A DLL-based frequency synthesizer with selective reuse of a delay cell scheme for 2.4 GHz ISM band

Abstract

This work describes a 2.4 GHz frequency synthesizer based on a delay-locked loop (DLL). Because the proposed frequency synthesizer is basically developed from a DLL, it has no jitter accumulation thereby resulting in a low close-in phase noise of -105 dBc/Hz. Although only 9 delay cells are used, the proposed delay cell reusing scheme realizes frequency multiplication factors greater than 240 and provides multiple frequency output with the resolution of phase detector (PD) comparison frequency. This architecture has been verified by implementing the synthesizer in a 0.18 mum CMOS technology.