diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Solid State (http://www.diyaudio.com/forums/solid-state/)
-   -   New super pair? (http://www.diyaudio.com/forums/solid-state/203482-new-super-pair.html)

kenpeter 31st December 2011 02:45 AM

New super pair?
 
2 Attachment(s)
Can such a simple trick nail MOSFET gate capacitance to a constant?
I have never seen an ESBT self-biased in this way before, is it new?
Can we now use MOSFET without squirming cap at stOOpid low VDS?

------

And a trio provides base current...

AKSA 31st December 2011 03:29 AM

Ken,

It's clever, but precisely what problem does it solve?

Hugh

kenpeter 31st December 2011 03:29 AM

1 Attachment(s)
Source switched MOSFET? (optimally different types of course).

kenpeter 31st December 2011 03:31 AM

Quote:

Originally Posted by AKSA (Post 2840556)
Ken,

It's clever, but precisely what problem does it solve?

Hugh

Unpredictable Miller capacitance at Low VDS.

Imagine the gate capacitance as-if an air bubble were squishing
back and forth from source to drain under a piece of Scotch Tape.
Situation I wish to avoid... Nothing against the Scotch.

PRR 31st December 2011 06:35 AM

Working an FET with Drain below turn-on voltage puts you into a very different mode of operation, with soft "plate resistance" and lower and more-variable Gm.

In a sense, instead of squishy C skewing your highs you have squishy resistance parameters skewing everything.

Your Trio looks to me like a 3-stage amplifier which is liable to self-oscillate.

Have you tried these on breadboard?

godfrey 31st December 2011 08:29 AM

1 Attachment(s)
Quote:

Originally Posted by kenpeter (Post 2840522)
Can such a simple trick nail MOSFET gate capacitance to a constant?
I have never seen an ESBT self-biased in this way before, is it new?

I think base current will be a bitch with your first two self-bias circuits. The third one (with 2 MOSFETs) looks interesting, if you can get it stable.

Wouldn't it be easier just to use an ESBT as intended? You get almost constant voltage across the MOSFET. Judging from the pic below (swiped from a datasheet), it seems normal to run these things with very low Vds.

BTW, Nelson Pass mentioned awhile ago that he'd been playing with ESBTs. I wonder if anything interesting will come of that?

kenpeter 2nd January 2012 07:12 PM

Quote:

Originally Posted by PRR (Post 2840677)
Working an FET with Drain below turn-on voltage puts you into a very different mode of operation, with soft "plate resistance" and lower and more-variable Gm.

In a sense, instead of squishy C skewing your highs you have squishy resistance parameters skewing everything.

Your Trio looks to me like a 3-stage amplifier which is liable to self-oscillate.

Have you tried these on breadboard?

I'm not sure how the dynamic resistance of a cascode or ring of
two could be squishy? Gm might be reduced or curved or both...
Some curves are useful. If it turned out to be square law, that
might be a very good thing. Other curves, maybe not so useful.
But my magic eight ball don't tell me whats gonna happen.
Time to consult the entrails on a breadboard, or whatever...

Bigun 2nd January 2012 07:52 PM

Looks interesting,


http://www.st.com/internet/com/TECHN...ivCta_2008.pdf

Look at the linearity in fig6


All times are GMT. The time now is 02:46 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2