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schematic

simulate this circuit – Schematic created using CircuitLab

I am reading a paper on TIA for optical recievers. On one of the improvements regarding the noise the writers replace the feedback resistor with a common gate MOSFet biased on the triode.

I can see how the MOSFET provides better flexibility regarding the value of feedback resistance (as it can be manipulated through Vg), but I can't tell why, as they say, it is used "in order to optimize the noise".

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  • \$\begingroup\$ A circuit diagram may help., As may a reference to the paper. It may be that the MOSFET provides a degree of constant current action or have some other "law" which makes it suit in some way. | A bipolar transistor operated in that manner is used to create a log voltage amplifier - I'd need to play (if only thought experiment wise) with a FET and TIA version to see if it made sense. \$\endgroup\$ – Russell McMahon Feb 23 at 11:30
  • \$\begingroup\$ Can you refer (ideally link) to the paper? I feel there's some context missing. Perhaps this is in the context of large dynamic range, where a resistor big enough to prevent overload would impose a noise penalty, but a non-linear device gives the best of both worlds? \$\endgroup\$ – Brian Drummond Feb 23 at 14:37

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