Re: RF power chain mods and improvements..

Jerry Gaffke

I'm learning here, never knew that a push-pull configuration for MMIC's was a thing.
But plenty of google hits, figure 2 on page 4 here shows one:

Even configured for push-pull, there aren't many MMIC's that can deliver
the nearly 1W of power needed to drive those IRF510 gates at 30mhz.
There are MMIC's that could deliver the 100mW needed to replace Q911,912
when configured as a single.

I'm really curious how well that ADA4895-2 works for driving the the IRF510's.

Still not sure about the 2v.
The MMIC's are designed for a specific operating voltage, if designed for 4.0v and
you drop it to 2.0v, it won't draw any current from the supply and won't work.
My guess is that the 4.0v (4.5v absolute max) spec on the cheap BGA616 MMIC is the "supply voltage",
used in calculating how many ohms for the dropping resistor from your particular supply rail
to get the desired 60ma quiescent current into the MMIC.  Signal rides on top of that, so it's fair to 
have instantaneous voltages in excess of 4.5v on the output pin of the MMIC.

Jerry, KE7ER

On Sat, Jun 9, 2018 at 12:25 pm, Howard Fidel wrote:
When you use a transformer with the push pull configuration like Q93, Q97. the collector sits quiescent at the supply voltage. Then you add the + signal swing on to that to get the maximum voltage the device sees. So with a +2 V supply, you can't go lower then 0 volts, so you can't go higher then 2+2= 4 volts. That leaves a 1/2 volt margin for derating the device.


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