3.3
Opamps inverseurs et non inverseurs
Dans un amplificateur inverseur, la tension d'entrée est connectée via une résistance à la borne inverseuse. Pendant ce temps, la borne non inverseuse…
L’amplificateur inverseur connecte la tension d’entrée via une résistance à la borne d’inversion, met à la terre la borne non inverseuse et dispose d’une résistance de rétroaction entre les bornes d’inversion et de sortie.
En appliquant KCL et en supposant que l’amplificateur opérationnel est idéal, l’expression du gain est déterminée.
Les amplificateurs inversés inversent la polarité du signal d'entrée tout en l'amplifiant, ce qui les rend utiles pour la suppression du bruit.
Le microphone sélectionne le signal de bruit d’entrée et inverse le signal dans le circuit d’annulation pour éliminer le bruit.
L’inversion des amplis opérationnels a des applications dans le traitement audio pour l’amplification, la conversion et le filtrage du signal.
Les amplificateurs non inverseurs ont la tension d’entrée appliquée directement à la borne non inverseuse, une résistance entre la masse et la borne inverseuse, et une résistance pour la rétroaction négative.
L’application de KCL à la borne inverseuse et la substitution des valeurs de tension permettent d’exprimer le gain de tension.
Si la résistance de rétroaction est court-circuitée ou si la résistance d’entrée est en circuit ouvert, le gain devient unitaire, créant un suiveur de tension.
Ils convertissent les entrées à haute impédance en sorties à faible impédance, ce qui permet un transfert efficace du signal vers des charges à faible impédance.
View the full transcript and gain access to JoVE Core videos
Q1: How does an inverting amplifier circuit configuration work?
An inverting amplifier connects the input voltage through a resistor to the inverting terminal, grounds the non-inverting terminal, and uses a feedback resistor between the inverting and output terminals. By applying Kirchhoff's Current Law and assuming an ideal operational amplifier, the voltage gain expression is derived. The gain depends solely on the external resistors: feedback resistance divided by input resistance.
Q2: What is the primary function of an inverting amplifier in signal processing?
Inverting amplifiers reverse the input signal's polarity while simultaneously amplifying it. This capability makes them valuable for noise cancellation applications, where the inverted signal eliminates unwanted noise in audio processing. They are also used for signal amplification, conversion, and filtering in various audio systems.
Q3: How does a non-inverting amplifier differ from an inverting amplifier?
A non-inverting amplifier applies input voltage directly to the non-inverting terminal, with a resistor connecting the inverting terminal to ground and a feedback resistor for negative feedback. Unlike inverting amplifiers, non-inverting amplifiers maintain signal polarity while amplifying. Applying KCL at the inverting terminal yields the voltage gain expression, which again depends on the feedback and input resistances.
Q4: What is a voltage follower and when is it used?
A voltage follower, or unity gain amplifier, forms when the feedback resistor is short-circuited or the input resistor is open-circuited in a non-inverting amplifier, resulting in a gain of one. It possesses high input impedance and functions as a buffer amplifier to segregate one circuit from another. This configuration efficiently converts high-impedance inputs to low-impedance outputs for signal transfer to low-impedance loads.
Q5: Why is input impedance important in non-inverting amplifier applications?
Non-inverting amplifiers have high input impedance, making them ideal intermediate-stage buffer amplifiers. This high impedance allows efficient signal transfer to low-impedance loads while minimizing loading effects on source circuits. The voltage follower configuration particularly leverages this characteristic to isolate circuit stages and preserve signal integrity across cascaded systems.
Q6: How does gain calculation differ between inverting and non-inverting amplifiers?
Both inverting and non-inverting amplifiers calculate gain using external resistor values through KCL analysis. For inverting amplifiers, gain equals negative feedback resistance divided by input resistance. For non-inverting amplifiers, gain equals one plus feedback resistance divided by input resistance. In both cases, the operational amplifier's characteristics of practical op amps determine the circuit's overall performance and accuracy.
Q7: What role does negative feedback play in op-amp amplifier circuits?
Negative feedback, established through the feedback resistor in both inverting and non-inverting configurations, stabilizes the amplifier gain and determines the amplification factor. The feedback path allows KCL analysis to derive predictable gain expressions independent of the op-amp's internal characteristics. This feedback mechanism ensures that gain depends solely on external resistor values, making amplifier performance reliable and controllable.