[Laser] Cloud bounce new optical receiver.

[F1AVYopto at aol.com]

Art

>If we were serious about preserving every single  partial db of noise 
>figure (without concern for $$), would these  transistors be the ones 
>to use???? Or are there better choices, although  more pricey?

These transistors are low cost and we do not find  better for today even with 
very high cost.
To go less than 1nV / s.r.Hz at  very high impedance seems only possible with 
a parallel input stages matrix but  the input capacitance and the input 
leakage dramatically increase.  

>Yves, did you spice model this?? Also, if you did, did you by  any 
>chance use LTSpice?

I am not a spice model specialist  but if somebody can do it that should be 
great !

>I wonder if  you have done any comparison between the OPT301 and your 
>modified PGP  rx?

We did no comparison with the OPT301 because the result should  be the one of 
a classical Op Amp transimpedance amplifier with a classical 2  FETs 
differential input (extra noise) and a feed back resistor (extra  noise).
If you have a look on the datasheet you will be  afraid:
http://focus.ti.com/lit/ds/symlink/opt301.pdf
The internal  photodiode has a 4000pF capacitance !
The input noise of the internal  amplifier is 15 nV / s.r.Hz ! 
To approach our K3PGP RX sensitivity with a  transimpedance Op Amp design it 
could be possible to use a LMH6624  with a  500 Mohm metal oxide feed back 
resistor.
However if you compare the noise  characteristics  between
http://www.national.com/pf/LM/LMH6624.html
and
http://www.ampslab.com/PDF/2sk170.pdf
you  will see the first device is the noisiest to less than 1  KHz.

Regards
Yves F1AVY