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excuse , common mode loop mean CMFB???do i simulate only CMFB(not with the OTA) block to see the gain and phase???
i have the CT CMFB, but , it work bad, i don't know why?
all transistor is operate in saturation.
that's my Vocm=((vo+)+(vo-))/2, and my Vcm=1.65v
and my bias is not ideal.
I think you should simulate the cmfb loop together with the rest of ota. Try to find a good spot were to open the cmfb loop and analyze(loopgain, phasemrgin). Have you tried to decrease the input/output swing?
Dear oxide:
this is my OTA with CMFB simulation,that is al i can find the best Vocm.
The following is my only OTA simulation.
The gain and phase margin is almost the same, the Vocm become better, but i can't loak it at the Vcm=1.65.why???but my all Vout=(vout+)-(vout-) shift toward to up of the graphic, so i think if i can solve this problem about cmfb , i will solve the integrator problem.
Why do you want me to decrease the in/output swing??In my knowledge, it is more widely more better, am i wrong???
I was just thinking if this is a large signal phenomena. to have a the ota stable at smal signal doesn't necessary mean that you have a stable large signal ota. also i noticed that your input signal freq is quite high compared to unity freq. Try to lower your swing and also the freq??
Dear oxide:
try to decrease the signal frequency at 1Mhz , but it become worse,
theoretically the output shoud all above the '0', but it is not ,i also accpet your opinion, the stability in small signal does not mean large signal will stable.
i ask my friend, no one to see the large signal , everyone just tell me they just notice gain and phase, but their IC still work well , why???
now i want to solve the CMFB problem, do you have an ideal??
1. I am afraid I do not understand that your signal "theoretically output should be all over 0"?
2. how do you generate you bias. are they ideal vdc or?
3. I have never used this kind of cmfb.
4. How does you vcc look like?
5. did you check your tb? initial conditions etc..
I am sorry that I could not help you ;-( .
Good luck!
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