This paper derives the theory and presents measurements of a new power amplifier based on the Doherty power amplifier topology. It is theoretically shown that the proposed amplifier can simultaneously provide high efficiency at both full output power and at output power back-off, over a much improved bandwidth compared to the conventional Doherty power amplifier. It is also shown that the proposed amplifier allows reconfiguration of the efficiency in power back-off without the need of tunable elements.A demonstrator circuit with individually controlled main and auxiliary amplifier input signals is designed to validate the theoretical findings. Measurements show state-of-the-art efficiency bandwidth with more than 49% drain efficiency at both full output power (42 dBm) and at 6 dB output power back-off (36 dBm) over a 1.5-2.4 GHz frequency range. The measurements also demonstrate that the efficiency in back-off can be conveniently reconfigured. The measurements thereby validate the presented theory and demonstrate the potential of the proposed amplifier for use in future wireless transmitter applications.Index Terms-Broadband amplifiers, Doherty, gallium nitride, GaN, high efficiency, power amplifiers, wideband.

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A new switch mode power amplifier (SMPA) topology particularly suitable for energy efficient amplification of radio frequency pulse width modulation (RF-PWM) signals is derived. It is analytically shown that high efficiency can be maintained over a wide power dynamic range if the imaginary part of the Class-E load impedance is varied along with the duty cycle (pulse width). Using the theory developed, an explicit design procedure is presented that allows practical realization of the proposed topology from the circuit and component specifications. Following the design procedure, and using in-house (Chalmers University) SiC varactor diodes to implement the tunable imaginary load impedance, a 2 GHz 10 W peak output power GaN HEMT circuit demonstrator is realized. RF-PWM input signals for characterization of the prototype PA is generated with a dedicated 65 nm CMOS modulator. The measurements show that a drain efficiency > 70% can be obtained over an 6.5 dB dynamic range, which verifies the theory presented and demonstrates the feasibility of the proposed PA topology.

The Sn-Co-Cu eutectic alloy can be a less expensive alternative for the Sn-Ag-Cu alloy. In order to find the eutectic solder composition of the Sn-Co-Cu system, the Sn-Co binary system has been thoroughly assessed with the calculation of phase diagram (CALPHAD) method. The liquid phase, the FCC and HCP Co-rich solid solution, and the BCT Sn-rich solid solution have been described by the Redlich-Kister model. The Hillert-Jarl-Inden model has been used to describe the magnetic contributions to Gibbs energy in FCC and HCP. The CoSn 2 , CoSn, Co 3 Sn 2 _β, and Co 3 Sn 2 _α phases have been treated as stoichiometric phases. A series of thermodynamic parameters have been obtained. The calculated phase diagram and thermodynamic properties are in good agreement with the experimental data. The obtained thermodynamic data was used to extrapolate the ternary Sn-Co-Cu phase diagram. The composition of the Sn-rich eutectic point of the Sn-Co-Cu system was found to be 224˚C, 0.4% Co, and 0.7% Cu.

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