# Simple Op Amps questions

1. Jun 17, 2006

### fargoth

ok, can someone explain these two circuits?

should be pretty simple, but i can't seem to do it right... the book im learning from doesn't have the full solution, so i have to guess what's wrong with my calcs, and i don't think it'd be a good idea to learn like this to my exam...

i'll explain what i did:
for the second one with the V_ref on both sides:
the v_out due to V_in and V_ref i'd get $$\frac{(V_{in}+V_{ref})R_F}{R_G}$$
and due to the other V_ref i'd get $$\frac{-V_{ref}R_F}{R_G+R_F}\frac{R_F}{R_G}=V_out-\frac{-V_{ref}R_F}{R_G+R_F}$$
because $$\frac{V_{ref}R_F}{R_G+R_F}$$ is the voltage of the entrance to the Amp, so the current would be $$\frac{-V_Amp}{R_G}$$ and so the voltage in V_out would be... oops, now that i explained what i did i found the problem.... i thought the voltage in the Amp is zero, but it isn't for the second time...
no i add them and it's fine

i'll write in a bit what i did for the other circuit... i nust run...

[EDIT]
you can just ignore this whole silly post... i found my error, just needed to go out with my friends and see a stupid movie to clear my head, i feel like so stupid i got stuck with such a simple circuit for so long...

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Last edited: Jun 17, 2006