Design methodology for reliable and energy efficient self-tuned on-chip voltage regulators
Chekuri, Venkata Chaitanya Krishna
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The energy-efficiency needs in computing systems, ranging from high performance processors to low-power devices is steadily on the rise, resulting in increasing popularity of on-chip voltage regulators (VR). The high-frequency and high bandwidth on-chip voltage regulators such as Inductive voltage regulators (IVR) and Digital Low Dropout regulators (DLDO) significantly enhance the energy-efficiency of a SoC by reducing supply noise and enabling faster voltage transitions. However, IVRs and DLDOs need to cope with the higher variability that exists in the deep nanometer digital nodes since they are fabricated on the same die as the digital core affecting performance of both the VR and digital core. Moreover, in most modern SoCs where multiple power domains are preferred, each VR needs to be designed and optimized for a target load demand which significantly increases the design time and time to market for VR assisted SoCs. This thesis investigates a performance-based auto-tuning algorithm utilizing performance of digital core to tune VRs against variations and improve performance of both VR and the core. We further propose a fully synthesizable VR architecture and an auto-generation tool flow that can be used to design and optimize a VR for given target specifications and auto-generate a GDS layout. This would reduce the design time drastically. And finally, a flexible precision IVR architecture is also explored to further improve transient performance and tolerance to process variations. The proposed IVR and DLDO designs with an AES core and auto-tuning circuits are prototyped in two testchips in 130nm CMOS process and one test chip in 65nm CMOS process. The measurements demonstrate improved performance of IVR and AES core due to performance-based auto-tuning. Moreover, the synthesizable architectures of IVR and DLDO implemented using auto-generation tool flow showed competitive performance with state of art full custom designs with orders of magnitude reduction in design time. Additional improvement in transient performance of IVR is also observed due to the flexible precision feedback loop design.