A high slew-rate push-pull output amplifier for low-quiescent current low-dropout regulators with transient-response improvement

A high slew-rate amplifier with push-pull output driving capability is proposed to enable an ultra-low quiescent current (I_q~ 1 μA) low-dropout (LDO) regulator with improved transient responses. The proposed amplifier eliminates the tradeoff between small I_qand 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 V_DOwith large-size pass transistor and ultra-low I_qcan 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-μm standard CMOS process and occupies 0.09 mm². The LDO regulator can deliver 50-mA load current at 1-V input and ~ 100-mV V_DO. It only consumes 1.2 μAI_qand is able to recover within ~ 4 μs even under the worst case scenario.