Design Of The Core Blocks In Low-Dropout Linear Regulator

In recent years, low-dropout (LDO) linear regulator has received more and more attentions in numerous power management chips because of its small area, low noise, low supply current, few off-chip components, etc. It has been widely used in kinds of cellular electronic products, especially, wireless communication equipments, video or audio products, hand-held computers, medical apparatus, test instruments and so on. However, the market of power management chips is mainly occupied by foreign enterprises nowadays, while the development in our country is in the initial phase, so it is very meaningful to develop the LDO linear regulator with our own intellectual property.Under the support of National Science Foundation of China and Sichuan Province Academic Leaders Foundation, we have studied fully on the LDO linear regulator. Two important blocks including the error amplifier and PMOS pass element are analyzed and designed.Firstly, we have analyzed the system configuration and working principle of the LDO linear regulator. Its main characteristics and choice principle are summarized.Secondly, an error amplifier based on BiCMOS technology is designed. The low voltage cascode current mirror load ensures high gain and power supply rejection ratio under low power supply. Its driver ability is improved by the push-pull buffer stage. Simulation results employing 0.5um HSPICE model show that its open-gain and PSRR are both about 80dB under 3.6V power supply. Its bandwidth is as high as 1.2MHz and the phase margin is 60°. However, its set-up time is no more than 1μs.In addition, we have summarized and compared the primary characteristics of some existing pass elements. A PMOS pass element with low leakage current is devised under the help of EDA tools.In the end, we have integrated the error amplifier and PMOS pass element together with the other blocks of the LDO linear regulator. Then, we have simulated the main characteristics of the LDO linear regulator. The simulation results show that the LDO linear regulator not only has low dropout voltage but also ultra-low line regulation and load regulation.