Low-Ripple and Dual-Phase Charge Pump Circuit Regulated by Switched-Capacitor-Based Bandgap Reference

This paper proposes a low-ripple and dual-phase charge pump circuit regulated by switched-capacitor-based bandgap reference. Due to design of a buffer stage, a system can have better bandwidth and phase margin, and thus, the transient response and driving capability can be improved. Besides, the dual-phase control can reduce the output voltage ripple by means of only one closed-loop regulation in order to improve the power conversion efficiency. Besides, the proposed automatic body switching (ABS) circuit can efficiently drive the bulk of the power p-type MOSFETs to avoid leakage and potential latch-up. Usually, the regulated charge pump circuit needs a bandgap reference circuit to provide a temperature-independent reference voltage. The switched-capacitor-based bandgap reference circuit is utilized to regulate the output voltage. This chip was fabricated by Taiwan Semiconductor Manufacturing Company (TSMC) 0.35 mum 3.3 V/5 V 2P4M CMOS technology. The input voltage range varies from 2.9 to 5.5 V, and the output voltage is regulated at 5 V. Experimental results demonstrate that the charge pump can provide 48 mA maximum load current without any oscillation problems.

I. Introduction

At the present, portable electronic devices such as mobile phones or digital cameras are the emerging market of electronic devices, even called the daily essentials. The demand for the portable electronic devices makes the power supply circuit more and more important. in general, the operating time or standby time of the portable devices all depends on the battery capacity. Efficient power distribution is the main concern in the portable device [1]–[4]. On the other hand, the size and weight of these power devices are also important for the designers. The miniaturization of the power modules and the reduction of the external components are essential in portable devices. Besides, the size of the power supply circuit is the major design consideration, no matter whether the circuit is fabricated as a single chip or integrated into a system-on-chip (SoC) chip. for the portable electronic devices, the reduction of the area on silicon and printed circuit broad (PCB) means lower fabrication cost and tinier size. in other words, a compact power supply system is necessary for the power management of the SoC systems. Therefore, the trend is to focus on the CMOS implementation of power converters and insert the power modules into any portable device. Table I shows the different implementation techniques that can be used to supply different applications. for today's designers, how to find an optimum solution has become an urgent issue. Table I Comparison of the Different Power Supply Devices

	LDO	Charge Pump	Switching Regulator
Efficiency	Bad	Good	Best Up to 95% and averageabout 90%
Cost	Best	Moderate Capacitor count,pin count, siliconarea drive costs	Most expensive Inductor and otherexternal componentsdrive costs
Difficulty in Design	Easv	Harder	Most difficult
PCB Area	Very small	Small	LargeDue to the height andarea of inductor
Output Ripple	Very low	Moderate	Moderate
EMI	Very low	Low	Moderate
Load Capability	ModerateUp to 150mA	ModerateUp to 250mA	BestAble to above 500mA
Transfonnation Type	Step down	Step up Step down Inverter	Step up Step down Inverter