10 Essential Op-Amp Circuits Every Engineer Should Know

If you’ve spent any time designing analog circuits, you know that operational amplifiers are absolutely everywhere. From the audio preamplifier in your guitar pedal to the sensor conditioning circuit on a medical device, op amp circuits form the backbone of analog signal processing. I’ve been designing PCBs for over a decade, and I can tell you that mastering these ten configurations will cover probably 90% of the op-amp applications you’ll encounter in real-world projects.

The beauty of op-amps lies in their versatility. With just a handful of external resistors and capacitors, you can build amplifiers, filters, comparators, oscillators, and mathematical function blocks. In this guide, I’ll walk you through ten essential op-amp circuits that every engineer should have in their toolkit, complete with practical design tips and the formulas you’ll actually use.

Why These 10 Op Amp Circuits Matter

Before we dive into each circuit, let me explain why I selected these particular configurations. These aren’t just academic exercises; they’re the circuits I reach for again and again in production designs. Whether you’re conditioning a sensor signal, driving an ADC, mixing audio signals, or building a power supply monitor, these circuits deliver reliable, predictable results.

Op Amp Circuit Fundamentals to Remember

Before we examine each configuration, let’s review the two golden rules that make op-amp analysis manageable. Assuming negative feedback and the op-amp operating within its linear region:

Rule 1: No current flows into the op-amp inputs (infinite input impedance)

Rule 2: The op-amp adjusts its output to make both inputs equal (virtual short)

These rules vastly simplify circuit analysis and allow you to quickly derive gain equations for almost any op-amp configuration.

1. Voltage Follower (Unity Gain Buffer)

The voltage follower is the simplest op-amp circuit you can build. It requires no external components other than the op-amp itself, and its gain is exactly 1. So why bother?

How It Works

The output connects directly to the inverting input, creating 100% negative feedback. Since the op-amp forces both inputs to be equal, and the non-inverting input receives the input signal, the output exactly follows the input.

Gain Formula: Av = 1

Voltage Follower Specifications

Practical Applications

The voltage follower’s real power is impedance transformation. Consider this scenario: you have a resistive sensor connected through a voltage divider. If you connect a low-impedance load directly, the loading effect will mess up your carefully calculated voltage ratio. Insert a voltage follower between the divider and the load, and problem solved.

I use voltage followers extensively when interfacing high-impedance sources like piezoelectric sensors or pH probes with ADC inputs. They’re also essential for driving long cables without signal degradation.

Pro Tip: Don’t forget that even though the voltage gain is 1, the current-driving capability improves dramatically. That’s often exactly what you need.

2. Inverting Amplifier Circuit

The inverting amplifier is probably the most commonly taught op-amp configuration, and for good reason. It’s simple to analyze, provides predictable gain, and works reliably in countless applications.

Circuit Operation

The input signal connects to the inverting input through an input resistor (Rin). A feedback resistor (Rf) connects the output back to the inverting input. The non-inverting input is grounded.

Gain Formula: Av = -Rf / Rin

The negative sign indicates that the output is 180° out of phase with the input.

Inverting Amplifier Design Parameters

Design Considerations

The input impedance of an inverting amplifier equals Rin, which is often its main limitation. If your source has significant output impedance, this will affect your gain calculation. For high-impedance sources, you might need a buffer stage first.

One common mistake I see is forgetting that high-value resistors can introduce noise. Try to keep resistor values between 1kΩ and 100kΩ for most applications. If you need higher gain, consider cascading stages rather than using extremely high resistance values.

When integrating op-amp circuits into complex systems—particularly those involving digital signal processing with FPGAs like the Altera FPGA series—proper level shifting and impedance matching become critical for clean signal acquisition.

3. Non-Inverting Amplifier Circuit

When you can’t tolerate phase inversion, or when you need very high input impedance, the non-inverting amplifier is your go-to choice.

