Spectral impact of the modulation index upon internal log-domain currents

This brief investigates quantitatively the impact of the input-signal modulation index upon the spectral content of internal log-domain currents. A second-order log-domain topology is treated as an example circuit and the quantitative dependence of the harmonic contributions to the total harmonic content of current signals internal to the topology upon different levels of strength of applied input tones is illustrated. Subsequently, this frequency-domain information is correlated with the transition frequency of the active devices which carry the nonlinear currents providing a certain degree of quantitative design insight.