Ultra low power capless LDO with dynamic biasing of derivative feedback

In this paper, a low power, output-capacitor-free, low-dropout regulator (LDO) is proposed with a new dynamic biased, multiloop feedback strategy. Initially, a theoretical macromodel is presented based on the analogy between the capless LDO and the mechanical non-linear harmonic oscillator, enabling to shed new light on the non-linear amplification, dynamic and adaptive biasing techniques used in the multiloop feedback LDO control in the large signal context. To implement some of the unexplored abilities of this model the new capless LDO topology is proposed. The output class AB stage of the error amplifier and the non-linear derivative current amplifier of the LDO feedback loop ensure dynamical extended close-loop bandwidth gain and dynamical damping enhancement for fast load and line LDO transients. Using the new dynamic biasing of the derivative loop, an improvement is obtained in the derivative sensing of the fast output voltage variations, enabling a significant enhancement in the transient response of the capless LDO. The proposed LDO, designed for a maximum current of 50 mA in UMC RF 1P8M 0.13 μm, requires a quiescent current of only 4.1 μA and presents excellent transient response when compared to the state-of-the-art.