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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I actually tried to make an AM transmitter with a ZVS driver that we all know and love, and it worked, sort of.
Op amp circuits are so annoying it's criminal...
Basically, the way the AM modulation works with the circuit I have, and the one I tried to build, is it's basically a class D amplifier, and compares the carrier wave to the signal you want to transmit. Thus changing the amplification of the carrier wave as such, just using a ZVS driver as a base.
However, I couldn't and still cannot get a normal class D amplifier to work, and it's really bugging me. I don't know what i'm doing wrong, or why it seems op amps hate me.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I think part of the problem you have with opamps may just be due to that falstad circuit simulator you are using, it really is not good for more than very simple circuits.
When I was in my junior level circuit design class a few groups figured they would save time calculating/prototyping and designed their circuit in falstad, only to find that when they tried to build them they did not work at all like expected. Then they tried to simulate the designs everyone else had come up with, and were known to work, and sure enough they didn't work in falstad
I have had slightly better luck using spice (I like Qucs as a frontend for it, it is quite nice), but you still have to be very careful since it has its quirks as well.
This circuit might work if you built it, the choice of opamp will probably be somewhat critical to the performance of the circuit. Since you are running at at MHz you will need to find an opamp with a gain bandwidth product on the order of 100MHz (which will give you a gain of 100, which is still on the low side, since falstad assumes infinite gain) which will be expensive and probably require a fair bit of compensation to keep the whole mess from going into uncontrolled oscillation.
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ZVS driver into an AM transmitter
