The concept of Large signal voltage gain 's measurement condition ?

Question

Hi 
 I would like to know how to decide the condition of "Large signal voltage gain". 
 For example, AD8542's condition is 
 Vs=2.7V VCM=1.35V 
 RL=100Kohm Vo=0.5 to 2.2V 
 Vs=5V VCM=2.5V 
 RL=100Kohm Vo=0.5 to 2.2V 
 How to decide this vo condition? 
 Why 0.5? Why 2.2V? 
 Other case, OP295's condition is 
 Vs=5V VCM=2.5V 
 RL=10Kohm 0.005V<= Vout <= 4.0V 
 Vs=+/-15V 
 RL=10Kohm no output voltage description. 
 in this case why 0.005V? Why 4.0V? 
 In AD8542 case, Vs=5.0V, 3.0V's vo conditions are same as Vs=2.7V. It means to cut the test ? and Avo does not depend on Vs voltage? 
 For example, condition is Vo= 0.1V to 2.5V,then how much the Avo will degrade? 
 In OP295's case, why vo is very low? 
 I would like to know the concept of vo decision. 
 Regards 
 moto

ADIApproved · Accepted Answer

Hi, moto. 
 Avo depends on supply voltage but the AD8542 does not follow this. I don't know why. Usually, for the newer datasheets, the Vo is set to be between 0.5V to 1.5V away from the rails in order to have a better Avo value and this Vo depends on Vsy. 
 For the OP295, the Vo range was chosen because it is the range that gives a good Avo number. 
 Hope this helps. 
 Regards, 
 Anna