From: Paul Burridge
Subject: Re: Transistor amplifiers v. frequency in SPICE
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Date: Fri, 17 Jan 2003 20:55:04 +0000
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On Fri, 17 Jan 2003 17:34:42 +0000, Terry Pinnell
>Eh, why do you think that? I suspect you've misinterpreted the Bode
>Analysis scale. For example, '300.0 V' means a gain of 300, not an
>output. Reference is 1 V.
Doh! That would explain a lot. Can do an AC sweep that shows output
voltage level as a function of source voltage frequency for a fixed
Vin of 2mV?
>>However, I've modified my circuit to be *exactly* the same as
>>yours now (why the 1M load?)
>As I said earlier, it was an assumption "...(with my arbitrary
>assumption of 1M load)". What load are you using?
Since the purpose of this stage is undefined in practical terms, it's
not terribly important, I guess. Certainly if it were an RF output
stage, I'd use typically 50, 70 or 300 ohms depending on the radiation
resistance of the antenna the stage was intended to feed. One meg just
seemed inordinately large; certainly for an output stage but also for
a small signal intermediate stage, too. I can't see the Zin of a
real-world following stage being anything like that high. But it's not
relevant for our purpose anyway, so long as we're both modeling
>Not sure I follow that. Results seem as expected to me.
I'll be in a better position to tell if you can set the sweep
parameters as suggested above...
"What is now proved was once only imagin'd"
- William Blake, 1793