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Old 7th December 2013, 11:33 PM   #1
sbrads is offline sbrads  United Kingdom
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Default Linearity

Just a thought..... has anyone ever managed to devise a bipolar amplification stage that is linear before feedback? I'm thinking is there a way of combining an inverse square law type of transfer with the usual square law type of transistor b/e transfer characteristic so that they balance out over a decent range and have a straight line effective overall Vbe at least over that range. A lack of suitable devices would seem to be the main problem. Possible?
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Old 7th December 2013, 11:43 PM   #2
DF96 is offline DF96  England
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BJT are not square law but exponential. You need a logarithmic response to compensate. Possible for small signals - Barrie Gilbert did this. Elsewhere the only realistic option is feedback.
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Old 8th December 2013, 12:26 AM   #3
sreten is offline sreten  United Kingdom
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Hi,

It has been shown that no form of bipolar output stage can be linear.
Given that various options exist to to make it more linear, but they
require analysis to the level that indicates the first case to be true.

rgds, sreten.
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Old 8th December 2013, 01:08 AM   #4
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Quote:
Originally Posted by sbrads View Post
Just a thought..... has anyone ever managed to devise a bipolar amplification stage that is linear before feedback?
I think you'd do well to define your temrs a bit more precisely at the start. For example, do you mean 'linear' as determined by listening or by measurements? If the latter then which measurements over which operating ranges?

If linear means 'sounding good' (which would be my initial assumption) then you could look at amps which use no global NFB (Ayre comes to mind - Bob Cordell says they sound great). Bob also has a schematic of a no-GNFB amp in his book. You'd also do well to distinguish global NFB from local or no amps with emitter followers will qualify....
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