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？

fumes

悬浮电流镜难道就是作为传输电阻，给输出级m25和m26管偏置电压的吗？
那这个偏置稳定吗？静态时，m19和m20管的电流需要相等吗？
如果驱动1K电阻负载，这个运放是开环用吗？

梧桐

谢谢分享！！

liliheqing

这么复杂，没见过！！！

luodennis

可以参考一下这篇文章

sniper711

这貌似是个挺常见的电路

fumes

可以参考一下这篇文章
luodennis 发表于 2010-12-28 20:52

                               
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    看了，没说明白19和20管到底是怎么工作的

jerry8600

谢谢分享！

fhchen2002

No, the current through M19 and M20 are not necessarily equal.
But, you have the freedom to make the current roughly the same in your design.

These two devices are used to bias the output M25 and M26 devices.
VG of M25 is set at VDDA - VGS_M21 - VGS_M22 + VGS_M20.  (approximately 1 "diode" drop from power.)
VG of M26 is set at 0 V + VGS_M23 + VGS_M24 - VGS_M19. (approxaimately 1 "diode" drop above ground.)

DC analysis
Assuming balanced inputs,
The current through M16, I(M16) = Ib4 - 0.5 * Ib1
I(M19) + I(M20) = I(M16)
I(M19) is mirrored from Ib8.  I(M19) = (W_M19 / W_M23) * Ib8 (assuming same lengths for M23 and M19)
I(M20) is mirrored from Ib5.  I(M20) = (W_M20 / W_M22) * Ib5 (assumping same lengths for M20 and M22)

Additional notes
Usually M25 and M26 output directly drives off-chip (i.e., they are large devices) and are subject to ESD design rule.
So are M19, M20, M22 & M23 subject to ESD rule, since we want good VTH tracking.  (They are small devices.)

Yes, this OpAmp is able to drive 1 KOhm resistive load.

fumes

No, the current through M19 and M20 are not necessarily equal.
But, you have the freedom to make th ...
fhchen2002 发表于 2010-12-30 07:29

                               
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    悬浮电流镜偏置电流不准吧，难道要求不高吗？只要让19和20管导通就行了吗？
　 这个Vth跟踪特性不好吧？体效应影响明显，要是三极管就好了

wulong527

thanks for patience~~