High frequency performance of LEDs

Forum for discussion of narrow-bandwidth mechanical television

Moderators: Steve Anderson, Dave Moll, Andrew Davie

High frequency performance of LEDs

Postby Panrock » Fri Oct 26, 2012 9:28 am

What are the fastest types of LEDs available and how fast can they be made to work, given suitable a driving arrangement and pre-emphasis of the signal? Is there a luxeon that could be modulated at (say) 50 MHz ?

Thanks.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 863
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby Steve Anderson » Fri Oct 26, 2012 1:01 pm

I think you can take a cue from fibre-optic links which go to GHz. They use small-junction IR LEDs and similar photo-diodes. With a very stiff temperature-compensated voltage drive the junction capacitance is 'drowned'. At the receive end the photodiode produces a current which is converted to a voltage via a transimpedance stage such that there is no varying voltage across the device, hence no charge/discharge of the junction capacitance. This is for on/off (binary) applications though.

In the visible spectrum I would think that applying similar techniques would result in similar results.

There must be some data for the screens used in LED TV's..no need for GHz bandwidth, but fast enough to convince the human eye-brain that the motion is smooth.

The exception are those LEDs that use a phosphor to convert UV to visible spectra...e.g. white...or at least what some call white.

Steve A.
User avatar
Steve Anderson
"Fester! Don't do that to 'Thing'"
 
Posts: 4219
Joined: Fri Mar 30, 2007 10:54 pm
Location: Bangkok, Thailand

Postby Panrock » Fri Oct 26, 2012 6:43 pm

Looks hopeful then...?

I am looking into an application involving high intensity red luxeons. Good linearity of modulation would also be required but the bandwidth would be relatively modest.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 863
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby Steve Anderson » Fri Oct 26, 2012 7:33 pm

Panrock wrote:I am looking into an application involving high intensity red luxeons. Good linearity of modulation would also be required but the bandwidth would be relatively modest. Steve O


If I can help...here I am...

Steve A.
User avatar
Steve Anderson
"Fester! Don't do that to 'Thing'"
 
Posts: 4219
Joined: Fri Mar 30, 2007 10:54 pm
Location: Bangkok, Thailand

Postby Panrock » Fri Oct 26, 2012 7:43 pm

That's a typically generous offer! :D

You'll be the first to hear more about this, should it go ahead.


Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 863
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby Steve Anderson » Fri Oct 26, 2012 8:44 pm

Panrock wrote:You'll be the first to hear more about this, Steve O


You know that it would be commercially confidential if that's the final objective...

Steve A.
User avatar
Steve Anderson
"Fester! Don't do that to 'Thing'"
 
Posts: 4219
Joined: Fri Mar 30, 2007 10:54 pm
Location: Bangkok, Thailand

Postby Panrock » Mon Oct 29, 2012 6:52 am

I have done some googling about the following, though with inconclusive results.

Are there such things as near infra-red (say 800-1000 nm) luxeons ?

Thanks.
Panrock
Green padded cells are quite homely.
 
Posts: 863
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby Steve Anderson » Mon Oct 29, 2012 3:00 pm

Not that I'm aware of...I think there are a few UV versions but near-IR I can't say I've seen. The major application of Luxeons or other power LEDs is illumination where the output has to be visible.

Standard 3/5mm IR LEDs are powerful enough for their major use, short-range remote control up to 20 or so metres.

I have an idea what the application for these may be but I'll cover that in a PM.

Steve A.
User avatar
Steve Anderson
"Fester! Don't do that to 'Thing'"
 
Posts: 4219
Joined: Fri Mar 30, 2007 10:54 pm
Location: Bangkok, Thailand

Postby dominicbeesley » Tue Oct 30, 2012 11:09 pm

I'm guessing SteveP's thinking along similar lines to me, I'd like an optical broadband link and have been trying to figure what to use...

I notice from RadCom that there's been quite a lot of optical comms work recently but manly sound at base-band. I'd like to do something with a subcarrier of around 10MHz as a starting point but not sure how to drive the LEDS. I'd like something, near infra-red or visible and capable of a good few miles.

(I didn't think that OLED TV leds don't needed to be at all fast, they only change state once every 50th/60th of a second...or are the PWM modulated?)

D
User avatar
dominicbeesley
Anyone have a spare straightjacket?
 
Posts: 683
Joined: Sat Sep 13, 2008 11:32 pm
Location: Hebden Bridge

Postby Panrock » Wed Oct 31, 2012 12:49 am

dominicbeesley wrote:I'm guessing SteveP's thinking along similar lines to me, I'd like an optical broadband link and have been trying to figure what to use...

Didn't know SteveP (Steve Pendlebury) was looking into this. Steve O (Steve Ostler) certainly isn't! :)

dominicbeesley wrote:I notice from RadCom that there's been quite a lot of optical comms work recently but manly sound at base-band. I'd like to do something with a subcarrier of around 10MHz as a starting point but not sure how to drive the LEDS. I'd like something, near infra-red or visible and capable of a good few miles.


So would I! If you come up with anything, please post about it.

Steve O
Panrock
Green padded cells are quite homely.
 
Posts: 863
Joined: Mon Feb 05, 2007 8:25 am
Location: Sedgeberrow, England

Postby dominicbeesley » Wed Oct 31, 2012 12:53 am

Whoops, sorry, wrong key!

Will do, is just a thought exercise at the moment...the workshop is so full of clutter I've not managed anything useful in months!

D
User avatar
dominicbeesley
Anyone have a spare straightjacket?
 
Posts: 683
Joined: Sat Sep 13, 2008 11:32 pm
Location: Hebden Bridge


Return to Mechanical NBTV

Who is online

Users browsing this forum: No registered users and 13 guests

cron