Multi-standard CMOS frequency synthesizers for cognitive radios

This paper presents a wideband LC-based VCO using a divide-by-fractional-N injection-locked frequency divider (ILFD), and the fractional-N division is realized by the proposed gated injection technique. The feedback gating of incident signals eliminates unwanted injections, which contributes to enlarge the locking range. The ILFD consists of a 2-stage differential ring oscillator, which achieves the multi-decade frequency tuning with quadrature outputs. The proposed circuit is implemented by using a 90 nm CMOS process, and the measured results achieves 10 MHz-to-7 GHz of continuous frequency tuning range with 9.6-15.6mW of power consumption. The chip area is 250 × 200 μm².