Capacitive-Coupled Stacked Class-D Oscillators for Galvanic Isolators

This brief presents a novel class-D oscillator topology conceived for galvanically isolated data transfer based on RF planar coupling. In its general implementation, it consists of n capacitively coupled stacked class-D oscillators, each one loaded by a primary transformer winding. Capacitive coupling between the oscillators guarantees robust frequency/phase synchronization. The oscillation voltages are combined at the secondary transformer winding, thus ideally producing the same oscillation amplitude of a class-D topology with a power consumption reduced by a factor of 1/n thanks to the current-reuse configuration. With respect to traditional topologies, capacitive-coupled stacked class-D oscillators also allow standard MOS transistors (i.e., with a low breakdown voltage) to be reliably operated at higher supply voltages. The oscillator advantages have been highlighted in comparison with the traditionally adopted complementary cross-coupled topology within an isolated data link based on RF planar coupling in a 0.18- $\mu \text{m}$ CMOS technology.