Doubt in defining transfer function

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Discussion Overview

The discussion revolves around the definition and implications of transfer functions in the context of circuit analysis, particularly regarding the treatment of initial conditions. Participants explore the mathematical foundations and practical applications of transfer functions, including their use in analyzing RC circuits.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions why transfer functions are defined with the assumption of zero initial conditions, noting that applying the Laplace transform to integro-differential equations typically includes initial condition terms.
  • Another participant agrees that initial conditions should be considered, suggesting that they are a special case in transfer function analysis and can be incorporated later in the analysis.
  • A participant requests a mathematical explanation using a simple RC circuit, expressing difficulty in resolving the equations for input-output relations when initial voltage is present on the capacitor.
  • One participant provides a link to examples of Laplace transforms, indicating a resource for further understanding.
  • A later reply acknowledges the definition of transfer functions as being convenient for calculations, suggesting that the zero initial condition is a matter of simplification rather than a strict necessity.
  • Another participant reiterates their request for a specific example involving a two-port RC network, emphasizing the need to include initial conditions in the transfer function analysis.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and implications of including initial conditions in transfer function definitions. There is no consensus on whether the simplification to zero initial conditions is justified or if it overlooks important aspects of circuit behavior.

Contextual Notes

The discussion highlights the limitations of transfer function definitions, particularly regarding the treatment of initial conditions and their impact on circuit analysis. Participants note that the mathematical steps involved in incorporating initial conditions remain unresolved.

bharath423
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why in a transfer function it is written by considering the initial condition to zero..
because if we individual write the integro-differential equation
and apply Laplace transform to them
and obtain a output/input relation,it definitely contains the initial condition terms in it also..
so removing these terms in the transfer function would definitely effect the result,but why do we not consider them while writing a transfer function??
 
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Well, if there is an initial condition, then it WOULD be taken into account. Your premise IS correct.

Especially when beginning circuit analysis, I recall circuit conditions often being assumed at zero...Also the initial conditions are simply a special case of the overall transfer function analysis...after determing the circuit response as a function of time, you can always restart the analysis at some t = a time...all it does is add a constant...I don't think that would be all that interesting.
 
Naty1 said:
Well, if there is an initial condition, then it WOULD be taken into account. Your premise IS correct.

Especially when beginning circuit analysis, I recall circuit conditions often being assumed at zero...Also the initial conditions are simply a special case of the overall transfer function analysis...after determing the circuit response as a function of time, you can always restart the analysis at some t = a time...all it does is add a constant...I don't think that would be all that interesting.

can u explain me with equations... i mean..take a simple RC circuit...with measuring,output voltage at the capacitor...say it has a initial voltage..
i had done it but i was not able to resolve the equation for input to output form..
 
thank you naty...but i came to know that transfer function is just defined like that to have zero intial conditions...so there isn't any particular reason to define it so,but they defined it only to get the ease of calculations..i think so..
 
but previously i was not asking to explain the impedance function to for capacitor..
anyway thank u for that link...
i was asking you to take two port RC network just like low pass filter..and asked for the transfer function i.e, input voltage(to RC network) to output voltage(at capacitor) with capacitor having some initial voltage..
so transfer function we will be left with a term containing initial values too..that was my problem actually..
:smile:
 

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