This paper reviews the state-of-the-art of high switching frequency, integrated DC-DC converters and presents the main trade-offs and challenges emerging from this review. Various converter structures (1-phase buck, 2-phase buck, 2-phase coupled buck and 3-level converter) are then discussed and analyzed through simulation from a losses point-of-view. Considering the review, the architecture analysis and the technology model, 4 converters are designed for a given set of specifications: 3.3 V to 1.2 V, 280 mA output current at high switching frequency (100-200 MHz) in 40 nm bulk CMOS. A cascode power stage is used in order to enhance power conversion efficiency, and 1-phase and 2-phase structures are designed. Post-layout simulation results are presented, showing an efficiency above 90 % for a 2-phase converter.