Transimpedanzwandler

Transimpedanzwandler, also known as current-to-voltage converters, are electronic circuits that convert an input current into an output voltage. They are commonly used with photodiodes and other current-output sensors. The fundamental principle of a transimpedance amplifier is to use an operational amplifier (op-amp) in a feedback configuration. The current to be measured is fed into the inverting input of the op-amp. A resistor, known as the feedback resistor, is connected between the output of the op-amp and the inverting input.

The op-amp attempts to keep its inverting and non-inverting inputs at the same voltage. Since the non-inverting input is typically grounded, the op-amp forces the inverting input to be at virtual ground. This means that any current flowing into the inverting input must flow through the feedback resistor. According to Ohm's law, the voltage across the feedback resistor is the product of the current and the resistance. Since the inverting input is at virtual ground, this voltage across the feedback resistor directly becomes the output voltage of the transimpedance amplifier. Therefore, the output voltage is proportional to the input current, with the feedback resistor determining the conversion gain.

Transimpedance amplifiers are characterized by their low input impedance, which is crucial for efficiently collecting current from devices like photodiodes without loading them down. They also offer high gain and wide bandwidth. Parasitic capacitance at the input can affect the stability and frequency response of the circuit. To mitigate this, a small capacitor is often placed in parallel with the feedback resistor. This forms a low-pass filter, which helps to compensate for the op-amp's internal capacitance and improve stability.