[Amps] New NXP BLF578XR 1200W LDMOS FET is "indestructible"

[Dr. David Kirkby]

On 07/23/11 04:34 PM, jeff millar wrote:
> This email describes what I've learned from looking at these modern transistors
> for the last few months.  It seems to me like a fundamental crossover point has
> been reached.  Silicon processing technology has produced rugged VHF/UHF
> transistors, with reasonable impedance matching for a reasonable cost,
> especially considering all the other costs associated with an amplifier.  These
> parts will only get better and cheaper as time goes on.

These is an equation, based on the physics of semiconductors, that shows:

P f^2 R = constant.

P = power
f = frequency
R = output impedance

I can't recall the derivation of that, but could dig it out. (It was one of the 
things I learned while doing an MSc in microwaves and optoelectronics)

So basically doubling the frequency, you are going to only get one quarter of 
the power for the same output impedance.

I don't know how close we are to the theoretical limits of what is possible, but 
perhaps not too far.

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