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AD633 as amplitude modulator - not working


New Member

Please can someone help on what has got to be a simple oversight by me.

I am using the AD633 in spice as an amplitude modulator, but it's just giving me a rubbish output. Output is a few mV when the input is a few V, and it is not what I'd expect from an AM signal. My circuit is from the datasheet example, and plenty of entries online allude to using this circuit, I can't get it to work. This is the second AM arrangement I've tried, the first with a transistor and I got similar rubbish results. I am clearly missing something, but after nearly 8 hours of searching I can't find the issue and it's driving me nuts!

If anyone has experience with this IC, please can you take a look?

Attached is the spice simulation (LT spice - I haven't used this package before, so could be an error there), also the green trace is the output. Input conditions are labelled on the schematic.

Any pointers / ideas really appreciated.




Well-Known Member
Most Helpful Member
It looks like there is 5V offset on the input signals.
Set that to 0v.


Well-Known Member
Most Helpful Member
Here's my LTspice simulation:
I removed the input signals' DC offset.



Well-Known Member
Please verify the actual polarity on pins 5 and 8. Use a DMM for that.

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