Engineering guide

Op-amp signal-chain sanity check workflow

A signal chain that meets the ideal gain equation can still fail on bandwidth, slew rate, coupling, or output swing. A quick workflow keeps those checks in the right order.

Reviewed 4 July 2026

Quick answer

What should you check after choosing an op-amp gain target?

Start with the ideal gain and resistor ratio, convert that gain into dB only when it helps communication, then check closed-loop bandwidth, large-signal slew-rate requirement, and any AC-coupling or RC filtering that shapes the real signal path.

Model summary

Core equations

First-pass model summary

Use these equations, assumptions, and variables as the shared model behind the guide before moving to the worked example and linked calculators.

Non-inverting gain

A_{v} = 1 + \frac{R_{f}}{R_{g}}

Closed-loop bandwidth

BW = \frac{GBW}{A_{v}}

Small-signal bandwidth limit from GBW and closed-loop gain.

Minimum slew rate

SR \geq 2 π f \times V_{pk}

Slew rate needed to pass a sine wave without distortion.

Variables and natural units

These symbols match the guide equations and use the same engineering-unit conventions as the linked calculators.

`A`_v: Closed-loop gain

Unit: V/V

Signal gain from input to output.

`GBW`: Gain-bandwidth product

Unit: Hz

Op-amp speed parameter from the datasheet.

`BW`: Closed-loop bandwidth

Unit: Hz

Usable signal bandwidth at the selected gain.

`SR`: Slew rate

Unit: V/µs

Maximum output voltage change rate; limits large-signal bandwidth.

`f`: Signal frequency

Unit: Hz

Highest frequency in the output signal requiring undistorted slewing.

`V`_pk: Peak output voltage

Unit: V

Signal amplitude (zero-to-peak) at the op-amp output.

Model boundary

Closed-loop gain comes from the resistor network, but real output behaviour still depends on gain-bandwidth product, slew rate, output swing, and loading.
Bandwidth from GBW is a small-signal estimate; slew-rate checking covers large-signal behaviour.
Coupling and filter capacitors add frequency limits that can dominate low-frequency behaviour even when the amplifier itself is fast enough.

Worked example

100 mV sensor signal amplified to 2 V

This example checks gain, closed-loop bandwidth from GBW, and slew rate requirement for a 4 V<sub>pp</sub> output at 10 kHz.

Inputs

V_in: 100 mV signal
V_out: 2 V target output
GBW: 1 MHz gain-bandwidth product
V_pp: 4 V peak-to-peak at 10 kHz

Equation and substitution

G = \frac{V_{out}}{V_{in}} = \frac{2 V}{100 mV} = 20 V/V

{BW}_{CL} = \frac{GBW}{G} = \frac{1 MHz}{20} = 50 kHz

{SR}_{min} = π \times f \times V_{pp} = π \times 10 kHz \times 4 V \approx 0.126 V/μs

Required gain

20 V/V (26 dB)

Closed-loop bandwidth

BW_CL = 50 kHz

Slew rate minimum

0.126 V/µs at 10 kHz, 4 V_pp

Calculator workflow

Work through these calculators in order for a complete first-pass check.

Ideal maths versus the real op amp

Use the gain equation to set the target, but treat it as the beginning of the review rather than the end. A real op amp still has finite GBW, finite slew rate, limited output swing, input common-mode constraints, noise, bias current, and stability conditions that the ideal calculation does not prove.

Coupling and filtering belong in the same review

AC coupling and simple RC filters can move the low-frequency or high-frequency corners enough to change the effective signal chain even when the op amp itself is adequate. Keep those passive checks in the same workflow so the stage is not analysed in isolation.

Common mistakes

Stopping at the ideal gain equation without checking GBW or slew rate.
Using dB conversion as if it were the design check instead of a way to express gain.
Ignoring output swing, input common-mode range, or coupling capacitor behaviour.

When the model breaks down

These calculators are ideal or first-pass checks and do not replace stability analysis, noise review, distortion checks, or datasheet validation.
Capacitive loading, source impedance, output current, rail headroom, and phase margin can dominate the real result.

Further checks and references

Review the op-amp datasheet for input common-mode range, output swing, output current, noise, offset, bias current, and stability guidance.
Check the source impedance, load impedance, and capacitor tolerance when coupling or filtering components shape the passband.
Use measurement or simulation when distortion, phase margin, or transient settling matters to the final design.

Stylised op-amp gain circuit with feedback resistor network

Next check

Op-amp gain calculator

Start with the ideal resistor ratio and nominal output target.

Stylised op-amp bandwidth path linking closed-loop gain to frequency roll-off

Next check

Op-amp bandwidth from gain calculator

Check the first-pass small-signal bandwidth limit.

Hub

Analogue and filter calculators

Return to the analogue hub for related op-amp and filter checks.

FAQ

Can a low-gain op-amp still fail slew rate?

Yes. Slew rate is a large-signal speed limit independent of small-signal bandwidth. A low-gain stage with a large voltage swing and high output frequency can exceed the slew rate even when GBW is adequate.

Should coupling capacitors be included in gain calculations?

No. Coupling capacitors set the low-frequency corner, not the closed-loop gain. Calculate gain from the resistor network. Determine the high-pass corner from the coupling capacitor and its effective resistance separately.

Is GBW the only bandwidth limit?

No. Capacitive loading, phase margin, input and output common-mode range, and external compensation can all restrict usable bandwidth. The GBW figure in the datasheet is a small-signal, room-temperature, unloaded reference.

Op-amp signal-chain sanity check workflow

What should you check after choosing an op-amp gain target?