100GHz transistors
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From: Joerg on 7 Feb 2010 12:14 Paul Keinanen wrote: > On Fri, 05 Feb 2010 23:28:40 GMT, Jan Panteltje > <pNaonStpealmtje(a)yahoo.com> wrote: > >> Even more interesting is the maximum speed it can do >> I am not talking about 100GHz. > > What exactly does cut off frequency mean for a FET ? > > In bipolars the current gain drops below 1 at fT but you still can get > some usable power gain in common base configuration at higher > frequencies. > Common gate is even done with FETs. A professor at our university once proclaimed that would be stupid. Until I showed him the schematic of my amp and then that of a commercial transceiver ... > Before the invention of real microwave tubes (such as klystrons, > magnetrons TWTs etc.) much of the UHF/microwave amplification was done > my grounded grid tubes. > Still is. The nice advantage of that is that you don't have to burn off the drive power in the form of heat. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jamie on 7 Feb 2010 12:43 Joerg wrote: > Paul Keinanen wrote: > >> On Fri, 05 Feb 2010 23:28:40 GMT, Jan Panteltje >> <pNaonStpealmtje(a)yahoo.com> wrote: >> >>> Even more interesting is the maximum speed it can do >>> I am not talking about 100GHz. >> >> >> What exactly does cut off frequency mean for a FET ? >> >> In bipolars the current gain drops below 1 at fT but you still can get >> some usable power gain in common base configuration at higher >> frequencies. >> > > Common gate is even done with FETs. A professor at our university once > proclaimed that would be stupid. Until I showed him the schematic of my > amp and then that of a commercial transceiver ... > JFETS I presume?
From: Joerg on 7 Feb 2010 12:43 Jamie wrote: > Joerg wrote: >> Paul Keinanen wrote: >> >>> On Fri, 05 Feb 2010 23:28:40 GMT, Jan Panteltje >>> <pNaonStpealmtje(a)yahoo.com> wrote: >>> >>>> Even more interesting is the maximum speed it can do >>>> I am not talking about 100GHz. >>> >>> >>> What exactly does cut off frequency mean for a FET ? >>> >>> In bipolars the current gain drops below 1 at fT but you still can get >>> some usable power gain in common base configuration at higher >>> frequencies. >>> >> >> Common gate is even done with FETs. A professor at our university once >> proclaimed that would be stupid. Until I showed him the schematic of >> my amp and then that of a commercial transceiver ... >> > > JFETS I presume? > Sometimes. But the one I dealt with on my very first job was a MOSFET. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 8 Feb 2010 12:17 Fred Abse wrote: > On Sun, 07 Feb 2010 09:14:24 -0800, Joerg wrote: > >> Common gate is even done with FETs. A professor at our university once >> proclaimed that would be stupid. > > Why so? Hadn't he heard of grounded grid triodes? > Definitely not because his eye popped open when I showed him a schematic of a grounded grid RF power amp. I tended to build mine grounded cathode but only because I didn't have enough drive power or back then as a student not enough dough to buy the required new tubes. Or to be honest, I didn't want to raid the beer kitty to buy those. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
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