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In this paper, the effects of limited drain current and transistor's on resistance on the performance of an LDMOS inverse class-E power amplifier (PA) are analyzed using a simplified transistor model of piecewise linear dc I-V curves. The minimal magnitude of driving signal, the maximal voltage gain, and the maximal output power of an inverse class-E PA can be defined with the maximal drain kept. The theoretical and simulated results of amplifier performance, such as drain efficiency and output voltage, are compared to verify the analysis, and the nonlinear relation among the drain dc supply voltage, input/output voltage, and phase of an inverse class-E PA caused by limited drain current are presented. The effects on the amplifier performance are further verified by the measured results of a 945-MHz transmission-line inverse class-E amplifier in comparison with the corresponding theoretical and simulated results.