# op amp problem

Discussion in 'Homework Help' started by hani114, Feb 22, 2009.

1. ### hani114 Thread Starter New Member

Feb 22, 2009
3
0
could somebody please help me solve this problem? i've been working on it for the last hour but i came up with nothing, i have a quiz in this problem tomorrow in the morning, so please i need the assistance.

Thanks a lot for your time

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2. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Go ahead and post your own efforts so that we can see where you have encountered the snag.

hgmjr

3. ### hani114 Thread Starter New Member

Feb 22, 2009
3
0
i used the two rules that vp=vn & ip=in=0

so i tink no current flows in Vc & Vd and the 60kohm resistor.. as for Va & Vb we apply kcl on the input voltage node and solve for Vo

current in Va is Ia and so forth.. and current in 375kohm(Re) resistor is Ie

so Ia + Ib + Ie = 0
Va/Ra + Vb/Rb + Vo/Re = 0
so we calculate Vo from that

for the second part we need to calculate the range for Vb so that -20<Vo<20
so i think we have to put Vo in terms of Vb and replace that in the range so that we get Vb

can anyone help me with this??? it's late now and that's the best i can do..

4. ### hgmjr Moderator

Jan 28, 2005
9,030
214
You seemed to have failed to account for the contributions to Vo from Vc and Vd.

It is probably obvious but the equation for Vo will take on the form:

$V_o = G_a(V_a) + G_b(V_b) + G_c(V_c) + G_d(V_d)$

Where Ga, Gb, Gc, and Gd are the gain coefficients associated with each of the four inputs.

Can you take a stab at calculating the gain cooefficients? Perhaps you can find something helpful in your text book or by researching the topic on the Internet.

hgmjr

5. ### hani114 Thread Starter New Member

Feb 22, 2009
3
0
i tried that, it didn't help can you just help me please with the solution, i've worked a lot on this problem and i have to go to sleep (it's 11pm here).. and as i mentioned i need this for my quiz tommrow

Last edited: Feb 22, 2009
6. ### hgmjr Moderator

Jan 28, 2005
9,030
214
The best thing for you to do at this point is get some rest. You will be able to perform better on the test overall if you are not sleepy during the test.

hgmjr