Low-power and fast-transient capacitor-less LDO with double loops

This brief proposed a capacitor-less low-dropout regulator (CL-LDO) with two loops to reduce quiescent power consumption and keep fast transient performance at the same time. Using class-AB operational amplifier to replace Class A operational amplifier can greatly improve the load transient performance of (CL-LDO). However, the complex bias circuit of Class-AB operational amplifier significantly increases the static power consumption of the system. To solve this problem, a small-loop composed of five-transistor operational transconductance amplifier (OTA) is added to replace the large-loop composed of class-AB operational amplifier when the system work under low load current. The large-loop and small-loop are used to achieve the design requirements of high transient response and low static power consumption respectively, which greatly reduces the static power consumption of the regulator from 12uA to 3.4uA. Additional detection circuit needs to be introduced to the small-loop, this means that the system's static power consumption will rise again, This paper put forward that using the output voltage of operational amplifier in large-loop and small-loop to represent the output current, and make system feedback load current signal to control circuit without introducing sampling resistance, making the system follow the load current changes automatically complete the opening and closing of the large-loop.