At 08:38 PM 11/19/2006, you wrote:
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>id kAK1cVeA025855
>
>
>  Spehro,
>
>>The requirement for high voltage operation *and* R-R operation is quite
>>rare, in fact I suggest it might be an error to add that constraint. Usually
>
>  Yeah, don't I know it!
>  Unfortunately it's just one application.  This particular part is 
> being used for doing some analog math on control voltages to some 
> CCA gain blocks.  The greater the rail voltages, the greater the 
> headroom in the system.
>The gain blocks are set up to be "off" when the CV is at the 
>negative rail, hence the negative rail requirement.  The positive 
>rail would be nice, too, but getting close to the negative rail is a 
>lot more important or else there'll be bleed-through.
>
>  I've used the 324 lots of times and like it fine, but it has this 
> goofy output stage (well, not really goofy -- it's designed for 
> low-power consumption, which I don't care about) that has a 
> noticable glitch at the crossover point into high-ish impedance 
> loads.  It's really visible on a scope and audible if the signal in 
> question is audio.  But the 324 does go down to 20mV or so of the 
> negative rail, and it's cheap, and has a wide range of operating 
> voltages.  As for the other specs, any parameter I didin't list 
> isn't something I'm overly concerned with.
>
>  If I can't find a part that works, I'll just use the 324 or bring 
> down the rails and recalculate the biasing.  But I'd  like to not 
> have to.  Even a R-R (or just the negative rail) part that was okay 
> with +/- 10 would be pretty great.

Okay.

The LT1013 Dwayne mentioned is a pretty good precision bipolar dual op-amp.
It handles common mode input voltage down to ground and the output swings to
ground. It can also do +/-15V supplies with ease. Try looking for "single
supply" op-amps rather than R-R types and you'll find lots of others that
should work for you, if you can live without the inputs/outputs going to
the positive rail (there are other problems associated with the inputs
if there's a lot of common mode voltage anyway).

Sometimes you can trick the LM324 into doing what you want by loading it
with a resistor to one of the supply pins (usually "GND"), thus keeping the
output in the class A mode.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff 


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