TI高精度实验室-稳定性 3.pdf.pdf

 Hello, and welcome to part three of the TI Precision Labs on op amp

stability.

The previous videos discussed the type of issues that op amp stability can

cause in production systems, how to identify issues in the lab, and a review

of Bode plots and stability theory.

This video will explain how to perform open-loop SPICE simulations to obtain

the rate of closure and phase margin of op amp circuits . Please be sure

之前的视频中讨论了不稳定性在实际系统中导致的问题，如何在实验室

中识别，及波特图与稳定性判据理论。此视频将会解释如何用开环 SPICE

仿真来得到放大电路的闭合速率与相位裕量。

在开始运放稳定性分析的课程学习之前，建议先完成运放带宽 1－3 系列

课程。

 The Aol, 1/ß, and Aolß curves required for rate of closure and phase margin

measurements can not be obtained from a circuit in a standard closed-loop

configuration.

To generate these curves, the feedback loop of the amplifier needs to be

opened up, or “broken”. Then, a small signal source is used to excite the

high-impedance side of where the loop was broken.

为了获得这几组曲线，电路的反馈回路需要断开，然后用一个小信号在

断开处进行激励。

然后在运放的反相端得到 Vfb，在输出端得到 Vo，通过这两项可以推导

得到我们所需要的曲线。

 However, simply breaking the feedback loop of a circuit will not produce

correct simulation results! Without a proper dc bias, the output will saturate

to one rail or the other, reducing the performance of the output stage.

As shown here, the op-amp output is near the positive rail, resulting in

erroneous Aol and Aolß curves.

直流偏置，输出会直接饱和到任意一个电源轨，导致不正确的输出。

如图所示，运放输出接近正向电源，得到错误的 Aol 与 Aolß 曲线。