A high slew-rate amplifier with push-pull output driving capability is proposed to enable an ultra-low quiescent current (Iq ~ 1muA) low-dropout (LDO) regulator with improved transient responses. The proposed amplifier eliminates the tradeoff between small Iq and large slew-rate that is imposed by the tail-current in conventional amplifier design. Push-pull output stage is introduced to enhance the output driving ability. Small dropout voltage (Vbo) with large-size pass transistor and ultra-low Iq can thus be used to minimize power loss of LDO regulator without transient-response degradation. The proposed amplifier helps to improve stability of LDO regulators without using any on-chip and off-chip compensation capacitors. This is beneficial to chip-level power management requiring high-area efficiency. An LDO regulator with the proposed amplifier has been implemented in a 0.18- mum standard CMOS process and occupies 0.09 mm 2 . The LDO regulator can deliver 50-mA load current at 1-V input and ~ 100-mV V DO  . It only consumes 1.2 muA Iq and is able to recover within ~ 4 mus even under the worst case scenario.
['Tsz Yin Man', 'Philip K. T. Mok', 'Mansun Chan']
A High Slew-Rate Push–Pull Output Amplifier for Low-Quiescent Current Low-Dropout Regulators With Transient-Response Improvement