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1Définition

2L’échantillonage du signal

L’échantillonage du signal est la prise d’une valeur à un intervalle régulier de temps. L’intervalle entre deux valeurs s’appelle période d’échantillonage. On la note TeT_e (en secondes). On parle aussi de fréquence d’échantillonage fe=1Tef_e=\frac{1}{T_e} (en Hertz), qui correspond au nombre de valeurs prises chaque seconde.

Le quantum correspond au plus petit écart quantifiable (la “hauteur d’une marche”). On le note qq et son unité est celle du signal d’entrée (généralement le Volt).

La tension de pleine échelle ou tension de référence est la tension maximale quantifiable par le CAN. On la note VpeV_\text{pe} ou VrefV_\text{ref}.

Le nombre de valeurs que peut générer le convertisseur se note NN et dépend du nombre de bits nn du convertisseur. Ainsi : N=2nN=2^n.

On obtient la relation suivante : q=VpeN=Vpe2nq=\frac{V_\text{pe}}{N}=\frac{V_\text{pe}}{2^n}.

3Exemple de conversion

On donne en Figure 1 l’exemple d’un CAN de tension de référence 5 V fonctionnant sur 3 bits avec une fréquence d’échantillonage de 2 Hz.

La caractéristique du CAN est la courbe représentant la valeur numérique en sortie en fonction de la valeur analogique en entrée (Figure 2).

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<Figure size 768x432 with 2 Axes>

Figure 1:Signal analogique et signal numérisé.

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<Figure size 768x432 with 1 Axes>

Figure 2:Caractéristique du CAN.