John Williamson wrote:
On 15/10/2017 08:40, Don Pearce wrote:
On 14 Oct 2017 23:47:58 -0400, (Scott Dorsey) wrote:
The minimal op-amp is at least four transistors, maybe five if you want
decent output current drive. Two for the differential input, one for the
intermediate gain stage, then one (or two if you want to make it push-pull)
for the output stage. Add a couple constant current sources, a compensated
reference on the output pair, and the number of components climbs pretty fast.
Unless you use an integrated op amp. 5532 is probably my favourite
do-everything op amp. The count becomes one op amp and two resistors.
I think that Scott is making the point that inside the black box of the
op amp IC, there are many, many active components, all of which have a
potential effect on noise and linearity.
Yes, and the bad news is that the designers are severely constrained in the
components they can use and don't get much thermal isolation between them.
On the other hand they also get great matching and great thermal coupling
between them.
On the third hand, they're designed by Jim Williams and Bob Pease who
likely have put a lot of very smart work into them so you don't have to.
On the fourth hand sometimes they are designed by people who aren't as
smart as they needed to be but the datasheet was written by marketing people
who were smarter, such as in the case of some recent "audiophile" monolithic
op-amps.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."