This article proposes an LDO with fast response to load transients that can handle any practical capacitive loads. These features are mainly due to a novel frequency compensation circuit tailored for its error amplifier, which is based on an improved version of the popular common gate amplifier. A simple yet effective approach to the small-signal analysis of LDO with multiple feedback loops is employed to analyse intuitively the LDO and derive key design constraints. Simulation and measurement results performed on a test chip implemented in standard 130nm CMOS process validated the proposed LDO. It requires only 0.7µA quiescent current but exhibits an excellent response to load transients: when the load current jumps from 0A to 100mA in 1µs the output voltage presents an undershoot of 76mV and an overshoot of 198mV, without decoupling capacitors. It compares well against seven LDOs designed with common gate error amplifiers for similar levels of supply voltage, output voltage and current and against seven fast LDOs employing different error amplifiers. A figureof-merit that considers the quiescent current, the maximum load current and capacitance, as well as the output voltage deviation, yielded a value for our LDO 39.8 times better than for the nearer competitor that employs common gate amplifier and 6 times better than the one employing a different error amplifier. When considering edge time and process scaling the performance of the proposed LDO is 4.8, respectively 4.5, times better than the second best in both comparisons.

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This paper proposes a low dropout voltage regulator (LDO) that exhibits both a fast response to load transients and the ability to handle practically any load capacitor. Starting from a typical LDO topology, an error amplifier (EA) that drives a PMOS pass transistor and a passive feedback network, we inserted a novel circuit, with the input AC-coupled to the LDO output and the output connected directly to the pass transistor gate. This circuit creates an inner feedback loop able to react quicker than the main feedback loop to variations in the output voltage, and appropriately inject or sink current to/from the gate node. Moreover, the inner feedback loop helps reduce the equivalent small-signal impedance at the LDO output, which in turn reduces the impact the pole associated with the output node has on the LDO stability. A compact circuit implementation of this topology is presented in this paper: it combines the proposed fast transient & frequency compensation circuit with a high slew-rate EA. The resulting LDO was integrated in a 130 nm standard CMOS technology. The measurement results are in good agreement with simulations and validate the concept and design. The LDO provides a steady 1 V output with the supply voltage varying from 1.2 V to 1.5 V and the load current going up to 100 mA. Its fast response to load transients helps maintain the output voltage overshoot and undershoot below 250 mV for CL = 0 and under 60 mV for CL =1 μF, when the load current varies between 1 μA and 100 mA in 1 μs. The LDO requires only 6.2 μA of quiescent current and occupies 0.018 mm 2 of die area.INDEX TERMS any load capacitor, fast-transient LDO, high slew-rate error amplifier, fast response to load transients

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