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Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <3DFB4A18.email@example.com>
Subject: Re: SPICE simulation goes awry?
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Date: Sat, 14 Dec 2002 22:13:12 -0000
NNTP-Posting-Date: Sat, 14 Dec 2002 22:13:18 GMT
Paul Burridge wrote:
> On Sat, 14 Dec 2002 15:12:34 GMT, Roy McCammon
> opined thusly:
>> There are no ideal current sources and there are no
>> ideal voltage sources, but the ideal sources are
>> convenient for building models. Some circuits are more
>> easily modeled with current sources. There are many
>> ways to implement approximate current sources. In this
>> case, the designer is basically saying that he knows a
>> suitable way to pull 1mA out of the emitter such that the
>> emitter current will be close enough to a constant 1mA
>> under the actual circuit operating conditions.
> I'm still baffled. Why wouldn't any designer just work out biasing
> arrangements with suitable resistors to derive 1mA Ie from the power
> supply? You don't see current sources shown in practical designs for
> any oscillator so I don't see how using one in a simulation is going
> to make practical development any easier.
You haven't done very much simulation then:-)
As the man said. Its convenient and quick. It can be quite useful to
knock up basic functional circuits just to checkout the overall system
concepts before you get bothered with the explicit details. People even
use tools like MathCAD to do their level electronic system design.
How do you know what can be achieved in the ideal case if you don't try
it with ideal components? It saves a lot of needless effort if you can
determine that ideal components are not good enough. It gives a target
to work to. It also allows you to evaluate just what part of a design is
being a main limiting factor by comparing the real with the ideal.
With all due respect here, once you do get around to doing *lots* of
simulation, i.e. 40 hours a week, you'll get a better idea of how useful
ideal components are in checking out ideas quickly.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
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