Post subject: PA emitter area Posted: Fri Nov 18, 2005 7:52
The issue for power output is current density in the emitter-base
junction - you can't increase that without limit. So the more area,
the more power, given a limit on current density.
Ft is (among other things) the width of the base junction. Since junctions
are usually the result of diffusion, smaller emitters often result in
narrower base junctions.
Nf, on the other hand, is largely due
to the resistivity in the base region.
Hope this helps.