A Single-Inductor–Multiple-Output (SIMO) 0.8-V/1.8-V/12-V Step-Up/Down Converter With Low-Quiescent Current for Implantable Electroceutical SoCs

This letter presents a single-inductor–multiple-output (SIMO) step-up/down dc–dc converter for an implantable electroceutical system on chip (SoC), which generates the supply voltages of 0.8, 1.8, and 12 V from a battery (3–4.2 V). To extend the battery lifetime during a long standby period, the load-adaptive frequency-scaling (LAFS) without an active load sensor is proposed, effectively reducing the quiescent current under light loads at no expense of transient response performance. Also, this letter introduces a new design of a low-power adaptive on-time (AOT) generator to achieve a consistently low-output ripple regardless of battery voltage variation. The proposed chip fabricated in 0.18- $\mu \text{m}$ BCD consumes a quiescent current of only 217 nA and offers the output recovery time of ≤ 1 ms at a zero-to-full load transition. The measured efficiency was 86% with a load of 500 $\mu \text{A}$ and 55% even with an ultra-light load of 1 $\mu \text{A}$ .

I. Introduction

Implantable electroceutical system-on-chips (SoCs), which directly measure vital signals and perform electrical stimulation inside the body, have been widely studied for therapeutic purposes [1]. In this SoC, various internal supply voltages converted from the battery must be necessary to operate analog and digital blocks. Specifically, the supply voltage for stimulation must be higher than 10 V to avoid voltage saturation. A sub-1-V supply (0.8 V) is required for a digital biosignal processor with low-power consumption. A supply voltage of 1.8 V with a low ripple noise is required to operate sensitive analog front-end (AFE) sensing circuits. Because the battery lifetime is one of the major concerns in implantable SoCs, it is crucial to generate these internal supply voltages while consuming low-quiescent current [2]. To reduce the standby power, several efforts have been made to develop a low-power dc–dc converter designs [2]–[4]. However, multiple inductors, which potentially increase the footprint and the cost, are required for simultaneous step-up and step-down voltage conversions [4]. Moreover, it is challenging to realize high-voltage (≥ 10 V) step-up conversions with sub- standby power [2], [3].