Digitally Enhanced Switched-Mode RF Transmitters for Efficiency, Bandwidth and Fidelity

Power efficiency, bandwidth, and signal fidelity are critical specs of wireless transmitters, which are often traded off in transmitters with conventional analog circuit and antenna design. For example, high quality factor antennas and components help to achieve high efficiencies but often suffer bandwidth limitations. Switched-mode amplifiers and antennas have been proposed to achieve both high efficiency and broad bandwidth but the quantization noise issues prevent those techniques from being practically deployed. In this research, digitally enhanced techniques are proposed to enhance the design of switched-mode RF transmitter toward higher data rates, better power efficiency and lower quantization noise. Two specific research projects will be discussed. In the first project, an active noise filtering technique called Channelized Active Noise Elimination (CANE) is used to actively suppress the quantization noise in the bitstream modulated transmitter by employing the delaying and combining structure of multiple power amplification channels. The power efficiency of each of the power amplifier is preserved by a load modulation mechanism in the power combining operation. The proposed technique is implemented in a transmitter with a FPGA based signal processing module and the experimental results prove that the CANE technique can be a software-controlled, robust and flexibly tunable filter solution. The second project is utilizing the Direct Antenna Modulation (DAM) technique to surpass the physical bandwidth limit imposed by the high radiation quality factor of the electrically small antenna. The DAM concept has been proposed with various types of digital modulations, such as On/Off Keying, BPSK and QPSK, etc. A newly proposed DAM frequency shift keying (FSK) is developed to synthesize the parasitic components of switches with the matching circuit to improve the switching quality and signal integrity in the switched-mode electrically small antenna system