Photo-diode amplifier using opa381/opa380 op-amp

This Simple Photo Diode Amplifier project is based on OPA381 Trans-impedance amplifiers. The circuit Convert Current Output of Photodiodes to Voltage. The circuit ideally suited for low noise amplification of very small photodiode current. The circuit required 5V DC and provides approx. 0.5V to 4V DC.


  • Supply 5V DC
  • Output 0.5V to 4V Approx.
  • Convert Current Output of Photodiodes to Voltage

About OPA381

The OPA381 family of Trans-impedance amplifiers provides 18MHz of Gain Bandwidth (GBW), with extremely high precision, excellent long-term stability, and very low 1/f noise. The OPA381 features an offset voltage of 25μV (max), offset drift of 0.1μV/°C (max), and bias current of 3pA. The OPA381 far exceeds the offset, drift, and noise performance that conventional JFET op amps provide. The signal bandwidth of a trans-impedance amplifier depends largely on the GBW of the amplifier and the parasitic capacitance of the photodiode, as well as the feedback

resistor. The 18MHz GBW of the OPA381 enables a trans-impedance bandwidth of > 250kHz in most configurations. The OPA381 is ideally suited for fast control loops for power level measurement on an optical fiber. As a result of the high precision and low-noise characteristics of the OPA381, a dynamic range of 5 decades can be achieved. This capability allows the measurement of signal currents on the order of 10nA, and up to 1mA in a single I/V conversion stage. In contrast to logarithmic amplifiers, the OPA381 provides very wide bandwidth throughout the full dynamic range. By using an external pull-down resistor to –5V, the output voltage range can be extended to include 0V.