Op-Amp Circuit Builder: Master Operational Amplifier Configurations

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The op-amp calculator and circuit builder is an essential tool for electronics engineers, students, and hobbyists working with operational amplifiers. Whether you are designing inverting amplifiers, non-inverting amplifiers, summing circuits, or comparators, this interactive op-amp simulator provides real-time visualization of circuit behavior with animated waveforms and instant gain calculations.

Introduction

You wire up a textbook inverting amplifier with a gain of 100. The input is a clean 10kHz sine wave. The output should be a perfect inverted sine, 100 times larger. Instead, you see a rounded, phase-shifted mess that barely resembles the input. What went wrong?

The datasheet says the 741 has a gain of 200,000. In practice, that open-loop gain drops to about 100 at 10kHz because of the gain-bandwidth product. Your closed-loop gain of 100 is now fighting against an open-loop gain of only 100, and the negative feedback cannot do its job properly. The signal sees an amplifier that is running out of loop gain, and distortion appears.

In an ideal world, op-amps have infinite gain, infinite bandwidth, infinite input impedance, and zero output impedance. But real circuits use real op-amps, and experienced engineers find themselves constantly navigating the gap between ideal models and actual behavior. That gap is where debugging happens [1].

This interactive op-amp circuit builder offers six essential configurations: inverting amplifier, non-inverting amplifier, voltage follower, summing amplifier, difference amplifier, and comparator. Each configuration demonstrates different aspects of op-amp behavior, from phase inversion to signal addition. When you probe this node, the simulator shows real-time animated waveforms with visual indication of output saturation when signals exceed supply rails.

A key feature of this simulator is the ability to switch between ideal and real op-amp models. The ideal model assumes infinite gain, bandwidth, and input impedance. The real model (based on the classic 741 op-amp) incorporates gain-bandwidth product limitations, showing how high-gain configurations suffer reduced bandwidth. Circuit designers know this tradeoff intimately: gain and bandwidth are not independent, and your design choices determine where you spend your GBP budget.

How to Use This Simulation

In an ideal world, op-amps deliver exactly the gain your resistor ratio dictates. But real circuits have finite gain-bandwidth products, slew rate limits, and output saturation. This simulator exposes those boundaries so you can design around them before your prototype surprises you.

Configuration Selection

Input Parameters

Op-Amp Model Selection

The signal sees the difference between these models most clearly at high frequencies. An ideal inverting amp with gain of 100 works perfectly at 100 kHz. A real 741 at that configuration has only 10 kHz of useful bandwidth (GBP / gain = 1 MHz / 100).

Output Display

The waveform canvas shows input (green) and output (red) signals in real-time. When output would exceed supply rails, the display shows clipping to illustrate saturation. The statistics panel provides:

• Gain (Av): Closed-loop voltage gain (negative for inverting)
• Gain (dB): 20 times log10 of absolute gain
• Vout: Peak output voltage
• Input Impedance: What the signal source sees
• Bandwidth (f-3dB): Frequency where gain drops 3 dB (real model only)
• Status: Linear operation or clipping indication

Gain Presets

Tips for Exploration

When you probe this node in a real circuit, remember that your oscilloscope adds capacitive loading. The signal sees this as extra phase shift that can turn your stable amplifier into an oscillator at high gains.

1. Start in Ideal mode with the inverting configuration. Set gain to -10 and observe the clean phase inversion. This is textbook behavior.

2. Switch to Real (741) mode without changing anything else. If your frequency is above 100 kHz, you will see the output amplitude drop as you hit the GBP wall.

3. Increase Vin until the output clips. The waveform shows flat tops and bottoms at the supply rails. Real op-amps saturate about 1-2V below the rails, and the simulation reflects this.

4. Try the Voltage Follower. Notice gain is exactly 1, but output impedance is now very low. This is why followers drive cables and capacitive loads that would destabilize a high-gain stage.

5. Compare Summing and Difference configurations. Summing adds signals (great for audio mixing). Difference rejects common-mode noise (critical for instrumentation amps in noisy environments).

6. Use arrow keys for fine resistor adjustment. Left/right adjusts Rf, up/down adjusts Rin. Watch how gain changes in real-time.

Understanding Operational Amplifiers

What is an Op-Amp?

