- 23rd May 2006, 09:17 #1

- Join Date
- Jan 2005
- Posts
- 21
- Helped
- 0 / 0
- Points
- 1,570
- Level
- 9

## difference between laplace and fourier transform

What are the differences?

I mean when we will make a decision "hmm now i must use laplace transform or now i must use fourier transform".

What are the absences in laplace transform so fourier design a new transfom?

I want to know these transforms' main idea, differences.

I am looking for your answers.

Thanks .

Sincerely;

- 23rd May 2006, 09:17

- 23rd May 2006, 10:15 #2

- Join Date
- Nov 2004
- Location
- Tamilnadu
- Posts
- 657
- Helped
- 36 / 36
- Points
- 5,970
- Level
- 18

## laplace vs fourier

for all signals we can have laplace transform but we can have fourier transform only for ceratin cases...Fourier transform needs certain conditions caled as Dirchlet conditions whereas laplace wont need anything like this....

1 members found this post helpful.

- 23rd May 2006, 11:07 #3

- Join Date
- Jan 2005
- Posts
- 21
- Helped
- 0 / 0
- Points
- 1,570
- Level
- 9

## difference between laplace and fourier

Originally Posted by**electronics_kumar**

Thanks...

- 23rd May 2006, 11:07

- 23rd May 2006, 11:45 #4

- Join Date
- May 2006
- Posts
- 4
- Helped
- 2 / 2
- Points
- 1,261
- Level
- 8

## fourier vs laplace

1 members found this post helpful.

- 23rd May 2006, 15:26 #5

- Join Date
- Dec 2004
- Location
- Iran
- Posts
- 152
- Helped
- 34 / 34
- Points
- 2,487
- Level
- 11

## laplace vs. fourier

in a simple expression:

**Laplas Transform**does a**real transformation**on**complex data**but**Fourier Tranform**does a**complex transformation**on**real data**.

it means:

L(σ1+jω1)=σ2+jω2

F(ω1)=|ω2|<ω2

at the presence of some condition you can take the Fourier transformation by placing jω instead of s in Laplas tranform.

- 23rd May 2006, 16:01 #6

- Join Date
- May 2006
- Posts
- 6
- Helped
- 2 / 2
- Points
- 1,209
- Level
- 7

## laplace vs fourier transform

theoretically..laplace represents σ + jw and is in all of the s-plane while in fourier its only in the jw axis of this s-plane..so basically we are setting the real part of the exponenntial to 0 and hence

it will give you the features for steady state for a sinusoidal input

and in the case of laplace it will tel u for rising or fallin sinusoidal.

i hope that shud answer ur question..

2 members found this post helpful.

- 24th May 2006, 04:27 #7

- Join Date
- Mar 2006
- Location
- Culiacán, Sinaloa, Mexico
- Posts
- 479
- Helped
- 68 / 68
- Points
- 3,875
- Level
- 14

## laplas transform

For a good explanation you can consult the book PLL, or Roland E. Best, that you can find in this forum.

As my colegees said Laplace transform translate f(t) to σ + ωi domain, while Fourier translate f(t) to w domain.

that means Laplace has information of time and frequency that's why we use to study transitory circuits. But Fourier dosn't have all the information i this case fase and wave forms only frecquency and amplitude.

- 24th May 2006, 10:07 #8

- Join Date
- Nov 2004
- Location
- Tamilnadu
- Posts
- 657
- Helped
- 36 / 36
- Points
- 5,970
- Level
- 18

## fourier versus laplace

Originally Posted by**shivamrules**

for lapalce transform, it is (σ + jw) when you are going to Fourier transform it become (0 + jw )..i mean σ =0 no attenuation in the system...