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The purpose of this paper is to estimate the limits imposed on the computations made by logic gates fabricated in CMOS technology. It is assumed that the most rigorous constraints on computations originate from the thermodynamically irreversible processes that the computations consist of. In this paper, a model of CMOS logic gate is given based on the additive white Gaussian noise (AWGN) channel. It is found that the ultimate limit on energy spent to process one bit of data estimated by the proposed model of a CMOS logic gate is equal to the famous Landauer limit. This limiting energy cannot be obtained without sophisticated coding of the processed data. If one wants to avoid the processing of coded data, then much more energy has to be used to process one bit. In this paper, three limiting energies were estimated based on the proposed model of a logic gate. The limiting energies found in this study can be used, with Moore's law, to predict time after which development of CMOS technology is not possible.