[sdiy] discrete DAC accuracy

[Magnus Danielson]

From: Neil Johnson <nej22 at hermes.cam.ac.uk>
Subject: Re: [sdiy] discrete DAC accuracy
Date: Wed, 14 Jan 2004 13:50:41 +0000 (GMT)
Message-ID: <Pine.SOL.4.58.0401141347030.5698 at yellow.csi.cam.ac.uk>

> 
> [lots deleted!]

I realized that I forgot to do it just after sending it. I just didn't want to
put my hand down the Internet to pull the mail off the Internet so I could
resub it in improved version.

> > Well, yes... you're probably right. For resistors that is. For other stuff it
> > doesn't work that way simply because there isn't the same distribution of
> > target-values.
> 
> Quite probably!  I should check out capacitors as well, just to satisfy my
> curiosity!

Capacitors should behave similar to that of resistors. Crystal oscillators is
however more bell-shaped.

> > The point here is anyway that you can't trust the distribution, whatever
> > it is supposed to be. Real values of resistors will be much better.
> 
> Indeed.  Even so far that datasheets do not specify distribution curves at
> all, so there is no data to base any assumption on.

Exaktly.

> Also, many things can change resistors, from handling to humidity, to how
> they are soldered onto the board.  High-precision resistors are treated
> very carefully.

Indeed. For high-precision resistors may fat-oil from the fingers on the
resistor form a shunting resistor low enought to degrade the resistancevalue.

Cheers,
Magnus