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LED Response Time

Discussion in 'LEDs and Optoelectronics' started by Johnny101, Jul 24, 2014.

  1. Johnny101

    Johnny101

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    Jul 13, 2014
    Guys I found an led (visible range) with a response time of 20ns does it mean that it will support a switching speed of 25MHz. Also if true are there any leds with lower response time in range of 1-10ns.
    Cheers.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The response time sill be on to off (or off to on) so assuming both times are identical, the switching time for a single cycle would be 50ns. That would imply a maximum speed of 20MHz. However a lot depends on how you're driving the diode.

    Practical fiber-optic drivers capable of 30Mb/s have a rise time of 3.5ns and a fall time of 20ns, however even at this speed, they are recommended for speeds only up to 5Mb/s. Doing the math on this is seems that they would be capable of over 40MHz.

    There are fiber-optic drivers capable of up to 40Gb/s, but I'm not aware of any of these that use other than semiconductor lasers.

    Rise and fall times may be specified for normal LEDs, but they're generally so unimportant that they're not easily searchable using the parametric search engines I've tried.
     
  3. Johnny101

    Johnny101

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    Jul 13, 2014
    Steve thanks for the reply. I couldn't understand your second point also even if I get a driver capable of handling high frequency the response of my led would still be the bottleneck?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    What are you actually trying to do?
     
  5. Johnny101

    Johnny101

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    Jul 13, 2014
    Data transmission through light
     
  6. shumifan50

    shumifan50

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    Jan 16, 2014
    You are going to encounter a few problems. IR LEDs typically don't produce enough light to be picked up by a sensor more than a few centimeters away. Remote controls get around this by pulsing the LED and overdriving it(the carrier frequency). That way you can get several meters. To transmit data, as remotes do, you then have to 'pulse' the data bits. AFAIK this does not produce very high data rates.
    IR is also susceptible to ambient IR, so it will be best to use a device that filters that like a Vishay TSOPxxxx for reception.
    It would be much better to go for laser transmission.
     
  7. BobK

    BobK

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    Jan 5, 2010
    The sensors mentioned by shumifan can actually go up to 40m and in a normal sized room, you can point the sender in any direction and the receiver will pick it up by reflection.

    But the max data rate of these would be a few K bits per second, since they require about 10 cycles to lock onto the modulation.

    Bob
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Yeah, the obvious description of what he wants to do was almost useless. There is a huge difference between transmitting data down a fiberoptic cable and broadcasting it to potentially misaligned receivers in a noisy environment (that's light noise from ambient sources).
     
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