What is the transfer function and when to use it ?

What is transfer fuction

DO you know what is transfer fuction, and why and when should we
use it in our circuit analysis?

Re: What is transfer fuction

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Re: What is transfer fuction

Transfer function can be rightly elucidated as the ratio of output from the system(circuit) to the applied input.

What is transfer fuction

Does it stand for the ratio of output singal to input,
with message including amplitude ans phase?

What is transfer fuction

The transfer funtion of a system is the relation of output and the input, this funtion can appear in Laplace domain , Z domain and Fourie domain.

What is transfer fuction

Why we need different domains to explain the transfer fuction? can you give more details, Joseleoardo?

Re: What is transfer fuction

The mapping of inputs to outputs is not always very simple to solve in the time domain. Ie they often involve higher order differentials and time delays which are generally a nightmare to solve if you've done D.Es. Consider a circuit containing capacitors and inductors and you would understand where the differentials comes from.

It was found that a transformation of the mapping function into another domain would convert differential equations into a linear one, and hence easily solvable. Coupled with the fact that the inverse transformation is equally easy, hence it's really a god-send tool if you've gone through it.

What is transfer fuction

There is different language used everywhere but keep in mind

1. (input * impulse response) = output

2. (output/input) = impulse response

3. (output/impulse response) = input

the last 2 are both called (impulse) transfer functions.

Re: What is transfer fuction

The transfer is simply the graph of voltage and current.

What is transfer fuction

Atransfer function is the relationship between the inputs and the outputs in a system. In a circuit ypu can have diferents relation current-vltage, voltage-voltage, all in terms of the circuit parameters.

Re: What is transfer fuction

You may find many answers and all are true but not total i think... If you forget for a while cirucits, motors etc. you may see Transfer Function (TF) as:

the Laplace transformation of the impulse response of a linear and time invariant system (and only for this). That means that it is the laplace trasformation of the state matrix [A B
C D ]
. Impulse response is the output of a system when its inputs are all impulses ( dirac delta). For a multiple input-multiple output system that is a matrix and for a single input-single output system that is only a function. If the system is linear and time varying then impulse response is a pracical tool for analysis since the output for every other inpu can be find by convoluting the new input with the impulse respone matrix(in general). Under such a thought we have defined Transfer Function since using laplace properties we take the convolution in time domain and make it a simple multiplication in frequency domain... So we define Transfer Function as the laplace transformation of impulse response of linear time invariant system since it helps us for an easy analysis...

h(t): impulse response
y(t)=Integral(u(t-T)h(T)dT= h(t)*u(t) (convolution) <---Lalplace--->
Y(s)=U(s)H(s) ==>
H(s)=Y(s)/U(s) the transfer function for a single input-single output system

Hope i have helped!!!

Re: What is transfer fuction

If you define an input for your circuit and an output for it , the relation between the output and input is a differential equation in time domain and a laplas transfer in frequency domain. In the system design it determins if your system satisfy the CASIN creteria (can be implement or not), about the stability of system, gain, and also about the function of circuit. for example if your transfer function has two pols, it trats as a lowpass filter, if it has on zero at zero frequency and two poles it trats like a bandpass filter.

Re: What is transfer fuction

you can find a fine description about this topic at:
fundamental networks theory by desor

Re: What is transfer fuction

savadi said:

for example if your transfer function has two pols, it trats as a lowpass filter.

if it has on zero at zero frequency and two poles it trats like a bandpass filter.

Click to expand...

That is not always necessarily true!

It is true for what you are saying but it is not true that if "IT has two poles" is a lowpass filter.
It maybe not be a filter afterall.

What is transfer fuction

Transfer function is the gain of a system in the frequency domain.

What is transfer fuction

The transfer function of a system is a relation between output of the system and input of the system. It can be in time or frequency domain. It can be relation between voltage-voltage, voltage-current, current-voltage, and current-current. Transfer function can be thought as the system response to certain input excitation. What kind of transfer function to use in the system design or analysis depends on the system characteristics and the problem you want to solve.

What is transfer fuction

The transfer function of the system (not necessarily a circuit) can be seen as the transform (could be in Fourier/frequency, Laplace or Z domains - I haven't sudied other transforms) of the time domain impulse response of the system.

Re: What is transfer fuction

For the best defination of Transfer Function,please read through SIGNALS AND SYSTEMS by B.P.LATHI......As far as i know this book gives the best explanation for any rudimentary concepts in signal processing.......He don't concentrates more on mathematical explanation rather on qualitative reasoning.If you cannot find this book,do intimate me i will give the explantion.It may be subjective but certainly not hypothetical

Re: What is transfer fuction

Transfer function gives the relation between input and output of a system. It is the laplace transform of the impulse response of the system. It is defined only for linear time invariant systems. It does not give any information about the physical structure of the system. And also it is not unique i.e. there may be many different systems with the same transfer function.

Re: What is transfer fuction

A transfer function tells what is the behavior of the system when an input goes thru it. It describes how is the output related to input. It can help you solve circuits, plot it's behavior in phase and frequency and it tells you about stability of the system. It can help you correct the errors in output thru feedback.