From: John Woodgate
Subject: Re: Amplifying stage with *negative* Voltage gain??
Date: Sun, 8 Dec 2002 05:30:46 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Sun, 8 Dec 2002 06:29:32 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Fred Bloggs
wrote (in <3DF2AD8F.email@example.com>) about 'Amplifying stage with
*negative* Voltage gain??', on Sun, 8 Dec 2002:
>John Woodgate wrote:
>> What is very difficult to understand is that, AIUI, you measure 8 V
>> input with the probe on X1 setting but only 2.2 V out. If the probe has
>> 100 pF capacitance, that suggests that your output coupling capacitor is
>> about 30 pF.
>> But then you measure 8 V in with the probe on X1 but 2.2 V with it on
>> X10. That seems utterly inexplicable.
>This is not so inexplicable when you consider the GND clip inductance
>and 100p, or more, of probe and scope capacitance on X1 to make a nice
>resonate ckt at 3.57MHz with a function generator requiring termination.
To resonate with 100 pF at 3.57 MHz, the ground lead inductance has to
be 20 uH. That's an AWFUL long ground lead.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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