ABSTRACT
This chapter discusses the choice of modulation and examines the various proposed techniques that can eventually lead to an energy and spectral efficient high–data rate transmitter. It shows the evolving trends on adopted modulations for transmitters at the industrial, scientific, and medical band, millimeter-wave band, and sub–1-GHz band. High–data rate uplink is required to upload critical biomedical data and low–data rate downlink is used only for configuring the implanted device. Phase-locked loop is widely adopted for frequency and phase generation. The injection-locked oscillator has been found to be an energy-efficient way of obtaining accurate frequency reference without the need of additional components, such as frequency divider, phase frequency detector, and charge pump. The chapter illustrates the digital power amplifier with phase modulator circuit topology. It summarizes the performance of the prototype and compares it with the state-of-the-art designs. The chapter discusses the trend of moving toward complex modulation to maximize spectral efficiency.
