Symmetric Amplification

[DonMack]

In many amplifying topologies, the devices used(all that I know of) all have
asymmetric voltage input characteristics. Are their any devices and/or
topologies that give a true symmetric voltage input characteristic? For
example, with matched devices a differential amplifier or push pull
topologies can offer symmetric output even when the devices used are
asymmetric. This is not the type of example I am looking for.

I'm more interested in a single monolithic device the has the inherent
symmetric characteristics due to design/geometry rather than some paring up
two asymmetric devices.

Tubes, bjts, mosfets, jfets, all have asymmetric characteristics. It seems
that the asymmetry may be due to the asymmetric nature of electron flow?
i.e., electrons only *freely* flow in the direction(or rather opposite) of
the electric field and a tube exemplifies this. i.e. nature imposes this
asymmetry and all designs will have to resort to "tricks" to overcome it.

 

[Nemo]

In many amplifying topologies, the devices used(all that I know of) all
have asymmetric voltage input characteristics. Are their any devices
and/or topologies that give a true symmetric voltage input
characteristic? For example, with matched devices a differential
amplifier or push pull topologies can offer symmetric output even when
the devices used are asymmetric. This is not the type of example I am
looking for.

I'm more interested in a single monolithic device the has the inherent
symmetric characteristics due to design/geometry rather than some paring
up two asymmetric devices.

Tubes, bjts, mosfets, jfets, all have asymmetric characteristics. It
seems that the asymmetry may be due to the asymmetric nature of electron
flow? i.e., electrons only *freely* flow in the direction(or rather
opposite) of the electric field and a tube exemplifies this. i.e. nature
imposes this asymmetry and all designs will have to resort to "tricks"
to overcome it.

Class A amplifier? As a side benefit, you can fry your breakfast on it.

On a related note, I recently tried powering a front end with asymmetric
supplies (+4V and -6V instead of +/-5V) to see if biasing the
amplifier's input stage a little off the 0V rail would reduce crossover
distortion. I tried this with two high spec JFET input op amps
(ADA4817-1 and AD86something) with a gain of about 1 million in that
stage. I could see no performance improvement. I concluded that modern
op amps are so good that input stage distortion is negligible.

Nemo

 

[Jamie]

---
Perhaps you meant "pairing up"?
---




There are no straight lines in nature.

Speak for yourself..

Jamie

 

[[email protected]]

Bob Newhart was pretty good at delivering them.

 

[Martin Brown]

Get real. There are gravitational forces _everywhere_. So there are NO
absolutely straight lines... except in Larkin-land... and that's because of
the fairies ;-)

He *is* being real. Light travels in straight lines to an incredibly
good approximation as soon as you are more than a few diameters away
from a normal matter or plasma based gravitating object. If it didn't we
would see the sky altering and being distorted around the moon.

Most of the universe is empty space so a ray leaving the any star will
travel in a straight line by default unless it passes really quite close
to or through a strong gravitational potential well.

The effect that Eddington measured at the total solar eclipse for stars
with light passing extremely close to the sun was barely measurable at
under 2" arc as predicted by Einstein against a reference plate taken
six months later. The deviations from a straight line are tiny even for
stellar mass objects at grazing incidence.

http://www.esa.int/esaSC/SEMDYPXO4HD_index_0.html

So whilst you could argue that light doesn't travel in *perfectly*
straight lines (to be accurate it travels along the null-geodesics or in
classical terms along the path of minimal time) they are the closest we
get to straight lines in the universe and span huge chunks of it.

The effects of objects in the way can be rather pretty through the
influence of galactic clusters on even more distant objects.

http://spacetelescope.org/images/heic0404b/

Regards,
Martin Brown

 

[Uwe Hercksen]

Gravity is not everywhere - it is only where mass is. Hence light is
straight unless to insist on measuring it near planets and stars (etc)

Hello,

gravity is everywhere on the long way between the sun and pluto,
otherwise all big and small planets between both would not keep their
orbits as they do. Of course gravity is still present outside the orbit
of pluto, because there are a lot of other Kuiper belt objects.
You need an infinite distance to any mass to get zero gravity.

Bye

 

[John Devereux]

Depends on your frame of reference and your definitions doesn't it?

<http://en.wikipedia.org/wiki/Geodesic>

 

[[email protected]]

Get real. There are gravitational forces _everywhere_. So there are NO
absolutely straight lines... except in Larkin-land... and that's because of
the fairies ;-)

Nonsense. Light travels straight in free space. OTOH, the universe curves
around gravitational wells.