Name: dft through the unit circle
Uploaded: 2024-09-26T13:17:11.000Z
Duration: 1 min 20 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Physical Science

waves-and-their-applications-in-technologies-for-information-transfer

Waves and Their Applications in Technologies for Information Transfer

HS-PS4-2

Relation of DFT to z-Transform

La transformée de Fourier discrète (DFT) analyse le contenu fréquentiel des signaux à temps discret.
Il mappe la séquence temporelle discrète échantillonnée à N à sa séquence fréquentielle discrète, où k représente l’indice de fréquence de 0 à N moins un.
Pour une suite à temps discret, la transformée z est définie en additionnant les termes de la séquence multipliés par les puissances de l’inverse de z.
Considérons la transformée z d’une suite discrète. Pour une suite causale, la transformée z se simplifie en une somme finie.
En échantillonnant la transformation z en des points équidistants sur le cercle unité, représentés par des exponentielles complexes, ces valeurs sont substituées dans la transformation z.
L’expression résultante correspond à la définition de la DFT, montrant que la DFT de la séquence est une version échantillonnée de sa transformation z sur le cercle unité.
La DFT est une version échantillonnée de la transformée z évaluée à des points spécifiques du cercle unitaire dans le plan complexe, reliant les séquences du domaine temporel à leurs représentations dans le domaine fréquentiel.
Cela montre que la DFT est un cas spécifique de la transformée z évaluée sur le cercle unité.

relation entre la dft et la transformée en z

La transformée de Fourier discrète (DFT) est un outil essentiel pour analyser le contenu fréquentiel des signaux à temps discret. Elle convertit une séquence de N échantillons du domaine temporel en sa séquence correspondante dans le domaine fréquentiel, où chaque échantillon représente une composante fréquentielle spécifique.

Pour comprendre le fonctionnement de la DFT, il est utile de considérer la transformée en z, qui est une méthode de représentation de séquences discrètes dans le domaine fréquentiel complexe. La transformée en z consiste à additionner les termes de la séquence, chacun multiplié par la puissance d'un nombre complexe. Pour les séquences qui commencent à un moment précis dans le temps et progressent vers l'avant (séquences causales), la transformée en z peut être exprimée comme une somme infinie ou finie, selon la longueur de la séquence.

En évaluant la transformée en z à N points également espacés autour du cercle unité dans le plan complexe, les valeurs qui correspondent aux coefficients de la DFT sont obtenues. Ces points sont les racines de l'unité, et l'évaluation de la transformée en z à ces points échantillonne efficacement le contenu en fréquence du signal à ces fréquences spécifiques.

Ainsi, la DFT peut être considérée comme une application spécifique de la transformée en z, axée sur l'évaluation de la séquence à ces emplacements précis sur le cercle unité. Ce processus traduit les séquences du domaine temporel en leurs équivalentes dans le domaine fréquentiel, ce qui permet d'analyser les différentes composantes de fréquence des signaux à temps discret.

La capacité de la DFT à révéler le contenu en fréquence des signaux souligne son importance dans le traitement du signal numérique et d'autres domaines connexes. Elle est largement utilisée dans des applications telles que le traitement du signal audio, l'analyse d'images et les systèmes de communication. De plus, la transformée de Fourier rapide (FFT) est un algorithme efficace couramment utilisé pour calculer la DFT, permettant le traitement en temps réel des signaux.

Relation entre la DFT et la transformée en Z

La transformée de Fourier discrète (DFT) analyse le contenu fréquentiel des signaux à temps discret.
Il mappe la séquence discrète du domaine temporel N-échantillonnée à son ...

Education

Enseignement

JoVE Core

Electrical Engineering

Génie électrique

Unit 1

Unité 1

z-Transform

Transformée en Z

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

dft through the unit circle

The Discrete Fourier Transform (DFT) shows how a discrete-time signal breaks into frequency parts. It takes N samples from the time domain and gives N values in the frequency domain. Each value represents one frequency component.

The z-transform helps explain this process. A z-transform represents a discrete sequence in the complex frequency domain by summing sequence terms multiplied by powers of a complex number. For causal sequences, which start at a fixed time and move forward, the sum can be infinite or finite, depending on the sequence length.

