[Laser] OPT-101 vs PIN diode

[Art]

Yves,

I haven't looked at the file, but the information 
is interesting. Thank you for pointing out the paper.

Rather than 'improving' the bandwidth without 
adding the noise component of a large value 
resistor, I'd think that 'controlling' the bandwidth would be most useful.

I've never built the PGP front end, mostly 
because it was so difficult to quantify it's 
bandwidth. And, the opt-101 and opt-301 gives you 
a graph of resistance vs bandwidth-and you simply 
select the bandwidth you want by putting in the proper value resistor.

I'm curious though....the FET has a very large 
(100 megohms +/-) input impedance, wouldn't the 
presence of this large value resistor built into 
the FET contribute a noise itself, that would be impossible to negate?

I'll read the paper....  If it turns out I can 
adjust the bandwidth of the PGP front end without 
compromising it's performance, I'll definitely 
build on up to try it against the opt-101.

Regards,

Art






At 05:43 AM 12/14/2006, you wrote:
>Dans un e-mail daté du 13/12/2006 19:53:20  Paris, Madrid,
>skavanagh73 at yahoo.ca a écrit :
>
> >As I understand it the  bandwidth of the K3PGP front
> >end (and similar designs) is controlled by  the
> >parallel combination of a resistance (gate-to-ground
> >resistor,  FET input resistance, photodiode resistance
> >and stray leakage in  parallel) and a capacitance
> >(photodiode capacitance and FET input  capacitance in
> >parallel, plus stray capacitance from  wiring).
>
> >I agree that some of these quantities are a bit  hard
> >to define.
>
>The PGP front end can be bandwidth improved by a  low impedance feed back at
>the photodiode cold point.
>A very good work had  been done by Kalevi Hyyppa and Klas Ericson to avoid
>the noise due to the  classical big resistor feed back effect.
>The pdf file can be loaded  at:
>http://pageperso.aol.fr/F1AVYopto/opto/Hyyppa-lownoisephotodiodepreampPIF.pdf
>
>Yves  F1AVY
>http://pageperso.aol.fr/YvesF1AVY/
>
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