No, we are talking about a REAL short, because the following claim was made (Post #17): "I remember thinking that in this circuit if an actual short is placed between nodes 3 and 4 the circuit behavior is not changed, but the unity gain buffer between nodes 7 and 6 can't be replaced by a true short." So, yes, I'm stressing that it cannot be an actual short because the claim was made that it could be and the context of that is made clear in the material that was quoted in my responses.

Hi,

Ok yes i agree, but it must have been a typo or something or just an off the cuff response as i am sure he knows you can't short the two inputs. You can't detect a difference if they are both always exactly the same.
It's also interesting that it does take some time for them to become equal, or nearly equal, in a real circuit. That difference, as it changes, helps drive the output to the correct level.

 

Hi,

Ok yes i agree, but it must have been a typo or something or just an off the cuff response as i am sure he knows you can't short the two inputs. You can't detect a difference if they are both always exactly the same.
It's also interesting that it does take some time for them to become equal, or nearly equal, in a real circuit. That difference, as it changes, helps drive the output to the correct level.

It wasn't a typo. It may have been close to "off the cuff" initially, but the follow-up post made it clear that some additional thought was given (possibly just a mental thought experiment) regarding the solution to the network equations if a resistor was placed across those nodes, even if the resistance was allowed to go to zero. The reasoning was that if the opamp gain was allowed to go to infinity, that there would be zero voltage across that resistor and therefore it would drop out of the equations. But this is only true for non-zero values of the resistance. As soon as the resistance is allowed to go to zero, the current in it becomes indeterminant.

 

It wasn't a typo. It may have been close to "off the cuff" initially, but the follow-up post made it clear that some additional thought was given (possibly just a mental thought experiment) regarding the solution to the network equations if a resistor was placed across those nodes, even if the resistance was allowed to go to zero. The reasoning was that if the opamp gain was allowed to go to infinity, that there would be zero voltage across that resistor and therefore it would drop out of the equations. But this is only true for non-zero values of the resistance. As soon as the resistance is allowed to go to zero, the current in it becomes indeterminant.

Hi,

Ok, no problem