Op-Amp Gain & Bandwidth Calculator
Calculate resistor-set gain, estimate closed-loop bandwidth, and check a sine wave against slew-rate and output-swing limits. Compare the GBW you have with the GBW needed for your allowed gain loss.
Circuit & signal
For voltage-feedback op amps approximated by a dominant-pole response and a resistive feedback network. Defaults are illustrative, not a specific device.
Gain & frequency response
Calculate to see the stage response.
Bandwidth requirement
- Estimated gain loss at signal frequency
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- Additional single-pole phase lag
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- GBW needed for allowed gain loss
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- Frequency ceiling for allowed gain loss
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The phase value is additional lag relative to the low-frequency response. An inverting stage already contributes polarity inversion. This is not phase margin.
| Check | Comparison | Result |
|---|---|---|
| Minimum noise gain | — | Meets minimum |
| Small-signal gain loss | — | — |
| Slew rate at requested amplitude | — | — |
| Requested output swing | — | — |
Sine-wave amplitude & slew
- Requested output at ideal low-frequency gain
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- Linear-model output at signal frequency
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- Slew required at requested output
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- Slew required by linear-model output
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- Slew-only frequency limit at requested output
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- Slew-only sine amplitude limit at f
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Normalized small-signal response
Text report includes circuit values, model assumptions, and limit checks.
Signal gain is not always noise gain
Use signal gain to estimate the input-to-output amplitude ratio. Use noise gain for the GBW-based bandwidth calculation in this model.
Non-inverting amplifier
Noise gain = 1 + Rf / Rg
The signal is applied to the non-inverting input. In this resistive circuit, signal gain and noise gain are equal. Gain is positive and at least unity.
Inverting amplifier
Noise gain = 1 + Rf / Rin
The negative sign denotes polarity inversion. A −1 V/V stage has a noise gain of 2, so its estimated bandwidth is GBW/2, not GBW.
Voltage follower
Noise gain = 1
A direct feedback connection gives a unity-gain buffer. Use an amplifier suitable for unity noise gain and the intended load; a gain-of-one connection does not guarantee stability.
Gain definitions and dominant-pole bandwidth model: Analog Devices MT-033 — Voltage Feedback Op Amp Gain and Bandwidth.
Plan for gain flatness
The −3 dB point is not the end of a perfectly flat passband. At the calculated corner, a single-pole response has about 70.7% of its low-frequency amplitude. Enter an allowed gain loss to plan around your actual signal frequency.
|A(f)| ≈ |A₀| / √[1 + (f / fc)²]
Loss D = 10 log₁₀[1 + (f / fc)²]
Required GBW ≈ NG × f / √(10^(Dallowed / 10) − 1)
For example, a noise gain of 10 and a 100 kHz signal need approximately 2.86 MHz GBW for 0.5 dB maximum modeled loss. This is a calculated illustration, not a guaranteed device requirement under all conditions.
Bandwidth flatness context: Analog Devices MT-045 — Op Amp Bandwidth and Bandwidth Flatness.
Check the sine-wave slope
Slew rate limits how quickly the output voltage can change. A larger sine-wave amplitude needs a higher slew rate at the same frequency. GBW alone cannot establish that the desired output waveform is achievable.
SRrequired = π × f × Vout,pp
fslew = SR / (π × Vout,pp)
Use hertz, volts, and volts per second in these equations. The calculator converts V/µs automatically. The slew-only limit is evaluated at the requested output amplitude, not at an assumed rail-to-rail swing, and is not a distortion specification.
Sine-wave slew requirement and operating-condition limitations: Texas Instruments — Ramping Up on Slew Rate.
Review the rest of the signal chain
Check the datasheet conditions
- GBW and minimum gain: use the specified architecture and compensation conditions. Higher-order response and gain peaking are not included here.
- Slew rate: confirm the applicable signal level, supply, load, and slower transition direction. Slew-boost behavior can make a headline figure misleading for another signal.
- Output swing: use the available symmetric AC swing around your actual output bias. If the allowed output is Vmin to Vmax, use 2 × min(Vbias − Vmin, Vmax − Vbias), with Vbias inside that range.
Check what the model leaves out
- Input and DC errors: common-mode range, source impedance, bias current, offset, finite DC open-loop gain, and resistor tolerances.
- Loading and stability: output current, capacitive loads, feedback capacitance, PCB parasitics, phase margin, and settling.
- Signal quality: noise, THD, overload recovery, clipping shape, and slew-limited waveform distortion. No “within limits” result certifies these.
Op-amp calculator FAQ
Why is the inverting bandwidth based on 1 + Rf/Rin?
The feedback loop responds to noise gain rather than the signed input-to-output gain. For this simple inverting circuit, signal gain is −Rf/Rin and noise gain is 1 + Rf/Rin. Ignoring the added 1 is especially significant for gains near or below unity.
Can I use the tool for a current-feedback amplifier?
No. This GBW/noise-gain approximation is intended for a suitable voltage-feedback amplifier. Current-feedback devices require their own feedback-resistor and bandwidth guidance. Filters and transimpedance stages also need analysis of their frequency-dependent impedances.
Does a larger GBW solve slew-rate problems?
Not by itself. The small-signal response and the required output slope are separate checks. A circuit can have enough small-signal bandwidth but still be unable to reproduce a large-amplitude sine wave at the requested frequency.
Why show two output amplitudes?
The requested amplitude is input Vpp multiplied by the ideal low-frequency gain magnitude. The linear-model amplitude includes the modeled frequency roll-off. If the latter exceeds the entered slew or swing limit, it is not a prediction of the actual output; nonlinear waveform behavior is not simulated.
Can I enter an RMS voltage?
The amplitude inputs require peak-to-peak values. For a sine wave only, Vpp = 2√2 × Vrms, or 2 × Vpeak. Do not apply that conversion to arbitrary waveforms.
Does meeting the minimum noise gain prove stability?
No. It only avoids a known conflict with the minimum you entered. The device response, load, feedback network, and layout must still be checked. If the calculated noise gain is below the entered minimum, this tool stops rather than presenting a bandwidth result as usable.
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