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offset voltage in opamp (Read 27 times)
shri
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offset voltage in opamp
Jan 18th, 2005, 3:55am
 
Hello,
Please can you help me how to measure offset voltage in an opamp in cadence env, it would be great if you can elaborate on the simulation setup. Thanks in advance.

Shri
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sheldon
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Re: offset voltage in opamp
Reply #1 - Jan 20th, 2005, 5:13pm
 
Shri,

  Just setup your circuit as you intend to use it and
measure difference, run a dc operating point simulation,
and then in the voltage of the input terminals. There are
several cavaets:
1) If the op-amp has a biplolar input pair you will need to match
    the resistances at the input. There will be a slight amount
    of residual offset due to offset current.
 
2) Or if you are worried about the effect of offset current
    then you can take the difference in the base-emitter
    voltage.

3) The bigger issue to the above discussion is that the
    measured offset voltage is the "systematic" offset
    voltage. In order to measure the offset voltage due
    to mismatch in the devices, you will need to run
    Monte Carlo analysis.

    Accurate Monte Carlo analysis is non-trivial since you
    need to setup the model files correctly, see the
    following link:
        http://www.designers-guide.com/Modeling/montecarlo.pdf

4)  For a quick estimate, you can also use dc mismatch
    analysis. It assumes a 3 sigma mismatch in devices
    - dc mismatch needs special model setup, different
       than the setup mentioned above.
    - dc mismatch only works for selected models: bsim3v3,
       VBIC, and 2 terminal resistors.

                                                        Regards,

                                                           Sheldon
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