A GHz-level ring-counter-based multi-modulus fractional LO divider with on-the-fly tunability

A novel architecture of multi-modulus fractional LO divider is presented in this paper. The ring-counter-based sub-N downsamplers are used to generate fractional division ratios. A LO divider with division ratios of /2.5, /3.5 and /6.5 utilizing the proposed method is designed in 40-nm CMOS process to cover the 2/3/4G cellular band. Components are reused to reduce the chip area. The division ratios can be changed on-the-fly. The divider consumes 9.61 mA from 1.1 V supply. Other division ratios can be achieved by changing the downsample factor N of the sub-N downsamplers.