Optimized architectures for carbon nanotube field-effect transistors (CNTFETs) with lightly doped source and drain have been proposed. Simulations are based on self-consistent solution of two dimensional non-equilibrium Green's function (NEGF) with Poisson's equation. By utilizing special designs in the lightly doped regions of the CNTFETs, their characteristics could be improved. Four CNTFET structures have been designed and compared to the conventional CNTFET which are lightly doped source and drain (LD_CNTFET), double lightly doped source and drain (DLD_CNTFET), linear lightly doped source and drain (LLD_CNTFET) and step-linear lightly doped source and drain (SLLD_CNTFET). In order to get to the optimized electrical characteristics, for the first time, the geometry and the doping of the new designed CNTFETs have been optimized. The target of optimizations has been achieving the best Ion/Ioff, cutoff Frequency and transconductance independently. The proposed designs have been optimized based on particle swarm optimization (PSO) method. The optimized length and doping level of source and drain lightly doped regions then have been used and the features of the proposed optimized CNTFETs have been compared. The results show that with the help of the proposed designs, great improvements have been achieved in the dc and ac characteristics of CNTFETs compared to the conventional CNTFETs.