Transimpedance amplifier

Transimpedance amplifier

The following circuit, which is referred to as a current-voltage converter or transimpedance converter (TIA), converts an input current I_IN into a defined output voltage V_OUT:

Transimpedance amplifier

The basis of the current-voltage converter is the inverting amplifier. Since the input current of the OP-Amp is negligibly small, we derive from the node rule:

I_IN = - I_f

Applying the law of Ohm:

V_OUT = V_f = I_f × R_f = - I_IN × R

This makes it clear that the output voltage is proportional to the input current. The ratio of input current to output voltage is determined by the resistance R_f.

Exercise Op-Amp as Transimpedance Amplifier

Below you can see an Op-Amp circuit that converts a sensor signal of 4 ... 20 mA into a voltage signal of 0 to 10 V.

Op-Amp as Transimpedance amplifier - exercise

1. What tasks do these two Op-Amp´s have in this circuit?
2. What advantage does a sensor with a current signal of 4 to 20 mA offer compared to a sensor with a voltage signal of 0 to 10 V?
3. In the diagram below, add the characteristic curve V₁ depending on the sensor signal!

Op-Amp as Transimpedance amplifier - diagrams

1.  Op-Amp 1 as transimpedance - Converter, Op-Amp 2 as summer

2. Current signal can also be kept constant or stable via a long signal line. Minimum current 4 mA means wire break protection.

3. See diagram below:

Op-Amp as Transimpedance amplifier - solution