# Transimpedance Amplifier

A transimpedance amplifier is a circuit that will produce a scaled output voltage that is proportional to a supplied input current (this type of circuit is often considered a current controlled voltage source). This type of amplifier can be implemented using an op-amp circuit configuration, as shown in Fig. 1. Transimpedance amplifiers are commonly used to convert the small currents generated by sensors into quantifiable voltages. Figure 1 depicts a transimpedance amplifier connected to a current source. The current source represents the current that would be generated by a sensor connected to the amplifier.

The current generated by most sensors (seen as Ip in Fig. 1.) is very small. This means for the transimpedance amplifier to produce any meaningful voltage, an appropriately large resistor value (Rf ) must be chosen. To choose component values and predict how the amplifier will operate, you can use the governing equation shown below. As the equation illustrates, the resistance value you choose for this circuit is equivalent to the gain (multiplication factor) of the amplifier.

$\mathbf{-I}_p \times \mathbf{R}_f = \mathbf{V}_{out}$