Multiple Adaptive Current Feedback Technique for Small-Gain Stages in Adaptively Biased Low-Dropout Regulator

Abstract

Adaptive bias scheme, which can be used to provide a current proportional to the current flowing through the power transistor under high current load, avoiding the need for providing additional large fixed bias current to the circuit, has been adopted in many low-dropout regulators (LDO). When an adaptive bias scheme is applied to an LDO with a current mirror buffer, although a low chip area consumption and a better transient response can be achieved, the loop gain of LDO at high-load current and loop bandwidth at low load are still low. In previous works, multiple small-gain stages can effectively improve the gain and bandwidth but may lead to stability problems or even need to consume large currents to ensure stability, thus affecting current efficiency. This article proposes the multiple adaptive current feedbacks technique for small-gain stages in adaptively biased low dropout regulator (AB-LDO) with a current mirror buffer, improving the loop gain and bandwidth and eliminating the need for frequency compensation to meet stability requirements. Moreover, in the case that multiple adaptive bias loops can be introduced after the proposed technique is applied to this design, an intuitive and simple method is adopted to analyze the whole circuit. The designed AB-LDO was fabricated in Semiconductor Manufacturing International Corp (SMIC) 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m process. The measured results show that the designed LDO realizes 30.75-mV transient performances with a step of 10 ns.