How the Circuit Works

The input signal connects directly to the non-inverting input. A voltage divider made of Rf and R1 connects between the output and ground, with the junction feeding back to the inverting input.

Gain Formula: Av = 1 + (Rf / R1)

Notice that the minimum gain is always 1 (when Rf = 0), so you cannot make a non-inverting attenuator using this configuration.

Non-Inverting vs Inverting Comparison

Why Choose Non-Inverting?

The non-inverting amplifier’s input impedance is essentially the op-amp’s input impedance, which can be gigaohms for FET-input devices. This makes it perfect for buffering high-impedance sensors without loading them.

I frequently use non-inverting amplifiers in sensor conditioning circuits where maintaining signal phase is important, such as in feedback control systems where an accidental 180° phase shift could cause oscillation.

4. Summing Amplifier Circuit

Need to combine multiple signals into one? The summing amplifier, also called an adder circuit, does exactly that. It’s the foundation of audio mixers and is used extensively in analog computing.

Inverting Summing Amplifier

The inverting summer is more popular because you can add any number of inputs without changing resistor values. Each input connects to the inverting input through its own input resistor.

Output Formula: Vout = -Rf × (V1/R1 + V2/R2 + V3/R3 + …)

If all input resistors are equal (R1 = R2 = R3 = R), the formula simplifies to:

Vout = -(Rf/R) × (V1 + V2 + V3 + …)

Summing Amplifier Applications

Practical Design Notes

One thing I always keep in mind is that the virtual ground at the inverting input means all inputs are effectively isolated from each other. This prevents interaction between input sources, which is crucial in audio mixing applications.

For a clean audio mixer, use 1% tolerance metal film resistors and consider adding input coupling capacitors to block DC from each source.

5. Differential Amplifier Circuit

The differential amplifier amplifies the difference between two input signals while rejecting any signal common to both inputs. This common-mode rejection is essential for dealing with noise.

Basic Differential Amplifier

Using a single op-amp with four resistors, you can build a basic difference amplifier. When R1 = R2 and Rf = Rg, the output is:

Vout = (Rf/R1) × (V2 – V1)

Differential Amplifier Performance

Limitations and Solutions

The single op-amp differential amplifier has a significant limitation: its input impedances aren’t equal or particularly high. If your source impedances aren’t matched, you’ll degrade CMRR.

For applications requiring better performance, consider the instrumentation amplifier configuration discussed later in this article. For the basic differential amplifier, use 0.1% precision resistors if you need good common-mode rejection.

6. Op-Amp Integrator Circuit

The integrator produces an output proportional to the integral of the input signal over time. It’s fundamental to analog computers, ramp generators, and control systems.

Integrator Circuit Design

Replace the feedback resistor in an inverting amplifier with a capacitor, and you have an integrator. The output voltage is:

Vout = -(1/RC) × ∫Vin dt

For a constant input voltage Vin, the output ramps linearly:

Vout = -(Vin × t) / RC

Integrator Component Selection

Practical Issues with Integrators

Pure integrators have a problem: any DC offset at the input, no matter how small, will cause the output to drift toward saturation over time. The solution is to add a high-value resistor (10 to 100 times R) in parallel with the integrator capacitor. This limits the DC gain while maintaining good integration at higher frequencies.

In control systems, I typically use integrators as part of PID controllers, where the proportional and derivative terms provide overall stability while the integrator eliminates steady-state error.

7. Op-Amp Differentiator Circuit

The differentiator outputs a voltage proportional to the rate of change of the input signal. It’s the mathematical complement to the integrator.

Differentiator Configuration

Swap the resistor and capacitor positions from the integrator, and you get a differentiator. The output is:

Vout = -RC × (dVin/dt)

Differentiator Characteristics

Why Differentiators Are Tricky

Here’s the challenge with differentiators: they amplify high frequencies. This means they’ll also amplify high-frequency noise, potentially causing oscillation or output noise that swamps the desired signal.

