How to calculate the systematic offset of the opamp?

[shaq]

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.

 

[elbadry]

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

 

[songjunjian]

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)

 

[shaq]

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)

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.

 

[deffu]

ur design has zero systematic offset bz it is symmetric

 

[LvW]

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.

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).