An extended phase-locked loop for clock synchronization applications

Proposes a new tracking loop suited to track an unmodulated sine wave corrupted by an additive disturbance with inphase (I) and quadrature (Q) components correlated, Situations of this kind arise often in clock recovery circuits, where one of the sources of disturbance is the self-noise that must be described in terms of cyclostationary processes and leads to I and Q components with different power spectral densities and often correlated. The new loop explores this correlation by extracting the I component which is then used to perform some cancellation of the Q component, allowing an improvement relative to a conventional PLL. A small signal analysis of the new loop is presented and its performance derived. Numerical results of the tracking performance are presented for unipolar RZ signaling and bipolar data with elementary pulses time limited to two time slots, this latter case with an absolute value non-linearity to regenerate the discrete line at the clock rate. Both examples show that considerable improvements may be achieved relatively to the conventional PLL if the self noise is the main source of disturbance