In this paper, the evolution and milestones of RFEH and related breakthroughs over the years are reviewed and presented. The review begins with an overview of the surging energy crisis due to the increasing demand for wireless communication devices. Furthermore, the RFEH mechanism that discusses the frequency bands utilized, the near field, and the far field propagation are also presented. Various rectification techniques in CMOS RFEH, from the fundamental rectification method to cross-coupleddifferential-drive (CCDD), are also examined and discussed. The performance is gauged through harvested output DC voltage and the power conversion efficiency (PCE) as well as the RF input power sensitivity. An assessment on the non-CMOS RFEH that includes the Schottky diode and Rectenna is also concisely described to analyze their contribution to RFEH's performances enhancement. Finally, a special highlight of the 5G RFEH in mmWave is provided in the presentation of this work as an ongoing future solution to reduce the electronic circuit's battery dependency. The pros and cons of all the presented RFEHs are summarized and discussed as well. Continuous research and development activities are extensively being executed in developing a system that could ultimately solve the world's energy crisis and RFEH seems to be a revolutionary approach.

This paper presents a comprehensive design of a fully integrated multistage GaAs HBT power amplifier that achieves both linearity and high efficiency within a chip area of 0.855 mm 2 for 4G and 5G applications covering the lower frequency band of 700-800 MHz. A novel linearizer circuit is integrated to a dual stage class-AB PA to minimize the AM-PM (Amplitude Modulation-Phase Modulation) distortion generated by the parasitic capacitance at the PN-junction under low bias current condition. The linearized power amplifier is able to operate within a 100 MHz linear operating bandwidth (700-800 MHz) while meeting the adjacent channel leakage ratio (ACLR) specification for 4G and 5G application. The fully integrated PA achieves a wideband efficiency of 57.5% at 28.5 dBm output power. Observing a respective input and output return losses of less than 13 dB and 10 dB, the PA delivers a power gain within the range of 34.0-37.0 dB across the operating bandwidth while exhibiting an unconditional stability characteristic from DC up to 5 GHz. The proposed linearization method paves the way of reducing the complexity of linear and high efficiency PA design which is associated with complicated and high-power consumption linearization schemes.

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