An operational amplifier is a DC-coupled high-gain electronic voltage amplifier with differential inputs. In its basic form, an op-amp amplifies the voltage difference between its two inputs (V+ and V-) by a very large factor (typically 100,000 or more in the open-loop configuration).

Ideal vs Real Op-Amp Characteristics

The datasheet says "2 megohms input impedance." In practice, that number varies with common-mode voltage, frequency, and temperature. When you probe this node at high frequencies, the input capacitance (around 1.4pF for a 741) starts to dominate, and your "high impedance" input becomes a low-impedance capacitive load. Experienced engineers find that real op-amp behavior requires reading beyond the first page of the datasheet.

Op-Amp Configurations

Inverting Amplifier

The inverting amplifier configuration provides a phase-inverted output signal with gain determined by the ratio of feedback to input resistance.

Gain Formula: $A_v = -\frac{R_f}{R_{in}}$

The negative sign indicates 180° phase inversion. The input impedance equals Rin, and the virtual ground concept makes analysis straightforward.

Characteristics:

• Output is inverted (180° phase shift)
• Gain can be less than, equal to, or greater than 1
• Input impedance equals Rin
• Virtual ground at inverting input

Non-Inverting Amplifier

The non-inverting configuration maintains signal phase while providing voltage gain.

Gain Formula: $A_v = 1 + \frac{R_f}{R_{in}}$

Characteristics:

• Output is in-phase with input
• Minimum gain is 1 (unity)
• Very high input impedance
• Commonly used for buffering

Voltage Follower (Buffer)

A special case of the non-inverting amplifier with 100% feedback.

Gain Formula: $A_v = 1$

Characteristics:

• Unity gain (no amplification)
• Extremely high input impedance
• Very low output impedance
• Ideal for impedance matching

Summing Amplifier

Combines multiple input signals with weighted addition.

Output Formula: $V_{out} = -R_f\left(\frac{V_1}{R_1} + \frac{V_2}{R_2} + \frac{V_3}{R_3}\right)$

Applications:

• Audio mixing
• Digital-to-analog conversion
• Signal averaging

Difference Amplifier

Amplifies the difference between two input signals while rejecting common-mode signals.

Output Formula: $V_{out} = \frac{R_f}{R_{in}}(V_2 - V_1)$

Applications:

• Instrumentation amplifiers
• Noise cancellation
• Bridge signal conditioning

Comparator

Operates in open-loop or positive feedback mode to compare two voltages.

Output: $V_{out} = V_{cc} \times sign(V_+ - V_-)$

The output saturates to the positive or negative rail based on which input is larger.

Key Parameters

Key Equations and Formulas

Closed-Loop Gain Equations

Inverting Amplifier: $A_v = -\frac{R_f}{R_{in}}$

Non-Inverting Amplifier: $A_v = 1 + \frac{R_f}{R_{in}}$

Where:

• Av = voltage gain (dimensionless)
• Rf = feedback resistance (Ω)
• Rin = input resistance (Ω)

Gain in Decibels

Formula: $A_{dB} = 20 \log_{10}|A_v|$

Example: A gain of 100 equals 40 dB.

Bandwidth Calculation

Formula: $f_{-3dB} = \frac{GBP}{|A_v|}$

Where:

• f-3dB = bandwidth at -3dB point (Hz)
• GBP = gain-bandwidth product (Hz)
• |Av| = magnitude of closed-loop gain

Output Saturation

Formula: $V_{out,max} \approx \pm(V_{cc} - 1.5V)$

For rail-to-rail op-amps: Vout,max ≈ ±Vcc

Learning Objectives

After completing this simulation, you will be able to:

1. Calculate the gain of inverting and non-inverting amplifier configurations
2. Design op-amp circuits for specific gain requirements
3. Predict when output clipping/saturation will occur
4. Understand the gain-bandwidth tradeoff in real op-amps
5. Select appropriate configurations for different applications
6. Analyze the effect of component values on circuit performance
7. Recognize the differences between ideal and real op-amp behavior

Exploration Activities

Activity 1: Investigating Inverting Gain

Objective: Understand how resistor ratio determines inverting amplifier gain

Setup:

• Select "Inverting" configuration
• Set Vin = 0.5V, Vcc = ±12V

Steps:

1. Set Rin = 10kΩ, Rf = 100kΩ
2. Observe gain = -10 and output waveform
3. Note the phase inversion (output opposite to input)
4. Change Rf to 50kΩ and observe gain = -5
5. Try Rf = 10kΩ for unity gain (-1)

Observe: The output amplitude is |gain| × input. The negative sign causes the waveform to be inverted.

