Noise Performance of Fractional-Order Phase-Locked Loop

An analog fractional-order phase-locked loop (FOPLL) is investigated under noisy conditions. The FOPLL using fractional voltage-controlled oscillator (FVCO) and a fractional loop filter (FLF) outperforms its integer-order counterpart for both noisy and noiseless signals. Reducing the loop fractional orders increases both the locking and capturing ranges, and the bandwidth of the FOPLL, which substantially improves the loop transient behavior. However, an increase in the FOPLL bandwidth makes it susceptible to noisy signals. Hence, a compromise has to be made between the loop gain and the loop fractional order to alleviate the effect of noisy signals. The main points of this work are illustrated via simple numerical example.