[Ronja] new receiver design

[mohamad al-jamal]

happy easter to all ...

gullik , do you mean the filter should look like in this image ?? i think we
need a freewheeling diode after the L , don't you think ??

http://img163.imageshack.us/img163/668/filterj.jpg

as for the noise , actually we happen to have a crappy old oscilloscope ...
i might be able to obtain a better one after the holidays ..


On Tue, Mar 30, 2010 at 12:45 PM, Gullik Webjörn <
gullik.webjorn at corevalue.se> wrote:

> On Tue, 2010-03-30 at 02:03 +0300, mohamad al-jamal wrote:
> > the design is performing very nicely ... distance without lenses was
> > roughly 1.5m .  i'am still experimenting though ... as for the
> > sensitivity and noise , i intend to increase the feedback resistor to
> > 400K or so , it will form a pole almost at the same point inferno
> > does , but with better sensitivity and noise performance ( at least
> > theoretically !!)  .. the signal at the output of the TIA is a
> > sawtooth with 450mV p-p ... i don't know how to measure the noise
> > properly !! but without an optical signal,we get a random noise
> > (without oscillations) with about 80mV p-p .
>
> My simplistic view 450/80 = 15 dB. If you use a good oscilloscope,
> measure the signal, then increase gain and measure vertical "thickness"
> of the trace, this works best on a square wave.
>
> >  the strange thing we found is that the smaller R3 is , the better the
> > performance gets !! any explanation !?!? as for the B.W , we used a
> > function generator as a signal source , and the we ranged the
> > frequency from 1MHz up to 13MHz or so , and nothing went wrong ..
> >
> Measure voltage drop across R3 on various signal conditions. Maybe
> you find you are saturating the pin, causing large voltage drop,
> decreasing bias on PIN, causing less gain.
>
> What about a small R3, cap to ground, small L (ind), cap to ground??
> Since the other node, PIN cathode goes to OP input / feedback resistor,
> a low R3 will not increase risk of excessive current in PIN.
>
> Regards,
>
> Gullik
>
>
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