AW: [sdiy] discrete SSM2018?

[Scott Bernardi]

In chip design it is fairly easy to get good matching between components,
but much harder to control the absolute value of a component. For
example, IC resistor values are typically +/-20%, but with care you can
match two resistors to 0.1%.
Vos is caused by manufacturing mismatches.  High precision design
techniques can minimize these (when we did the OP-27 at PMI, we typically
had 0.25mV or less Vos even before trimming), but the LM13700 is _not_ a
precision design.  In general an OTA is difficult because the main bias
current varies.  The CA3280 is one of the higher precision OTAs.


>
> > I know the 13600 has a tight matching of *gm* for both amps, but
> > why would the vos be matched as well ? (Excuse my ignorance about
> > chip design, but I'd expect if they manage to build two amps
> > with almost perfect matching of two vos of two amps, they should be
> > able to build a single amp with much lower vos with the same
> > technique,
> > shouldn't they ?)
> >
> > JH.
> >

--
Scott Bernardi
sbernardi at home.net