Alt-BEAM Archive

Message #10311



To: beam@sgiblab.sgi.com
From: "Dane Gardner" dane@foremostspring.com
Date: Wed, 16 Feb 2000 17:14:10 -0800
Subject: [alt-beam] Re: pdiode ptransistor?



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>>From: William Cox

There is only two pins.... the light functions as the base.<<

Awe man, I really wasn't thinking when I wrote that...I'm sorry. I've been working on two term
papers...and trying to study for finals which are next week. So, I've really had my mind elsewhere
for the last couple of days.

>>From: Sathe Dilip

It's not that simple. A photo transistor, when its base is properly
biased, can give you some current (induced by photons/light in this
case) amplification. A photo diode will just give you the increase in
leakage current when exposed to light. Getting the first stage of
amplification right at the source is important when you are dealing with
low noise requirements in a circuit. In BEAM environment where usually
we are using the sensor to give us a presence/absence of light type of
indication, this may not matter that much. But say you want to build a
light beam communicator, and you will see the need for a low noise input
stage. <<

Your absolutely right.



Dane Gardner



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Awe=
man, I =

really wasn't thinking when I wrote that...I'm sorry.  I've been worki=
ng on =

two term papers...and trying to study for finals which are next week. =
So, =

I've really had my mind elsewhere for the last couple of days. >


    >>From: Sathe =

Dilip
    
    It's not that =

simple.  A photo transistor, when its base is =

properly
    biased, can give you some current (induced b=
y =

photons/light in this
    case) amplification.  A ph=
oto =

diode will just give you the increase in
    leakage curr=
ent =

when exposed to light.  Getting the first stage of
  &nbs=
p; =

amplification right at the source is important when you are dealing =

with
    low noise requirements in a circuit.  In BE=
AM =

environment where usually
    we are using the sensor to =
give =

us a presence/absence of light type of
    indication, th=
is =

may not matter that much.  But say you want to build =

a
    light beam communicator, and you will see the need =
for a =

low noise input
    stage.  <<


Your absolutely right. T>


 



face=3D"Comic Sans MS">        &nbs=
p;   =

Dane Gardner





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