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Very High-Frequency Integrated VR for Small Portable Devices

Fig. 1. Front (left) and back (right) views of existing voltage regulator for iPhone 6 using multiple cores
Voltage regulators are widely used to power multi-core processors in small, portable elec-tronics such as smartphones and tablets. A four-phase buck converter and a two-phase buck converter, for instance, drive the two-core CPU and the GPU in an iPhone 6, as shown in Figure 1. The power inductor is placed on the front of the motherboard close to the processor, whereas the power management IC and capacitors are placed on the back.

Power consumption would be reduced dramatically if the supply voltage could be modu-lated rapidly based on the power demand of each core. However, the voltage regulator in Figure 1 is unable to offer this feature because of its low switching frequency and the high interconnect impedance between the voltage regulator and the processor.

Integrated voltage regulators with high granularity, small size, near-load integration, and very high switching frequencies have been successful in improving the efficiency of power delivery to multi-core processors, such as those implemented in Intel's Haswell and Broadwell processors. This work extends this concept to create the 3D integrated architecture illustrated in Figure 2 for small portable electronics. The converter is running at tens of MHz to track the core voltage. The multi-phase one-turn inductors are integrated into one magnetic core featuring a simple structure, ultra-low profile, small size, lateral non-uniform flux distribution, and air-gap free (to effectively confine very high-frequency stray flux). The inductor is designed with 0.5 mm in thickness and tens of mm2 in footprint to fit the stringent space requirements of smartphones, and placed directly under the processor die to facilitate a short power delivery path. The inductor will be stacked with the power-management IC to reduce the footprint traditionally occupied by the passive components. In the case of Figure 1, for example, a total area of about 100mm2 can be saved.

Fig. 2. 3D integrated very high frequency voltage regulator for small portable electronics.
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