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Problem with negative gain and phase margin when doing AC analysis

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dewabantura

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Hi there! I'm developing low voltage 0.35um op amp (1.5V). Currently i'm doing AC analysis and the gain and phase margin are in negative values (-56.35dB and -112degrees). Why is it like that? I am using LTSPICE

Thank you
 

AC analysis

is your amp connected as unit amp?
 

Re: AC analysis

yup, already as a unit op amp. Someone said that my op amp is attenuating not amplifying. Is it true?
 

Re: AC analysis

Well, there might be many reasons,
1) The transistors are not all in saturatino
2) Problem in the source difinition
3) You are using the wrong nodes
 

AC analysis

Are you sure that you DC op-point is OK?
 

AC analysis

2 possible reason

1) wrong expression in you input deck
2) congradulation you get a regulator
 

AC analysis

Hi dewabantura: can you show us the schematic and netlist of the OPA?
 

Re: AC analysis

Where do you open the loop?
How do you give the stimulus for AC analysis?
 

Re: AC analysis

hi guys, thanks to sadegh and waxtomato and other replies. Actually i'm using the wrong nodes. The order of my op amp subcircuit is not correct. It should be noninverting, inverting, Vin+,Vin-,Vout.

Thanks again frens! Good luck in your future undertakings
 

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