Low-power Transient-enhanced Capacitor-less LDO

Low dropout regulator (LDO) is used to provide a stable voltage independent of load impedance,input voltage and temperature.Because of its characteristics such as light, inexpensive and well integrated, LDO is widely applied in our daily lives such as cell phones, computers and other mobile power devices.This article first briefly introduced the LDO’s operation principle and basic performance parameters,then analyzed the transient characteristics of traditional LDO and capacitor-less LDO circuit. Based on this, a fast transient response capacitor-less LDO circuit with fast transient response was designed.In this design,a push-pull output stage of the error amplifier with high slew rate is used.In order to enhance the transient responses latch is joined to build fast discharge current loop.Controlled by the output signal of the LDO circuit.Transient enhancement circuit could modulate bias current of the transconductance amplifier to enhancing transient response of LDO.Different voltage reference structure is analyzed by simulation result.And we can obtained that for high slew rate current-transconductance amplifier, the stronger of the drive current, the greater of the circuit transient performance. Pass transistor operating in the linear region while large current can flow through.We use small size PMOS transistor to reduce chip area.To optimizing the circuit structure, we build small-signal model of the LDO.To analyze and to calculate the loop gain. And deduce the distribution of the circuit pole-zero location.Make sure that the circuit will working in stable state.By considering the stability,transient response performance and low power consumption,this design implemented a low power transient enhanced capacitor-less low-dropout (LDO) regulator.This circuit design is completed based on SMIC 0.18um CMOS process. We use Cadence Spectre to simulation the circuit. We use virtuoso to complete circuit layout design and drawing. Simulation results show that when the input voltage is 1V, the output voltage is 900mV,the load current changed 49.9mA in just 0.1μs, transient response time is less than 0.62μs.The load transient response overshoot voltage and undershoot voltage are less than 300mV.When the load current changed 49.9mA in 1μs.The transient response time is less than 1.5μs.The load transient response overshoot voltage and undershoot voltage are less than 69.4mV.