Calculator Inputs
Formula Used
Inverting gain: Av = -Rf / Rin
Non-inverting gain: Av = 1 + Rf / Rin
Noise gain: NG = 1 + Rf / Rin
Input high-pass cutoff: FL = 1 / (2 × pi × Req × Cin)
Closed-loop bandwidth: BW = GBW / NG
Feedback capacitor pole: Fcf = 1 / (2 × pi × Rf × Cf)
High-pass factor: HP = f / sqrt(f² + FL²)
Low-pass factor: LP = 1 / sqrt(1 + (f / FH)²)
Effective gain: Avf = |Av| × HP × LP
Required slew rate: SR = 2 × pi × f × VoutPeak
How to Use This Calculator
- Select inverting or non-inverting topology.
- Enter the input signal value and its voltage type.
- Add resistor, capacitor, load, supply, and op amp limits.
- Press the calculate button.
- Review gain, cutoff, phase, slew rate, and clipping checks.
- Use the CSV or PDF button to save the result.
Example Data Table
| Topology | Vin RMS | Frequency | Rin | Rf | Cin | GBW | Expected Use |
|---|---|---|---|---|---|---|---|
| Non-inverting | 0.1 V | 1000 Hz | 10 k ohm | 100 k ohm | 1 uF | 1 MHz | Audio preamplifier |
| Inverting | 0.05 V | 5000 Hz | 4.7 k ohm | 47 k ohm | 2.2 uF | 3 MHz | Signal conditioning |
| Non-inverting | 0.2 V | 10000 Hz | 20 k ohm | 180 k ohm | 0.47 uF | 5 MHz | Sensor gain stage |
Understanding an Op Amp AC Amplifire
An op amp AC amplifier raises small alternating signals. It blocks unwanted DC when a coupling capacitor is used. The calculator estimates gain, cutoffs, output level, phase, and practical operating limits. It is useful for audio stages, sensor interfaces, filters, and lab checks.
Why AC Gain Matters
AC gain tells how much the input waveform is enlarged at a chosen frequency. An inverting stage reverses polarity. A non-inverting stage keeps polarity. Real circuits also include capacitors, load resistance, bandwidth limits, and slew rate limits. These effects change the final output before clipping happens.
Important Design Checks
The lower cutoff comes from the coupling capacitor and the resistance it sees. Below that point, bass or slow signals fade. The upper cutoff comes from the op amp gain bandwidth and any feedback capacitor. Above that point, high frequencies reduce. The tool compares both limits with your test frequency.
Output Headroom and Slew Rate
A calculated gain can look perfect on paper. The output may still fail in hardware. Supply rails set the maximum swing. The selected headroom reduces usable peak voltage. Slew rate limits how fast the output can change. When the required slew rate is higher than the device rating, distortion can occur.
Using Results in Practice
Use realistic resistor values. Choose a coupling capacitor that supports your lowest useful frequency. Keep load current within the op amp rating. Leave margin between output peak and rail limits. Check the closed loop bandwidth when using high gain. High gain reduces usable bandwidth in many voltage feedback op amps.
Better Experiments
Try several frequencies and compare results. Increase the feedback resistor to raise gain. Increase the input capacitor to lower the high pass cutoff. Add a small feedback capacitor when noise needs reduction. Always confirm critical designs with a simulator and bench measurement.
Common Mistakes to Avoid
Do not select capacitors by gain alone. Their reactance changes with frequency. Do not ignore the source resistance. It can shift the lower cutoff. Do not use rail voltage as the output limit. Most op amps need margin. Do not trust one frequency point. A full response check gives safer insight. This habit improves stable and repeatable amplifier designs.
FAQs
1. What does this op amp AC calculator find?
It finds ideal gain, effective gain, cutoff points, phase shift, output swing, slew rate demand, load current, and clipping risk for an AC coupled op amp stage.
2. What is the difference between inverting and non-inverting gain?
Inverting gain equals negative feedback resistance divided by input resistance. Non-inverting gain equals one plus that resistance ratio. The inverting output has opposite polarity.
3. Why is the input coupling capacitor important?
The input coupling capacitor blocks DC. It also creates a high-pass cutoff with the resistance it sees. Small capacitors reduce low frequency output.
4. Why does high gain reduce bandwidth?
Many voltage feedback op amps have a gain bandwidth product. When closed-loop gain rises, available bandwidth usually falls. The calculator estimates that limit.
5. What does slew rate warning mean?
It means the op amp may not change output voltage fast enough. High output amplitude and high frequency both increase required slew rate.
6. What causes clipping in this calculator?
Clipping occurs when estimated output peak voltage exceeds available swing between the supply rails after headroom and bias reference are considered.
7. Can I use single supply values?
Yes. Enter the positive rail, zero as the negative rail, and a mid-supply output bias reference. Then set realistic rail headroom.
8. Are these results final for production design?
No. The calculator gives strong estimates. Always check the selected op amp datasheet, simulate the circuit, and test important designs on hardware.