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tyanata
Joined: 27 Nov 2003
Posts: 83
Helped: 2
Location: Sofia
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 27 Oct 2004 15:23 Op Amp simulation problem |
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| 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?!
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Hughes
Joined: 10 Jun 2003
Posts: 712
Helped: 84
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| 28 Oct 2004 0:44 Re: Op Amp simulation problem |
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| tyanata wrote: |
| It is strange, when I simulate the all scheme the bandgap works properly but when I simulate only the bandgap, it doesn't work. |
Does the 'all scheme' have a feedback network (outside the 'bandgap')?
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tlihu
Joined: 02 Jan 2002
Posts: 627
Helped: 5
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| 28 Oct 2004 3:03 Op Amp simulation problem |
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| 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.
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cetc1525
Joined: 08 Oct 2004
Posts: 177
Helped: 3
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| 28 Oct 2004 6:15 Op Amp simulation problem |
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| how did you include the capacitor? does it not in the models?
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tyanata
Joined: 27 Nov 2003
Posts: 83
Helped: 2
Location: Sofia
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| 28 Oct 2004 7:33 Re: Op Amp simulation problem |
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| 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.
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Humungus
Joined: 10 Jul 2001
Posts: 417
Helped: 25
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| 28 Oct 2004 8:10 Re: Op Amp simulation problem |
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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.
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rtpq
Joined: 12 Oct 2004
Posts: 15
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| 28 Oct 2004 8:14 Re: Op Amp simulation problem |
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| You must figure out what characteristic of opamp you want.
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tyanata
Joined: 27 Nov 2003
Posts: 83
Helped: 2
Location: Sofia
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| 28 Oct 2004 14:00 Re: Op Amp simulation problem |
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| 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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