| Electronics > Projects, Designs, and Technical Stuff |
| Looking for Cheap, Ultra Fast LEDs (2-3ns) |
| << < (6/12) > >> |
| supperman:
--- Quote from: StillTrying on January 26, 2020, 11:22:50 pm --- --- Quote from: supperman on January 26, 2020, 03:52:42 pm ---so I think I'm happy with LEDs giving me around 400 Mbit... I think it should be possible.. --- End quote --- I think you could do a 4Mb/s channel for $0.50, but I think there's no chance of 400Mb/s. --- End quote --- Not sure where you are coming from. I'm running at 3ns switching times now.. and am looking for help finding other LEDs to test. I am of course open to other circuits as well.. but most of what I see online are inferior at this point. |
| supperman:
--- Quote from: Marco on January 26, 2020, 10:08:30 pm ---Did you see the speedup circuit in the paper? That should fit in your budget and might eek out some extra performance from indicator LEDs if necessary. --- End quote --- Yes, I have seen this and decided to go a different way. I find that it is limited in how I can tweak it.. and it does not run efficiently for continuous data. (As I think they even point out in their paper). I don't use capacitors or inductors.. I use separate circuits to drive pos and neg spikes and have complete control over duration and current on them. when you look at LED data sheets you can quickly see that continuous drive current may be 70ma.. but they can handle spikes up to an AMP. The above circuit can't deliver that. |
| supperman:
--- Quote from: TheUnnamedNewbie on January 27, 2020, 03:19:36 pm ---This sounds a lot like an x-y problem. Incidentally, getting lots (>>gigabit) data from A-to-B for cheap is the field I'm working in, so perhaps I could help with some outside-of-the-box ideas if you can give more information/limits you are facing. What volume are you looking at? Depending on what output type you have, you might be able to do something with larger symbol size? instead of OOK, consider 4 or even 8 ASK to lower symbolrate? --- End quote --- I'm not sure I know what you are talking about? Encoding data for error correction? I'm not there yet.. just doing single channel bit-rate speed tests. I'll take the problems as they come.. but distances are short and I'll layout all paths with matched lengths so I'm hoping that data will be reasonably in sync and that I don't need to worry. It is video so 100% lossless is also not required.. and I'm hoping to sit on top of some protocol used by the FPGA to serialize and combine.. |
| skylar:
--- Quote from: supperman on January 26, 2020, 03:52:42 pm ---I'm using it to send data across about a 1 cm air gap.. and I use around 10+ of them to get the data I need. Not easy.. since we are talking about serious data over very cheap components. I always have to remind myself that light travels about one foot at 1ns.. to get some perspective.. Also - running this with an FPGA which is limited to about 600 Mbit per pin so taking it down to say a single laser would add all sorts of cost to serialize multiple channels.. etc.. so I think I'm happy with LEDs giving me around 400 Mbit... I think it should be possible.. --- End quote --- Is the 1cm air gap critical or just part of this particular LED implementation? A single SERDES pair and an AC coupled differential pair is about the same cost as 10x of your LED circuits and is good for our isolation needs and certainly meets your speed requirements. For better isolation, the guts of a GigE SFP provides the optical link in our stuff (get a FC 4Gb since you need the speed, they even go up to >16Gb these days). Cost wise you could probably buy one and split the Tx and Rx side onto your own boards with only a little tweaking. Overall it does probably double your parts cost, but its proven tech :/ |
| supperman:
--- Quote from: skylar on January 27, 2020, 08:06:40 pm --- --- Quote from: supperman on January 26, 2020, 03:52:42 pm ---I'm using it to send data across about a 1 cm air gap.. and I use around 10+ of them to get the data I need. Not easy.. since we are talking about serious data over very cheap components. I always have to remind myself that light travels about one foot at 1ns.. to get some perspective.. Also - running this with an FPGA which is limited to about 600 Mbit per pin so taking it down to say a single laser would add all sorts of cost to serialize multiple channels.. etc.. so I think I'm happy with LEDs giving me around 400 Mbit... I think it should be possible.. --- End quote --- Is the 1cm air gap critical or just part of this particular LED implementation? A single SERDES pair and an AC coupled differential pair is about the same cost as 10x of your LED circuits and is good for our isolation needs and certainly meets your speed requirements. For better isolation, the guts of a GigE SFP provides the optical link in our stuff (get a FC 4Gb since you need the speed, they even go up to >16Gb these days). Cost wise you could probably buy one and split the Tx and Rx side onto your own boards with only a little tweaking. Overall it does probably double your parts cost, but its proven tech :/ --- End quote --- Yes, there is unfortunately a physical requirement - air gap AND about 10+ units... so I have to work with that. Also.. if I could use a single link.. now we are talking about an FPGA with 2x 5 gbit ports - or a dedicated chip to do the same.. and that certainly blows the budget, right? I have not gotten FPGA quotes with high speed ports.. but adding them seems to triple the price at least at retail. |
| Navigation |
| Message Index |
| Next page |
| Previous page |