Robust power oscillator design for inductive-power link applications

Microelectronic devices are widely used in biomedical applications such as infusion pumps, artificial organs, dialysis machines, cochlear and dental implants, etc. For continuous operation of implantable medical devices, the implanted units need to be powered up from an external source. Use of implantable batteries poses potential battery fluid leakage and biohazard. Unlike the batteries, wireless power transmission shows better promises for implanted micro devices. Previously reported differential cross-coupled power oscillator based scheme showed more than 90% link efficiency designed in a 0.5-μm standard CMOS process. However, the variation of mutual coupling between the link coils affects the resonance condition and lowers the power-added efficiency of the power oscillator. To make the power oscillator robust, injection-locking mechanism is incorporated with the differential power oscillator. The new injection-locked differential oscillator can lock the frequency with the variation of coupling coefficient by injecting weak differential current signals. Simulation results indicate that with the injection-locking, the oscillation frequency and the power-added efficiency are improved by 4.18% and 24.4%, respectively compared to the regular power oscillator structure for a coupling coefficient of 0.4.