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8th October 2011, 09:02 AM  #1 
diyAudio Member
Join Date: Nov 2009
Location: Ghaziabad (Delhi NCR)

Transfer Funtion of the given circuit ?
Hi,
Please give me the transfer function of the following circuit. Where R1,R2,R3,R4 and R5 are not equal.
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Regards, Sameer Dhiman 
8th October 2011, 12:00 PM  #2 
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Join Date: May 2007

How many marks will your teacher give me for the answer?

8th October 2011, 03:42 PM  #3 
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Join Date: Jun 2002
Location: USA, MN

You should check out a neat little program called sapwin
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8th October 2011, 04:20 PM  #4 
diyAudio Moderator

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.
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8th October 2011, 08:57 PM  #5 
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Join Date: Feb 2003
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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 
8th October 2011, 09:24 PM  #6 
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Join Date: Mar 2011
Location: St Louis, Mo

What method do you think is best for solving this problem, and how far along did you get?
Dale 
10th October 2011, 03:48 PM  #7 
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Join Date: Nov 2009
Location: Ghaziabad (Delhi NCR)

@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 NonInv voltage. R3RD forms Rg and R4 forms Rf. So NonInv, Inv output voltage will be Vninv = V1*[R2/(R1+R2)]*[1+{R4/(R3RD)}] Vinv = V1*(R4/R3) Vout = Vninv + Vinv
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Regards, Sameer Dhiman 
10th October 2011, 05:22 PM  #8 
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Join Date: Oct 2006
Location: Charlotte, NC

Would you not want Vout in terms of V1 ?

10th October 2011, 05:49 PM  #9  
diyAudio Member
Join Date: May 2007

Quote:
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? 

10th October 2011, 07:17 PM  #10 
diyAudio Member
Join Date: Nov 2009
Location: Ghaziabad (Delhi NCR)

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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Regards, Sameer Dhiman 
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