请教关于差分放大器仿真的问题

仿开环就开环呗，有反馈不就成闭环了?

一楼问题是对的；
二楼回答是错的；
三楼在围观；
请四楼给出答案。

看了三楼的话，没人敢在四楼发言了O(∩_∩)O~
用开环和闭环的方法都可以仿真；开环仿真要手动设置消掉电路的system offset，用闭环的方式，采用夸张的电容和电阻（或电感）值，近似实现开环仿真。

怎么仿啊，观望。

接成闭环是为了稳定运放的直流工作点，具体办法看看allen的书吧，里面说的很清楚。

If it is a differential input and single-ended output amplifier, since the output common-mode level is not defined, a feedback is required to stabilized the output cm voltage. It may slightly effect the open loop gain, but shouldn't be large if the feedback is setup properly.
If it's a fully-differential amplifier, since there is a cmfb building block to define the output cm voltage, no feedback is required.

Thank you very much！

这个。

小编为什么多谢7楼而不是6楼?

好好学习 哈哈

If you don't want this feedback, the output CM level maybe set close to the middle of the power rails by introducing a very small DC offset at the differential input.
However this DC offset changes when you sweep the process corners. So the most convenient way is to add a very large feedback resistor (for cmos input differential pair only); or maybe a very large inductor.

正解逐步浮出水面

开环仿真就可以了，在输出加一个理想的cmfb

对头，论坛里牛人多