what's the differnces of the two kinds resistance???

[ZengLei]

Today when I read the datasheet of OP07 two parameters below catch my eyes~~~~,

Question:

1.what’s the differences between the two kinds of resistance????

2.why we must define the two kinds resistance??????????????

3.How the two kinds of resistance affect the work of a OP???????

4.Which resistance is the larger the better,and which one is the smaller the better???????????

5.Usually,When we talked about a OP,we always said the input resistance of a OP is infinity!!!and the input resistance here mean which one??the Common Mode input resistance or the Differential Mode input resistance???

6.Why some datasheet of OP emphasis the two kinds of resistance, and some others are not????

 

[TwinT]

1 two kind of resistance: Differential mode: for differential signals
Common Mode: for common signals

OK, but what's diff. or common?
One input is positive( +) and the other is minus ( - ), then

Common signals = [V(+) + V(-)] / 2
Diff. signals = [V(+) - V(-)]

All voltages referenced to ground (0v)

OPAMPs amplify differential signals very much, and reject common signals. I don't know about the specific values that you got, but I think that both resistances have to be high.

An example: if you force +5.01V in (+) and 5.00V in (-), the OPAMP differential gain (Ad) and the OPAMP common gain (Ac) act like this:

Vo (Output) = Ad*(0.01V) + Ac*(5.05V) and remember that Ad >>>> Ac

regards

 

[Kral]

ZengLei,
Since the downloads bear no relation to your question, can you specify exactly what parameters you are asking about? Use exactly the same terminology that is stated in the data sheets.
Regards,
Kral