STOP THE PRESS - thanks guys did not know that - WOW have learnt something.
> A photo-diode can be operated in one of two ways.  It can be used as a
small
> "solar cell", i.e. it will generate a small current when exposed to light.
> If used in this manner, the device would be forwards biased.
>
> The other property of photodiodes is that the "leakage" current when
> reversed biased is proportional to the intensity of the light it is
exposed
> to.  This is how the device is used in the circuits you have seen.  This
> method has the advantage of moving carriers from the depletion region out
> very quickly, and gives the device a much faster response than using it
> forwards biased.
>
> Typicaly you can get PIN based photodiodes that can operate with a
bandwidth
> of 7GHz or even higher for high speed data over optical fibres.
>
> Regards
>
> Mike



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