modulating a ramp into a IR transmitter

Have a look at a multiplier/modulator chip. Jim Thompson's MC1496

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

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

Why do you want to use a ramp?

Have you considered PWM?

-- Joe 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

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.

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

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

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

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

can handle higher voltage levels

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