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https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> offset voltage in opamp https://designers-guide.org/forum/YaBB.pl?num=1106049326 Message started by shri on Jan 18th, 2005, 3:55am |
Title: offset voltage in opamp Post by shri on 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 |
Title: Re: offset voltage in opamp Post by sheldon on 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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