A Novel Design Method for CML Frequency Divider Based on C/Id and G/Id and Application for Quadrature-Injection CML Frequency Dividers

Abstract

A novel design method for current-mode-logic (CML) frequency divider based on ${C/I} _{\boldsymbol {d}}$ and ${G/I} _{\boldsymbol {d}}$ is proposed. The design method proposes using ${C/I} _{\boldsymbol {d}}$ and ${G/I} _{\boldsymbol {d}}$ as independent design parameters, where C and G are the equivalent capacitance and conductance of coupling pair (C cell) and negative- $\boldsymbol {g}_{\boldsymbol {m}}$ pair (N cell) in CML frequency dividers. Different from the traditional design method optimizing the maximum operating frequency ( $\boldsymbol {f}_{\textit {in,max} }$ ) by adjusting the self-resonant frequency ( $\boldsymbol {f}_{\textit {SR} }$ ), the proposed design method directly targets $\boldsymbol {f}_{\textit {in,max} }$ and output amplitude ( $\boldsymbol {V}_{\textit {out} }$ ) to obtain the ${C/I} _{\boldsymbol {d}}$ and ${G/I} _{\boldsymbol {d}}$ and solve the size and bias current of C and N cells, which realizes efficient design. Based on the proposed design method, several design examples are provided showing less than 3% error between the simulation results and design goals, and the proposed quadrature-injection CML (QI-CML) frequency divider is implemented and proven to have an improved sensitivity curve (SC). To validate the efficacy of our proposal, a frequency divider that can switch between differential-injection (DI) and QI is designed and fabricated in 110-nm CMOS process. For QI mode, the measured locking range (LR) is 141% (5-29 GHz) while consuming 5.47 mW. The achieved two figure of merits FOM $_{\textbf {Pdc}}$ and FOM $_{\textbf {A}}$ are 24.1 dB and 52.8 dB, respectively, which are superior to most published works.