ZHCSNI6A March 2023 – April 2024 OPA928
PRODUCTION DATA
Some photodiode applications operate in dark conditions and require low-light detection. In these cases, the current output from the photodiode can be miniscule. To make the small diode current measurable, a transimpedance amplifier (TIA) with a very large gain is required. The ideal transfer function of a resistive transimpedance amplifier is given by Equation 1:
The photodiode current (IPD) flows through the feedback resistor (RF) and forces an output voltage (VOUT) equal to the voltage drop across RF. Equation 1 gives an intuitive understanding of TIA operation. In practice, however, nonidealities must be taken into consideration to achieve the desired performance. Figure 7-11 illustrates important nonidealities of the transimpedance amplifier circuit. The following sections describe how the op amp dc and ac performance interacts with the circuit.