Inductively Coupled 180-nm CMOS Charger With Adjustable Energy-Investment Capability

Although wireless microsensors can add performance-enhancing and energy-saving intelligence to factories, hospitals, and others, their tiny onboard sources are exhausted quickly. Luckily, coupling power inductively can both energize system components and recharge a battery. Miniaturized receiver coils, however, capture a small fraction of the magnetic energy available; thus, coupling factors kC and, as a result, power-conversion efficiencies are low. In other words, damping the magnetic source so it outputs maximum power is difficult. Investing energy into the coil increases its ability to draw power, but only when optimized. Since state-of-the-art systems can only recycle harvested energy, they are optimal only at one kC value. The inductively coupled 180-nm CMOS charger prototyped, measured, and presented here invests programmable amounts of battery energy into the pickup coil to generate 8-390 μW when kC is 0.009-0.076 and raise output power by 132% and 24% at kC's of 0.020 and 0.076, respectively.