Electronics > RF, Microwave, Ham Radio

Matching RF power transistors

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kg4arn:
apologies if this has been previously discussed


How are RF power transistors matched, say for push pull service?

dave_k:
Generally for bi-polar transistors hFE (DC current gain) is measured, and for FETs forward trans-conductance and
gate threshold voltage is measured.

T3sl4co1l:
For BJTs, Vbe is more important than hFE.  Connect B+C together, and measure at some constant current (say 1mA, or whatever a DMM's diode test does).  Beware that, if the transistor is oscillating in this configuration (for some reason), you'll get wrong numbers.

FET threshold is measured the same way (G+D tied, apply a constant current). :-+

Tim

kg4arn:
Thanks. I will give it a try.

BigBoss:

--- Quote from: kg4arn on August 05, 2017, 08:26:00 pm ---apologies if this has been previously discussed


How are RF power transistors matched, say for push pull service?

--- End quote ---

RF Power Transistor Matching is quite different than well known Complex Conjugate Matching. Because small signal conditions are not valid anymore.
You can do 2 things..
You obtain an accurate nonlinear model and you find Optimum Load Impedance ( this is not really accurate in reality) for that transistor in a professional RF simulator than you realize the matching circuit in according with..
or
You get Measured Load-Pull Data ( much more accurate if applicable) from the manufacturer and you realize  the matching circuit

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