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From: "Helmut Sennewald"
Subject: Re: Q. medium-power RF transistor
Date: Sat, 9 Nov 2002 00:22:00 +0100
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
"Winfield Hill" schrieb im Newsbeitrag
> I'm thinking about making 20 to 30V pulses with a
> 1ns max risetime into a 50-ohm line...
> What's a good low-capacitance transistor to use with
> say Vceo 30V, 500mA capable (h_fe >10 at 500mA) and
> with f_T of at least say 1GHz at Ic 200mA, Vce 15V?
I would try four cascodes in parallel with BFG135 transistors.
The product of output capacitance of your transistor(s) and
the load(50Ohm) has to be below the wanted rise time.
The layout will be important important.
Try a star(+) configuration.
> For example in the old days we'd consider a 2n3866,
> etc., but this falls short of the mark for the above
> specs, and is clearly far behind today's curve. Hmm,
> what's a common transistor to get 5 watts at 900MHz?
This is a very different application. It is narrow band only.
The output capacitance of the transistor(s) is compensated with
the inductive collector load(resonance circuit).
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