Logarithmic Amplifier Calculator

Calculate output voltage for a logarithmic amplifier circuit.

Circuit Parameters

Input Voltage (V) - Must be positive

Input Resistor Rin (Ohms)

Transistor Saturation Current Is (A)

Typical: 1e-12 to 1e-15 A

Temperature (C)

Reference Voltage (V) - for log10 output

-473.46 mV

Natural Log Output

0.000 V

Log10 Output (1V/decade)

Thermal Voltage (Vt)25.70 mV

Input Current100.000 uA

Sensitivity (dVout/dVin)-25.70 mV/V

Typical Dynamic Range3 decades

Vout = -Vt * ln(Vin / (Rin * Is))

Where Vt = kT/q is the thermal voltage (~26mV at 25C). Temperature compensation is critical for accuracy.