一种低静态电流高瞬态响应无片外电容LDO设计

Design of Capacitor-less LDO with Low Quiescent Current and High Transient Response

基于SMIC 0.18μm BCD工艺设计了一种低静态电流、高瞬态响应的无片外电容低压差线性稳压器(Low Dropout Regulator, LDO)。误差放大器采用一种跨导提升技术,在低静态电流的情况下,实现更高的环路增益及单位增益带宽。由于采用高增益误差放大器,可以通过适当减少功率管尺寸来增强瞬态响应。采用有源反馈,在不引入额外静态电流情况下,增大环路的次极点。同时当LDO输出电压变化时,能够增大功率管栅极的动态电流,实现高瞬态响应。此外在有源反馈的基础上,采用反馈电阻并联小电容的方式,以提高环路稳定性。利用Cadence Spectre软件对LDO进行仿真验证。结果显示,LDO的静态电流仅为10μA;在负载电流为1 mA的情况下,相位裕度最高可达70.9°;LDO负载电流在500 ns内从1 mA切换到100 mA时,下冲电压为134.7 mV,下冲电压恢复时间为1μs;负载电流在500 ns内从100 mA切换到1 mA时,过冲电压为155.5 mV,过冲电压恢复时间为430 ns。

A capacitor-less Low dropout regulator(LDO)with a low quiescent current and high transient response was designed through a SMIC 0.18μm BCD process.The error amplifier adopts trans-conductance enhancement to achieve higher loop gain and unit gain bandwidth under low static current conditions.Owing to the use of high gain error amplifiers,the transient response can be enhanced by appropriately reducing the power transistor size.The secondary pole of the loop was increased using active feedback,without introducing additional static current.Simultaneously,when the output voltage of the LDO changed,the dynamic current of the power transistor gate could be increased,achieving a high transient response.In addition,through active feedback,a feedback resistor connected in parallel with a small capacitor was adopted to improve the loop stability.The software Cadence Spectre was used to simulate and verify the LDO circuit.The results show that the static current of LDO is 10μA.When the load current is 1 mA,the maximum phase margin reaches 70.9°.When the LDO load current is switched from 1 to 100 mA with a switching time of 500 ns,the undershoot voltage is 134.7 mV,and the recovery time of the undershoot voltage is 1μs.When the LDO load current is switched from 100 to 1 mA with a switching time of 500 ns,the overshoot voltage is 155.5 mV,and the recovery time of the overshoot voltage is 430 ns.