A Fully Integrated 4:1 DC-DC Converter Using Electromagnetically Coupled Class-D LC Oscillators Achieving 74.5% Peak Efficiency and 0.78W/mm² Peak Power Density

Fully integrated DC-DC converters enable direct power supply to integrated circuits (ICs) from DC sources such as battery or USB ports. However, a high conversion ratio is necessary since the DC power sources’ voltage is much higher than that required by the ICs. Achieving a high conversion ratio unfortunately results in a significant degradation in performance, including power density and efficiency, due to increased power transfer steps or high voltage switch drivers. To overcome these challenges, a couple of research efforts have been introduced recently. In [4], an integrated converter using a resonant switched capacitor technique is proposed, which achieves a $3: 1$ conversion ratio with a high efficiency of 78.3%. However, it suffers from a low power density of $16 \mathrm{~mW} / \mathrm{mm}^{2}$ due to a low switching frequency of 30 MHz. In [5], an on-chip DC-DC converter based on electromagnetically coupled LC oscillators (EMLC) is introduced, which achieves a high power density of $4.1 \mathrm{~W} / \mathrm{mm}^{2}$. Unfortunately, it is restricted to conversion ratios of 2:1 or 1:2 and exhibits a low efficiency of 60.4% at peak power density.