Fractional-N Injection-Locked Ring Oscillator Based on Two Points, Varying Strength Injection

This paper proposes a fractional-N injection-locked ring oscillator (ILRO) based on sequential 2-point injection with programmable injection strength on each point. The 2-point injections effectively achieve an equivalent vector-summed injection, leading to programmable injection position and injection strength. By gradually changing the ratio of the two-point injections, the vector-summed injection can achieve injection at fractional phase step and obtain fractional output frequency resolution. As no delta-sigma modulator (ΔΣM) is employed, the high-frequency shaped quantized phase noise issue can be avoided. A 16-phase, 2-point ILRO composed of delay cells with 8-level of programmable injection strength has been designed and simulated, and an output frequency resolution of f
REF
/(16×8) has been achieved as analyzed. Meanwhile, the phase noise improvement is similar to the case with fixed single point injection.