Based on an 0.18 μm process, this paper proposes a fully integrated 1.8 V output 300 mA load low-dropout linear regulator (LDO) with a fast transient response. By inserting a transient-enhanced biased Class AB super source follower at the gate of the output power transistor, this LDO can quickly adjust the gate voltage of the power transistor without additional power consumption. By adding an active capacitor circuit composed of a fast comparator with offset voltage at the output point, this LDO can quickly charge/discharge the transient current and accelerate the transient response without reducing the circuit stability. Simulation results show that the proposed LDO has an output voltage of 1.8 V, when the input voltage is 2 V to 5 V while consuming 66.4 μA of quiescent current. The proposed capless LDO has a 1.94 µV/mA load regulation, a 0.55 mV/V linear regulation, and a −60 dB@1 kHz power supply rejection. When the load current steps from 3 mA to 300 mA in 300 ns, the LDO settles in 400 ns with an overshoot and undershoot of 67 mV and 86 mV, respectively.

A high-voltage, external capacitor-less low-dropout regulator (HVLDO) with a transient enhancement loop is presented in this work. The proposed HVLDO is designed with high withstand voltage LDMOS transistors and a transient enhancement loop is proposed to properly inject or sink current to/from the gate and output nodes of the power transistors to achieve fast transient response under wide load range conditions and high stability. This HVLDO is fabricated in 0.5 μm SOI BCD process with an active area of 0.29 mm2. It operates over an input voltage range of 5.2 to 20 V, provides an output voltage of 5 V and a maximum load of 100 mA, while supporting load capacitances from 0 pF to 1 μF. Measurements show that this design has a line regulation of 0.88 mV/V and a load regulation of 0.22 mV/mA. The proposed HVLDO features fast line transient response of 60/20 mV@9.8 V/µs, fast load transient response of 30/70 mV@100 mA/µs, and recovery time of 2 µs without external capacitors. Compared with the prior art, this work achieves the best transient FOM of 12.19 fs.