Narrow pulse signal generation is an important part in high- speed systems design. Utilizing the voltage and current phase difference of inductor and diode, a very short pulse can be generated from a sinusoidal voltage source. Such systems usually include highly nonlinear components and complicated 3D structures. Dispersion, field effects and the interaction between electromagnetic field and components cannot be ignored in the simulation of these electrically small and complicated systems. Therefore, time-domain and full-wave analysis is necessary. This paper presents a full wave FDTD analysis using an improved field-circuit model for hybrid system simulation, which includes both lumped elements and field effect. 2 and 3D hybrid (distributed and lumped) circuits are constructed and analyzed in this paper to demonstrate the versatility of the time-domain simulator.