A Fast Locking 5.8–7.2-GHz Fractional-N Synthesizer With Sub-2-us Settling in 22-nm FDSOI

This letter presents a fast frequency hopping all-digital fractional-N synthesizer with linear frequency tuning word estimation and aggressive type-I and type-II loop settling. It has a linearized DCO allowing wide-band and closed-loop operation and employs digital zero-phase reset to reduce phase transients during switch over due to type-I settling. The DCO gain is equalized by exploiting routing inductances and a hybrid binary-thermometric segmentation provides improved DNL performance for closed-loop operation in a 5.8-7.2-GHz range. The circuit was processed in a 22-nm FDSOI technology and achieves a settling time below 2 μs in a 200-MHz hopping range.