连续时间共模反馈拆环的问题？

supertramp

大家帮我说说 连续时间共模反馈拆环时  差模负反馈环需要断开吗？ 为什么？ 先谢谢了

confiope

共模反馈也是负反馈

要清楚反馈环路，也很容易着手

supertramp

共模反馈是反馈没错  问题是共模拆环时 整个放大器是闭环还是开环啊

depend135

我觉得不需要，因为差模信号进不了共模环路，所以无所谓

hi_china59

If the load of your differential amplifier is a pair of active current mirror, you need to add a common mode feedback and make sure it bias in the sauration region.  Otherwise, the active current mirror may go into ohmic or triode region dure to the variaion of common-mode voltage, process or temperature.  Please read the attached file for detailed discussion.  

If the load of your differential amplifier is resistors or diode-connected MOSs, you don't need common mode feedback circuit at all.  Because the common-mode voltage is well-defined.

hi_china59

If the load of your differential amplifier is a pair of active current mirror, you need to add a common mode feedback and make sure it is biased in the sauration region.  Otherwise, the active current mirror may go into ohmic or triode region dure to the variaion of common-mode voltage, process or temperature.  Please read the attached file for detailed discussion.  

If the load of your differential amplifier is resistors or diode-connected MOSs, you don't need this common mode feedback circuit at all.  Because the common-mode voltage is well-defined.

supertramp

谢谢楼上两位
差模通路 和共模通路 有相同的管子啊  差模接成闭环感觉更真实
为什么差分信号进不了共模环路。

其实我也不希望差模闭环  仿真出来差模开闭环对共模环的影响是很大的。
再仿仿 再想想

depend135

连续的共模反馈环路中有一部电路是用来提取两个输入信号中的共模成分的，差模成分经过这过程后就没了

lqlcug

可以不拆环，的确差模信号进不了共模环路。做共模反馈环路AC分析的时候，要保持直流通路，交流断开！加个低通滤波器！

depend135

楼上说的对，或者在共模环路中插入一个iprobe,然后作stb分析，这更加方便