| A class-E power amplifier (PA) is a kind of high efficiency switch-mode power amplifier, and the polar transmitter based on class-E PAs can be adopted to improve the efficiency of the traditional transmitters. Considering the intrinsic technical requirements on the class-E PA in the polar transmitter, the researches on the class-E PA and its applications in this dissertation can be concluded as the following three major parts, the improved design methods of a high efficiency class-E PA, the analysis of the effects of drain modulation on the performance of class-E PAs, and the experimental validation of a prototype polar transmitter as well as the analysis of its non-ideal characteristics in the amplitude path.The new methods and new ideas proposed in this dissertation are listed as follows,1.The design method of a class-E PA with tuned series-parallel network is proposed, and it is verified by theoretical analysis, simulations and measured results. With adjustable combinations of the series and parallel resonance frequencies, the power output capability, load resistance, and maximum operation frequency of this proposed class-E PA can be improved.2.The design method of a single-ended class-E/F2 PA with finite dc feed inductor is proposed.With adjustments on the design parameter of the load network and the equivalent parallel resonance frequency, the power output capability, the load resistance, and the maximum operation frequency of the proposed class-E PA can be improved. This design method is verified by simulations and measurements.3.The causes of the performance degradation for increased drain dc supply voltage are analyzed for an LDMOS inverse class-E PA. The phenomena of efficiency degradation, output power compression, and phase distortions are verified to be caused by the limited maximum drain current of the transistor. Based on these conclusions, the gain and the maximum output power of inverse class-E PAs are also defined. 4. The cause of performance degradation of a MOSFET class-E power amplifier is analyzed for decreased drain dc supply voltage, and it is verified to be affected by the nonlinear transistor output capacitance. Meantime, an efficiency boosting method at low drain dc supply voltage is proposed by decreasing the gate dc bias voltage.The other problems solved and analyzed in this dissertation are listed as follows,1.The effects of transistor's output capacitance are analyzed for the drain efficiency, the amplitude response and the phase response of the inverse class-E PA.And the maximum operation frequency of the inverse class-E PA is defined to be affected by the transistor parasitic inductance and its drain-source breakdown voltage.2.A prototype WCDMA polar transmitter based on a class-E PA is built, and the feasibility of this transmitter is verified by both the frequency-domain and the time-domain measured results. The quality of output signals is found to be affected by the linearity of the drain modulation of the class-E PA and the linearity of the dc supply modulator.3.The bandwidth extension of the amplitude signal, after signal separations in the polar transmitter, is analyzed. And the relation between the EVM performance of the transmitter and the bandwidth of the reconstruction low-pass filter is analyzed in explicit expressions.The divergence of the AM-AM response in aΔΣsupply modulator is analyzed to be caused by the limited bandwidth of the amplitude path. While the nonlinear gain of the AM-AM response, in theΔΣsupply modulator, is caused by the pulsewidth inaccuracy caused by the nonzero transition time of the transistor. At last, the Hammerstein ARMAX model is used for modeling the nonlinearity with quasi memory effects of theΔΣsupply modulator, within the requirements of normalized mean square errors by simulations.
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