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+++ title = "Transimpedance Amplifiers" author = ["Dehaeze Thomas"] draft = false category = "Equipment" subcategory = "Amplifiers and Conditioning" +++
- Tags
- [Electronics]({{< relref "electronics.md" >}})
Description
A transimpedance amplifier is a "current to voltage converter" and is also named a current controlled voltage source.
It is generally used to interface a sensor which outputs a current proportional to the measurement parameter ([Quadrant Photodiodes]({{< relref "quadrant_photodiodes.md" >}}) for instance).
Basic Circuit
A basic transimpedance amplifier circuit is shown in Figure 1.
It produces an output voltage \(V_{\text{out}}\) proportional to the input current \(I_{\text{sig}}\):
\begin{equation} \boxed{V_{\text{out}} = -I_{\text{sig}} R_f} \end{equation}
The gain of the amplifier is simply \(-R_f\) in [V/A].
The feedback resistor creates a Johnson noise that corresponds to a current noise:
\begin{equation} i_{n} = \sqrt{4kT/R_f} \quad [A/\sqrt{Hz}] \end{equation}
This is usually larger than the amplifier input current noise.
{{< figure src="/ox-hugo/transimpedance_amplifier_schematic.png" caption="Figure 1: Transimpedance Amplifier; Current in, Voltage out" >}}
More information about transimpedance can be found in (Horowitz 2015), chapter 8.11.4, especially on the trade-off between gain, noise and bandwidth.
See this open hardware design.
Manufacturers
| Manufacturers | Country |
|---|---|
| Kistler | Swiss |
| MMF | Germany |
| Femto | Germany |
| FMB Oxford | UK |
| Thorlabs | UK |
| Koheron | France |
| SRS | |
| Basel Precision Instruments | Swiss |