It is important to separate random jitter from deterministic jitter to quantify their contributions to the total jitter. This paper identifies the limitations of the existing methodologies for jitter decomposition, and develops a new and efficient approach using time lag correlation functions to decompose different jitter components. The theory of the approach is developed and it is applied to a ring oscillator simulated in a 0.6-/spl mu/m AMI CMOS process. Results show good agreement between the theory and Hspice simulation.