Help, Op-Amp with positive and negative feedback

[runandrew]

Hello I have a homework problem that involves solving for the voltage gain in an op-amp circuit with both positive and negative feedback. I need to find the relationship between in input voltages V_s1 and V_s2, and the node just before R_L, which I will refer to as V_o.

 

 

 

 

I have never dealt with positive feedback before. But, I plan on using super-position to solve the problem. So, the final relationship will look like V_o = k_1*V_s1 + k_2*V_s2, where k_1 and k_2 are some gain constants.

 

By, turning V_s1 off, I get an inverting amplifier, so V_o' = (-R_4/R_2)*V_s2. Is this right?

 

And then, by turning V_s2 off, I get a positive feedback circuit, but I am not really sure how to solve it.

 

Could someone help me out?

 

Thanks.

[Kit]

This is Kit. I think your problem resembles the circuit of a Wien Bridge Oscillator with the exception that, in your case, all components are resistors, whereas the oscillator has some reactive components. Go to this link and you may find all your problems are solved.

 

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&ved=0CDcQFjAAOAo&url=http%3A%2F%2Fnonlinear.eecs.berkeley.edu%2Fchaos%2Fintroduction_nonlinear_circuit_analysis.pdf&ei=FkRAT_mhEan9iQLln8SgAQ&usg=AFQjCNFBis5WULr2qNwHsepSsqTkF0uO3w&sig2=D1rtIasQ8rgdEfo8xC8_Gw

 

 

Hello I have a homework problem that involves solving for the voltage gain in an op-amp circuit with both positive and negative feedback. I need to find the relationship between in input voltages V_s1 and V_s2, and the node just before R_L, which I will refer to as V_o.

 

 

 

 

I have never dealt with positive feedback before. But, I plan on using super-position to solve the problem. So, the final relationship will look like V_o = k_1*V_s1 + k_2*V_s2, where k_1 and k_2 are some gain constants.

 

By, turning V_s1 off, I get an inverting amplifier, so V_o' = (-R_4/R_2)*V_s2. Is this right?

 

And then, by turning V_s2 off, I get a positive feedback circuit, but I am not really sure how to solve it.

 

Could someone help me out?

 

Thanks.

introduction_nonlinear_circuit_analysis.pdf