Input offset voltage for the two stage opamp design

[joehwang]

Hi,

This is an two-stage opamp with miller compasation cap and Vdd=1.8v, Vss=0v.

I am measureing the input referred offset voltage (Vos) for this op-amp.
I bias DC=0.9v for both Vin+ and Vin- and AC=1 for the Vin+. Then, when Vin=0.9v, the Vout=0.912v, where both vout and vin are in the transition region(linear region) as shown in the attachment. So, the Vos=0.012v~~is it correct?

 

[zhaoqin]

Hi,

This is an two-stage opamp with miller compasation cap and Vdd=1.8v, Vss=0v.

I am measureing the input referred offset voltage (Vos) for this op-amp.
I bias DC=0.9v for both Vin+ and Vin- and AC=1 for the Vin+. Then, when Vin=0.9v, the Vout=0.912v, where both vout and vin are in the transition region(linear region) as shown in the attachment. So, the Vos=0.012v~~is it correct?

in fact 0.012V is the output offset voltage,and the input offset voltage=0.012/Av;
my method is add a DC voltage source between Vin+ and Vin- ,and you can change the dc voltage until the output voltage of opamp is 0.9v,then the voltage is input offset voltage .

 

[joehwang]

Thanks! zhaoqin~

1.
So, with your method, if I change the Vin until Vout=0.9v when Vin=0.91v, Vos=0.01v. Is it correct?

2.
So, similarly, if the Vdd is 5V and Vss=-5, with your method, I need to change the Vin until the Vo=0v, then if the Vin=0.12mv, Vos=0.12mV. Is it correct?

3.
Conclusion: Vo=0 is not necessary in everycase when defining the Vos(input). It depends on the Vdd and Vss. Is it correct?

Thank you so much!

 

[zhaoqin]

Thanks! zhaoqin~

1.
So, with your method, if I change the Vin until Vout=0.9v when Vin=0.91v, Vos=0.01v. Is it correct?

2.
So, similarly, if the Vdd is 5V and Vss=-5, with your method, I need to change the Vin until the Vo=0v, then if the Vin=0.12mv, Vos=0.12mV. Is it correct?

3.
Conclusion: Vo=0 is not necessary in everycase when defining the Vos(input). It depends on the Vdd and Vss. Is it correct?

Thank you so much!

1.right
2.right
3.right