Photodiode sensors are widely used in many applications, and understanding how they work—especially their connection with transimpedance amplifiers (TIAs)—is very useful. A transimpedance amplifier, also called a current-controlled voltage source (ICVS) amplifier, is one of four types of negative feedback amplifier commonly used to convert and amplify the small current generated by a photodiode into a usable voltage signal. Another type of negative feedback is voltage controlled voltage source(VCVS) amplifier which was covered in the blog post non-inverting amplifier with transistors.
The following shows the basic circuit topology of a transimpedance amplifier with a photodiode.
This is a simple dual power supply circuit of transimpedance amplifier with photodiode D1 where LM358 op-amp is used as the negative feedback amplifier. The +ve terminal of the op-amp is grounded while the output is feedback to the -ve terminal of the op-amp. The diode with its anode connected to the -ve terminal and anode connected to the ground acts as current source whose magnitude is in the order or 1nA to 1mA. This can be difficult to detect and many microcontroller or microprocessor have ADC that actually measure voltage and not current(see Arduino with Photodiode tutorial). So the transimpedance amplifier senses the very low current intensity that is generated by the photodiode in response to the light impinged on it.
For a transimpedance amplifier or ICVS negative feedback amplifier we have the approximate relation between the input current and the output voltage,
\[ V_{out} = (-)I_{in}R_f \]
Calculating with \(I_{in}\)=1mA and negative feedback resistor \(R_f\)=1kohm then the output voltage should be,
\[ V_{out} = (-)I_{in}R_f = (-) 1mA \times 1K\Omega=1V\]
So the output should be 1V which is shown by the circuit simulation and the graph.
If one wishes to power the transimpedance circuit with single power supply, then the following circuit can be used.
