Input Offset voltage...

[dr.power]

Hi guys,

The below circuit is an inverting amplifier that boost an AC signal by the gain of 25 and then adds a dc offset to it by dc gain of just 1.
If the Input Offset voltage happens to be 10mV then what woulf be the output offset voltage due to this Input Offset voltage plz?

Thanks a bunch

 

[audioguru]

Your opamp has a DC gain of 1.
If its DC input offset voltage is 10mV then its DC output will be plus or minus 10mV from the expected output voltage.

 

[dr.power]

Your opamp has a DC gain of 1.
If its DC input offset voltage is 10mV then its DC output will be plus or minus 10mV from the expected output voltage.

Thanks guru,
But I was talking about the INSIDED Input offset voltage. I guess that the said offset will acquire regardless of the input signals being dc or AC... In our cause we have an input AC gain of 25 and a dc gain of 1, so how the 10mV insided input offset voltage (the datasheet for tl074 say that the input offset voltage for this chip is almost 10mV) affects on the output and how much of OUTPUT voltage we would see at the OUTPUT due to this input offset at the my above pic?

 

[audioguru]

The opamp has a maximum input offset voltage of -10mV to +10mV. It might have zero input offset voltage.
Since your opamp circuit has a DC gain of 1 then the input offset voltage is added to or subtracted from the output voltage.

 

[dr.power]

Thanks for your input.

I know that, but Actually plz I would like to know the output offset voltage due to this 10mV input offset voltage when both inputs in my first pic are open or grounded?

 

[audioguru]

I would like to know the output offset voltage due to this 10mV input offset voltage when both inputs in my first pic are open or grounded?

Each opamp has a different amount of DC input offset voltage. A few have the maximum amount which is 10mV. If your opamp has +10mV of input offset voltage and since your opamp inverts and has a voltage gain of 1 if the input is at 0VDC then the output will be -10V or the output will be +10mV if the input is open.

 

[dr.power]

Each opamp has a different amount of DC input offset voltage. A few have the maximum amount which is 10mV. If your opamp has +10mV of input offset voltage and since your opamp inverts and has a voltage gain of 1 if the input is at 0VDC then the output will be -10V or the output will be +10mV if the input is open.

Right, But isany formula to explain how much of amplification this 10mV ofset will have at the output? Is there any reklationship between the amount of the amplification of this offset and the gain formula for the inverting, noninverting op-amps? For instance how much of output offset I will have if the gain of the op-amp happens to be 100 while the input offset volatge is 10mV?

 

[audioguru]

If the opamp circuit has a DC gain of 100 then obviously the 10mV input offset will be amplified and will be 100 times more at the output which is 1V.

 

[dr.power]

If the opamp circuit has a DC gain of 100 then obviously the 10mV input offset will be amplified and will be 100 times more at the output which is 1V.

It is strange!!! The input dc offset is INSIDE of the Op-amp, It should be at the input of Rin (the right pin of Ri) so that be amplified!!!!!

 

[audioguru]

All single opamps have input offset voltage null pins so that the small input offset voltage can be nulled and is not amplified.
The input offset voltage is not amplified when the opamp has an input coupling capacitor that blocks DC so it cannot amplify DC.