High-PSR LDOs: Variations, Improvements, and Best Compromise

Low-Dropout Regulators (LDOs) are used to power noise sensitive applications. Power Supply Rejection (PSR) is a performance metric that measures the LDO’s ability to reject noise. Improving PSR has been the focus of many research groups. However, the state of the art does not recognize the best PSR enhancement schemes and collate them under comparable grounds. Further, the pass transistor’s diode connection (through the Gate-Drain capacitance) impacts the PSR, and this effect is not quantified in the state of the art. This research aims to bridge these gaps first by explicating the constitution of a high PSR LDO. Then, the impact of the pass transistor’s parasitics on PSR are quantified. Following this, the best state of the art PSR enhancement schemes are analyzed and simulated over a high-PSR core under similar conditions. This study reveals the strengths and limitations of each scheme, which unfolds each technique’s applications. Results convey that the LDO Filter yields the best PSR improvement at low frequencies, Series feedback at mid frequencies, and RC filter at high frequencies. Assessment concludes that Series Feedback provides the best compromise with respect to PSR enhancement.