Re: low noise amplifier for high impedance source

Thanks Win,
I appreciate the explaination. It makes complete sense to me now.
Earlier, i was misled about matching the capacitance stuff.
I have been working a design using JFETs from Interfet having en =
5nV/rtHz @10kHz, input capacitance 25pF and CRss of 5pF. Clearly i was
not doing the right thing and i can certainly improve by selecting the
proper device.
So besides the en in my frequency range and min. capacitance - sh'ldn't
i look at the leekage current numbers as well. As i understand it would
determine how large input resistor i can put at the input (instead of
1M ohm) without disturbing the gate bias.
I cannot do anything about the 20pF capacitance at the input, its
intrinsic to the detector and i am already keeping my preamplifier as
close as possible.
I am sorry about the reference to the paper earlier, i thought its free
online access - as i'm in school never encountered subscription
problems. I have uploaded it at the following url, incase people are
interested.
http://www.yourfilehost.com/media.php?cat=other&file=Singnal_modelling_Comisarow.pdf
Thanks again for helping.
-Arch

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