Expected Result: With Rf/Rin = 10, the 0.5V input produces a 5V output (inverted).

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Activity 2: Non-Inverting vs Inverting Comparison

Objective: Compare the two fundamental amplifier configurations

Setup:

• Set Rin = 10kΩ, Rf = 90kΩ, Vin = 0.5V

Steps:

1. Select "Inverting" - observe gain = -9
2. Select "Non-Inverting" - observe gain = +10
3. Compare the output waveforms
4. Note the phase relationship in each case

Observe: Non-inverting always has gain ≥1. Inverting can have any gain magnitude but inverts phase.

Expected Result: Inverting: Av = -9, Non-inverting: Av = 1 + 9 = 10.

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Activity 3: Output Saturation and Clipping

Objective: Understand when and why op-amp output saturates

Setup:

• Inverting configuration
• Rin = 10kΩ, Rf = 100kΩ (gain = -10)
• Vcc = ±12V

Steps:

1. Set Vin = 0.5V - output is 5V (linear region)
2. Increase Vin to 1.0V - output should be 10V (near rails)
3. Increase Vin to 1.5V - observe clipping
4. Watch the "Status" indicator change to "CLIPPING!"
5. Increase Vcc to ±15V and observe clipping threshold change

Observe: The output cannot exceed approximately 95% of the supply rails. Signals beyond this are clipped flat.

Expected Result: With ±12V supply, clipping occurs when output exceeds ~±11.4V.

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Activity 4: Gain-Bandwidth Tradeoff

Objective: Observe how real op-amps trade bandwidth for gain

Setup:

• Non-inverting configuration
• Switch to "Real (741)" mode
• Vin = 0.5V, Freq = 1kHz

Steps:

1. Set gain = 10 (Rin = 10kΩ, Rf = 90kΩ)
2. Note bandwidth = 100 kHz
3. Increase gain to 100 (Rin = 1kΩ, Rf = 99kΩ)
4. Note bandwidth drops to 10 kHz
5. Compare to ideal mode (infinite bandwidth)

Observe: The gain-bandwidth product (GBP) is constant. Higher gain means lower bandwidth.

Expected Result: GBP = 1 MHz for 741. At gain 100, BW = 1MHz/100 = 10kHz.

Real-World Applications

Understanding op-amp circuits is essential across many fields:

1. Audio Electronics: Op-amps form the core of audio preamplifiers, mixers, equalizers, and headphone amplifiers. The inverting summing amplifier configuration is the basis for audio mixing consoles.

2. Instrumentation: Precision measurement systems use instrumentation amplifiers (built from op-amps) to amplify small sensor signals while rejecting common-mode noise. Applications include strain gauge bridges, thermocouples, and medical sensors.

3. Signal Conditioning: Before analog-to-digital conversion, signals often need amplification, filtering, and level shifting, all accomplished with op-amp circuits. Active filters using op-amps provide better performance than passive RC filters.

4. Power Supply Regulation: Voltage regulators use op-amps in feedback loops to maintain stable output voltage. The error amplifier compares output to a reference and adjusts the pass transistor.

5. Comparator Circuits: Zero-crossing detectors, window comparators, and Schmitt triggers use op-amps in comparator mode for threshold detection and signal conditioning.

Reference Data

Common Op-Amp ICs

Gain Configuration Quick Reference

Challenge Questions

Level 1: Basic Understanding

1. What is the gain of an inverting amplifier with Rin = 4.7kΩ and Rf = 47kΩ?

2. Design a non-inverting amplifier with a gain of exactly +5 using a 10kΩ input resistor.

Level 2: Intermediate

1. An op-amp circuit has ±15V supplies. What is the maximum input voltage for an inverting amplifier with gain = -20 before clipping occurs?

