how to get OFFSET voltage of THE OP-AMP

• Apr 26, 2007

• #1

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wael_wael

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how to get the offset voltage for an op amp

Hi,
i am try to simulate MY OP-AMP but i dont know how to simulate offset voltage, any suggestaion
thanx in advanced

 

• Apr 26, 2007

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zizu

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offset and span op amp

u should take the mismatching effect into account.
Adjust the W/L from being matched manually or utilize Monte-Carlo analysis.

 

• Apr 26, 2007

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wael_wael

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opamp_adv

thanks, but still i need the circuit which be used for measuring the offset, and how to do that.
regads

 

• Apr 26, 2007

• #4

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kwkam

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You can simulate the a Av=+1 feedback config, and input a vcc/2 to +ve input. If your opamp have systemic offset, you will read it on -ve input. For random offset, you better to model it from the principle.

 

• Apr 26, 2007

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isong

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If the OPAMP has only random offset, you can get it by introducing some mismatch purposely. However,I think the correct modelling is not easy.

wael_wael said:

Hi,
i am try to simulate MY OP-AMP but i dont know how to simulate offset voltage, any suggestaion
thanx in advanced

Click to expand...

 

• Apr 26, 2007

• #6

rush3k

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the way you can do that is to sweep your differential input from say about -0.5V to +0.5V, your offset should fall within this range. the output (Vout vs Vsweep/in) will look like a step. Vsweep/in @ Vout=0 is your offset voltage Vos. so long as in the graph, the point vin=0 falls in the linear region of the step, you will have reasonable results.

 

• Apr 27, 2007

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wael_wael

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thanx alot, could u show me the circuit configration which used for this measurment
regds

 

• Apr 27, 2007

• #8

rush3k

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there's a spice netlist for such a simulation on page 22 here:
h**p://webpages.eng.wayne.edu/cadence/ECE7570/doc/OPAMP_ADV.pdf

 

• Apr 27, 2007

• #9

Meridian

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wael_wael said:

Hi,
i am try to simulate MY OP-AMP but i dont know how to simulate offset voltage, any suggestaion
thanx in advanced

Click to expand...

Try this:

 

• Apr 28, 2007

• #10

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wael_wael

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hi everybody,
thanx for your help, i would like to till MY OP-AMP for Track and Hold T/H application that deal with small term of capacitance.
any way my T/H work as well but still ineed to increase its SFDR.
this measurment of the OP AMP is so complex for me especially CMRR bcz my OPAMP is fully differential .
still i didnt get the solution as well for my case. if there any datasheet or notes can help pls suggest it to mt
regards

 

• Apr 28, 2007

• #11

Sadegh.j

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since your opamp is ideal, you will get nothing, in practice, we gorund the inputs of the opamp and check the outpur, I believe it is a good idea to model the disturbing effect via a source

 

• Apr 28, 2007

• #12

saubhik

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wire ur opamp as vtg follower connect i/p to ground . the vtg of o/p shuld be zero . but due to offset it will not be zero . this will be of very less measure it with some precesion measuring instrument

wael_wael said:

thanks, but still i need the circuit which be used for measuring the offset, and how to do that.
regads

Click to expand...

 

• Apr 28, 2007

• #13

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rfzheng

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you may connect you OPAMP as a voltage follower, then sweep the dc voltage at the postive input stage, and check the difference of output voltage with your input voltage .
the offset will be showed by their difference