What is an Op Amp? A Beginner’s Guide to Operational Amplifiers (Part 1)
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Time to read 6 min
What exactly is an op amp, and why does it matter in electronics?
If you've ever looked inside a circuit that amplifies sound, processes signals, or builds filters, chances are it contains one of the most widely used components in analog electronics: the operational amplifier, or simply op amp.
Despite the intimidating name, op amps are surprisingly approachable once you understand their basic role. Whether you're just starting to learn electronics or looking to brush up on the fundamentals, this guide breaks down the core concepts behind op amps in a clear and hands-on way.
Key Parameters of an Operational Amplifier
An operational amplifier , or op amp , is a high-gain electronic voltage amplifier with differential inputs and typically a single-ended output. The has five important terminals as specified in the symbolic diagram as shown:
The output voltage of the op-amp is determined by its two inputs. More specifically, it takes the voltage difference between two input pins (called the inverting and non-inverting inputs) and amplifies it to produce a much larger output voltage. This basic function makes it a core building block in analog circuits like amplifiers, filters, oscillators, and signal conditioners.
📌 Key Parameters of an Operational Amplifier
VCC, Positive supply voltage, typically +5V to +12V
VEE, Negative supply voltage or ground (e.g., 0V, −5V, −9V etc.)
v+, High-impedance input, ideally draws no current
v−, Also high-impedance, no current ideally flows in
vout is determined by differential voltage multiplied by open-loop gain
How Does an Op Amp Work? The Core Equation
At the heart of every op amp is a simple but powerful principle: it amplifies the difference between two input voltages, where the two inputs are:
- inverting input, denoted as v− or vn
- non-inverting input, denoted as v+ or vp.
And the output voltage, vout, is calculated by multiplying the differential voltage by the amplifier’s open-loop gain AoL.
In ideal cases, this gain is infinitely large (usually over 100,000 for practical devices), meaning that even a tiny difference between vp and vn can swing the output voltage close to its limits, either supply ceil or supply floor.
Because the open-loop gain of an op amp is extremely high, it is inherently unstable when used without feedback (to be discussed soon). In the example below, the op amp is powered by ±9V, with the non-inverting input grounded and the inverting input set to 1V. Since the inverting input is higher than the non-inverting, the output instantly hits the negative rail, going to −9V .
This behavior reflects the ideal op amp model. In practice, due to internal design limitations like output stage headroom, most op amps can’t reach the exact rail voltage. However, op amps specied as rail-to-rail are designed to get much closer, making them preferred in low-voltage or precision applications.
Negative Feedback
Negative feedback is what makes op amps truly useful in analog circuit design. Instead of letting the op amp swing uncontrollably to its limits, negative feedback connects part of the output voltage back to the inverting input . This simple idea changes everything.
Setting up negative feedback is actually very simple: you just connect a resistor (or a circuit network that connects output with input) from the output back to the inverting input. DO NOT connect to the non-inverting input since that will create a positive feedback.
This feedback path shown in the right figure's configuration creates a mechanism where the Op Amp continuously adjusts its output to reduce the voltage difference between the two inputs. As a result, in a properly designed feedback circuit, the op amp will always try to make v+ ≈ v−.
This condition where the two inputs are held at nearly the same voltage (despite not being directly connected) is known as the virtual short. It doesn’t mean the inputs are electrically shorted, but rather that the voltage difference between them is close to zero due to the action of negative feedback.
When an Op Amp is configured in negative feedback, the phenomenon of virtual short occurs and we have v+ = v-. This is crucially important for op-amp circuit analysis. You will see this immediately after when introducing inverting amplifer.
Two Typical Applications: Inverting and Non-inverting Amplifiers
Inverting Amplifier
The term "operational amplifier", or Op Amp in short, comes from its original role in analog computing, where it was used to perform mathematical operations like addition, subtraction, integration, and differentiation. Among these functional circuits, the inverting amplifier is one of the most fundamental examples. It offers a clean way to achieve both signal inversion and controlled voltage gain.
In a negative feedback configuration:
- The inverting input is held at virtual ground (0V) due to negative feedback.
- The input terminals draw zero current because of their extremely high input impedance.
- As a result, all input current flows through the feedback path, not into the op amp.
- Apply KVL around the feedback loop, to derive the gain expression.
Non-inverting Amplifier
The non-inverting amplifier is another fundamental op amp configuration, where the input signal is applied to the non-inverting input (v+), and the inverting input (v−) is connected to a voltage divider between the output and ground. Like the inverting amplifier, it relies on negative feedback to stabilize operation.
Here is an example that shows how an inverting amplifier handles a signal containing both a DC offset and an AC waveform. By applying the gain equation, we can see how the entire signal, with both DC and AC portions, is inverted and amplified according to the resistor ratio.
Key Takeaways from This Article
Op amps amplify the voltage difference between two inputs, and their behavior is governed by the equation: vout = Aol (vp − vn).
Negative feedback connects the output back to the inverting input through a resistor network, forcing the op amp to continuously adjust its output so that vp ≈ vn.
The concept of virtual short arises from negative feedback, where the two inputs are held at nearly the same voltage despite not being directly connected.
Two core configurations: inverting amplifier and the non-inverting amplifier, demonstrate how feedback and resistor ratios define gain.
Some FAQs on Op Amp Basics
What is the main purpose of using negative feedback in an op amp circuit?
Negative feedback forces the op amp to adjust its output so that the voltage difference between the inputs becomes nearly zero. This improves stability, accuracy, and bandwidth, while reducing distortion.
Why can’t I connect the feedback to the non-inverting input (+)?
Connecting feedback to the non-inverting input creates positive feedback, which drives the output toward the supply rails and can cause the circuit to latch or oscillate.
How do I choose resistor values for a basic op amp amplifier?
The gain of an inverting amplifier is determined by the ratio Rf/Rin. Choose values that provide the desired gain while keeping resistor noise and loading effects manageable, which is typically in the range of 1 kΩ to 1 MΩ.
Why does my op amp output not match the expected value?
This could be due to input offset voltage, limited output swing (especially if not using rail-to-rail op amps), power supply issues, or incorrect wiring. Checking each of these step-by-step usually resolves the problem.
We will dig more into this in future articles on this topic.
Can an op amp work without feedback?
Yes, but in open-loop mode the gain is extremely high, so even a tiny input difference drives the output to saturation. That’s why most practical op amp circuits use feedback to control gain.
What’s the difference between inverting and non-inverting configurations?
Inverting amplifiers reverse the signal’s polarity and set gain with −Rf/Rin. Non-inverting amplifiers keep the signal’s polarity and have gain set by 1+(Rf/Rin).
Daniel Cao
Daniel Cao is the founder of EIM Technology, where he creates hands-on, beginner-friendly electronics education kits that blend practical hardware with clear, structured learning. With a background in engineering and a passion for teaching, he focuses on making complex concepts accessible to learners from all disciplines.
