A controllable resistor and its applications in pole-zero tracking frequency compensation methods for LDOs

This paper presents a controllable resistor, which is formed by a MOS-resistor working in the deep triangle region and an auxiliary circuit. The auxiliary circuit can generate the gate-source voltage which is proportional to the output current of an low dropout regulator for the MOS-resistor. Thus, the equivalent output resistance of the MOS-resistor is inversely proportional to the output current, which is a suitable feature for pole-zero tracking frequency compensation methods. By switching the type of the MOS-resistor and current direction through the auxiliary circuit, the controllable resistor can be suitable for different applications. Three pole-zero tracking frequency compensation methods based on a single Miller capacitor with hulling resistor, unit-gain compensation cell and pseudo-ESR （equivalent serial resistor of load capacitor） power stage have been realized by this controllable resistor. Their advantages and limitations are discussed and verified by simulation results.     

受控电阻及其基于LDO零极点追踪频率补偿方案的应用

本文利用工作在深度线形区的MOS管电阻和辅助电路设计了一个受控电阻。其中辅助电路为MOS电阻提供正比于LDO输出电流的栅源电压,从而使得MOS电阻的等效阻值反比于LDO的输出电流,这种反比关系非常适合零极点追踪的频率补偿方案。通过调整MOS电阻的类型和流过辅助电路中的电流方向,受控电阻可以应用于不同的电路结构。利用该受控电阻,本文提出了三种分别基于带去零电阻的米勒电容、单位增益补偿模块和伪ESR功率级电路结构的零极点追踪频率补偿方案。三个方案都通过了仿真验证,并对其优缺点进行比较和讨论。