The solution is to limit the high-frequency gain by adding a resistor in series with the input capacitor and a small capacitor in parallel with the feedback resistor. This creates a “practical differentiator” that still performs differentiation over the frequency range of interest while remaining stable.

I use differentiators in rate-of-change monitoring applications, such as detecting rapid temperature changes in thermal protection circuits.

8. Op-Amp Comparator Circuit

While dedicated comparator ICs exist, op-amps can serve as comparators in many applications. The comparator compares two voltages and outputs a high or low level depending on which input is greater.

Basic Comparator Operation

With no feedback, the op-amp’s very high open-loop gain means even a small voltage difference between inputs will drive the output to saturation. If V+ > V-, the output goes to positive saturation (near V+). If V+ < V-, the output goes to negative saturation (near V-).

Adding Hysteresis (Schmitt Trigger)

For noisy inputs or slowly changing signals, a simple comparator can produce multiple transitions or “chatter.” The solution is hysteresis, implemented with positive feedback:

Hysteresis Voltage: VH = (Vsat × R1) / (R1 + R2)

Comparator Circuit Considerations

When to Use a Real Comparator

Op-amps designed for linear operation aren’t optimized for switching between rails. For high-speed or precision threshold detection, dedicated comparators like the LM311 or LM339 offer faster switching, better-defined output stages (often open-collector), and are designed for no-feedback operation.

9. Instrumentation Amplifier Circuit

When you need precision differential amplification with high input impedance and excellent CMRR, the instrumentation amplifier (in-amp) is the answer. It’s the go-to circuit for sensor interfaces in medical, industrial, and scientific applications.

Three Op-Amp Instrumentation Amplifier

The classic in-amp uses three op-amps: two input buffers and one difference amplifier. A single gain-setting resistor (RG) between the two buffer stages sets the overall gain:

Gain Formula: Av = 1 + (2R/RG)

Instrumentation Amplifier Advantages

Discrete vs Integrated In-Amps

You can build an instrumentation amplifier from three separate op-amps, but integrated solutions like the INA128, AD620, or INA333 offer much better performance because the internal resistors are laser-trimmed for matching.

For bridge sensor applications—strain gauges, load cells, pressure sensors—an integrated in-amp saves board space and provides performance that’s nearly impossible to achieve with discrete components.

10. Active Filter Circuits

Active filters use op-amps combined with resistors and capacitors to create frequency-selective circuits. Unlike passive RC filters, active filters can provide gain and sharp roll-off without using inductors.

Common Active Filter Types

Sallen-Key Low-Pass Filter

The Sallen-Key topology is popular for second-order filters. With equal resistors (R) and equal capacitors (C):

Cutoff Frequency: fc = 1 / (2π × R × C)

For a Butterworth (maximally flat) response, the gain should be set to 1.586.

Filter Design Parameters

Butterworth vs Chebyshev vs Bessel

Choose your filter type based on what matters most:

Butterworth: Maximally flat passband, good all-around choice

Chebyshev: Steeper roll-off but with passband ripple

Bessel: Best phase response, preserves waveform shape

For anti-aliasing filters before an ADC, Butterworth is usually the best balance. For audio crossovers where phase matters, Bessel filters preserve transient response.

Read more IC types:

ADC vs DAC: Analog-to-Digital and Digital-to-Analog Converters Guide

ASIC Design Guide: Application-Specific Integrated Circuits

Audio Amplifier ICs: Types, Selection Guide & Applications

BGA (Ball Grid Array) Package: Guide to High-Density ICs

Codec ICs Explained: Audio & Video Encoding/Decoding

Comparator IC: Working Principle, Types & Applications

CSP & WLCSP: Chip Scale Packaging for Miniaturization

Data Converter ICs: ADC, DAC & Sigma-Delta Converters

Digital Logic ICs: AND, OR, NOT Gates & Flip-Flops Guide

Digital PCB & IC Design: Logic Circuit Board Layout Guide

DIP (Dual In-Line Package): Classic IC Package Explained

DSP (Digital Signal Processor) IC Guide for Beginners

ECL (Emitter-Coupled Logic): High-Speed IC Technology

FPGA vs ASIC: Complete Comparison Guide [2025]

