[Laser] Re: Lazer} daytime receiver

[Jim Moss]

All BB apnotes here:
http://www.nalanda.nitc.ac.in/industry/AppNotes/BurrBrown/Index.html
you want AB-061


A couple papers on the same subject
http://www.eecg.toronto.edu/~kphang/papers/ISCAS99.PDF
http://www.eecg.toronto.edu/~kphang/papers/ISCAS98.PDF


--- 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
> 
> 
> 
>