I'm working on a problem with an operational amplifier circuit . The exercise is as follows:

"Determine the effect of the operational amplifier’s input bias currents on the output voltage and find the relationship between resistors".

I understand that bias currents cause a small offset in the output, but I'm not sure how to calculate the exact effect or determine the resistor values to minimize this offset.


this is the circuit and my teacher has put one similar to this in one of our lectures(photo below)

Please help i have a laboratory test tommorow

 

The bias current simply generates an IR voltage crop across the input resistors, which then is amplified by the circuit gain.
You need to observe the polarity of the voltage drop and the op amp input polarity as it pertains to the output voltage generated.

 

The bias current simply generates an IR voltage crop across the input resistors, which then is amplified by the circuit gain.
You need to observe the polarity of the voltage drop and the op amp input polarity as it pertains to the output voltage generated.

Indeed, but on the test i need to write the voltage error of both Ib+ and ib- and the effect the have on the output voltage, one of my collegue. sent me this. We don't know what the Verror generated by these current sources is, can you please provide an expression we would be beyond thankful

 

Indeed, but on the test i need to write the voltage error of both Ib+ and ib- and the effect the have on the output voltage, one of my collegue. sent me this. We don't know what the Verror generated by these current sources is, can you please provide an expression we would be beyond thankful

Hi,

First, why post a schematic upside down?
Here is a cleaned up version for easier viewing.

Isn't this just a matter of using Ohm's Law with the two current sources and the two resistances?
Then just use the gain of the circuit to figure out the output voltage.
Does that sound like all you are supposed to do?
Keep in mind that the feedback from the output forces the two inputs to be the 'exact' same voltage with an ideal op amp (ideal except for the bias currents). I presume for now that you do not have to consider the actual internal open loop gain of the op amp.

Here's the diagram...

 

If you understand how an op amp works, then you should be able to write the equations for the offset.
If you don't, then you need to study how they do work.
Plugging values into a formula you don't understand does little to help you learn about the circuit.

This is a homework help forum, not a homework do.

 

I figured it out after talking with one of my lab teacher and seeing the comments i remember why i don't ask on forums anymore. All of them feel like reddit where everyone is so far up their asses and does not actually help or even provide something useful

 

I figured it out after talking with one of my lab teacher and seeing the comments i remember why i don't ask on forums anymore. All of them feel like reddit where everyone is so far up their asses and does not actually help or even provide something useful


[/QUOTE}]We did provide you with useful information, but you are apparently not smart enough to realize it.
We won't miss you.

 

I figured it out after talking with one of my lab teacher and seeing the comments i remember why i don't ask on forums anymore. All of them feel like reddit where everyone is so far up their asses and does not actually help or even provide something useful

Hi,

I hope I have helped a little I just tried to explain in a clear way that I think could have been understood.

You're right though, on some forums some people blurt out some condescending comments and it hurts the individual. We have to be tough skinned though because that's just part of the ugly side of life. There will always be people like that and if we ignore every single one (barring those we have to) we won't be able to obtain any information at all and it might even get a little lonely.

There are a lot of A type people on the net and they want to make sure you know they are A type people