GaAs & SiGe: High-Frequency Semiconductor Technologies

IC Fabrication Technologies: CMOS, BiCMOS, TTL & More

IC Package Types: Complete Guide (DIP, SMD, QFP, BGA)

LDO vs switching regulatorLDO vs Switching Regulator: Which Voltage Regulator to Choose?

Microprocessor vs Microcontroller: Key Differences Explained

Mixed-Signal ICs: Bridging Analog and Digital Worlds

Operational Amplifier (Op-Amp) Basics: Complete Beginner’s Guide

PLL (Phase-Locked Loop) IC: Working Principle & Applications

Power Management IC (PMIC): Complete Selection Guide

RF IC Basics for Wireless Applications: A Practical Radio Frequency IC Guide

SiP (System in Package) & MCM: Advanced IC Packaging Guide

SMD vs Through-Hole Components: Complete Comparison

SOIC vs SSOP vs TSSOP: Small Outline Package Comparison

TTL vs CMOS Logic: Complete Comparison Guide

Types of Analog Integrated Circuits: Complete Guide

Types of Digital Integrated Circuits: Complete Guide

Types of Memory ICs: RAM, ROM, Flash, EEPROM Explained

Voltage Regulator ICs Explained: LDO, Linear, and Switching Types

What is a Microcontroller? Beginner’s Complete Guide

Bonus: Transimpedance Amplifier (Current-to-Voltage Converter)

While not in the original ten, the transimpedance amplifier deserves mention because it’s essential for photodiode interfaces and any application requiring current-to-voltage conversion.

Transimpedance Configuration

The current source (like a photodiode) connects to the inverting input, which is held at virtual ground. A feedback resistor (Rf) converts the current to voltage:

Vout = -Iin × Rf

Transimpedance Amplifier Stability

Photodiodes have significant junction capacitance, which can cause oscillation. A small feedback capacitor (Cf) parallel to Rf stabilizes the circuit:

Recommended Cf: Start with a value that creates a pole at about the unity-gain frequency of the op-amp

For low-light applications requiring high gain (large Rf), use a FET-input op-amp with low bias current to minimize offset.

Selecting the Right Op-Amp for Your Circuit

The best circuit design can be ruined by choosing the wrong op-amp. Here’s a quick guide to matching op-amp parameters to circuit requirements:

Op-Amp Selection Criteria by Application

Common Design Mistakes to Avoid

After reviewing countless op-amp circuits (including my own early disasters), here are the mistakes I see most often:

1. Forgetting bypass capacitors: Every op-amp needs a 0.1µF ceramic capacitor between each supply pin and ground, placed as close as possible to the IC.

2. High-impedance nodes without protection: A 10MΩ feedback resistor combined with stray capacitance creates a noise antenna. Consider guarding techniques or shielding.

3. Ignoring gain-bandwidth product: If your op-amp has a 1MHz GBW and you set the gain to 100, your bandwidth is only 10kHz. Plan accordingly.

4. Not accounting for input bias current: In high-impedance circuits, bias current through source resistance creates offset voltage. Add a compensating resistor when needed.

5. Single-supply headroom issues: Many op-amps can’t swing to the rails. Make sure your signal has adequate headroom above ground and below the supply.

