A question about op-amp


Joined Apr 20, 2004
The paper gives the calculation of E1 as:

- which looks fairly detailed. It also appears as if this is a calculation specific to the application, so a generalized definition of E1 may not be forthcoming. This applies to termination losses driving coax.

The Electrician

Joined Oct 9, 2007
Look on page 3. There is an expression for the gain if the opamp were ideal. Now compare that to the non-ideal gain expression on page 2 that has as its last term the parenthetical (1 + E1)^-1. The gain expression for a non-ideal opamp is very complicated. E1 is just what it takes so that if you multiply the ideal gain expression by (1 + E1)^-1 you will get the full, complicated, expression for the gain of a non-ideal opamp.

The E1 expression is clearly incorrect, because if the opamp gain, Aop-amp, becomes zero, the E1 expression becomes infinite, and then the infinite term (1 + E1)^-1 divides the Vo/Vin expression, causing it to go to zero. But, plainly, if the opamp gain is zero, the input signal will find its way to the output through R1 and R2 and Rtheta in series (if Rool is not zero).