本次模拟面试中的几个精华问题

wch

大家挺强悍的么  不错

hellolab

好，谢谢！

hte2000

大家各抒己见，学习了。

ant_analog

建立时间，保持时间，保持精度，系统频率，采样频率。

九黎

谢谢大家  分享了

zhouran011

回复 15# refugee


    前辈，求教第六条 为何电流放大器不受增益带宽积的限制啊。

dscd1900

CMFB是为了防止上下电流源互相竞争在失配的情况下高阻输出节点偏离而引入的，类似的问题出现在全差分结构与classAB类出现，在设计的过程中需要消除这种电流竞争的现象。

semico_ljj

nicer

QinrenYao

In OTA biased with current mirrors, one leg of the single ended amplifier has a diode-connected load(i.e. low impedance). This leg’s current is being mirrored to the other leg using pmos current mirror load. The other leg has a high output resistance, but the output voltage is under control due to synchronous current mirroring. The problems arise when there is any kind of mismatch like mismatch in loads, Vin_cm, differential pair mos mismatch etc. There is a slight shift in the Vo_cm voltage.
转关于cmfb：
But consider the case of Fully-Diff Amplifier, in which both the legs of the amp are high impedance. Any mismatch in the load or Vin_cm, leads to a huge impact on the Vo_cm voltage. Vo_cm1 - Vo_cm2 = delta(I) * Rout. This delta Vo_cm difference can above pmos to linear region, thereby losing all the DC gain. Therefore it is a good practice to apply Common Mode Feedback circuit to make sure the Vo_cm of both the outputs don’t shift irrespective of any mismatches.

kaedegong

阻抗匹配是什么意思：你可以假设源阻抗x，负载阻抗y，然后你去计算最大的能量传输VI, 就会发现最大的能量传输发生在real part相同，虚部共轭是VI最大的时候。这个就是阻抗匹配的大概的原因。