A capacitor-free LDO using a FD Si-MESFET pass transistor

The rapid growth in portable electronics has driven the market for ultra low dropout regulators (LDOs) that are more power efficient and lead to longer battery lifetime. Over the years various topologies based on P- or N-channel pass transistors have been introduced to meet these demands. For each of these implementations, the LDO has had a significant disadvantage whether it is stability issues and lower current drive associated with P-channel devices or the need for a charge pump to overcome the threshold voltage drop for enhancement mode N-channel devices. This paper presents a design methodology for an LDO that features a depletion-mode N-MESFET as the pass device that combines the advantages of both P and N devices allowing for ultra low dropout voltage and minimum layout area. The LDO also saves board space and simplifies design by achieving stability across all load and temperature conditions without the need of an output capacitor.