I've done a virtual ground using an op amp as a buffer. This is for a single supply audio filter. So happens, I have a spare op amp from quad. chip. Should I make the spare op amp a buffer too and put it in parallel with the other buffer in hopes that the combination will result a 'super' buffer with a 50% reduction in output Z? Or.. are the buffers going to fight each other?
Sounds dodgy, in that there will be at least a few mV difference between the outputs, depending on the op amps.
Make a voltage follower from a spare, then virtual ground the + input...
Regards,
Chris
They'll fight, because their offsets will be different. If the Vos is low enough, you can parallel them using ballast resistors, but you'll always be dissipating (delta Vos)**2/(2*Rballast).
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal
1st OpAmp: + terminal is input, - terminal to load, R from OpAmp output to load.
2nd (and subsequent) OpAmps: + terminal to output terminal of 1st OpAmp, - terminal to _this_ OpAmp output, R from _this_ OpAmp output to load. ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
Did you forget how to use google?
etc..
Why not wire the second circuit (including resistor) in parallel with the first (including resistor)? Basically, paralleled voltage followers with current sharing resistors. With your circuit I'd expect some load sharing issues on input transients.
Think about it for awhile ;-) ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
Most likely fight each other.
Maybe if you combine them with low value R's on their outputs.
[snip]
Posted more than 7 years ago...
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
If you're worried about the input impedance, get a better OpAmp.
Yes, I did miss the original problem (and it took a minute to understand than his "virtual ground" wasn't); no input transients. ;-)
Do you need the reduced Z? I'd just leave it connected as a buffer with grounded input and perhaps use it in the future. I hate quad opamps BTW. Things always seem to get to crowded.
George H.
=A0 =A0 ...Jim Thompson
=A0 =A0| =A0 =A0mens =A0 =A0 |
=A0 | =A0 =A0 et =A0 =A0 =A0|
=A0|
=A0 =A0 =A0 |
ber 2009- Hide quoted text -
Ahh, that looks nice!
George H.
n .
Hmm it gets rid of the offset issue. (Well doesn't get rid of offsets, but it looks like they are fighting less...)
George H.
Quad op-amps (and comparators) are the most retarded pinout ever. I will never use an LM339 again...
If it means you'll end up with a pair of e.g. LM358 instead, and one ends up extra, who cares... or you can just do the same thing, and have the pins where you need them this time.
Tim
The 339's pinout is great for doing window comparators and other wire-OR type things. Anyway, it takes a microsecond to do anything, and it takes real talent to have pickup or oscillation issues with that sort of speed.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal
A 339 pinout is quite good from a noise point of view, since all the outputs are at one end. The usual quad op amp is different, in that each op amps pin's are grouped together. For layout purposes, it doesn't seem to make much odds, but the the 339 can make it easier to fit feedback parts round the device.
One man's paradise is another man's hell ?...
Regards,
Chris
Neat. The verbal description was hard work, but a glance at the schematic makes it clear. Higher drive capability and current sharing through the 100r resistors...
Regards,
Chris
Does anyone care. The LM324 and LM339 are probably the _most_used_ jelly bean parts, EVER!
[snip] ...Jim Thompson-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
I actually came up with that before I had access to a simulator. I was driving telephone "muff cup" couplers for 300 Baud modems (~1980 ;-) ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
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