这种运放单位增益响应曲线是否正常？能用不？

selfsalvation04

呵呵，哥们来吐槽了

huanggc1989

回复 30# lgy747


    哥们，还没到“儿子”和“洋亲爹”的程度吧，就说人家一外国人，肯把我们的中文帖子翻译一下，回贴也尽可能的用将原话翻译成中文，而且，回答也挺有道理，虽然我承认自己是菜鸟，但是有所收获，说声谢谢，应该不算媚外吧……这可跟你的洋亲爹的儿子同事不一样

AcoAco

回复 29# huanggc1989

“that is On really apleasure to communicate with a foreign designer here, and thanks for your help... by the way, I do not know much about the relationship between the "gainmargin
"andthe
stability
of the opamp could you recommend somereferences about that? thank you ~”

huanggc1989   Ihave no doubt you know.

Opamp stability theory isdeveloped in “control theory” “ Linear systems”. An Opamp since having afeedback is a plant in control theory and subject to control theory laws.  There are numerous books in any library justskip other chapters and go to chapter where there is phase and gain margintreatment (one may use index at the end of the books).

Analog and Digital ControlSystem Design    Chen   is a good book.

I could not figure out how toattach any material to this forum as I have mentioned above. Please look into

Modern_Control_Engineering  5th Edition   _Ogata pages 385, 386 ….

Here in this example as in LZ s opamp there is a dominant polebut secondary pole is causing ringing during transition. There is no overshoot sincewith dominant 1st pole (low enough system order) has very good phase margin. Similar reasoning applies to LZ's Bode plot  results where we see zero doublet followed by a pole doublet just around unitygain crossing as a result there is no gain margin.

Page 466, 467

“AFew Comments on Phase and Gain Margins. The phase andgain margins of

acontrol system are a measure of the closeness of the polar plot to the –1+j0 point.

Therefore,these margins may be used as design criteria.

Itshould be noted that either the gain margin alone or the phase margin alonedoes

not givea sufficient indication of the relative stability. Both should be given in the

determinationof relative stability.

For aminimum-phase system, both the phase and gain margins must be positive for

thesystem to be stable. Negative margins indicate instability.

Properphase and gain margins ensure us against variations in the system components

and arespecified for definite positive values.The two values bound the behavior of theclosed-loop system near the resonant frequency.

For satisfactory performance,the phase marginshould be between 30° and 60°, and the gain margin should be greater than 6 dB.

Withthese values, a minimum-phase system has guaranteed stability, even if the open-loop

gain andtime constants of the components vary to a certain extent. Although the

phaseand gain margins give only rough estimates of the effective damping ratio ofthe

closed-loopsystem, they do offer a convenient means for designing control systems or

adjusting the gainconstants of systems.”

Here as we see 30 to 60 degree of Phase margin and 6dB of Gain Margin isaccepted as satisfactory (this is for general mechanical control systems wheresystems are slow and has quite a bit damping around to prevent oscillatory behavior. Also as in this example for a theoretical two pole system this margins are OK. For practical cases as in a real opamp designs atleast 65 degree phase margin and 16 degree of gain margin are necessary since system order is higher because there are many poles ad zeros around. Now ofcourse with ever increasing complexity and speed of circuits these phase margin and Gain margin requirement numbers to bechecked through simulations to verify acceptability J Inan opamp there are many poles and zeros we only threat major ones forpracticality but any one of existing pole and zero contribute its weight intostability.

You may use Google or equivalent for translation.  If you have access problem let me know I translate and paste it. Good luck.
您可以使用谷歌或等效的翻译。如果你有访问的问题，让我知道我翻译，并将其粘贴。祝你好运。

huanggc1989

回复 33# AcoAco


    thank you～

huanggc1989

回复 33# AcoAco


    thank you～

rrbice

这个明显是不行的

sweety320

回复 23# AcoAco

您好~我想请教一下，设计运放的时候，考虑到版图以及流片工艺等等对电路的影响，相位裕度的设计应该大于70，增益裕度大于15db么？谢谢~

zyw543716900

回复 1# jxjxhwx
相位裕度45~60

QQben

谢谢分享