[Ronja] new receiver design

[mohamad al-jamal]

Dear all

I have been trying to modify the Ronja inferno receiver for the sake of
better performance .. i have replaced the first stage ( transimpedance
amplifier ) with a conventional configuration : an opamp with an RC feedback
circuit .. instability is avoided by inserting a relatively high capacitor
in the feedback circuit .. the bandwidth is ruined though , therefore the
NE592 is used - just like in inferno - to compensate for the integrator
effect of the TIA . i used a high bandwidth opamp from texas instruments
(OPA657) . and used another PIN photodiode , a cheap one from vishay (
http://www.vishay.com/docs/81503/bp10nf.pdf) . the PIN is directly biased by
a -12 supply . and every thing went just fine !! the signal was nice and
clean . i'am still experimenting , but it seems promising .  this image
illustrates the new configuration .
http://img265.imageshack.us/i/rxfirststage.jpg/

i have a couple of questions though :
regarding R3 in the schematics , i thought that R3 should be as high as
possible in order to avoid thermal noise ... is that true ?
regarding the filtration practice of the supply connected to the PIN , is
the configuration in the image sufficient ?

any ideas are highly appreciated .
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