Name: op-amp gain, feedback, and saturation
Uploaded: 2025-05-22T09:06:14.000Z
Duration: 1 min 17 s
Channel: JoVE

Considere o modelo de circuito equivalente de um amplificador operacional. A seção de saída consiste em uma fonte controlada por tensão em série com a resistência de saída.
Na seção de entrada, v1 e v2 denotam tensões dos terminais inversores e não inversores para o terra, respectivamente.
A tensão de saída de um amplificador operacional é igual ao produto da diferença de tensão de entrada e o ganho de malha aberta.
Para pequenas diferenças de tensão, o amplificador operacional se comporta linearmente. Se a tensão exceder a tensão da fonte de alimentação, o amplificador operacional satura.
A combinação de tensão aplicada e feedback negativo garante que o amplificador operacional opere dentro de sua faixa linear.
Os amplificadores modernos têm grandes ganhos e resistência de entrada, permitindo que sejam aproximados como amplificadores operacionais ideais.
Um amplificador operacional ideal tem ganho infinito de malha aberta, resistência de entrada infinita e resistência de saída zero. Tanto as correntes do terminal de entrada quanto a tensão de deslocamento de entrada são zero em um amplificador operacional ideal.
Além disso, possui largura de banda infinita, permitindo amplificar sinais de qualquer frequência e taxa de variação infinita, significando sua capacidade de alterar a tensão de saída rapidamente ao longo do tempo.

características do amplificador operacional

O amplificador operacional, comumente conhecido no inglês como op-amp, é um componente de circuito eletrônico especialmente projetado. Sua finalidade é trabalhar em conjunto com outros elementos do circuito para executar uma operação de processamento de sinal definida. Considere um modelo de circuito equivalente de um amplificador operacional, conforme mostrado na Figura 1; a seção de saída compreende uma fonte controlada por tensão em paralelo com a resistência de saída Ro.

<img alt="Figure1" src="/files/ftp_upload/15077/15077_PT_Figure_1.svg" style="text-align: center; height: 166px;" />

Figura 1: O circuito equivalente do amplificador operacional não ideal

A Figura 1 mostra que a resistência de entrada Ri é igual à resistência equivalente de Thévenin observável nos terminais de entrada. Da mesma forma, a resistência de saída Ro corresponde à resistência equivalente de Thévenin discernível na saída. A tensão de entrada diferencial (vd) é calculada como a diferença entre a tensão do terminal não inversor em relação ao terra e a tensão do terminal inversor em relação ao terra.

O op-amp discerne a diferença entre essas duas entradas e amplifica-a pelo ganho A, gerando assim uma tensão que aparece na saída. Aqui, A representa o ganho de tensão em malha aberta - assim chamado porque significa o ganho do amplificador operacional na ausência de qualquer feedback externo da saída para a entrada.

O feedback é um conceito integral a ser compreendido ao estudar circuitos de amplificadores operacionais. O feedback negativo pode ser obtido alimentando a saída de volta ao terminal inversor do amplificador operacional. Quando existe um caminho de realimentação da saída para a entrada, a relação resultante entre a tensão de saída e a tensão de entrada é conhecida como ganho de malha fechada.

O op-amp tem suas limitações práticas. Uma dessas limitações é que a magnitude da sua tensão de saída não pode ultrapassar |VCC|. Essencialmente, a tensão da fonte de alimentação determina e restringe a tensão de saída. Dependendo da tensão de entrada diferencial, o amplificador operacional pode funcionar em um dos três modos: saturação positiva, região linear ou saturação negativa. Se for feita uma tentativa de aumentar vd além da faixa linear, o amplificador operacional atinge a saturação, produzindo vo = VCC ou vo = -VCC.

Características do amplificador operacional

Considere o modelo de circuito equivalente de um amplificador operacional. A seção de saída consiste em uma fonte controlada por tensão em série com a saída ...

Education

JoVE Core

Electrical Engineering

Engenharia Elétrica

Unit 1

Unidade 1

Operational Amplifiers

Amplificadores Operacionais

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

Characteristics of OpAmp

op-amp gain, feedback, and saturation

An operational amplifier, or op-amp, is an electronic circuit component used with other circuit parts to carry out a signal-processing task. It is often described with an equivalent circuit model. In that model, the output section includes a voltage-controlled source in parallel with the output resistance, R o.

The model also shows the input resistance, R i, which is the Thevenin equivalent resistance seen at the input terminals. The differential input voltage, v d, is the difference between the noninverting terminal voltage and the inverting terminal voltage, both measured relative to ground. The op-amp compares these two input voltages and amplifies the difference by the gain A to produce an output voltage.

A is called the open-loop voltage gain because it describes the op-amp without feedback from the output back to the input. Feedback is important in op-amp circuits. Negative feedback is created by connecting the output to the inverting terminal. When that feedback path exists, the output-to-input ratio is the closed-loop gain.

