A CMOS low-dropout regulator with current-mode feedback buffer amplifier

Current feedback amplifiers (CFAs) provide fast response and high slew rate with Class-AB operation. Fast response, low-dropout regulators (LDRs) are critical for supply regulation of deep-submicron analog baseband and RF system-on-chip designs. An LDR with an CFA-based second stage driving the regulation field-effect transistor is presented. The low dropout (LDO) achieves an output noise spectral density of 67.7 nV/[square root of Hz], and PSR of 38 dB, both at 100 kHz. In comparison to an equivalent power consumption voltage feedback buffer LDO, the proposed CFA-based LDO settles 60% faster, achieving 0.6-[micro]s settling time for a 25-mA load step. The LDO with CFA buffer is designed and fabricated on a 0.25-[micro]m CMOS process with five layers of metal, occupying 0.23-[mm.sup.2] silicon area. Index Terms--Current feedback amplifier (CFA), low-dropout regulators (LDRs), power supply rejection.