High Speed IR receiver design

Feb 12, 2007 4 Replies
O

I've seen lots of schematics on the net for receiving signals modulated at around 30-40kHz, but I'm trying to design a system that will work at around the 1Mhz range. I've practically tried the designs at those frequencies, but there seems to be a lot of atenuation at higher frequencies. I've been told this is because the photodiode acts like a cpaacitor when reverse biased, and that capacitor causes attenuation with high frequencies. Is there any way round that?



I know it must be possible because IRDA manages data rates of up to



4Mbps (although using a PPM system). I'm trying to achieve a data rate or atround 500bps, using any standard as I'm designing transmitter and receiver. Any suggestions?
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T

If IRDA has solved this problem already, why not use it? If not the whole of IRDA, how about finding front-end designs for its receiver?

My knee-jerk reaction to this is to use a good fast PIN diode, and feed it into a common-base transistor stage. So long as you use a modulation method that can be AC coupled this should be pretty easy to do.

Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
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R

Have a look at the Vishay IR receiver modules at 455Khz.

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These will comfortably give you 10K+ bps. - they are cheap and easy. Similar modules are available from others

Don't forget to drive the LED(s) properly - at these speeds the diode capactance can become significant and you need to drive the LEDs on and off. Sticking the LED(s) on a collector with a series R will not do unless you are only looking for a short range. Also, whilst you are playing around with any cicuitry, be aware of the eye hazard of IRleds.

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A

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I always thought the eye hazards were minimal. After all, IR is what is used in Laser Tag/MILES and its deemed safe in that application. I don't see why it would be unsafe here.

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R

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What makes you think the eye hazard is minimal. What do others do to avoid eye hazard with IR? A class 1 product is indeed not deemed a hazard (under normal conditions).Class2 and upwards may be hazardous. Start off with EN (or IEC) 60285. A reading and understanding of this is imperative and has a legal enforcement.

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