Under the assumption of large scale antenna, we analyze the sum rate of circular layout distributed antenna systems (CL-DAS). First, we propose a concept of virtual base station and an expected large scale fading (E-LSF) for an arbitrarily located user as a function of the locations of users and distributed antennas and a path loss exponent. Based on E-LSF, we derive an approximated sum rate of CL-DAS whose form is identical to the sum rate of centralized multiple-input multiple-output (C-MIMO) systems. These results make it possible that the sum rate of CL-DAS with arbitrary beamforming schemes or power allocation algorithms can be evaluated using the existing approaches for C-MIMO systems. Simulation results verify that our analyses with E-LSF are valid for practical systems.