High-speed RF multi-modulus prescaler architecture for Σ-Δ fractional-N PLL frequency synthesizers

This paper describes the design of a multi-modulus prescaler for Sigma-Delta fractional-N frequency-synthesizers. A new architecture is proposed to increase the critical time window for correct division. Quantification of the improvement of the architecture is done on the behavioral and transistor levels. The architecture is used to implement a multi-modulus prescaler with division factors 64-127 in a SiGe 0.35mum BiCMOS technology with f(1) of 60GHz. The architecture improves the maximum operating frequency of the prescaler by 50%. Post layout simulations indicate that the prescaler can operate at an input frequency of 3.2GHz while consuming only 6.4mW, with a phase noise floor of -132dBc/Hz, and up to 4.6GHz while consuming 14mW.