Op-amps also have practical limits. Their output voltage cannot exceed the magnitude of the supply voltage, |VCC|. The power supply sets this limit. Depending on the differential input voltage, the op-amp can operate in positive saturation, the linear region, or negative saturation. If v d is pushed beyond the linear range, the output saturates at either v o = VCC or v o = -VCC.

Op-Amp Gain, Feedback, and Saturation

operational amplifiers

Operational Amplifier Pinout and Signal Use

An operational amplifier, or op-amp, is a flexible circuit building block used in many electronic designs. It can act like a voltage-controlled voltage source, and it can also be used to create a voltage- or current-controlled current source. When resistors and capacitors are connected to its terminals, an op-amp can perform mathematical operations on signals. Op-amps are able to sum signals, amplify a signal, integrate it, or differentiate it. These features make them useful in practical...

design example: vintage mixing console

Op-Amp Preamp for a Vintage Console

A sound engineer designs an op-amp pre-amplifier for a vintage mixing console. The console’s output is too low for modern recording equipment, so the signal must be boosted before it can be used. The goal is to build a preamp that raises the audio level without changing the console’s character. The design must meet three clear requirements. It needs a gain of 10, an input impedance above 10 kilo-ohms so the console is not overloaded, and a frequency range that covers the full audio spectrum...

characteristics of opamp

An operational amplifier, or op-amp, is an electronic circuit component used with other circuit parts to carry out a signal-processing task. It is often described with an equivalent circuit model. In that model, the output section includes a voltage-controlled source in parallel with the output resistance, R o. The model also shows the input resistance, R i, which is the Thevenin equivalent resistance seen at the input terminals. The differential input voltage, v d, is the difference between...

inverting and non-inverting opamps

Op-Amp Gain: Inverting, Noninverting, Buffer

Operational amplifiers can be used as inverting, noninverting, and buffer amplifiers. In these circuits, the output voltage depends on the input voltage and the resistor setup around the op-amp. In an inverting amplifier, the input voltage is sent through a resistor to the inverting terminal. The non-inverting terminal is grounded, and a feedback resistor links the inverting terminal to the output. Using Kirchhoff's Current Law and an ideal op-amp model, the gain can be found. This circuit...

sum and difference opamps

Op-Amp Adders and Subtractors

Operational amplifiers can be wired to add or subtract signals. In these two op-amp setups, the summing amplifier combines several input signals into one output, while the difference amplifier compares two inputs and amplifies their difference. A summing amplifier is also called an adder. Input signals, such as audio signals, enter through input resistors. These resistors send currents through the feedback resistor, which produces an output voltage. Using Kirchhoff's current law and Ohm's Law,...

characteristics of practical op amps

Op Amp Noise Rejection and Buffering

Practical op amps are used to separate useful signals from unwanted noise. A difference amplifier should ideally amplify only the difference between two input signals. In real circuits, though, the output depends on both differential gain and common-mode gain. The common-mode rejection ratio, or CMRR, measures how well an op amp rejects common-mode signals. Common-mode signals are the same on both inputs. A higher CMRR helps an op amp ignore noise and amplify the wanted signal, such as music...

integrator and differentiator

Op-Amp Circuits in Cruise Control

Op-amp circuits are used in cruise control systems to help cars keep a constant speed. In these systems, operational amplifiers, or op-amps, can work as integrators and differentiators. Both circuits use resistors and capacitors, which makes them compact and cost-effective. An integrator circuit produces an output that is proportional to the integral of the input signal. It is made by replacing the feedback resistor in a standard inverting amplifier with a capacitor. The output and input...

cascaded op amps

Op Amp Stages in Series

Operational amplifiers can be connected in series as separate stages. This cascade works because op-amps have very high input resistance and very low output resistance. Those properties help each stage keep its input-output relationship while driving the next stage. In a cascaded op-amp circuit, the output of one stage becomes the input of the next. Each stage adds gain to the signal as it passes through. The overall gain is the product of the gain of each stage. This design can improve...

instrumentation amplifier

ECG Signal Amplifier Design

An ECG signal amplifier helps an electrocardiography machine measure the heart’s electrical activity. ECG electrodes detect tiny voltage changes on the skin that come from depolarization of the heart muscle during each heartbeat. These signals are in the microvolt range, so they can be easily hidden by noise or interference. To solve this problem, ECG machines use an instrumentation amplifier. This amplifier boosts the ECG waveform while reducing common-mode noise, which is interference that...

key terms and concepts

Learn how an op-amp compares input voltages, uses open-loop and closed-loop gain, and reaches positive or negative saturation when output limits are exceeded.

Op-Amp Gain, Feedback, and Saturation | 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

Op-Amp Gain, Feedback, and Saturation

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