A Recursive Switched-Capacitor DC-DC Converter Achieving <formula formulatype="inline"><tex Notation="TeX">$2^{N}-1$</tex></formula> Ratios With High Efficiency Over a Wide Output Voltage Range

Abstract

A Recursive Switched-Capacitor (RSC) topology is introduced that enables reconfiguration among 2 N -1 conversion ratios while achieving minimal capacitive charge-sharing loss for a given silicon area. All 2 N -1 ratios are realized by strategically interconnecting N 2:1 SC cells either in series, in parallel, or in a stacked configuration such that the number of input and ground connections are maximized in order to minimize cascaded losses. Importantly, all ratios are dynamically reconfigurable without disconnecting a single capacitor, all while ensuring optimal capacitance/conductance relative-sizing. The RSC topology is inherently regular, enabling recursive inter-cell connection and recursive binary-slicing that implement ratio-reconfiguration with minimum complexity and losses. A scalable all-digital binary search controller is employed to perform ratio-reconfiguration among the available 2 N -1 ratios without using any ratio-threshold generation circuitry. To validate the topology, a 4 bit RSC is fully integrated in 0.25 μm bulk CMOS using MIM capacitors, achieving greater than 70% efficiency over a 0.8-2.2 V output voltage range with 85.8% peak-efficiency from a 2.5V input supply. Compared to a co-fabricated three-ratio (1/3, 1/2, 2/3) Series-Parallel SC converter, the RSC achieves a 40.4% larger output operating range (from 0.04 to 2.2 V), and fills the efficiency-drops in-between the three-ratios by 8% with a 940 Ω load.