Op-Amp Offset Error

Estimate output offset from input offset voltage (Vos) and input bias current effects. Includes Show Work and percent-of-full-scale error.

How to Use

  1. Enter the op-amp input offset voltage (Vos) and select units (µV/mV/V).
  2. Choose the configuration and provide the gain (or resistors if you want the tool to compute it).
  3. If you want bias-current effects, enter input bias current and your source/equivalent input resistance.
  4. Optional: enter output full-scale to show percent error.
  5. Open Show Work for formulas and intermediate steps in base units.
Offset Model View
Vos is amplified by noise gain. Bias current can create an input drop across source resistance.
Vos
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Noise Gain
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Vout Offset
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FS Error
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Status: —
+ − Vos — Vout — Noise gain applies to Vos Model: Vout_offset ≈ (Vos + Vbias_drop) × NoiseGain
Inputs & Settings
Enter values to compute output offset. Tool stays deterministic and updates locally.
Datasheets often list Vos in µV or mV (typ/max).
Noise gain differs from signal gain for inverting configs.
If unknown, enter resistors below and let the tool compute NG.
Used to compute %FS error: |Vout_offset| / FS × 100.
Bias Current Effects (optional)
If you provide bias current and source/equivalent input resistance, the tool estimates input drop.
Use typical or worst-case per datasheet.
Bias drop estimate: Vbias_drop ≈ Ib × Rs (simple model).
If provided with Rg, tool can compute noise gain for common configs.
Non-inverting: NG = 1 + Rf/Rg. Inverting: NG = 1 + Rf/Rg.
Show Work (step-by-step)
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Work is shown in base units (V, A, Ω). This is a simplified offset estimate; real circuits may include input offset current, resistor mismatch compensation, and temperature drift.

Reference

A common first-order estimate for output offset is: Vout_offset ≈ (Vos + Vbias_drop) × NG

  • Vos: input offset voltage (modeled as a small DC source at the input).
  • NG (noise gain): gain applied to input-referred offsets (often 1 + Rf/Rg in classic feedback networks).
  • Vbias_drop: simple estimate Ib × Rs (optional), where Rs is the source/equivalent input resistance seen by the bias current.
Tip: Datasheet specs are often temperature-dependent; worst-case can be much larger than typical.

FAQ

What is “noise gain” and why does it matter for offset?

Input-referred errors (like Vos) are amplified by the feedback network’s noise gain, which can differ from the signal gain in some configurations.

Why include input bias current?

Bias current flowing through source or resistor networks creates a small DC voltage at the input. That input drop can be amplified to the output.

Is this exact for every op-amp circuit?

It’s a practical first-order estimate. Real offset can include offset current, resistor mismatch compensation, input common-mode effects, output swing limits, and temperature drift.

Tool Info

Last updated:

Updates may include additional circuit models, improved validation, and expanded unit handling.