A Capacitor-Less LDO With High-Frequency PSR Suitable for a Wide Range of On-Chip Capacitive Loads

This paper presents an on-chip, low drop-out (LDO) voltage regulator with improved power-supply rejection (PSR) able to drive large capacitive loads. The LDO compensation is achieved via a custom, wide bandwidth capacitance multiplier (c-multiplier) that emulates a nanofarad-range capacitance at the LDO output node. The LDO frequency response resembles that of externally compensated LDOs, leading to a wide PSR frequency range without using an off-chip capacitor. To drive large capacitive loads without stability concerns, the supply-line capacitance of the load circuit is incorporated to the design of the LDO compensation scheme. The power-stability-performance tradeoffs involved in the design are discussed in detail. The LDO and the c-multiplier are implemented in 0.18-mu m CMOS technology and target applications with load currents in the 10-mA range. Experimental results show that the LDO achieves a PSR better than -39 dB up to 20 MHz at 1.2 V output voltage, while maintaining a 97.4% current efficiency.