This paper presents a novel approach to the identification of output power and efficiency contours in microwave power transistors in compressed regime. The formulation is based on a polynomial representation of the drain-source voltage profile accounting for the knee region. Closed-form equations for the output power and efficiency as function of the fundamental load are demonstrated, enabling the plot of contours on a Smith Chart. From these, a further simplified drawing procedure for approximated contours is also derived, differentiating between two families of output characteristic. The first, with smooth knee, is usually experienced in GaN devices, while the second exhibits a steep knee which can be associated with GaAs devices' typical behavior. A 5-W GaN HEMT, a 2.5-W GaN HEMT, and a 0.7-W GaAs pHEMT are characterized with load-pull measurements. In all the three cases, the proposed method results in a very accurate contour construction, despite being based on an approximated output current/voltage profile and on a rough estimate of output equivalent capacitance.
IndexTerms-Field-effect transistors, high-efficiency amplifiers, power amplifiers (PAs).
The load modulated balanced amplifier (LMBA) technique uses a control signal, injected at the output coupler, to modulate the impedance of the balanced amplifier transistors. A 14.1-W X-band LMBA is reported, integrating for the first time the balanced, driver, and control signal amplifiers in a single microwave monolithic integrated circuit. Load modulation and bias settings are used to demonstrate that high circuit efficiency can be achieved as the LMBA is adjusted for operation in three RF-power regimes; 1.5, 5.6, and 14.1 W for a constant input power of 22 dBm. Power-added efficiencies above 37% are observed in all power regimes from 8 to 9 GHz under saturated conditions.
This letter presents wide bandwidth and high efficiency hybrid balanced and push-pull amplifier circuit topologies using Gallium Nitride (GaN) transistors and Liquid Crystal Polymer (LCP) multilayer circuit techniques. Push-pull circuit configurations allow differential and common mode impedances to be presented at even and odd harmonics independently, enabling the continuous mode (class BJ) design space to be exploited. Push-pull amplifiers display drain efficiencies > 40%, output power > 5 W over a bandwidth of 3.5 to 8.5 GHz at 2 dB compression levels, and under CW conditions. By comparison, although designed with identical performance goals, a conventional quadrature balanced amplifier performance is below that of the push-pull configuration.Index Terms-Broadband amplifiers, liquid crystal, power amplifier (PA).
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