Implantable medical devices have been implemented to provide treatment and to assess in vivo physiological information in humans as well as animal models for medical diagnosis and prognosis, therapeutic applications and biological science studies. The advances of micro/nanotechnology dovetailed with novel biomaterials have further enhanced biocompatibility, sensitivity, longevity and reliability in newly-emerged low-cost and compact devices. Close-loop systems with both sensing and treatment functions have also been developed to provide point-of-care and personalized medicine. Nevertheless, one of the remaining challenges is whether power can be supplied sufficiently and continuously for the operation of the entire system. This issue is becoming more and more critical to the increasing need of power for wireless communication in implanted devices towards the future healthcare infrastructure, namely mobile health (m-Health). In this review paper, methodologies to transfer and harvest energy in implantable medical devices are introduced and discussed to highlight the uses and significances of various potential power sources.

In this article, a continuous-mode inverse class GF (CCGF⁻¹) power amplifier is introduced based on a new closed-form expression for the drain current. This analytical expression is utilized to exploit second source harmonic impedance manipulation in order to expand the design space of the output matching circuit resistively. This approach allows to diminish the complexity of the design of the load matching network at the fundamental and harmonic frequencies and to achieve wider bandwidth while simultaneously improving drain efficiency across the new optimum admittance points. Using the nonlinear model of a commercially available 10-W gallium nitride (GaN) device, load--pull and source-pull techniques are used to design a wideband CCGF⁻¹. The designed amplifier is fabricated using the selected transistor in low-temperature co-fired ceramic (LTCC) technology. Measurement results show that, over the frequency band between 3.05 and 3.85 GHz, a drain efficiency of more than 70%, 11-12.4-dB gain, and 39.9-41.4-dBm output power at 3-dB gain compression have been achieved. Although not designed for linearity, the fabricated amplifier shows an adjacent channel power ratio better than 26 dBc under a 20-MHz long-term evolution (LTE) signal having a 10.45-dB peak-to-average power ratio.

In this letter, the second source harmonic in continuous-mode class GF (CCGF) is optimized to flatten the power amplifier's (PA) frequency response over a wideband. A new design space is explored by considering the effects of controlling the input nonlinearity of the gate-source capacitance ( $C_{{gs}}$ ) on the drain current waveforms under continuous-mode drain voltage waveforms. A wideband CCGF PA is designed and fabricated using a commercial 10-W gallium nitride (GaN) device and low-temperature co-fired ceramic (LTCC) technology. Results of the measurement show a flat frequency response from 3.3 to 4.3 GHz with variations less than ±0.4 dB for 40 dBm output power, and 17 dB large signal gain at 3-dB compression point. A drain efficiency of 66 ± 2% is achieved over the entire bandwidth.

This paper proposes a new amplifier architecture based on the outphasing technique intended for the efficiency enhancement of linear amplification with nonlinear components (LINC) transmitters. The proposed mode-multiplexing linear amplification with nonlinear components (MM-LINC) scheme operates according to the LINC concept for input signal magnitude drive levels below a certain threshold and as a balanced amplifier beyond this threshold. The setting of this threshold level influences the performance of the amplifier in terms of average power-added efficiency and linearity. A 2-W up-link transmitter prototype for worldwide interoperability for microwave access (WiMAX) applications was designed using this new architecture and optimized for a WiMAX signal with an 11.3-dB peak-to-average power ratio. The experimental results revealed a significant increase in power-added efficiency, from 6% for a LINC transmitter to 21% for the MM-LINC amplifier, while maintaining an error vector magnitude value under 8%, which is compliant with the standard requirement