Analysis of limit-cycle oscillations in a log-domain filter

A circuit is presented for a class-AB fully differential log-domain parallel resonator. If floating rather than shunt capacitive loads are used, the circuit can be triggered into steady-state limit-cycle oscillations by large-enough transient input stimuli. The nature of the instability is explored. Transient analysis in SPICE is used to locate the separatrix between stable-equilibrium-point-seeking and limit-cycle-seeking regions of state space