How to Build a High-Sensitivity Gigahertz Current Amplifier for Photocurrents?

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Building a low noise current amplifier with a bandwidth from 10Hz to 1GHz for amplifying photocurrents presents significant challenges due to the inherent high 1/f noise of suitable high-frequency transistors. The discussion highlights that while amplifying signals in the pA range against a background of nA is the goal, achieving low noise across such a wide frequency range is problematic. The Johnson noise will also be considerable at 1GHz bandwidth, influenced by source impedance. Matching the high impedance of the photocell to a conventional 50-ohm cable is essential for optimal performance. Overall, the feasibility of creating such an amplifier remains questionable due to these technical limitations.
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Does anyone know how to build a low noise current amplifer that has wide bandwidth from ~10Hz to ~1Ghz, and together with high sensitivity (can amplify ~nA/pA)

I need one for my project to amplify photocurrent, but am struggling to find any suitable products or design guides...

cheers
 
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Define "low noise"...
The general answer would be that no, it is not possible to build such an amplifier. All transistors that work well at high frequencies (GaAs, InP etc) have very high 1/f noise meaning they are extremely bad at amplifying low frequencies. Also, remember that the Johnson noise will be quite high for an amplifier with 1GHz BW (how high will obviously depend on the source impedance).
 
"low noise" as in i need to amplify something in the order of "pA" in the background level of "nA"...
i would be amplifying a pulse with width in the nanoseconds range, i would guess most of the frequency component are in the high range, so I may be able to withstand a amplifier which is bad at amplifying low frequencies...
the source impedance "photocell" is extremely large ~Gigaohm/square...so I think it is a must to match that to a conventional 50 ohm cable prior to the amplifier..

cheers
 

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