The Q-PLL is a nonlinear circuit which can maintain a locked state when forced by two incommensurate frequencies.
The locked state is a third frequency parametrically selected among those prescribed by the theory of three-frequency resonances in dynamical systems.
In particular, the locked frequency forms a three-frequency resonance with the frequencies of the quasi- periodic input and is closely related to the pitch perception of complex sound in humans.
The circuit is able to lock also in case of deterministic perturbation (harmonics of the input frequencies) and stochastic perturbation (wide-band noise).It is also an extension of the Phase Locked Loop (PLL) with the additional ability of locking simultaneously to more than one frequency.
Due to the robustness of the locked states, the Q-PLL represents a basis for the development of applications, for example, in medicine (hearing aids, and cochlear implants), in robotics (artificial senses), and in industrial and consumer electronics (improvement of speech intelligibility, pitch- based processing, etc.). As an extension of the PLL, through further development and, it could find unexpected applications, which includes but also goes beyond those of the PLL and could generate a new family of nonlinear circuits for widespread application.
Italy, PCT