A 0.9V 0.35¿m Adaptively Biased CMOS LDO Regulator with Fast Transient Response

Portable applications often need multiple voltages controlled by a power management IC to power up many functional blocks. A switching pre-regulator is usually followed by a low dropout (LDO) regulator to provide a regulated power source for noise-sensitive blocks. The LDO regulator has to be stable for all load conditions and frequency compensation is usually needed to stabilize the regulation loop. The output voltage droop due to rapid and large load changes could be minimized with a fast regulation loop, such that functional blocks powered by the same LDO regulator would have low crosstalk noise. A low-voltage fast transient-response LDO regulator using an inexpensive 0.35 mum CMOS process is presented in this paper. It features a current-efficient adaptively biased regulation scheme using a low-voltage high-speed super current mirror and does not require a compensation capacitor. It is stabilized by a low-cost low-ESR ceramic filter capacitor of 1 muF The adaptively biased error amplifier EA drives a small transconductance cell to modulate the output current through a transient-enhanced super current-mirror (SCM).