Techniques to reduce folding of noise and interferers in PLL charge-pump

Due to its strongly non-linear operation, charge-pump Phase Locked Loops (PLL) suffer from folding of noise and interferers. Analysis and methods reducing this effect are scarce. We analyze and propose firstly band-limiting the charge pump currents and secondly carefully selecting the minimum phase detector pulse width to eliminate specific interferers. A PLL has also been measured confirming the predicted results. Measured improvements are typically 5 dB and 20 dB for the two methods, respectively.