Don't design a full-differential OTA just because the output stage is asymmetric. Point of fully differential circuits is they have good common-mode and supply noise rejection. With good supply and bias it is just much harder to design a fully differential OTA then an asymmetric output amplifier.
And there is no common-mode feedback circuitry above. Those pull-up PMOS devices just can't leave the output to go any lower voltage levels.
The CMFB amp doesn't need such high gain.i have designed the ideal vcvs using a gain of 100
... 'cause you load its output impedance of perhaps 5..10MΩ with a much lower impedance for the vavg generation.however the output gain from the opamp is messed up
The CMFB amp doesn't need such high gain.
... 'cause you load its output impedance of perhaps 5..10MΩ with a much lower impedance for the vavg generation.
Won't be enough to increase the resistance if you want to connect the common mode feedback circuitry to the differential circuit.
I think you want to connect the asymmetric OTA's output to the 'vcmfb' nodes of the differential OTA. But your asymmetric OTA's NMOS tail current source will be in triode region. You should implement an other asymmetric OTA with PMOS tail current source.
I think it would help. Let's give it a trial.Won't be enough to increase the resistance if you want to connect the common mode feedback circuitry to the differential circuit.
No, NM8 is in saturation region (region=2): vds > vdsatyour asymmetric OTA's NMOS tail current source will be in triode region.
Against what should this help? Simply the other way round?You should implement an other asymmetric OTA with PMOS tail current source.
Oh, you thought of the CMFB-amp. Sure, clear.He is using a non-differential OTA (=asymmetric output) to create common-mode feedback for his differential OTA.
Right.The common mode feedback input of his differential OTA are the NMOS current sources at the bottom (NM1 and NM4).
Understand now: Because of the ≈900mV CMFB output voltage mismatch to the ≈300mV required CMFB input voltage.NM12 and NM11 won't be in saturation if he connects the drain of NM11 to the CMFB input of the differential OTA.
Yes, you're right. Would probably fit better.If he wants to control those NMOS gates I think a PMOS input, single-ended (=asymmetric output) OTA should be implemented.
My misunderstanding, sorry. Always thought you were speaking of the main OTA - because I'm used to call the other one the CMFB-amp.You misunderstood me, NM8 is not affected, I didn't talk about that amplifier. The single ended OTA (=asymmetric output) will have problems.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?