The DFT comes from evaluating the z-transform at N equally spaced points on the unit circle in the complex plane. These points are the roots of unity. Sampling the z-transform at these locations gives the DFT coefficients, which capture the signal’s frequency content at specific frequencies.

This view makes the DFT a special case of the z-transform. It turns a time-domain sequence into a frequency-domain sequence by checking the signal at exact points on the unit circle. That is why the DFT is so useful in digital signal processing and related fields.

The DFT is widely used in audio signal processing, image analysis, and communication systems. The Fast Fourier Transform, or FFT, is the efficient algorithm often used to compute the DFT. The FFT makes real-time signal processing possible in many applications.

DFT Through the Unit Circle

definition of z-transform

z-Transform for Discrete-Time Signals

The z-transform is a key math tool for analyzing discrete-time signals and systems. It is the discrete-time counterpart of the Laplace transform used for continuous-time systems. In signal and systems analysis, it works alongside the discrete-time Fourier transform. The z-transform changes a discrete-time signal into a power series with a complex variable, z. Each term in the series represents one sampling instant of the signal. This form makes it easier to study the signal in detail and solve...

region of convergence

Z-Transform Convergence and Stability

The z-transform and its Region of Convergence (ROC) are key ideas in discrete-time signals and systems. The z-transform is a mathematical tool for analyzing signals that change at separate time steps. Its values do not always converge, so the ROC identifies the range of complex numbers z where the transform is valid. The ROC can appear in different shapes in the complex plane. It may lie inside a circle, outside a circle, or within an annulus, which is the space between two circles. For an...

properties of the z-transform i

Z-Transform Rules for Signals

The z-transform rules for signals help students analyze discrete-time systems in digital signal processing. These rules turn time-domain changes into simpler expressions in the z-domain, which makes signal work easier to follow. Linearity is one key rule. It means the z-transform of a linear combination of two discrete-time signals equals the same linear combination of their individual z-transforms. This is useful when signals are added together or superimposed. Time-shifting is another...

properties of the z-transform ii

Z-Transform Rules for Sum and Convolution

The z-transform rules for sum and convolution help analyze discrete-time signals in signal processing. These rules show how changes in the time domain connect to the z-domain, which is the transform domain used for discrete-time systems. The accumulation property comes from the accumulated sum of a discrete-time signal. By applying the time-shifting property, the z-transform of the summed signal can be found from the z-transform of the original signal. The result is a simple multiplicative...

inverse z-transform by partial fraction expansion

inverse-z-transform-by-partial-fraction-expansion

Inverse z-Transform Using Poles and Residues

The inverse z-transform converts a function from the z-domain back to the time domain. One useful approach is the partial fraction method. It breaks a complex function into simpler fractions with distinct coefficients. The process starts by identifying the poles of the function. A pole is a value that makes the function grow without a finite limit. The function is then written in terms of these poles, and each pole adds one term to the partial fraction form. Next, the coefficients for each...

difference equation solution using z-transform

difference-equation-solution-using-z-transform

Solving Discrete-Time Responses with z-Transform

The z-transform helps solve discrete-time systems that are written as linear difference equations. These equations are common in digital signal processing and control systems. For a higher-order difference equation, you need the input signal and the initial conditions up to one term less than the order of the equation. The method also makes delayed signals easier to handle. A delay in time becomes a shift in the z-domain. An advance in time is shifted in the opposite direction. This link...

relation of dft to z-transform

The Discrete Fourier Transform (DFT) shows how a discrete-time signal breaks into frequency parts. It takes N samples from the time domain and gives N values in the frequency domain. Each value represents one frequency component. The z-transform helps explain this process. A z-transform represents a discrete sequence in the complex frequency domain by summing sequence terms multiplied by powers of a complex number. For causal sequences, which start at a fixed time and move forward, the sum can...

key terms and concepts

Learn how the DFT connects to the z-transform by sampling points on the unit circle, and see why this method matters in signal processing and the FFT.

DFT Through the Unit Circle | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

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HS-PS4-5

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HS-PS4-4

DFT Through the Unit Circle

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