IntermediateTopic 68 of 104Engineering Mathematics

Transfer functions

Ratio of output to input in the Laplace domain; characterises a linear system completely.

In depth

A transfer function G(s)=Y(s)/U(s) for zero initial conditions describes a linear system's input-output behaviour. Its poles set stability and speed, zeros shape the response. Series blocks multiply and feedback gives G/(1+GH).

Key points

  • Poles: denominator roots
  • Stable if poles in the left half-plane
  • Frequency response G(jω)
Example

G(s)=1/(τs+1) is a first-order low-pass.

Why it matters

A transfer function summarises a linear system in one expression, so you can predict its response to any input without re-solving the equations.

Where this is used

  • Designing a filter that meets a required cutoff and attenuation.
  • Predicting the output of a sensor amplifier chain.
  • Specifying the gain needed for a feedback loop.

Frequently asked questions

What is Transfer functions?

Ratio of output to input in the Laplace domain; characterises a linear system completely.

Why is it important to understand transfer functions?

A transfer function summarises a linear system in one expression, so you can predict its response to any input without re-solving the equations.

How do I get a transfer function from an ODE?

Take the Laplace transform of the equation with zero initial conditions, then divide the output transform by the input transform.

What does the denominator of a transfer function show?

Its roots, the poles, determine stability and natural behaviour of the system.

How is Transfer functions used in practice?

Typical applications include designing a filter that meets a required cutoff and attenuation, predicting the output of a sensor amplifier chain and specifying the gain needed for a feedback loop.

What should I learn before Transfer functions?

Study "Laplace transform" first (topic 67 of 104 in Engineering Mathematics). It covers the groundwork this topic builds on.

What are the key points of Transfer functions?

Poles: denominator roots. Stable if poles in the left half-plane. Frequency response G(jω).

Can you give an example of Transfer functions?

G(s)=1/(τs+1) is a first-order low-pass.

What comes after Transfer functions?

The next topic is "Systems of ODEs", which builds directly on this one.

How difficult is Transfer functions?

It is classed as Intermediate in Engineering Mathematics (topic 68 of 104). It is an intermediate topic. Work through the beginner topics in Engineering Mathematics first.

Learning path

Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.

Related topics