How do inverting and non-inverting gains differ?

In an inverting amplifier the input reaches the inverting node through R1, Rf feeds back from the output and the non-inverting input is grounded. The virtual-short rule gives Vout = −(Rf/R1)·Vin, so the output is inverted and the input impedance equals R1. A non-inverting amplifier takes the signal on the non-inverting input with gain 1 + Rf/Rg, always at least 1, and a very high input impedance. Both have a noise gain of 1 + Rf/R1 (or 1 + Rf/Rg), and that is what sets the closed-loop bandwidth.

How does the gain-bandwidth product set the bandwidth?

A typical voltage-feedback op-amp has an open-loop gain close to a single pole, A(s) = A₀/(1 + s/ω_p). Above that pole, gain times frequency stays constant at the GBW. In a closed loop, bandwidth is roughly GBW divided by the noise gain: an LM741 with GBW = 1 MHz wired as a ×10 non-inverting amplifier has a −3 dB bandwidth of about 100 kHz. In non-ideal mode the tool uses this model to compute the full transfer function, so you can see the phase change too.

Why does the output get flattened or turn triangular?

An op-amp cannot swing beyond its supplies, and most need 1–2 V of headroom (rail-to-rail parts excepted), so when gain times input amplitude exceeds that range the peaks are clipped. The other limit is the slew rate SR: the output cannot change faster than SR, and a sine needs a peak slope of 2πf·V_pk, so beyond that the output becomes a triangle. The tool shows the full-power bandwidth SR/(2πV_pk) for reference.

How are f₀ and Q of a Sallen–Key filter found, and how do I design one?

A Sallen–Key second-order filter has f₀ = 1/(2π√(R1R2C1C2)), and the low-pass Q = √(R1R2C1C2)/(C2(R1+R2) + R1C1(1−K)), where K is the non-inverting gain. At unity gain with R1 = R2, Q = ½√(C1/C2), so a Butterworth response (Q ≈ 0.707) needs C1 ≈ 2C2. The design helper takes a target f₀, Q and chosen C2, computes R and C1 and snaps them to standard values. Push K too high and Q goes negative, so the circuit oscillates.

How do you find the thresholds of a Schmitt trigger?

Take the inverting type: the input goes to the inverting pin, and the non-inverting pin connects to Vref through R1 and to the output through R2, so V+ = (Vref·R2 + Vout·R1)/(R1+R2). With the output saturated high the threshold is higher, and with it low the threshold is lower. The difference, ΔV = (V_sat+ − V_sat−)·R1/(R1+R2), is the hysteresis. It stops the output from chattering when a noisy input hovers near the threshold, which is why Schmitt triggers are used to square up slow or noisy signals.

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🔺Op-Amp Calculator - Inverting & Non-Inverting Gain, Active Filters, Schmitt Trigger, Bode Plot

Pick one of 14 common op-amp circuits and type component values as 10k, 4.7u, 100n or 2k2. The tool draws a labelled schematic and reports the ideal gain, the actual gain and phase, input impedance, noise gain and closed-loop bandwidth. Switch between an ideal op-amp and models such as the LM741, TL072 or NE5532: the finite open-loop gain and gain-bandwidth product show up in the Bode plot. Feed in a sine, square or triangle wave and the output is clipped at the rails and slope-limited by the slew rate. A design helper suggests E24/E96 resistor pairs for a target gain or designs a Sallen–Key low-pass from f₀ and Q.

Free · No sign-up · Runs in your browserLast updated: 2026-10-29

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How to use Op-Amp Circuit Calculator

1Pick a circuit and edit the component values (engineering and RKM notation both work)
2Choose an op-amp model and supply voltages; the difference between ideal and real op-amps shows in gain, bandwidth and waveforms
3Set the input waveform, amplitude, frequency and DC offset, and for multi-input circuits choose which input carries the signal
4Read the result cards, waveforms and Bode plot, and use the design helper to pick standard values for a target gain or cut-off and apply them in one click

FAQ

How do inverting and non-inverting gains differ?: In an inverting amplifier the input reaches the inverting node through R1, Rf feeds back from the output and the non-inverting input is grounded. The virtual-short rule gives Vout = −(Rf/R1)·Vin, so the output is inverted and the input impedance equals R1. A non-inverting amplifier takes the signal on the non-inverting input with gain 1 + Rf/Rg, always at least 1, and a very high input impedance. Both have a noise gain of 1 + Rf/R1 (or 1 + Rf/Rg), and that is what sets the closed-loop bandwidth.
How does the gain-bandwidth product set the bandwidth?: A typical voltage-feedback op-amp has an open-loop gain close to a single pole, A(s) = A₀/(1 + s/ω_p). Above that pole, gain times frequency stays constant at the GBW. In a closed loop, bandwidth is roughly GBW divided by the noise gain: an LM741 with GBW = 1 MHz wired as a ×10 non-inverting amplifier has a −3 dB bandwidth of about 100 kHz. In non-ideal mode the tool uses this model to compute the full transfer function, so you can see the phase change too.
Why does the output get flattened or turn triangular?: An op-amp cannot swing beyond its supplies, and most need 1–2 V of headroom (rail-to-rail parts excepted), so when gain times input amplitude exceeds that range the peaks are clipped. The other limit is the slew rate SR: the output cannot change faster than SR, and a sine needs a peak slope of 2πf·V_pk, so beyond that the output becomes a triangle. The tool shows the full-power bandwidth SR/(2πV_pk) for reference.
How are f₀ and Q of a Sallen–Key filter found, and how do I design one?: A Sallen–Key second-order filter has f₀ = 1/(2π√(R1R2C1C2)), and the low-pass Q = √(R1R2C1C2)/(C2(R1+R2) + R1C1(1−K)), where K is the non-inverting gain. At unity gain with R1 = R2, Q = ½√(C1/C2), so a Butterworth response (Q ≈ 0.707) needs C1 ≈ 2C2. The design helper takes a target f₀, Q and chosen C2, computes R and C1 and snaps them to standard values. Push K too high and Q goes negative, so the circuit oscillates.
How do you find the thresholds of a Schmitt trigger?: Take the inverting type: the input goes to the inverting pin, and the non-inverting pin connects to Vref through R1 and to the output through R2, so V+ = (Vref·R2 + Vout·R1)/(R1+R2). With the output saturated high the threshold is higher, and with it low the threshold is lower. The difference, ΔV = (V_sat+ − V_sat−)·R1/(R1+R2), is the hysteresis. It stops the output from chattering when a noisy input hovers near the threshold, which is why Schmitt triggers are used to square up slow or noisy signals.

Features

14 circuits: inverting, non-inverting, follower, summing, difference, 3-op-amp instrumentation amp, integrator, differentiator, 1st-order and Sallen–Key 2nd-order active filters, transimpedance amp and Schmitt trigger
Automatically drawn SVG schematics labelled with component values
Ideal op-amp vs single-pole finite-gain model (A₀, GBW) with closed-loop −3 dB bandwidth and a Bode plot including open-loop gain
Steady-state output for sine, square and triangle inputs, clipped at the rails and limited by slew rate
Schmitt trigger thresholds, hysteresis and the hysteresis loop
E12/E24/E48/E96 resistor pairs for a target gain, plus RC design for Sallen–Key and first-order filters

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