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The OPA381 family of transimpedance 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 transimpedance 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 in 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 pulldown resistor to –5V, the output voltage range can be extended to include 0V.

The OPA381 and OPA2381 are both available in MSOP-8 and DFN-8 (3mm x 3mm) packages. They are specified from –40°C to +125°C.