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From: Mike Monett
X-Mailer: Mozilla 2.02 (Win16; I)
Subject: Re: Amplifying stage with *negative* Voltage gain??
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Date: Wed, 11 Dec 2002 12:21:54 -0800
NNTP-Posting-Date: Wed, 11 Dec 2002 12:21:55 EST
Organization: Bell Sympatico
Tony Williams wrote:
> In article ,
> Paul Burridge wrote:
> > > Clip say a 1k resistor in series with the scope probe
> > > and have a look again. All voltages will be reduced,
> > > but the 1k will provide some local resistive isolation
> > > of the scope probe.
> > Have now done so.
> > Now getting 0.3v p-p in when probe set on x1;
> > getting 1.3v p-p in when probe set on x10;
> > gwtting 0.32v p-p out with probe set on x1;
> > getting 1.5v p-p out with probe set on x10.
> > Does that tell us anything?
> Slightly inconclusive. But it does suggest.
> The Gain of your follower is 1, (it's ok).
> The x1 input impedance of the scope probe is capacitive,
> enough to affect both input and output (o/p slightly).
> The signal source is quite tender (as you have just
> confirmed in another post). Perhaps the addition of
> a x1 scope probe is inducing a resonance or oscillation.
> The oscillation could even be the emitter follower itself
> Is your signal source buffered, or are you coming straight
> off a resonant circuit within it?
> Is the signal-source built on that same bit of stripboard?
> Sharing the same power rail even?
> Tony Williams.
Golly, you are brave. But I think you may have opened Pandora's box.
None of the measurements previously posed are really consistent. I can
see all kinds of uglies creeping out. Problems with the source
oscillator, layout and grounding, bypassing, parasitic oscillations,
measurement problems, unknown test equipment problems, lack of
calibration standards, and so on.
This could turn into a complete electronics design course!
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