rail to rail 输出级用到的悬浮电流镜的作用是什么？怎么工作的？

bsaqycx

thank you for your reply
you mean at dc situation the output NMOS/PMOS are biased at the slightly open status and in ac situation one of the output transistors should be cutoff, right?
If so, my question is whether the phase of the gate voltage of output NMOS/PMOS are the same.  And if the output NMOS/PMOS are biased at totally open status which means the gate of NMOS/PMOS should drop/raise about 100mV to turn off, this structure would make the gate of NMOS/PMOS drops simultaneously when the output is to rise, right?

fumes

我们来分析下面一半的管子哈，即M19 M23 M24 M26
假设Ib4=2Ib8      I26=N*Ib8   
如果（W/L）26=N*（W/ ...
jlinky 发表于 2011-1-21 10:15

                               
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    你说的为节省功耗，Ib3那一路用悬浮电流源产生电流是怎么产生？如果m11和m12管（原图中的m11和m12）做成低压cascode，那还需要共模反馈电路吧？你指的是全差分输出吗？要是单端输出，还需要在Ib3那一路加悬浮电流镜吗？有一个图确实是这样做的，你说的是这个电路吗？

jlinky

回复 31# bsaqycx

    我解释的可能不太清楚哈，可以这样理解，当小信号的上半部分过来时，只有驱动管M26传输信号，由于设置的是微导通，
那么M19源级由于上半部分信号原因，导致其截至(放大器闭环使用时，这个信号足以让其截止，并且肯定是截止的，不然工作状态要影响)，此时所有的电流都流过M20这个管子，M19可以看做一个等效的大电阻，此时的M20的漏极到源级是不是等效一个cascode结构，那么M20漏端由于小信号上半部分而引起的电压变化在其源端的影响非常小。我用手粗略的划了下哈，浮动电压源两端的电压在加有ac信号时，如图：

   
    所以说是屏蔽掉交流信号，不过要注意的是，在M19截至的时候流过M20的电流时原来的两倍，此时M20栅极偏置固定，
所以其源级的电压是有一些变化的，也就是所提高了些。

bsaqycx

回复 33# jlinky


    Thank you for your reply
    Now I totally understand what you mean.
    One more thing: because this output stage could be called as class AB, the phase of gate voltage of M25 and M26 should be the same. The strange thing in my simulation is that: when the gate voltage of M26 rise, the gate voltage of M25 drops; while the gate of M26 drops, the gate of M25 still drops.

bsaqycx

回复 34# jlinky

it seems that W1 and W2 are not voltage bias, and they should be connected to the drain of input transistors. I guess you just mean the bias Vp1 and Vp2, right?

jlinky

回复 36# bsaqycx


    呵呵，我看晕了，应该是省掉了电流镜像，采用自偏置结构，省掉了vp1

jlinky

回复 34# bsaqycx


    能不能把图发上来看看哈，两个驱动管的gate电压，应该是我手画的那个样子才是正常的

bsaqycx

I guess I get the answer: when the source of M19 rise, I find that the source of M16 also rise. As the gate of M16 is fixed, the sum of M19 and M20 decreases. As jlinky said, at this time M19 is shut off, therefore the current flowing through M20 maybe decrease. Because the gate of M20 is also fixed, the source of M20 rise.

fumes

m25和m26管的偏置怎么做到让这两个管子在静态下低功耗？

HNwh2011

给输出管M25、M26提供静态偏置点用的。