A low-noise resonant input transimpedance amplified photodetector

We present the design and characterisation of a low-noise, resonant input transimpedance amplified photodetector. The device operates at a resonance frequency of $90 \,\textrm{MHz}$ and exhibits an input referred current noise of $1.2\,\textrm{pA}/\sqrt{\textrm{Hz}}$---marginally above the the theoretical limit of $1.0\,\textrm{pA}/\sqrt{\textrm{Hz}}$ set by the room temperature Johnson noise of the detector's $16\,\textrm{k}\Omega$ transimpedance. As a result, the photodetector allows for shot-noise limited operation for input powers exceeding $14\,\mu\textrm{W}$ at $461\,\textrm{nm}$ corresponding to a noise equivalent power of $3.5\,\textrm{pW}/\sqrt{\textrm{Hz}}$. The key design feature which enables this performance is a low-noise, common-source JFET amplifier at the input which helps to reduce the input referred noise contribution of the following amplification stages.