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Abstract
Advancements in low power circuits and batteries have enabled the design of miniature sensors with tiny batteries. In such systems, implementing dynamic voltage scaling (DVS) is crucial for maximizing system lifetime. In this paper, a new switched capacitor (SC) converter that is capable of handling a wide range of load currents and output voltages is presented for on-chip DVS implementation. The proposed converter consists of multi-ratio multi-leaf SC stages and reconfigurable interconnect, enabling fine voltage resolution. The stage interconnect scheme enables cascaded or parallel connection of stages. The multi-leaf structure allows load-dependent switch size selection, offering a better trade-off between losses over a wide load range. A limited-voltage-swing switch-driving scheme allows efficient down-conversion from high battery voltage input. A prototype was fabricated in a 180 nm process, providing an output voltage with effective resolution of 16 mV over a load current range of 300 nA to 300 μA (1000×) from a 4 V battery. Efficiency greater than 62% and a peak efficiency of 77% are achieved under a light load (500 nA) over a voltage range of 400 mV to 1.6 V. Efficiency greater than 64% and a peak efficiency of 72% are achieved under a heavy load (200 μA) over a voltage range of 700 mV to 1.6 V.
Highlights
With the recent advancements in low power circuit design, packaging and battery technologies, the volumes of computing systems have been significantly reduced
A prototype test chip was fabricated in a 180 nm complimentary metal-oxide-semiconductor (CMOS) process
An effective die area of 1.525 mm2 was utilized by the converter, which is dominantly occupied by 2.09 nF of on-chip MIM capacitors
Summary
With the recent advancements in low power circuit design, packaging and battery technologies, the volumes of computing systems have been significantly reduced. In active mode, the supply voltage should be increased for better performance and stable operation [4,5] This implies that the power management unit in miniature sensor systems should be capable of handling a wide voltage range. A few multi-stage SC converters, such as successive approximation (SAR) [20], recursive-tertiary [21], and recursive-binary [22] DC–DC converters, have been reported that provide high efficiency over a wide output voltage range These converters are only optimized for active operation state, and the minimum load current is on the order of a few microamperes. The proposed converter consists of multi-ratio multi-leaf SC stages and reconfigurable interconnect, enabling fine voltage resolution with switch width modulation, which is required for DVS over a broad load current range.
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