Name: diode bias and small-signal response
Uploaded: 2024-07-08T13:20:19.000Z
Duration: 1 min 18 s
Channel: JoVE

Dans un circuit de diode, une tension de polarisation continue entraîne le courant de la diode à travers une résistance, présentant un comportement exponentiel dans la courbe caractéristique courant-tension.
Lorsqu’un petit signal variant dans le temps est introduit, il se combine avec la tension de polarisation CC centrée autour du point Q.
Le terme exponentiel dans le courant de diode instantané total contribue à la fois au courant de polarisation et au courant du signal.
Si l’amplitude de la tension du signal est nettement inférieure à la tension thermique, la diode fonctionne dans un segment court et presque linéaire de la courbe caractéristique.
Sous cette approximation de petit signal, le terme exponentiel se simplifie.
En conséquence, le courant de diode devient la somme du courant de polarisation DC et du courant du signal.
La conductance des petits signaux de diode est définie comme le rapport entre le courant du petit signal et la tension du petit signal, qui est déterminé par la pente de la tangente à la courbe I-V au point Q.
L’inverse de la conductance des petits signaux de la diode, appelée résistance des petits signaux de la diode ou résistance incrémentale, est égale à la tension thermique divisée par le courant de polarisation.

modèle de diode à petit signal

Small-signal Diode Model

Lors de l'analyse du comportement des diodes dans les circuits, la relation entre le courant traversant une diode et la tension qui la traverse présente un intérêt particulier, en particulier lorsque l'on considère l'effet d'une tension de polarisation en courant continu (CC). Lorsqu'elle est appliquée, cette polarisation continue influence le point de fonctionnement de la diode, appelé point Q, autour duquel la caractéristique courant-tension (I-V) de la diode présente un comportement exponentiel. L'introduction d'un petit signal variable dans le temps au-dessus de cette polarisation facilite l'examen de la réponse de la diode aux fluctuations autour de ce point Q.
<img alt="Figure 1" src="/files/ftp_upload/15717/15717_Figure_1.svg" style="height: 250px;">
Lorsque l'amplitude de cette tension de signal supplémentaire reste considérablement inférieure à la tension thermique (V_T) de la diode, la réponse de la diode peut être considérée comme linéaire sur un court segment de sa courbe caractéristique. Ce scénario, appelé approximation des petits signaux, simplifie la relation exponentielle complexe en une relation linéaire plus gérable, permettant au courant instantané total de diode (i_D) d'être considéré comme une somme du courant de polarisation constant i_D (DC) et du courant de polarisation variable. courant de signal i_D(AC)
<img alt="Equation 1" src="/files/ftp_upload/15717/15717_Equation_1.svg" style="height: 24px;">
La mesure qui relie le courant du signal à la tension du signal est exprimée en termes de conductance, mesurée en mhos, et est appelée conductance des petits signaux de la diode. C'est la pente de la tangente à la courbe IV au point Q. À l’inverse, la résistance à petit signal ou incrémentale (r_d) de la diode est l’inverse de sa conductance. Il mesure la résistance de la diode aux petits changements de courant et est calculé en divisant la tension thermique par le courant de polarisation.
<img alt="Equation 2" src="/files/ftp_upload/15717/15717_Equation_2.svg" style="height: 46px;">
<img alt="Equation 3" src="/files/ftp_upload/15717/15717_Equation_3.svg" style="height: 46px;">
 Ces paramètres sont cruciaux pour la conception et l'analyse de circuits impliquant des diodes, en particulier dans les applications nécessitant un contrôle précis de l'amplification ou de l'atténuation du signal.

Modèle de diode à petit signal

Dans un circuit de diode, une tension de polarisation continue entraîne le courant de la diode à travers une résistance, présentant un comportement exponentiel dans la caractéristique courant-tension ...

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diode bias and small-signal response

Diode bias and small-signal response describe how a diode behaves when a steady DC voltage and a tiny changing signal act on the same circuit. The DC bias sets the diode’s operating point, or Q point. Around that point, the diode current and voltage follow an exponential I-V relationship.

A small time-varying signal can be added on top of the DC bias to study how the diode responds to small changes. When the signal voltage is much smaller than the thermal voltage, the diode’s behavior can be treated as linear over a short part of its curve. This is called the small-signal approximation.

With this approximation, the total diode current can be written as the sum of a constant DC part and a varying AC part. The signal current is linked to the signal voltage by the diode small-signal conductance, which is measured in mhos. This conductance is the slope of the tangent to the I-V curve at the Q point.

The inverse of conductance is the diode’s small-signal, or incremental, resistance, r d. It shows how much the diode resists small changes in current. It is found by dividing the thermal voltage by the bias current. These ideas are useful when analyzing and designing circuits that use diodes for signal amplification or attenuation.

Diode Bias and Small-Signal Response

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Ideal Diode I-V Curve and Rectification

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modeling-of-diode-forward-characteristics

Diode Forward Bias: I-V Curve and Models

Diode forward bias is analyzed with the current-voltage, or I-V, curve and two common circuit models. These models help describe how a diode behaves when current flows in the forward direction. They are useful for electronic circuit design and analysis. The exponential diode model is used when the source voltage rises above 0.5 volts. At that point, the diode current increases exponentially above the saturation current. The I-V curve shows this nonlinear response as the forward voltage...

small-signal diode model

Diode bias and small-signal response describe how a diode behaves when a steady DC voltage and a tiny changing signal act on the same circuit. The DC bias sets the diode’s operating point, or Q point. Around that point, the diode current and voltage follow an exponential I-V relationship. A small time-varying signal can be added on top of the DC bias to study how the diode responds to small changes. When the signal voltage is much smaller than the thermal voltage, the diode’s behavior can be...

modeling of diode reverse characteristics

modeling-of-diode-reverse-characteristics

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AC to DC Conversion with Bridge Diodes

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key terms and concepts

Learn how DC bias sets a diode Q point and how small AC signals can be modeled with conductance and incremental resistance for circuit analysis.

Diode Bias and Small-Signal Response | 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.

electrical engineering

Diode Bias and Small-Signal Response

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