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modulating a ramp into a IR transmitter

Hi All,

This is a circuit design question for IR data emitters.

Currently I am using a 455 Khz signal to drive an IR LED with pulsed data modulation at 20 KHz. I want to modulate the data using a ramp circuit instead of a data pulse (i.e. a ramp replaces the pulse). Does anyone know how I can modulate a ramp into the 455 khz driver signal? I already have a ramp generator using a timer circuit, but modulating the ramp into the LED using a single transistor provides too weak a drive signal to run the LED, hence reducing its range of operation. How can I modulate a ramp into the drive signal to get more output power, hence more range?

Thanks for your help!

-Andrew

Reply to
Bluespace Technologies
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Have a look at a multiplier/modulator chip. Jim Thompson's MC1496

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has it's fans, but the Analog Devices AD734 is easier to use

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There are a bunch of similar integrated circuits on the market.

--
Bill Sloman, Nijmegen (but in Sydney at the moment)
Reply to
bill.sloman

Why do you want to use a ramp?

Have you considered PWM?

-- Joe Legris

Reply to
J.A. Legris

Basically, that is the idea. I want a ramp to receive a pulse that varies with the strength of the transmitted signal. If the transmitted signal is strong then the received pulse width is longer, etc.

-Andrew

Reply to
Bluespace Technologies 

--
Use a 555 wired as an astable and send the modulating signal into
the voltage control pin.
Reply to
John Fields

Sounds a bit unorthodox. Well, but so are many of my circuits. One method to modulate is "robbing LED current". IOW use a current source to drive the LED and another circuit that gradually steers that current into ground. Or vice versa, depending which direction you want the ramp.

Look at laser diode driver app notes for details.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

Thanks Bill,

I happen to have a few AD835's handy. They seem to be similar to the AD734 but an 8-pin multiplier layout. What do you think?

-Andrew

Reply to
Bluespace Technologies

Lots faster than you need, and - IIRR - a bit more difficult to bias, but fine for proof of principle.

--
Bill Sloman, Nijmegen (but in Sydney at the moment)
Reply to
bill.sloman

I could not get this chip to modulate the signal. I have two signals 455 KHz and a ramp signal with period 20 khz. Both are zero to 5 volts max. I can modulate with a single 2N4401 transistor and am trying to amplify this with a hexfet IRLD014 (more than I need) but this may get the necessary output power to the emitter.

-Andrew

Reply to
Bluespace Technologies

The differential voltage limits on both x and y inputs are +/-1V. You are going to have to divided down your 0V to 5v signals before your feed them into the AD835. The AD734

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can handle higher voltage levels

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Like I said, the AD835 is more difficult to bias.

--
Bill Sloman,Nijmegen (but in Sydney at the moment).
Reply to
bill.sloman

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