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-   -   Transfer Funtion of the given circuit ? (http://www.diyaudio.com/forums/everything-else/198112-transfer-funtion-circuit.html)

 sameerdhiman 8th October 2011 10:02 AM

Transfer Funtion of the given circuit ?

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Hi,

Please give me the transfer function of the following circuit. Where R1,R2,R3,R4 and R5 are not equal.

 DF96 8th October 2011 01:00 PM

 Ron E 8th October 2011 04:42 PM

Quote:
 Originally Posted by sameerdhiman (http://www.diyaudio.com/forums/everything-else/198112-transfer-funtion-circuit-post2738584.html#post2738584) Hi, Please give me the transfer function of the following circuit. Where R1,R2,R3,R4 and R5 are not equal.
You should check out a neat little program called sapwin ;)

 SY 8th October 2011 05:20 PM

Just remember that the voltages at inverting and noninverting inputs are equal, that the current flowing into the inverting and noninverting inputs is zero, and it will be pretty easy to set up the basic equations to solve for Vo/Vi.

 jcx 8th October 2011 09:57 PM

it actually "safer" to explicitly include op amp gain "A" and derive the equations

you can always take the limit as A goes to infinity later - but by assuming it from the start you may save a term or two in the calculations or you may have your solution "blow up" from the infinity you are implicitly carrying around

the op amp Howland current source is a favorite nasty problem set for those not understanding the "null injection" implicit infinity

 dchisholm 8th October 2011 10:24 PM

What method do you think is best for solving this problem, and how far along did you get?

Dale

 sameerdhiman 10th October 2011 04:48 PM

@DF96
I am not a student in any institute so do not expect any Marks.

@SY, jcx
Thank you, I solved it using superposition theory.

R1 and R2 forms voltage divider for Non-Inv voltage. R3||RD forms Rg and R4 forms Rf. So Non-Inv, Inv output voltage will be

Vninv = V1*[R2/(R1+R2)]*[1+{R4/(R3||RD)}]
Vinv = V1*-(R4/R3)

Vout = Vninv + Vinv

 zigzagflux 10th October 2011 06:22 PM

Would you not want Vout in terms of V1 ?

 DF96 10th October 2011 06:49 PM

Quote:
 Originally Posted by sameerdhiman I am not a student in any institute so do not expect any Marks.
Good. Sorry for jumping to conclusions, but your question looked like homework.

I'm not certain that your result is correct. I would expect to see two simultaneous equations involving Vin and Vout, which you then invert to get Vout in terms of Vin. What is RD?

 sameerdhiman 10th October 2011 08:17 PM

Sorry, R5=RD (In practical circuit R5 will be variable resistor e.g. JFET or LDR)

I've verified the equation with LTSpice.

If you any other equation/solution please post that.

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