op amp calculator

What This Op Amp Calculator Does

This op amp calculator helps you quickly evaluate common amplifier designs without manually re-deriving formulas each time. It supports three practical configurations: inverting, non-inverting, and voltage follower (buffer). You can calculate:

• Closed-loop gain
• Expected output voltage from a given input
• Whether the output clips due to supply rail limits
• Feedback resistor values for a desired gain target

It is ideal for students, electronics hobbyists, and engineers doing fast design checks before simulation or prototyping.

Core Equations Used

1) Inverting Amplifier

Gain: Av = -Rf / Rin

Output: Vout = Av × Vin

The output is inverted, so it is 180° out of phase with the input.

2) Non-Inverting Amplifier

Gain: Av = 1 + (Rf / Rg)

Output: Vout = Av × Vin

The output is in phase with the input.

3) Voltage Follower

Gain: Av = 1

Output: Vout ≈ Vin

A buffer is useful when you need high input impedance and low output impedance without changing signal amplitude.

How to Use the Calculator

1. Select the circuit configuration.
2. Enter input voltage and resistor values.
3. Set supply rails (for clipping checks).
4. Click Calculate Output.

For resistor sizing, choose design mode, enter target gain and known resistor, then click Calculate Feedback Resistor.

Worked Examples

Example A: Inverting Stage

If Vin = 0.2 V, Rin = 10 kΩ, and Rf = 100 kΩ:

• Av = -100k / 10k = -10
• Vout = -10 × 0.2 = -2.0 V

With ±5 V rails, this is valid and not clipped.

Example B: Non-Inverting Stage

If Vin = 0.3 V, Rg = 4.7 kΩ, and Rf = 47 kΩ:

• Av = 1 + (47k / 4.7k) = 11
• Vout = 11 × 0.3 = 3.3 V

With a single 5 V supply and realistic output swing limitations, this may approach saturation depending on the op amp used.

Practical Design Notes

• Output swing is not ideal: Many op amps cannot reach exactly the supply rails.
• Bandwidth matters: Higher gain reduces usable bandwidth due to gain-bandwidth product.
• Slew rate limits large, fast signals: Distortion may appear even when DC gain math looks correct.
• Input common-mode range: The input must remain within limits for linear operation.
• Resistor choice: Very large values increase noise and bias-current errors; very small values waste power.

Common Mistakes to Avoid

• Mixing up inverting and non-inverting gain equations
• Ignoring polarity of gain in inverting designs
• Forgetting rail clipping checks
• Assuming every op amp is rail-to-rail
• Using unrealistic resistor values for the intended signal environment

FAQ

Can this replace SPICE simulation?

No. This calculator is a first-pass design tool. Use simulation and lab testing for final validation.

Does this include frequency compensation and stability analysis?

Not directly. It focuses on DC closed-loop gain and output-level estimation.

What resistor range is typically practical?

For many general-purpose circuits, values in the 1 kΩ to 100 kΩ range are common, but your optimal range depends on noise, source impedance, bandwidth, and power constraints.