2. Calculate the bandwidth of a 741-based amplifier (GBP = 1MHz) configured for a gain of 50.

Level 3: Advanced

1. Design a summing amplifier that produces Vout = -(V1 + 2×V2 + 0.5×V3) using Rf = 100kΩ. What are R1, R2, and R3?

2. A sensor produces 0-50mV output. Design an amplifier to convert this to 0-5V for an ADC, accounting for a 1mV input offset in the op-amp.

Common Misconceptions

Misconception 1: "Op-amp gain is always very high"

Reality: Open-loop gain is indeed very high (~100,000), but closed-loop gain with feedback is precisely set by the resistor ratio. A non-inverting amplifier with Rf = Rin has a gain of only 2.

Misconception 2: "The output can swing to the supply rails"

Reality: Most op-amps cannot reach their supply voltages at the output. The output typically saturates 1-2V below the rails. Only "rail-to-rail" output op-amps can approach the supply voltages.

Misconception 3: "Higher bandwidth is always better"

Reality: Higher bandwidth can make circuits more susceptible to noise and oscillation. Choose bandwidth appropriate for your signal frequency. The 741's 1 MHz GBP is adequate for audio applications.

Misconception 4: "Ideal op-amp assumptions always apply"

Reality: Real op-amps have finite input impedance, non-zero output impedance, limited bandwidth, and input offset voltages. These non-idealities become significant in precision applications.

Summary

Operational amplifiers are fundamental building blocks enabling countless analog circuit designs. The key configurations (inverting, non-inverting, follower, summing, difference, and comparator) each serve specific purposes:

• Inverting amplifier: Phase-inverted gain, controlled input impedance
• Non-inverting amplifier: In-phase gain, high input impedance
• Voltage follower: Unity gain buffer, impedance transformation
• Summing amplifier: Weighted signal addition
• Difference amplifier: Common-mode rejection
• Comparator: Threshold detection

Key takeaways:

• Inverting gain = -Rf/Rin; Non-inverting gain = 1 + Rf/Rin
• Output saturates at approximately ±(Vcc - 1.5V)
• Bandwidth × |Gain| = Gain-Bandwidth Product (constant)
• Virtual ground concept simplifies inverting circuit analysis

Use this simulator to explore these configurations interactively. Adjust component values, observe waveforms, and build intuition for op-amp circuit design.

Frequently Asked Questions

What is the virtual ground concept? In an inverting configuration, negative feedback forces the inverting input to nearly the same voltage as the non-inverting input (0V when grounded), creating a virtual ground at the inverting input. This simplifies circuit analysis since the inverting input can be treated as at 0V [1].

Why use a voltage follower? Voltage followers provide unity gain with very high input impedance and low output impedance, ideal for buffering high-impedance sources (like sensors) before low-impedance loads. They prevent loading effects that would otherwise distort the signal [2].

What determines the gain-bandwidth product? GBP is set by the op-amp internal compensation capacitor and is a fixed characteristic of each op-amp model. For the classic 741, GBP = 1 MHz means gain × bandwidth always equals 1 MHz. Higher-speed op-amps have larger GBP values [1].

How do I avoid output saturation? Keep peak output below ~95% of supply rails. For ±12V supplies, limit output to ~±11.4V by choosing gain and input amplitude appropriately. The formula is: V_in_max = V_sat / |gain| [2].

When should I use inverting vs non-inverting? Use non-inverting for high input impedance and in-phase gain ≥1. Use inverting for controlled input impedance (equal to R_in), phase inversion, or when summing multiple signals [1].

References

1. MIT OpenCourseWare - 6.002 Circuits and Electronics. Available at: https://ocw.mit.edu/courses/6-002-circuits-and-electronics-spring-2007/
2. Electronics Tutorials - Operational Amplifier Basics. Available at: https://www.electronics-tutorials.ws/opamp/opamp_1.html
3. Texas Instruments - Op Amp Design Guide. Available at: https://www.ti.com/lit/eb/slod006b/slod006b.pdf
4. Analog Devices - Op Amp Applications Handbook. Available at: https://www.analog.com/en/education/education-library/op-amp-applications-handbook.html
5. Electronics Tutorials - Inverting Operational Amplifier. Available at: https://www.electronics-tutorials.ws/opamp/opamp_2.html
6. HyperPhysics - Operational Amplifier. Available at: http://hyperphysics.gsu.edu/hbase/Electronic/opamp.html

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