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Shunt feedback in broadband RF amps

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October 31st 05, 02:11 PM

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Shunt feedback in broadband RF amps

On 30 Oct 2005 22:43:07 -0800, wrote:

Tim: Thanks again for your help, and thanks again to all the others
who've replied to my question.

I see what you are saying. I reached back to Terman's description of
these kinds of feedback netwoks in tube circuits. I think he describes
just what you are presenting (but I think your presentation is
clearer!)

Obviously I'm still struggling with some very basic amplifier issues.
Am I correct in thinking that shunt feedback would have a number of
different advantages in a common emitter transistor amp? Looks to me
like the feedback network would give the designer the chance to:
1). Manipulate the input and output impedances
2). Counteract the tendency of the amp to "take off" becasue of the
rising gain characteristic (as frequency is lowered).
3). Reduce any distortion (IMD) generated in the amplifier itself.

I'm most shaky on #3. Am I correct in thinking that if you have some
sort of spur or IMD product generated in the amp itelf (say in the
collector circuit)the negative feedback provided by the shunt tends to
nock some (most? all?) of this distortion down?

#3)
Negative feedback of any kind then to make a circuit with nonlinear
action (however small it may be) more linear. IMD (InterModulation
Distortion) is a mixing action from nolinearity that occurs when two
signals are passing through an amplifier that has distortion, less
distortion, less IMD.

Allison
KB!GMX

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