Название: Fully-Integrated Low-Dropout RegulatorsАвтор: Xiangyu Mao, Yan Lu, Rui P. Martins
Издательство: Springer
Серия: Analog Circuits and Signal Processing
Год: 2025
Страниц: 240
Язык: английский
Формат: pdf (true)
Размер: 20.4 MB
This book discusses in detail the key specifications of fully integrated low-dropout regulators (LDOs). It covers the various LDO architectures, including the classic analog architectures and the state-of-the-art digital and switching control methods. The design insight and comparison are discussed according to the key performance index. Readers will be enabled to find a suitable architecture when designing a fully integrated LDO.
A voltage regulator is normally a buffered reference. The low-dropout voltage regulator (LDO) is a linear voltage regulator. Its widespread application in various electronic devices is due to its low power consumption, low output noise, high reliability, compact size, low cost, and ease of CMOS integration. Conventional LDOs rely on off-chip capacitors in μF level, typically using ceramic capacitors. Due to the resonant frequency limitations of ceramic capacitors, the bandwidth of traditional LDOs generally remains within MHz range. In contrast, fully integrated LDOs can function without external capacitors, employing integrated capacitors on-chip or within the package. There are various ways to implement integrated capacitors, including metal-insulator-metal (MIM) capacitors, metal-oxide-metal (MOM) capacitors, metal-oxide-semiconductor (MOS) capacitors, deep trench capacitors, and in-package capacitors. The equivalent parasitic capacitor of the load can also be utilized and considered as the output capacitor. Due to the smaller output capacitor, a fully integrated LDO must achieve a sufficiently fast response to meet transient requirements. For some specific applications, the bandwidth of fully integrated LDOs can reach several hundreds of MHz.
Meanwhile, fully integrated LDO is known for various names, such as on-chip LDO, capacitor-less LDO, and capless LDO. Another variation, a cap-free LDO, is purported to operate without necessitating an output capacitor. In practical applications, since the load always has equivalent parasitic capacitance, the scenario with zero output capacitance does not exist. Therefore, accurately speaking, the cap-free LDO should be defined as capable of meeting load transient demands without an additional output capacitor while upholding loop stability and performance within a specified output capacitor range.
LDOs maintain stable output voltage by adjusting the impedance of the power transistor or the output current. Based on different control methods of the power transistor, fully integrated LDOs can be categorized into three types: analog LDO, digital LDO, and switching LDO.
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