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This work presents models which evaluate the propagation delay of an RC chain driven by a step input current generator. Starting from a rule of thumb model, involving network parameter values, three different approximations have been devised. The approximated models are quite simple and can be adopted in finding the number of stages after which repeaters can be introduced. In particular, one of the models can be used to optimize the propagation delay when inserting repeaters in a chain of transmission gates. Results from the new approach were compared with the traditional one with optimization by Spice simulation using a 0.35-μm CMOS technology. The optimization based on the proposed model shows both a lower propagation delay and the need for a smaller number of repeaters compared with the traditional approach, hence, lower power consumption and silicon area.