ago.
That trick works well with coarse buffers, e.g. NPN and PNP followers with their bases tied together.
It works better if you put the power amp inside the feedback loop, though. Otherwise the output impedance changes pretty radically, and one doesn't use buffers with high impedance loads.
Cheers
Phil Hobbs
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-power
=A0 =A0 =A0...Jim Thompson
=A0 =A0 =A0| =A0 =A0mens =A0 =A0 |
=A0 =A0 | =A0 =A0 et =A0 =A0 =A0|
=A0 =A0|
=A0 =A0 =A0 =A0 |
=A0|
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ow
rew
can
aike
Hi Jamie, Yeah I tried that too. I also tried Jan's 'feed forward' trick.
Here's what I finally got to work consistantly.
GND | |\ R Vin---|+\ | |\ | >-R--+--|+\ +-|-/ | >--+--Vout | |/ +-|-/ | +--10R-+ | |/ | | | +---R---+ R Vout | | R GND | GND
Sorry that's a bit bodged up.
(I'm too lazy to redraw it.)
George H.
OpAmp
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=A0 =A0 =A0 ...Jim Thompson
=A0 =A0 =A0| =A0 =A0mens =A0 =A0 |
=A0 =A0 | =A0 =A0 et =A0 =A0 =A0|
=A0 =A0|
=A0 =A0 =A0 =A0 |
=A0|
|food.- Hide quoted text -
know
into
I saw that later in the thread. Another thing i have found is that many opamps do not do well as buffers. A stage gain of +2 often works better in many subtle ways. Proposing stage gains of 5 followed by 2.
May not make any difference though.
?-)
George Herold a écrit :
quoted text -
In order to avoid input CM problems on the output stage amplifier, just eliminate it...
___ ___ .-|___|--+-------------------|___|-. | | | === | | GND | ___ | | .-|___|-+ | | | | |\ | | '-|+\ ___ | |\ | | >----|___|---+--|-\ | >---------|-/ | >-+---->
|/ .--|+/ | |/ === GND
Williams's Law: "Always invert, unless you can't."
Part of the problem with that approach is that the closed-loop bandwidth of the buffer stage drops, which makes it much harder to stabilize the loop.
Cheers
Phil Hobbs
But it drops too if you don't invert and build gain into the last stage for CM reduction.
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