From: Fred Bloggs
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Subject: Re: Amplifying stage with *negative* Voltage gain??
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Date: Sun, 08 Dec 2002 16:10:42 GMT
NNTP-Posting-Date: Sun, 08 Dec 2002 08:10:42 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
John Woodgate wrote:
> I read in sci.electronics.design that Fred Bloggs
> wrote (in <3DF2AD8F.firstname.lastname@example.org>) 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.
I realized that, it would have to be something with the function
generator behavior interacting with the probe being much more of a
parasitic effect on X1.