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Op Amp simulation problem

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tyanata

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operational amplifier simulation

I have a problem . I have to simulate operational ampliofier of one bandgap, but to include capacitances of all transistors connected to the output of the operational amplifier, I started to simultate the amplifier as a part of the bandgap. But there is a problem the output of the amplifier sets to 0V, The output to of the bandgap goes to 3.5V (VDD=5V). It is clear that the startup circuit doesn't work. It is strange, when I simulate the all scheme the bandgap works properly but when I simulate only the bandgap, it doesn't work. Can any one help me to cope with this probleme?!
 

stable amplifier simulation

tyanata said:
It is strange, when I simulate the all scheme the bandgap works properly but when I simulate only the bandgap, it doesn't work.
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Does the 'all scheme' have a feedback network (outside the 'bandgap')?
 

Usually bandgap circuit need a startup circuit to bring it out of initial condition, i.e., 0v or Vdd. So, I guess you can either include the startup circuit or set correct .ic when simulating.
 

how did you include the capacitor? does it not in the models?
 

There is no feedback circuit which includes all scheme. The output of the bandgap is applied on the positive node of one amplifier. There is a startup circuit in the scheme but obviously there is aproblem with its simulation. The amplifier is Miller type.
 

Are you sure of the connections you made with your OpAmp (positive and negative inputs)?

The voltage you see is from a DC or TRAN simulation? If it comes from a DC simulation, what you see is the initial state if some start-up circuit is there. Maybe you circuit have more than one stable solution.
 

You must figure out what characteristic of opamp you want.
 

I was in mistake. I had swapped the inputs of the amplifier.When I simulated all the scheme, used .net file with right configuration of the amplifier inputs. It seems when I have made the scheme for amplifier simulation, I made the mistake.
 

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