3.3
Op-amps inversores e não inversores
Em um amplificador inversor, a tensão de entrada é conectada através de um resistor ao terminal inversor. Enquanto isso, o terminal não inversor é ate…
O amplificador inversor conecta a tensão de entrada através de um resistor ao terminal inversor, aterra o terminal não inversor e possui um resistor de feedback entre os terminais inversor e de saída.
Ao aplicar KCL e assumir que o amplificador operacional é ideal, a expressão de ganho é determinada.
Os amplificadores inversores invertem a polaridade do sinal de entrada enquanto o amplificam, tornando-os úteis para cancelamento de ruído.
O microfone seleciona o sinal de ruído de entrada e inverte o sinal no circuito de cancelamento para eliminar o ruído.
Os amplificadores operacionais invertidos têm aplicações no processamento de áudio para amplificação, conversão e filtragem de sinal.
Os amplificadores não inversores têm a tensão de entrada aplicada diretamente ao terminal não inversor, um resistor entre o terra e o terminal inversor e um resistor para feedback negativo.
A aplicação de KCL no terminal inversor e a substituição dos valores de tensão fornecem uma expressão para o ganho de tensão.
Se o resistor de realimentação estiver em curto-circuito ou se o resistor de entrada estiver em circuito aberto, o ganho se torna unidade, criando um seguidor de tensão.
Eles convertem entradas de alta impedância em saídas de baixa impedância, permitindo a transferência eficiente de sinal para cargas de baixa impedância.
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.