From: John Larkin
Subject: Re: Q. medium-power RF transistor
Date: Sun, 10 Nov 2002 12:07:52 -0800
Organization: Posted via Supernews, http://www.supernews.com
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On 9 Nov 2002 13:50:44 -0800, Winfield Hill
>email@example.com (carltons) wrote...
>> Helmut Sennewald HelmutSennewald@t-online.de wrote:
>>> Winfield Hill schrieb ...
>>>> 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?
>>> Hello Win,
>>> 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.
> That's a nice transistor, reasonable beta at 100mA, with just
> over 3pF of Ccb+Coe capacitance. I could parallel four with
> a 50-ohm pullup to 25V (each in common-base mode, Vcbo = 25V),
> and still have RC under 1ns. And it looks easy to get.
> But I wonder, where have all the medium-current 25+ volt RF
> transistors gone? All the likely parts I have examined are
> discontinued. For example, an ON Semi MRF3010 or MRF134 RF
> MOSFET (65V, 1A, Coss + Crss < 12pF) would have been nice a
> few years ago. What's the ticket now?
Philips has a bunch of 'broadband' transistors that are thoroughly
modern widgets with awesome Ft's.
things like 250 mA at 21 GHz. PNP's too! They are sometimes hard to
get, but I think one of the major US distributors has taken them on
recently and stocks parts. Pioneer maybe?