Name: analyzing an op amp audio filter
Uploaded: 2024-04-11T12:48:50.000Z
Duration: 1 min 18 s
Channel: JoVE

Dans un système audio, le circuit de filtrage traite le signal audio amplifié d’un amplificateur, atténuant fortement les composantes du signal à basse fréquence.
Considérons le circuit de filtrage le plus simple composé d’un amplificateur opérationnel dans une configuration inverseuse couplée aux résistances R1 et R2 et au condensateur C1. Quel est le signal de sortie résultant d’un signal d’entrée connu ?
L'impédance du condensateur est calculée à l'aide de la fréquence angulaire dérivée de l'expression dans le domaine temporel de la tension d'entrée.
Le circuit équivalent dans le domaine fréquentiel représente le signal d’entrée sous forme polaire et les impédances Z1 et Z2. L’impédance Z2 correspond à la combinaison parallèle du condensateur C1 et de la résistance R2.
L'application de la loi du courant de Kirchoff et de la loi d'Ohm au nœud donne une équation nodale pour un ampli-op idéal. Cette équation, lorsqu’elle est réarrangée, indique que le rapport entre la tension de sortie et la tension d’entrée est égal au rapport négatif des impédances.
En substituant les valeurs connues et calculées dans cette équation, la tension de sortie est déterminée sous forme polaire, qui est ensuite convertie dans le domaine temporel.

circuits ca d'amplificateur opérationnel

Au sein d'un système audio, le circuit de filtrage joue un rôle central dans le traitement du signal audio amplifié provenant d'un amplificateur. Sa fonction principale est d'atténuer considérablement les composants du signal avec des fréquences plus basses, façonnant ainsi la sortie audio. Les opérations de ce circuit sont examinées, en se concentrant sur la configuration fondamentale du filtre. Cette configuration implique un amplificateur opérationnel disposé dans une configuration inverseuse couplée à des résistances ( R1 et R2) et un condensateur (C1).

<img alt="Figure1" src="/files/ftp_upload/15116/15116_PT_Figure_1.svg" style="text-align: center; height: 164px;" />

Face à un signal d’entrée connu, le défi consiste à déterminer le signal de sortie résultant. La première étape consiste à calculer l'impédance du condensateur, ce qui est obtenu en utilisant la fréquence angulaire dérivée de l'expression dans le domaine temporel de la tension d'entrée.

<img alt="Equation1" src="/files/ftp_upload/15116/15116_PT_Equation_1.svg" style="text-align: center; height: 36px;" />

En conséquence, l'analyse passe au domaine fréquentiel, où le signal d'entrée est représenté sous forme polaire aux côtés des composantes d'impédance Z1  et Z2. Z2  concerne explicitement la combinaison parallèle du condensateur C1 et de la résistance R2. Le cœur de l'analyse repose sur l'application de la loi du courant de Kirchhoff et de la loi d'Ohm à un nœud spécifique du circuit, formulant ainsi une équation nodale pour un ampli opérationnel idéal. Cette équation, une fois réorganisée, révèle un aperçu essentiel : le rapport entre la tension de sortie et la tension d'entrée est inversement proportionnel au rapport des impédances.

<img alt="Equation2" src="/files/ftp_upload/15116/15116_PT_Equation_2.svg" style="text-align: center; height: 36px;" />

Les valeurs connues et calculées sont habilement substituées dans cette équation pour dévoiler la tension de sortie sous forme polaire. Le résultat, représentant la tension de sortie, peut ensuite être transformé dans le domaine temporel, offrant ainsi une compréhension complète de la réponse du circuit de filtrage au signal d'entrée. Pour l'analyse, les propriétés idéales de l'ampli-op sont souvent supposées, y compris le principe selon lequel aucun courant n'entre dans l'une ou l'autre de ses bornes d'entrée et que la tension aux bornes de ses bornes d'entrée reste nulle.

Circuits CA d'amplificateur opérationnel

Dans un système audio, le circuit de filtrage traite le signal audio amplifié d’un amplificateur, atténuant fortement les composantes du signal avec de faibles ...

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JoVE Core

Electrical Engineering

Génie électrique

Unit 1

Unité 1

AC Circuit Analysis

Analyse des circuits CA

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

Op Amp AC Circuits

analyzing an op amp audio filter

An op amp audio filter shapes an amplified sound signal by strongly reducing the lower-frequency parts. In this circuit, the focus is on a basic filter setup used after an amplifier in an audio system. The filter uses an operational amplifier in an inverting arrangement with resistors R1 and R2 and a capacitor C1.

The analysis starts with a known input signal and asks for the output signal. To solve it, the capacitor impedance is found first. That requires the angular frequency from the time-domain form of the input voltage, so the work moves into the frequency domain.

In the frequency domain, the input signal is written in polar form. The impedances Z1 and Z2 are then used, with Z2 representing the parallel combination of capacitor C1 and resistor R2. At the same time, the ideal op amp assumptions are used. No current enters either input terminal, and the voltage across the input terminals is zero.

The final step is applying Kirchhoff's current law and Ohm's law at one node in the circuit. This creates a nodal equation for the ideal op amp. When that equation is rearranged, the output-to-input voltage ratio is shown to be inversely proportional to the impedance ratio. The known values are then substituted to find the output voltage in polar form, and that result can be converted back to the time domain for a full description of the filter response.

Analyzing an Op Amp Audio Filter

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An op amp audio filter shapes an amplified sound signal by strongly reducing the lower-frequency parts. In this circuit, the focus is on a basic filter setup used after an amplifier in an audio system. The filter uses an operational amplifier in an inverting arrangement with resistors R1 and R2 and a capacitor C1. The analysis starts with a known input signal and asks for the output signal. To solve it, the capacitor impedance is found first. That requires the angular frequency from the...

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Learn how an op amp audio filter reduces low-frequency signals. Follow impedance, nodal analysis, and polar-to-time-domain output calculations.

Analyzing an Op Amp Audio Filter | 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

Analyzing an Op Amp Audio Filter

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