calven303 said:a basic amplify circuit as follows.
the needed gain is 10.the power voltage is 1.8v.when the input dc voltage is 0.9v,because the feedback factor is 1/9,the output dc voltage should be 9v,so the opamp can not work.
how to resolve the problem?are there any other architechture?please introduce some!
LvW said:calven303 said:a basic amplify circuit as follows.
the needed gain is 10.the power voltage is 1.8v.when the input dc voltage is 0.9v,because the feedback factor is 1/9,the output dc voltage should be 9v,so the opamp can not work.
how to resolve the problem?are there any other architechture?please introduce some!
There is no solution because of contradictory requirements.
It has nothing to do with opamp "architecture".
With a 1.8 power supply and a gain of 10 you cannot accept an input of 0.9volts.
Increase the supply voltage or decrease the gain or lower the input voltage.
calven303 said:the dc voltage of the input signal is 0.9,which is needed to bias the input nmos of the opamp.while the small signal maybe is sevral mv.even in this condition,there is no other solution?
the dc voltage is amplified together?
r2d2droids said:can u give the detailed schematic?
calven303 said:the dc voltage of v2 is o.9v.the OTA is a one stage folded-cascode opamp.doing dc analysis,the circuit can not work.
regards
calven303 said:sorry,it is an OTA.i will try to add the cap,but the cap can change the dc characteristic?
regards
LvW said:calven303 said:sorry,it is an OTA.i will try to add the cap,but the cap can change the dc characteristic?
regards
Both of the circuits provided by you up to now show an operational amplifier.
If you now plan to change to an OTA, neither the amplifier symbol nor the feedback network apply anymore.
Do you know the function and the principle of an OTA ?
Do you still want feedback ?
calven303 said:it is an OTA,although the symbol is labled OPA.because it is an OTA,the feedback network needs to be changed?and how?
regards!
r2d2droids said:it is an OPA labelled OTA but doesnt work.
its very complicated.
i am confused...
LvW said:calven303 said:it is an OTA,although the symbol is labled OPA.because it is an OTA,the feedback network needs to be changed?and how?
regards!
My last question was if you really want to have feedback !
Before designing or changing a feedback network you have to decide if there must be feedback at all ! (Remeber: OTAs do not need feedback !).
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