LDO 放大器的增益

我们知道，在LDO的内部存在一个差分放大器，用于反馈控制MOSFET的导通阻抗。

另外，在看到一些资料分析LDO稳定性的时候，也是考虑在Gain=0dB时候的情况，对于此，有以下疑惑：

1. 分析0dB增益的情况，和运放的稳定有关系么？还是考虑整个大环路的稳定性？

2. 在分析LDO稳定的过程中，带宽（频率）指的是哪个信号的带宽？

Johnsin Tao：

Hi应该是与稳定性有关。

Shiwei Liu：

回复 Johnsin Tao:

是和稳定性相关，那么具体的怎么分析的呢？

Marvellous Liu：

应该是反馈回来的信号，正常与负载有关。

SIYUAN ZHONG：

   Normally,when we talk about the loop gain and loop phase to check stablility inside the  LDO. Then actually we need to check the stability of that feedback loop. Then if use Cadence to simulate, use the iprobe to send an AC signal into the feedback loop, then test the received signal at the other end node. Actually sometimes, the bandwidth of LDO will be larger than its operation frequency, so that mostly we need to concern about the stability of  the operation frequency point of LDO. Then the dominate pole of stablility analysis depends on the equivalent resistance of LDO itself or the load condition (load resistance).Sometimes, if the amplifier we designed inside LDO use a large amount of transistors, maybe its parasitic capacitance will be larger than the output capacitance, then the dominate pole will change. Under this condition, we need to think about the compensation of the loop phase, to make it stable.