| Electronics > Projects, Designs, and Technical Stuff |
| Looking for Cheap, Ultra Fast LEDs (2-3ns) |
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| skylar:
--- Quote from: supperman on January 27, 2020, 08:37:52 pm ---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. --- End quote --- I was talking about a dedicated chip, the SERDES (serial/de-serializer) I find in your ~10bit 4Gb use case are about $6/EA and let you use the same 10x 400Mb ports on your FPGA. Since you mentioned its a video application, there's even dedicated 16bit RGB video SERDES like the Renesas ISL76322ARZ that popped up in my search, not sure what you are doing with your FPGA but that's an interesting option to just shuttle video data around that may not need an FPGA? |
| dmendesf:
He was talking about increasing the data rate without increasing the simbol rate by coding more than one bit per simbol. Suppose instead of on / off you had 4 different brighteness levels... Then you could double the data rate without needing a faster diode. There are other coding schemes to achieve this. |
| supperman:
--- Quote from: dmendesf on January 27, 2020, 09:49:17 pm ---He was talking about increasing the data rate without increasing the simbol rate by coding more than one bit per simbol. Suppose instead of on / off you had 4 different brighteness levels... Then you could double the data rate without needing a faster diode. There are other coding schemes to achieve this. --- End quote --- Ah.. Understood! Not possible in this design since the brightness will vary based on external forces (i.e. LED and sensor will not always be aligned perfectly) I think I can safely clip on "on / off" but can get no more detail out of it. |
| supperman:
--- Quote from: skylar on January 27, 2020, 09:10:14 pm --- --- Quote from: supperman on January 27, 2020, 08:37:52 pm ---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. --- End quote --- I was talking about a dedicated chip, the SERDES (serial/de-serializer) I find in your ~10bit 4Gb use case are about $6/EA and let you use the same 10x 400Mb ports on your FPGA. Since you mentioned its a video application, there's even dedicated 16bit RGB video SERDES like the Renesas ISL76322ARZ that popped up in my search, not sure what you are doing with your FPGA but that's an interesting option to just shuttle video data around that may not need an FPGA? --- End quote --- Sorry - in my mind I thought you meant optical transceiver.. which of course I would still need.. at a high speed rate. I don't know of anything cheap here.. $10 for the transmitter, $10 for the receiver? Another $6 for 2nd SERDES.. optics? stuff adds up very quick. And debugging 4gbit signals.. am limited to 1ghz scope. I'm not saying no. perhaps you have links to come components here that simplify things? I just don't know of a transmitter or receiver that directly takes/sends a differential signal at that speed that does not cost an arm and a leg... and if I'm building one I think I may be in a world of hurt at that data rate.. This is how I always come back to the LED design :) (and for the people paying attention.. yes, potentially there is a way to use a single transmit/receive rather than 10+. It is either or) |
| StillTrying:
--- Quote from: supperman on January 27, 2020, 04:43:56 pm --- --- 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.. --- End quote --- If you're putting a digital 100Mb/s in one end and recovering a 100Mb/s digital output from the other I've no idea how you're doing that with a few $0.10 components! --- Quote ---and am looking for help finding other LEDs to test. --- End quote --- I think if any one here knows much about switching normal LEDs and photodiodes at these speeds they're keeping it to themselves. |
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