Operational Amplifier
Explore six ideal linear op-amp circuits, calculate their closed-loop response, and check when an expected output leaves the selected supply rails.
Inverting Amplifier
Set gain with an input and feedback resistor.
Selected topology
Ideal closed-loop equations
Expected linear response
VIN / VOUT chronogram
Drive one selected input with a waveform; other circuit inputs retain their entered DC value.
Ideal dynamic responseThe chronogram uses an ideal closed-loop model. It does not simulate bandwidth, slew rate, noise, stability, input common-mode limits or output clipping.
Analog design guide
Size fundamental operational-amplifier circuits
Inverting, non-inverting, follower, difference, integrator, and summing circuits use feedback to define a gain or transfer function. This tool relates resistor ratios and RC time constants to the required analogue function.
Method and assumptions
The calculation starts from an ideal op amp operating linearly: very high open-loop gain, zero input current, and negative feedback. Inverting and non-inverting gains depend on resistor ratios; the summing circuit weights each input, the difference circuit needs matched ratios, and the integrator relates R, C, and frequency to its response slope.
Inputs to verify
Circuit and intended function
Choose the circuit that matches the signal to be processed. Set a signed gain for the inverting stage, positive gain for the non-inverting stage, per-channel coefficients for the summing stage, or a time constant for the integrator.
Resistor network and capacitor
Use practical values and preserve the important ratios. A difference amplifier rejects common mode correctly only when its resistor ratios are matched; for an integrator, check the capacitor’s effective value and resulting RC time constant.
Signals, supply, and load
Compare expected input and output voltages with the rails, common-mode range, output-current capability, and load. A calculated gain is unusable if the op amp saturates or if its bandwidth and slew rate cannot follow the signal.
Recommended workflow
- 1Select the circuit, then set the gain, weighting, or time constant needed for the transfer function.
- 2Choose preferred values while preserving resistor ratios; for a difference amplifier, use matched resistors or an integrated network when common-mode rejection matters.
- 3Finally, verify voltage headroom, bandwidth, stability, and tolerances against the datasheet and complete schematic before locking the values.
Checkable example
In an inverting stage with Rin = 10 kΩ and Rf = 100 kΩ, ideal gain is −Rf/Rin = −10. A +0.20 V input therefore produces −2.0 V as long as the op amp’s rails, load, and dynamic limits allow it.
Limits to keep in mind
The ideal model does not cover input offset and bias currents, finite gain and bandwidth, slew rate, noise, CMRR, real rail swing, current capability, or stability issues with capacitive loads. A real integrator often needs a leakage resistor across its capacitor to prevent DC drift and saturation.
Frequently asked questions
Why does a difference amplifier need matched resistors?
Accurate subtraction and common-mode rejection rely on equal resistor ratios, not just nominal values. Independent tolerances convert part of the common-mode signal into output error; a matched resistor network usually improves this result.
Why does an integrator drift with a DC input?
Any DC component, including offset and bias currents, is integrated until the output reaches a rail. A resistor across the capacitor limits DC gain and creates a practical integrator, but changes the very-low-frequency response.
References to consult
- Method references: op-amp feedback equations, the selected part’s datasheet for input/output ranges, and manufacturer application notes for stability, noise, integrator, and difference-amplifier circuits.
Original educational content, reviewed for technical clarity on 20 August 2026. Always verify datasheets, applicable standards, and your design before power-up or manufacture.