Op-amp sensor gain and saturation

Study Op-Amp Sensor Front-End Contracts from the Electronics module guide by comparing non-inverting gain and supply-rail saturation.

Predict output peak from feedback ratio before inspecting both scopes., your practice guide

Predict output peak from feedback ratio before inspecting both scopes.
Predict the reading, then compare it with the measurement.

Falstad CircuitJS

Third party Tool

Study Op-Amp Sensor Front-End Contracts from the Electronics module guide by comparing non-inverting gain and supply-rail saturation.

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Version tested: CircuitJS live in Playwright Chromium on 2026-10-09; no simulator version exposed. Date: 2026-10-09.

Open the prepared circuit.

Open this circuit in Falstad (new tab)

Steps

Screens captured against Falstad CircuitJS CircuitJS live in Playwright Chromium on 2026-10-09; no simulator version exposed on 2026-10-09; the tool may have moved on — the text steps are the contract.

  1. Step 1

    Do
    Open the gain-two op-amp circuit on the Falstad canvas and inspect the input and output scopes.
    You will see
    Input: synthetic fixed-seed set, seed 15. Input source: 100 Hz sine, 0.5 V peak. Input scope: Max=500 mV. Output scope: Max=999.98 mV. Feedback resistor: 10 kΩ. Ground resistor: 10 kΩ.
    Why it matters
    The non-inverting feedback ratio 1 + 10 kΩ / 10 kΩ predicts gain two in the unsaturated range.

  2. Step 2

    Do
    Point to the output scope on the canvas and compare its peak with the input scope while reading the rail labels.
    You will see
    Input scope: Max=500 mV. Output scope: Max=999.98 mV. Positive rail: 3 V. Negative rail: -3 V. The output peak is below either rail.
    Why it matters
    This real waveform verifies linear gain at the starting input; the rail values set a ceiling for later steps.

  3. Step 3

    Do
    Open the gain-five circuit on the canvas and inspect both scopes after feedback rises to 40 kΩ.
    You will see
    Input source: 100 Hz, 0.5 V peak. Ground resistor: 10 kΩ. Feedback resistor: 40 kΩ. Input scope: Max=500 mV. Output scope: Max=2.5 V.
    Why it matters
    The output grows to five times the input without clipping because 2.5 V remains within the modeled 3 V rail.

  4. Step 4

    Do
    Open the 1 V input, gain-five circuit on the canvas and watch the output scope flatten near the rails.
    You will see
    Input scope: Max=1 V. Linear gain-five target: 5 V peak. Output scope: Max=3.002 V. Modeled rails: +3 V and -3 V. The output trace has flat plateaus.
    Why it matters
    The model saturates at its rails; the linear target cannot be reached with this supply.

  5. Step 5

    Do
    Open the 1 V input, gain-two circuit on the canvas and compare both scopes after reducing feedback to 10 kΩ.
    You will see
    Input scope: Max=1 V. Feedback resistor: 10 kΩ. Ground resistor: 10 kΩ. Output scope: Max=2 V. The output trace is sinusoidal again.
    Why it matters
    Reducing gain returns the 1 V input to an output range below the rails.

  6. Step 6

    Do
    Restore the initial circuit on the canvas and record the input and output scope readouts as the comparison baseline.
    You will see
    Input scope: Max=500 mV. Output scope: Max=999.98 mV. Feedback: 10 kΩ over 10 kΩ. Rails: +3 V and -3 V. The full circuit and both scopes remain visible.
    Why it matters
    The simulated gain and clipping boundary are reproducible in this model; they do not establish device offset, noise, bandwidth, or real output swing.

Chapter checks

These questions refer to the chapter’s examples. Use the return links to review their answers.

  1. With negative feedback and an unsaturated output, what do the two op-amp golden rules say?

    Return to the chapter’s knowledge check

  2. An op-amp circuit is powered from a single rail. Which check must precede a claim that its full sensor range is readable?

    Return to the chapter’s knowledge check

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