A −86.88 dBc/Hz @1 MHz K-band fractional-N frequency synthesizer in 90-nm CMOS technology

Abstract

Through 90-nm CMOS technology, a K-band fractional-N frequency synthesizer has been designed. This paper proposes a new analysis to evaluate the noise current of the charge pump in fractional-N frequency synthesizer. It also designs an improved charge pump (CP). In addition, it also presents the multi-modulus divider (MMD) by the retime technique. The measured phase noise achieves −93.5 dBc/Hz and −86.88 dBc/Hz for integer-N and fractional-N modes at 1 MHz offset, respectively. The in-band phase noise performance can be improved about 20 dB by the retime technique. −54.63 dBc and −50.7 dBc reference spurs are respectively revealed by the spectrum for integer-N and fractional-N modes.