In this paper, a novel circuit referred to as complex G_m-C sampler that can be used for sub-sampling IF signals is presented. The circuit employs a conventional cross-coupled G_m-C filter structure with a built-in sampler to combine the functions of complex anti-alias filtering and baseband downconversion by sampling in a single circuit block. The filter response of the individual G_m-C samplers can be tuned to a conventional lowpass response or a sinc type response depending on the circuit parameters thereby modifying the anti-alias filtering provided by the circuit. Input noise analysis and switch noise analysis of the complex G_m-C sampler is also performed and the results are presented. The G_m-C sampler and its complex version are designed using a 0.18 mum CMOS process and its operation are validated using Spectre RF. Simulation results of the designed complex G_m-C sampler are finally provided.