Wireless sub-mm sized distributed brain implants have been proposed as the next frontier of Brain-Machine Interface (BMI) design to achieve untethered, high-density neural recording and stimulation. Simultaneously improving the wireless power transfer (WPT) efficiency and reducing the specific absorption rate (SAR) will be crucial for its clinical success. Towards these goals, we present an EM simulation method, a lumped equivalent circuit model, and a theoretical analysis to accurately predict the power delivered to the recording/ stimulating nodes, as well as the power dissipated in biological tissues and all other lossy elements within the system. This comprehensive framework also explains how increasing the distance between the transmit coil and the scalp can beneficially reduce the SAR without undermining the WPT efficiency. This work presents a rigorous prediction technique for transmission loss and tissue heating towards performance optimization.

Future generations of wireless communications are expected to place increasing burdens on the efficiency and linearity of power amplifiers, due to the use of more complex waveforms and OFDM. This has implications for the design of transmitters in portable/mobile devices as well as base stations and access points. This paper summarizes the digital techniques that can be employed to improve the performance of wireless power amplifiers

Several new approaches are presented for the reduction of power dissipation in wireless transceivers for mobile wireless applications. In most cases, the power dissipation of the circuit can be dramatically lowered without a significant reduction in circuit dynamic range or linearity. These techniques involve the use of active bias circuits to continuously optimize the performance of the circuit under varying bias levels.

This paper reviews the principles and status of AlGaAs/GaAs heterojunction bipolar transistor technology. Comparisons of this technology with Si bipolar transistor and GaAs field-effect transistor technologies are made. Epitaxial materials, fabrication processes, transistor DC and RF characteristics, and modeling of AlGaAs/GaAs HBT's are described. Key areas of HBT application are also highlighted.>