A 2.3-GHz Fully Integrated DC–DC Converter Based on Electromagnetically Coupled Class-D LC Oscillators Achieving 78.1% Efficiency in 22-nm FDSOI CMOS

This letter introduces a fully integrated dc–dc converter based on electromagnetically coupled class-D LC oscillators featuring on-chip stacked 8-shaped transformers in a 22-nm FDSOI CMOS process. The GHz-range resonant frequency of the proposed converter enables high integration of the passive components, achieving up to 3.2-W/mm
²
power density. The on-chip 8-shaped stacked transformers reach 16.9 quality factor and 0.91 coupling coefficient, demonstrating 78.1% converter efficiency. Furthermore, the twisted nature of the 8-shaped transformers introduces a magnetic field cancellation mechanism that minimizes the parasitic coupling between the transformers, saving 25% area in one single converter unit and 47% in the converter array, with respect to a spiral transformer implementation. In addition, the field intensity is reduced by 27 dB outside of the transformer borders compared with a spiral implementation, which helps to mitigate issues, such as parasitic magnetic coupling with neighboring circuits and electromagnetic interference.