[sdiy] discrete SSM2018?

[jhaible at t-online.de]

Czech Martin schrieb:
> > Tracking of gm between two OTAs of one chip: typ: 0.3dB
> > 
> > So we have a variation of 2:1 of absolute gm, but a 
> typical gm 
> > tracking of only 3.5%.
> > 
> 
> This  is the beauty of integration. ;-> Absolute values 
> are (almost) 
> impossible,
> but matching or tracking is very good. I can see no 
> inconsistance here. 

The inconsistance is, like we discussed before, that apparently
the matching of transistors within one function block (mirror)
is worse than the matching between two blocks.

You don't need exact absolute values for *any* of this:
diff amp, one mirror, several mirrors. It's always the 
matching / tracking.

The only possibility I can imagine at the moment (other than
too loose specs in the data sheet): Maybe they can produce
mirrors with a block where transistors share some areas
(emitter for instance), and they have difficulties to get a 
tight current ratio within such a block, but no difficulties
to reproduce the same block with tight matching to the first
one. Does this make sense ? No bipolar chip designers on the
list ??

JH.