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   Argyle, Paul; Sprangle, Phillip (July 2022, IEEE Transactions on Plasma Science)
2. Black-hole powered quantum coherent amplifier

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   Abstract Atoms falling into a black hole (BH) through a cavity are shown to enable coherent amplification of light quanta powered by the BH-gravitational vacuum energy. This process can harness the BH energy towards useful purposes, such as propelling a spaceship trapped by the BH. The process can occur via transient amplification of a signal field by falling atoms that are partly excited by Hawking radiation reflected by an orbiting mirror. In the steady-state regime of thermally equilibrated atoms that weakly couple to the field, this amplifier constitutes a BH-powered quantum heat engine. The envisaged effects substantiate the thermodynamic approach to BH acceleration radiation. 

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3. A Quadrature Switched Capacitor Power Amplifier

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5. Chireix amplifier with enhanced bandwidth using active load

   https://doi.org/10.1109/IEEE-IWS.2018.8400841  

   Roblin, Patrick; Chang, Hsiu-Chen (May 2018, 2018 IEEE MTT-S International Wireless Symposium (IWS))

   The use of an active load has been recently proposed for the realization of power-efficient broadband balanced amplifiers. The application of an active load to a dual-input Chireix amplifier is investigated in this paper for the purpose of increasing their bandwidth. An embedding device model is used to established the optimal non-Foster loads required for both the transistors to remain operating in class F as the operating frequency deviates from the center frequency. Given the transistors must operate with a constant voltage swing between backoff and peak, it is found necessary for the two transistors to operate with different load impedances as the frequency varies. The required load impedance and outphasing angles for the Chireix operation are obtained using a generalized eigenvalue problem using the Y-matrix of the Chireix combiner loaded with the active load. It is verified that using an active load, it is possible to maintain a high efficiency not only at peak power but also under various backoff power levels over a bandwidth of 1 GHz. Within a 200 MHz bandwidth, the PA is predicted to be able to maintain an efficiency larger than 79% for 6 dB backoff. Further work is required to experimentally validate the proposed technique. 

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