[Ronja] What is holding back 100 mbps

[alex dinovitser]

This is surely analogous to the high speed fiber communications such as DWDM.
The current standard here is 10Gb/s per channel. That corresponds to an
electrical bandwidth of at least 5GHz. These optical devices are specified to
10GHz.

The diodes required for this application need to have a very low capacitance.
This capacitance (almost) solely determines the speed of the resulting
transimpedance amplifier. 
A diode's capacitance depends on its area. It also depends on the applied
reverse voltage. However, it would be wrong to use and avalanche diode in
avalanche mode! This diode detects individual photons, and each event has a
'quench time' (it works very similar in principle to a geiger-muller tube)
which means they will saturate with very low ambient light levels!

Avalanche type diodes can be suitable if operated at lower voltage because of
their small area and a wide pIn channel that results in lower capacitance. They
are very expensive however.

The small area for a suitably fast RONJA diode might requires some thought of
the optical system.

I still think the best detector theoretically would be a pyroelectric device.
No suitable affortable devices so far:-(


AD


--- Pavel Krejci <krepa at seznam.cz> wrote:


---------------------------------
  Can you tell us, please, at least which chipset from MAXIM it is?
Thanks

PK

CD930 napsal(a):        Sorry...no, maybe later. But...TX,RXis MAXIM chipset,
mediaconvertor MARVELL 1108  (beforeused Micro-Linear), laser is 870nm/10mW and
photodiode is PDB-C102.
  Tested (tx lens 11cm, rx fresnellens 20cm) on 2500m. RSSI go to AD and Atmel
CPU (LCD and RS232c).
  M.
   
      -----Original Message ----- 
    From:    Deepak Mishra 
    To:    Twibright Ronja 
    Sent:Thursday, February 21, 2008 9:48 AM
    Subject:Re: [Ronja] What is holding back 100 mbps
    
    
Hi CD930,
Sure dont release the PCB, but you could give us suggestions onimproving the
RONJA design to 100 Mbps.
You could point us in the right direction, like the modulationtechnique to use,
coding technique, or LED used ,or lasers, otherpitfalls you encountered ?
Would you like to support a "free" cause ?
    
Regards,
Deepak
    
    On 21/02/2008, CD930 <cd930 at centrum.cz> wrote:    HiVladimir.
Sorry, this development was for one firm from our city.
I must not publish circuit PCB  :(
But....some ideas i am here publish along the years.
      
In future looking on 1Gpbs..... avalanche photodiode with 200V dc :)))
roung again  toy gadget.
      
Martin
      
      
      
      
      
----- Original Message -----
From: "Vladimir Obradovic" <lepiaf at bgwireless.net>
To: "ronja-request at lists.pointless.net"<ronja at lists.pointless.net>
Sent: Thursday, February 21, 2008 1:35 AM
Subject: Re: [Ronja] What is holding back 100 mbps
      
      
>
      
>> From: "CD930" <cd930 at centrum.cz>
>> I tested on MAXIM and MARVELL chip-set....
>> http://www.youtube.com/watch?v=9h3hDm32kv4
>> http://www.youtube.com/watch?v=YcjaJhMHcNk
>
>> TX can by IR-LED, but with short peak to 1ns......
>> http://www.roithner-laser.com/LED_MID_IR.htm    or
>> http://www.roithner-laser.com/LED_HP_single_chip.html
>
>> I am after tested go to laser diode, it is simply.
>> Martin
>
> Nice demo Martin, is there some chance that documentation, tips or
> howtos be available about this project some time in future? Anyplans
> for some kind of open hardware licence like Ronja is, or it will be
> yet another of those projects that inherit Ronja's ideas/hw, showsome
> good
> stuff and then go into some factory for big bucks only :) ? Nowonder
> why Cl always gets upset when ppl start asking about 100mbps orxtra
> range versions :)
>
> cya
> LePiaf
>
>
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> Ronja at lists.pointless.net
> http://pointless.net/mailman/listinfo/ronja
>
>
      
      
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