A 400 mA Fast Transient LDO with Enhanced Level-Shifted FVF and Dynamic Compensation

To meet the fast-response and wide load-current requirements of X-ray detector readout chips, a Low-Dropout Regulator (LDO) based on an improved Level-Shifted Flipped Voltage Follower (LS FVF) is proposed in a 130 nm CMOS process. A fast Flipped Voltage Follower (FVF)-based feedback loop is introduced to improve transient response, while a level shifter is introduced to relax the DC operating-point coupling between the pass-transistor gate and the control transistor drain at light loads. To further enhance response speed, dynamic current-source biasing, which senses output-voltage variations through capacitive coupling, is proposed, and it is capable of adaptively increasing the LS FVF driving capability during large load transients. A positive-feedback auxiliary circuit is proposed to further accelerate the charging and discharging of the pass-transistor gate. To maintain stability over the 0–400 mA load range, dynamic pole-zero compensation is combined with Miller compensation to track load-dependent poles and preserve sufficient phase margin across operating conditions. Post-layout simulations with a 200 pF load capacitor and a 0–400 mA load-current step show an overshoot of 100.4 mV and an undershoot of 50.5 mV, with recovery times of 0.2 μs and 0.12 μs, respectively. The proposed LDO achieves a capacitance-normalized transient figure of merit of 0.113 ps, demonstrating a favorable trade-off among performance parameters.