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An Analog-Proportional Digital-Integral Multiloop Digital LDO WithPSR Improvement and LCO ReductionMo Huang, Yan Lu, and Rui P. MartinsIn CICC 2019 and JSSC 2020From Integrated Power research lineMotivationIn granular power management for SoCs, alow central supply is generated by aswitching converter first, and then distributedto fine-grained voltage domains usinglow-dropout regulators (LDOs). For a highpower efficiency, a small dropout voltage ofLDO is needed. Moreover, power supplyrejection (PSR) to the ripple up to severalMHz is required. Good PSR can beachieved by analog LDO only under a highsupply voltage. By contrast, digital LDO issuitable for low supply voltage, but suffersfrom poor PSR, slow transient responseand steady-state limit cycle oscillation(LCO). This work incorporates bothschemes and proposes a hybrid LDO withanalog-P and digital-I controls for a fast response,improved PSR and reduced LCOat a low supply voltage.ArchitectureFive-loop hybrid LDO is implemented.Loop-1 is the main analog-P path for fastresponse. Loop-2 is useful for light loadregulation and PSR. Loop-3 is the replicaloop of Loop-1 and -2 to bias Loop-1 andoffer 6dB PSR improvement. Loop-4 and -5are digital-I paths for coarse and fine tuning,respectively.ImplementationVerificationThe proposed hybrid LDO was fabricatedin a 65nm CMOS process.(a)(b)Measured transient response with the load currentchanging from 0 to 10mA within an edge time of5ns. A maximum 65mV output variation is observed,and no LCO at the steady state.A −22dB measured power supply rejection (PSR)under a 65mV, 1MHz input voltage ripple.
In Sensors and Actuators B: Chemical 2019Hydrodynamic-Flow-Enhanced Rapid Mixer for Isothermal DNAHybridization Kinetics Analysis on Digital Microfluidics PlatformMingzhong Li, Cheng Dong, Man-Kay Law, Yanwei Jia, Pui-In Mak and Rui P. MartinsFrom Multidisciplinary Research Area (Microfluidics)MotivationArchitectureDNA hybridization kinetics has been playing a critical role in moleculardiagnostics for binding discrimination, but its study on digitalmicrofluidic (DMF) systems is ultimately restrained by the laminarflow condition. The kinetic mixing technique is widely employed toensure a fast reaction rate, but poses intrinsic risk in cross contaminationand exhibits instable fluorescence intensity during the droplettransportation. While the electrothermal technique can providestationary droplet mixing through the established thermal gradientwithin the hybridization solution, the significant increase in thedroplet temperature will inevitably undermine the hybridizationequilibrium and jeopardize the binding discrimination. To enhancethe hybridization efficiency while ensuring a stable droplet temperature(within ±0.1°C), this paper presents a DMF platform that canperform isothermal hydrodynamic-flow-enhanced droplet mixing.Specifically, with a single electrode, droplet-boundary oscillationunder a slow AC actuation is studied for improving the reactionrate. The dependencies between the mixing efficiency and theactuation voltage, actuation frequency and the spacer thicknessare also systematically studied. Reliable mixing efficiency improvementis further validated over a wide range of solute concentrations.The results from real-time on-chip DNA hybridization kineticswith stationary droplets using the complete sandwiched DMF systemshows that the proposed rapid mixer can achieve the samehybridization equilibrium with >13 times faster reaction rate whencompared to the reference one through pure diffusion, while preventingbiased hybridization kinetics as demonstrated in the electrothermaltechnique.ImplementationVerification
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