The use of continuous-time domain or frequency domain analysis in switched-capacitor systems may often be formally inapplicable due to insufficient mathematical conditions based on the system operating properties itself. This paper introduces a switching time-frequency domain method for the estimation of noise in such systems, while there is no need for periodicity. The switching domain method requires stationarity of the noise process and exploits the system operating conditions. It combines both the time and the frequency domains properly to overcome the difficulties, which exist in nonlinear time-invariant systems. The method is very structured allowing the usage by less experienced professionals and offering a better understanding of the underlying problem to them. The sequential nature of the method makes it predestined to be implemented in existent simulation tools.