Direct noise analysis of log-domain filters

A direct method for analyzing noise in log-domain filters is proposed which exploits simplifying assumptions such as neglecting higher order noise terms, linearity in the current domain, the translinear principle, and time-averaging. Approaching from a conventional perspective, modulated-noise expressions are derived that account for every significant noise source in the filter. In addition, these noise sources are treated in situ and individually, without any need for moving or combining them. The accuracy of the derived results are compared and confirmed by Spectre radio frequency (RF) periodic noise simulations. Various examples given include a class-A biquad, class-A fifth-order ladder filter, and a class-AB third-order ladder filter.