[Laser] Re: Lazer} daytime receiver

[KY1K]

Hi Jim,

That's the circuit, but the discussion of the operation and the noise 
contributions of each component is missing. The document I'm looking for is 
the detailed description of that circuit.

Regards,

Art

At 08:57 PM 10/13/2004, you wrote:
>you can find all the BB OPT datasheets at:
>www.qsl.net/wb9ajz/laser/data
>Figure 12 in the OPT301 datasheet is what you are looking for.
>
>Jim
>N9JIM/6
>
>--- KY1K <ky1k at pivot.net> wrote:
>
> > At 03:43 PM 10/12/2004, you wrote:
> > >Those of you who have done some daytime laser stuff, what kind of RX
> > >circuit have you been using?   I have a hankering to throw something
> > >together this evening as I don't think the soldering iron has been on 
> in a
> > >month.   Basically I'm looking for something to use in the afternoon with
> > >some small lenses.  I'm thinking about cobbling together a potential club
> > >project.  How does this work?
> > >http://www.qsl.net/wb9ajz/laser/data/cheepo.txt
> >
> > Andy and Jim,
> >
> > All of the photodiode based schemes I have seen for this use a low value
> > load resistance for the photodiode and reverse biased for the photodiode.
> > Both of these techniques drastically reduce the sensitivity (but make a
> > wider bandwidth RX), basically 'dumbing down' the receiver so that high
> > ambient light levels don't overload the op amp that converts the photon
> > current to a voltage type signal. This is a horrible price to pay for
> > daylight operation, many 10's of db of sensitivity are thrown away.
> >
> > A better way is to use a 'leaky integrator' with a series resistor in the
> > output to feedback into the inverting input of the current to voltage
> > converter op amp. The secret of this is to select a time constant for the
> > integrator that is ~10 to ~20 times slower than the period of the signal
> > you are trying to receive. So, the time constant for an optical front end
> > with 1000 Hz bandwidth would be 10 to 20 milliseconds.
> >
> > The series resistor limits the absolute magnitude of the correction
> > current, so the less correction needed, the higher value of series
> > resistance needed.
> >
> > While the high value of the limiting resistor does appear in parallel with
> > the photodiode, it doesn't totally disrupt the functionality of the
> > receiver. There is some additional noise added because of the 
> additional op
> > amp, but the loss in sensitivity is minor.
> >
> > This type of receiver might take some time to stabilize when first powered
> > up, but this delay is tolerable.
> >
> > Burr-Brown had an ap note covering the design parameters with an actual
> > example, but I can't find it in my archives. It was 4 or 5 pages in a 
> .pdf,
> > with a name something like 'Ambient Light Cancellation in Photodiode
> > Amplifiers'. When TI bought Burr-Brown, the archives went away.
> >
> > If either of you sees this ap note, please pass it to me so I can add 
> it to
> > my archives.
> >
> > Regards,
> >
> > Art
> >
> >
> >
> >
>
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