transimpedancy

Transimpedance refers to the ratio of the output voltage to the input current in an electronic circuit. Essentially, it describes how effectively a circuit converts an input current into an output voltage. A high transimpedance means that a small input current will produce a large output voltage, while a low transimpedance means a larger input current is needed for the same output voltage.

This concept is particularly important in applications involving current sensors and photodetectors. For example, a photodiode generates a current proportional to the light incident upon it. A transimpedance amplifier (TIA) is then used to convert this small photodiode current into a measurable voltage. The transimpedance of the TIA is a critical parameter determining its sensitivity. A higher transimpedance allows for the detection of fainter light signals.

The unit of transimpedance is ohms (Ω), reflecting its nature as a resistance-like quantity that relates voltage and current. However, it's important to distinguish it from simple resistance, as transimpedance is specific to the gain characteristic of an active circuit, not just a passive component. In operational amplifier circuits, transimpedance is often determined by a feedback resistor. The value of this resistor directly sets the transimpedance of the amplifier.