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Due to the rising demand for low-power portable battery-operated electronic devices, there is an increasing need for low-voltage low-power low-drop-out (LDO) regulators. This provides motivation for research on high-gain wide-bandwidth amplifiers driving large capacitive loads. These amplifiers serve as error amplifiers in low-voltage LDO regulators. Two low-power efficient three-stage amplifier topologies suitable for large capacitive load applications are introduced here: single Miller capacitor compensation (SMC) and single Miller capacitor feedforward compensation (SMFFC). Using a single Miller compensation capacitor in three-stage amplifiers can significantly reduce the total capacitor value, and therefore, the overall area of the amplifiers without influencing their stability. Pole-splitting and feedforward techniques are effectively combined to achieve better small-signal and large-signal performances. The 0.5-μm CMOS amplifiers, SMC, and SMFFC driving a 25-kΩ//120-pF load achieve 4.6-MHz and 9-MHz gain-bandwidth product, respectively, each dissipates less than 0.42 mW of power with a ±1-V power supply, and each occupies less than 0.02 mm2 of silicon area.
Date of Publication: March 2005