17.3 A 1.25GHz Fully Integrated DC-DC Converter Using Electromagnetically Coupled Class-D LC Oscillators

Over the past years, the constant reduction in the size of consumer electronics has strengthened the demand for fully integrated power management circuits. Buck converters offer high efficiency, but they cannot satisfy the stringent size requirements because bulky off-chip inductors are required [1]. Switched-capacitor (SC) approaches provide fully integrated power management solutions; however, their power density is limited by the on-chip capacitance density [2]. Resonant switched capacitor (ReSC) converters need 3D die-stacked inductors or PCB-integrated inductors to achieve appropriate power density values, posing challenges for monolithic integration [3]. A fully integrated ReSC has been presented [4], which implements an on-chip resonator, avoiding any external or 3D stacked passive components. However, the switching losses associated with the four transistors driving the resonator limit the switching frequency to 10s of MHz, bounding the power density scaling to 0.097W/mm
²
.