The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Photodiodes in photovoltaic mode, speed considerations.
References: <3DACB831.F814C3D6@webaccess.net> <3DAD0481.A4004E95@NOSPAM.univ-lille1.fr> <3DAD0A0A.1F7BF2DD@webaccess.net> <email@example.com>
Date: Wed, 16 Oct 2002 13:14:35 GMT
NNTP-Posting-Date: Wed, 16 Oct 2002 06:14:35 PDT
fred bartoli wrote:
> Chuck Simmons a =E9crit dans le message :
> > "s.d." wrote:
> > >
> > > My two cents...
> > >
> > > If you want speed you may buffer your photodiode with a transimpeda=
> > > amplifier.
> > > That's the usual way. But still you'll need negative supply.
> > > At least you can try to put a low impedance load to your diode at t=
> > > expense of lower gain.
> > > Mind that in voltage mode the diode response is logarithmic with li=
> > > power.
> > A negative supply is outside of allowed parameters. If it costs $0.10=
> > is outside of allowed parameters. A load on the diode is not allowed
> > because because I cannot specify a buffer that operates that close to=
> > the negative rail. I figure I can just live with 100mV off the rail a=
> > since I see, in devices so far, 150 to 200 mV at desired power, I'm O=
> > The problem is speed for clock selection for the digital loop which
> > depends on the diode speed in photovoltaic mode. I know some clock
> > limits for some devices but I can't predict because I only get revers=
> > specs and I don't know how these or area relate to speed.
> > BTW, we did use loading for a while but it did not work with a
> > population of parts we had because the effect of the load on voltage =
> > less predictable and caused laser damage (i.e., the things failed).
> > Unloaded photovoltaic is safe it would seem from our experience. Some=
> > the population of lasers tend to require close to burnout current
> > levels. This is within spec for the lasers but a real pain for me.
> > Chuck
> > --
> What is your laser power (current) ?
> If it's low enough, you could simply sightly offset the laser & photodi=
> pair form the ground by inserting one diode (or two) in the lower branc=
> Then you'll have 0.7V (1.4V) room for a transimpedance amplifier with s=
> about 0.5V (1.2V) full scale output.
I thought about it but the manufacturers of the optical units connect
the laser cathode to power ground. I don't control the circuits on the
optical units. I live with them. This means that I definitely have a
photovoltaic diode referenced to system ground. The question is
predicting the speed of the diode given inadequate data and not one of
redesigning some other company's circuits. I want to select a clock
frequency for the power controller for each type of laser rather than
design additional circuits.
... The times have been, =
That, when the brains were out, =
the man would die. ... Macbeth =
Chuck Simmons firstname.lastname@example.org
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup