Problem with slant region of OpAmps output

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srivatsan

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Help regarding OPAMP

hi,
i have a problem. when i simulated the differential amplifier, i think i got a weird output. i have attached both the files.
Output 2 file: the output corresponds when the inverting node is set to ground and DC sweep at non-Inverting input node.
v(19) is the output node from N-input transistors and v(27) is the output node from the P-input transistors. (Comparative study of diff-amp)

the problem is: why does there is a slant region in Output one file?

please reply if you have seen this before or remotely connected.
also how to avoid this problem, if it can be done?

Info: AMIS 0.5um process. Model from MOSIS.org.
regards,
srivatsan
 

Re: Help regarding OPAMP

Could you upload the circuit you are simulating?
 

Re: Help regarding OPAMP

Post your schematic please. Without that it is impossible to answer your question.
 

Re: Help regarding OPAMP

accidently, i wrote OPAMP on the heading.. well i had a problem with overall circuit (OPAMP). but i think i reduced it to diff amp problem. sorry for the confusion.
here i have posted the circuit schematic.
i would like to know ASAP.
About the schematic: the left side is a startup circuit, there are two diffamps, one is n-input and other is p-input transistors. i hope this helps.
regards,
srivatsan
 

Re: Help regarding OPAMP

There might be something wrong with the file. I tried to download twice but both times my computer hang.
 

Re: Help regarding OPAMP

The slant region "around the zero point" in your simulation results are the circuit's gain regions.
In the simulation results, you can find the n and p type differential pair common mode voltage range. The common mode voltage range of n type differential pair (yellow curve) is about -1.X to 2.3X and the p type one (the blue curve) is -2.3X to 1.2X.
When the circuits out of the dc common mode range, the input pair will go to the tri-region, the circuits' gain will decrease (the slant region "far away the zero point").
 

Re: Help regarding OPAMP

sorry to andy1. well when i downloaded it, i did not have a problem. no virus or any crap. i checked all these when i uploaded. so i am not sure what is your problem.

well, ICMR is given in that range... i think i interpret the result as: one of the transistors has gone into the triode region. hence the problem. (probably the "Iss" transistor).

if i am wrong, please clear that up. i would be thankful.
regards,
srivatsan
 

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