Useful Resources for Op-Amp Design

Manufacturer Documentation

Design Tools

TINA-TI: Free SPICE simulator from Texas Instruments with extensive component library

LTspice: Free simulator from Analog Devices with excellent op-amp models

FilterPro (TI): Active filter design software

Analog Filter Wizard (ADI): Web-based filter design tool

Recommended Books

“Op Amps for Everyone” – Texas Instruments Design Reference (free PDF)

“IC Op-Amp Cookbook” by Walter Jung – Classic comprehensive guide

“Photodiode Amplifiers: Op Amp Solutions” by Jerald Graeme – Essential for transimpedance design

FAQs About Op Amp Circuits

Can I use any op-amp for any of these circuits?

Technically yes, but performance varies dramatically. A general-purpose op-amp like the LM741 will work for basic demonstrations, but for production designs, match the op-amp specifications to your requirements. Consider parameters like gain-bandwidth product, input offset voltage, bias current, noise, and supply voltage range.

Why does my op-amp circuit oscillate?

Oscillation usually indicates insufficient phase margin. Common causes include capacitive loading on the output, high source impedance, or operating near the op-amp’s unity-gain frequency with significant phase shift. Solutions include adding a small feedback capacitor, using a series output resistor, or choosing an op-amp specifically designed for the application.

What’s the difference between an op-amp used as a comparator and a dedicated comparator?

Op-amps are designed for linear operation with negative feedback and include internal compensation that limits switching speed. Dedicated comparators have push-pull or open-collector outputs designed for fast switching, no internal compensation (since they don’t need it), and often include hysteresis or latch inputs. For high-speed or precision threshold detection, always use a dedicated comparator.

How do I choose between inverting and non-inverting amplifier configurations?

Use non-inverting when you need very high input impedance or when phase preservation matters. Use inverting when you need a virtual ground at the input, want to sum signals, or need gain less than 1 (attenuation). The inverting configuration also allows gain of zero, which the non-inverting cannot achieve.

Can I cascade multiple op-amp stages?

Absolutely, and it’s often the best approach for achieving high gain or complex transfer functions. Each stage provides additional filtering, and keeping individual stage gains moderate improves overall bandwidth. Just ensure that each stage’s output can drive the next stage’s input without loading issues, and watch your power supply headroom.

PCB Layout Tips for Op-Amp Circuits

Good schematic design means nothing if your PCB layout introduces problems. Here are the layout practices I follow for reliable op-amp circuits:

Power Supply Considerations

Signal Integrity Guidelines

For precision circuits, keep high-impedance nodes short and use guard traces. A guard trace is a driven shield at the same potential as the node being protected, which eliminates leakage currents from adjacent traces.

In transimpedance amplifiers, minimize the area of the feedback loop to reduce noise pickup. Route the feedback resistor directly across the op-amp package if possible.

For high-frequency circuits, remember that even short traces have inductance. Keep trace lengths equal for differential signals, and consider controlled-impedance routing if your signal bandwidth exceeds 10MHz.

Thermal Management

High-current op-amps (audio power amps, for example) need thermal relief. Use thermal vias under the device and provide adequate copper area for heat spreading. Check the datasheet’s thermal resistance specifications and calculate your expected junction temperature.

Understanding Op-Amp Specifications Deep Dive

Selecting the right op-amp requires understanding key datasheet parameters. Let me walk through the specifications that matter most for circuit design.

DC Parameters

Input Offset Voltage (Vos): The voltage needed between inputs to force zero output. For precision circuits, look for op-amps with µV-level offset. Auto-zero or chopper-stabilized op-amps like the LTC2050 offer exceptional offset performance.

Input Bias Current (Ib): Current flowing into (or out of) the input terminals. For CMOS op-amps, this is typically picoamps, but bipolar op-amps can have nanoamp to microamp levels. This current creates voltage drops across source resistances.

Input Offset Current (Ios): The difference between the two input bias currents. This matters when source impedances aren’t equal, as it creates differential offset.

AC Parameters

Gain Bandwidth Product (GBW): The product of gain and bandwidth is approximately constant. A 1MHz GBW op-amp at gain of 10 has about 100kHz bandwidth.

