Research And Design Of Load Sense Circuit Applied To LDO

The change of times over the decades,numerous portable electronic devices(for example: mobile phones,electronic watches,laptops,etc.)have been born one after another.Their functions are diverse and colorful,and they have become an essential part of people's life.For many electronic devices,an efficient and stable power management chip plays a vital role.LDO(Low Dropout Regulator),also known as a low-voltage differential linear Regulator,has the advantages of simple structure,low cost,low power consumption and fast transient response.It is widely used in all kinds of power management chips and takes a large market share.Based on the theoretical knowledge of LDO,this thesis describes to the advantages and disadvantages of LDO with or without off-chip capacitance,and analyzes its various performance indicators and factors affecting each other,and designs a high-precision and high-stability LDO circuit without off-chip capacitance.In this thesis,the main research pointsare as follows:(1)Add a modifying circuit to the bandgap reference circuit to improve the accuracy of band-gap reference voltage and LDO output voltage.The PSRR is improved by adding the common source common gate input tube to the common gate input tube.(2)The frequency compensation of LDO circuit is carried out by using Miller compensation technology to split the primary and secondary poles.An improved source follower structure is designed to reduce the equivalent output impedance of the circuit,further increase the degree of pole splitting,and improve the stability of the circuit.The improved source follower structure contains a negative feedback buffer stage,which can speed up gate voltage recovery when the power tube gate voltage changes,improve transient characteristics of the load and enhance circuit stability.(3)Design the structure of load sense circuit to adjust LDO output voltage and reduce the influence of resistance deviation.A series resistance sense circuit is used to ensure the accuracy of detection,in which the sense circuit is composed of rail-to-rail transconductance amplifier circuit and two stages of operational amplifier,Mixed N and P type differential input pairs in track-to-rail transconductance op-amp circuits increase the input common-mode voltage range.To summarize the above research content,this thesis adopted GLOBALFOUNDRIES0.13 um RF SOI-CMOS process with an overall area of 350 um*280 um.The tested result is as follows: LDO output voltage was 2.9V;minimum dropout voltage was 89 mV;static current was 62 uA;temperature drift was 23.15ppm/?;sag voltage was 327 mV;recovery time was 1.48us;overshoot voltage was 358 mV;recovery time was 3.6us;PSRR was-52.5dB;The loop gain at low frequencies was 76 dB and the phase margin was 58.7deg.Bandgap output voltage variation was ±4mV and LDO voltage change was ±9mV,improve the accuracy of LDO output voltage;Resistance deviation change was ±10% and LDO output voltage change was 20 mV ±0.3mV.The error less than 1.5%.This sense circuit reduce the influence of resistance deviation,and achieve high precision and high stability LDO circuit without off-chip capacitance.