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Electrical & Electronics

Transimpedance Amplifier Calculator

Convert sensor current to voltage, choose a feedback resistor and estimate capacitance and bandwidth.

01

Your inputs

Use usable output voltages from the datasheet, not supply rails. The bounded output is an estimate.

Single-pole estimate. Include sensor, op-amp and stray capacitance; verify noise, input range, slew rate and stability.

Positive current flows into the inverting input; Vout = Vref − Iin × Rf.

TI SBOA122

02

Your results

Feedback resistor
—
Ideal resistance
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Ideal output voltage
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Bounded output estimate
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Estimated feedback capacitance
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Estimated small-signal bandwidth
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Current range for output limits
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Formula—

Balance current-to-voltage gain, headroom and bandwidth

Analyse an ideal transimpedance amplifier or size its feedback resistor from peak current and output change. Compare DC output with an estimated compensated bandwidth. The bandwidth model assumes an amplifier with a single-pole gain response, not a particular device.

Step by step

  1. Choose analyse or design mode. Enter signed current and reference, then feedback resistance or the peak-current design target using the selected units.
  2. Enter total input capacitance, amplifier GBW and target bandwidth. Optionally enter realistic output limits.
  3. Review output, clipping and current range alongside estimated feedback capacitance and bandwidth. A bandwidth pass does not imply adequate output headroom.

Settings and limits

Feedback resistance
Rf converts current into an inverted output change. Design mode rounds resistance downward so the stated peak current does not exceed the requested voltage change.
Capacitance and GBW
Include sensor, amplifier-input and layout capacitance. The tool estimates compensation for its simplified response; extra amplifier poles and parasitics may change stability.
Output and target limits
Output bounds clamp the ideal DC voltage and define the current range. Target bandwidth only compares against the estimate; it does not force that bandwidth.

Worked example

Use the example below: positive current lowers output below reference. The estimated bandwidth exceeds the target and the DC output stays within its bounds.

Example input

Iin = 10 µA; Vref = 2.5 V; Rf = 100 kΩ
Cin = 100 pF; GBW = 10 MHz; ft = 100 kHz
Vmin = 0 V; Vmax = 5 V
Expected result
Vout / Cf / BW / I≈
Vout1.5 V
Cf5.639651 pF
BW388.147316 kHz
Imin−25 µA
Imax25 µA

Increase current without changing feedback. The output can reach a limit despite the same bandwidth estimate; compare the displayed unclipped current range.

Questions and troubleshooting

Why does positive current reduce voltage?

The shown current direction feeds an inverting summing node. Reversing current changes the output shift relative to reference.

Why might estimated feedback capacitance be zero?

The simplified model may already have sufficient damping at low input capacitance. This does not mean board parasitics or a real amplifier can be ignored.

Is the bandwidth estimate a stability guarantee?

No. Verify device open-loop behaviour, compensation, noise, leakage, layout and output range against the datasheet and measurements.