Slew Rate: Maximum rate of change of the output voltage. If your signal frequency and amplitude require faster slewing than the op-amp can provide, you’ll see distortion. Calculate required slew rate as 2πfVpeak.

Phase Margin: Indicates stability with feedback. Values above 45° are generally stable; 60° or more is preferred.

Key Specifications Summary Table

Real-World Application Examples

Let me share some practical op-amp applications from actual projects to illustrate how these circuits work together.

Example 1: Temperature Measurement System

For monitoring temperature in an industrial controller, I designed a signal chain starting with a thermocouple. The millivolt-level thermocouple signal went through:

1. Instrumentation amplifier (INA128) with gain of 100
2. Active low-pass filter (2nd-order Sallen-Key, fc = 10Hz) to remove 50/60Hz interference
3. Voltage follower to drive the ADC input

The in-amp provided high CMRR to reject ground loop noise, the filter removed power line interference, and the buffer ensured the ADC saw a low-impedance source.

Example 2: Audio Mixer Design

A four-channel audio mixer used the following architecture:

1. Four non-inverting amplifiers as input buffers with adjustable gain
2. Inverting summing amplifier to combine all channels
3. Unity gain inverter to restore correct phase
4. Active band-pass filter for tone control (adjustable with potentiometers)

The key insight was using the summing amplifier in inverting mode, which allowed adding an unlimited number of channels without recalculating resistor values.

Example 3: Photodiode Light Meter

A light intensity meter used:

1. Transimpedance amplifier with 1MΩ feedback resistor
2. Logarithmic amplifier stage for extended dynamic range
3. Active low-pass filter to smooth the output
4. Non-inverting amplifier to scale for ADC full-scale

The logarithmic stage was critical because light intensity varies over several orders of magnitude, and a log response matched human perception better than a linear response.

Troubleshooting Op-Amp Circuits

When your circuit doesn’t work, systematic troubleshooting saves hours of frustration. Here’s my approach:

Common Problems and Solutions

Step-by-Step Debugging Process

Step 1: Verify power supply voltages at the op-amp pins (not just the source)

Step 2: Check that bypass capacitors are present and properly connected

Step 3: Measure DC operating points at all nodes

Step 4: Apply a simple DC or low-frequency signal and trace through the circuit

Step 5: Use an oscilloscope to look for oscillation or noise

Step 6: Temporarily reduce gain to see if the circuit works at lower performance

When All Else Fails

Sometimes the issue is a fundamental design problem. Go back to simulation and compare measured results to simulated behavior. If simulation works but hardware doesn’t, focus on layout issues, component tolerances, or thermal effects.

Conclusion

These ten op amp circuits represent the foundation of analog circuit design. Master them, and you’ll have the tools to tackle everything from simple sensor interfaces to complex signal processing chains. The key is understanding not just the gain equations but the practical considerations: when to use each topology, what limitations to watch for, and how component selection affects performance.

Throughout this guide, we’ve covered the essential op-amp configurations—from simple voltage followers and inverting amplifiers to sophisticated instrumentation amplifiers and active filters. Each circuit has its strengths and ideal applications, and knowing when to use which configuration is as important as understanding how they work.

Remember that op-amp applications extend far beyond these basic configurations. As you combine and modify these building blocks, you’ll discover solutions to problems you haven’t even encountered yet. Start with simulation (LTspice is free and excellent), breadboard your designs to verify operation, and always check the actual performance against your calculations.

The operational amplifier remains one of the most powerful tools in an engineer’s arsenal. Whether you’re designing audio equipment, sensor interfaces, control systems, or signal processing chains, these ten circuits will serve you well. Keep this guide handy as a reference, and don’t be afraid to experiment—that’s how real learning happens.

With these ten circuits in your toolkit, you’re well-equipped to handle the analog challenges that come your way. The next time you face a signal conditioning problem, an amplification requirement, or a filtering need, you’ll know exactly which op-amp configuration to reach for.