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How to calculate the systematic offset of the opamp?

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shaq

shaq

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Dear all,

I have a fully-differential opamp as shown below.

I want to calculate the systematic offset of this opamp by hand, but I don't know how to do.

Please help me if you know. Thanks.
 

To have zero offset, the output PMOS current must be exactly equal to the NMOS current

Any ΔI would result in a systematic offset. Simply find the differential input voltage Vin that when applied would cause ΔI to be zero
 
you can calculate the input mosfet size ,and calculate the offset by it , for the .35um process , the vth will induce the offset of 10mv/sqrt(area of input device)
 

songjunjian said:
you can calculate the input mosfet size ,and calculate the offset by it , for the .35um process , the vth will induce the offset of 10mv/sqrt(area of input device)
Click to expand...

Hi, songjunjian

I know what you say is pelgrom's model

σ(ΔVth)=Avt/√(WL)

But, I think this may cause random offset, not systematic.
 

shaq said:
Dear all,
I have a fully-differential opamp as shown below.
I want to calculate the systematic offset of this opamp by hand, but I don't know how to do.
Please help me if you know. Thanks.
Click to expand...

Please, be specific and tell us your DEFINITION of SYSTEMATIC offset.
I remember several book authors who are using the term "systematic offset" even for the BJT voltage Vbe≈0.7 volts (in contrast to other amplifying devices with no or only negligible input differential voltage).
 

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