS-95 signal having 27-dBm peak-output power resulted in more than four times improvement in the average efficiency compared to a fixed-supply class-AB PA while meeting the required performance specifications. In the IC solution fabricated in AMIs 0.5-micron CMOS process through MOSIS, a dual-mode, buck-boost converter with pulse-width modulation (PWM) control for high power and pulse-frequency modulation (PFM) for low power is designed and implemented to improve the PA efficiency during active and standby operation, respectively. The performance of the dynamically adaptive supply and bias control IC was validated by realizing a 25-dBm, 1.96 GHz center frequency, WCDMA PA over an input supply range of 1.4 4.2 V. The PA with dual-mode power supply and bias control IC showed an average-efficiency improvement of seven times compared to a fixed-supply class-AB PA, which translates to five times improvement in battery life assuming the PA is active for 2 % of the total time and in standby mode otherwise.

Capturing Believers provides a history of the reception of American conservative evangelical missionary broadcasting from its inception in 1931 through the rise of the commercial era in 1970. The dissertation narrates accounts of two major Protestant stations, HCJB and ELWA, located in Ecuador and Liberia, respectively, as well as the U.S.-based project to build a custom transistor radio for the mission field. Employing a case-study approach, the thesis demonstrates the innovativeness of religious broadcasters who formulated a range of pragmatic responses to the drastic shortage of receiving sets in the southern hemisphere, including the use of social convention and the development of pretuned receiver technology. Missionary stations imported not only radios, but a constellation of American values into host countries through their reception activities. Overall, officials employed creative methods to construct a particular type of listener experience known as radio capture, characterized by regular listening in a domestic setting. By penetrating into the home or village and exposing listeners to proprietary broadcasts on a continual, even daily, basis, missionary receiver programs legitimized American conservative evangelicalism abroad and sowed seeds for a widespread revival of Protestantism in Latin America and Africa after 1970.