From: "Jeff Verive"
Subject: Re: Limitations of the BC337
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Fri, 10 Jan 2003 16:52:13 -0600
NNTP-Posting-Date: Fri, 10 Jan 2003 16:52:14 CST
What's the application, common emitter, common base, common collector, class
C, class D, class S, etc? Depending on application, Ccb may be most
important, hoe may be a factor, etc. In most cases, the most important
factors may be experimentally determined by playing with the parameters in
SPICE, but that's just one possible starting point.
More info is needed.
"John Jardine" wrote in message
> Paul Burridge wrote in message
> > On Thu, 9 Jan 2003 21:19:39 -0000, "John Jardine"
> > opined thusly:
> > >That 200kHz will be due to, too high a gain, capacitive loading
> > >high source resistance...
> > [comprehensive discourse snipped]
> > Well, you've obviously amassed a formidable expertise in RF circuit
> > behavior judging by that posting! I'm grateful for the tips from you
> > and others who've contributed here. One point arises, however: is the
> > chief determining parameter of the maximum frequency a transistor can
> > handle its base/collector capacitance (both intrinsic and external)?
> > I mean, could one get a good idea of how fast an RF tranny is just by
> > the manufacturer's figure for intrinsic b/c capacitance? I'm assuming
> > such a figure is also a SPICE parameter?
> > --
> > "What is now proved was once only imagin'd"
> > - William Blake, 1793
> To be honest, I've only casual knowledge in this interesting area of
> design!. I've noticed though, a couple of this group's posters are -real-
> men and should have some good angles. As Jeff V mentioned, fluency with it
> comes from actually doing it and as is usually the case, the best learning
> come from figuring out why the stuff won't play ball.
> To a first guess the Ccb value is a very good pointer to a fast transistor
> but it is one of a host of other internal transistor factors that are
> waiting in the wings and ready to pounce. All the factors come into play
> some point as the frequency moves upwards.
> For HF use it's usually best in the first instance, to select a transistor
> from the lists specifically marked as 'RF' transistors. This ensures that
> most of the major, internal limiting factors, (particularly internal
> capacitances), will have been characterised and optimised to allow more
> predictable operation at the higher frequencies.
> Yes, the Ccb is an essential spice model value.
> Incidentally ... What was your rough gain and source impedance?.