A modified Park-Kim voltage-controlled ring oscillator for multi-Gbps serial links

This paper proposes a new multi-stage CMOS voltage-controlled ring VCO called modified Park-Kim ring VCO for multi-Gbps serial links. An in-depth comparative study of pros and cons of Park-Kim VCO and the modified Park-Kim VCO with both single and dual delay paths is given. We show that the modified Park-Kim VCO offers an improved oscillation frequency, large output voltage swing, comparable frequency tuning range and phase noise as compared with Park-Kim VCO proposed in [1, 2]. We further show that although the modified Park-Kim VCO with single delay path and that with dual delay path offer comparable oscillation frequencies when the number of stages of the VCOs is high, the former provides a large frequency tuning range and reduced circuit complexity. To verify performance improvement, both Park-Kim VCOs and the modified Park-Kim VCOs are implemented in TSMC’s-0.18 μm, 1.8 V CMOS technology and analyzed using SpectreRF from Cadence Design Systems with BSIM3.3 device models. Simulation results are presented.