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From: Paul Burridge
Subject: Re: Amplifying stage with *negative* Voltage gain??
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Date: Thu, 05 Dec 2002 09:29:34 +0000
NNTP-Posting-Date: Thu, 05 Dec 2002 10:58:03 GMT
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On Thu, 05 Dec 2002 04:34:56 -0500, Mike Monett opined
> I just modeled your buffer in SPICE, using a 2N2222 which is close
> to a BC337. I assumed 10pF for the scope probe capacitance.
> Here's the schematic.
> The input impedance is a bit less than 1.5k, mostly due to the
> parallel impedance of the 3k bias resistors. You say you are getting
> a solid 8V p-p at the input, so I assume the source impedance of the
> oscillator is around 150 ohms or less. I picked 150 ohms.
> The frequency response shows a 1 dB drop due to the source
> impedance. The -3dB bandwidth is over 100MHz, so it can handle
> 3.57MHz with no problem. I ignored the stray cap at the input.
> The 1.08k emitter resistance can easily drive the 10pF scope probe
> capacitance. Here's the waveforms.
> I hope this give you confidence your circuit should work.
Many thanks indeed, Mike. I haven't had a chance to view the URLs yet
but will do so later.
> But I have a question. If you can drive the buffer with a solid 8V,
> the output impedance of the oscillator must be pretty low.
Indeed! But this was only cobbled together for test purposes. I'm
aware that a practical stage would be best designed for much lower
output for stability reasons.
Thanks again for your efforts.
"I was going to help him up, but then I thumped him."
Michael Head's plea in mitigation to Weybridge Magistrates, Sept. 1975
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