Steve Hardy <PICLIST@MITVMA.MIT.EDU> wrote:

> given that each of 4 outputs can be in one of 3 possible states,
> one could conjecture that it is possible to make a DAC with 3^4 =
> 729 [sic] possible output levels.  Is this possible in practice?
> Ignore the imperfections of the outputs - assume they are exactly
> 0V or 5V or infinite impedance, and your resistors and opamp are
> perfect. Is it possible to make a linear (not just monotonic) DAC?

Steve:

If it IS possible, I'd really like to know how... I spent about a
month trying to replace a 256-step switched attenuator network with
an arrangement similar to the one you describe.

The best "solution" I found was one that used 12 voltage dividers
(which would have allowed 4096 possible output values in the
configuration we were using) and discarded a bunch of values in the
range... We ended up with 256 well-chosen (through exhaustive
computer simulation) steps that were SORT OF linear, but not close
enough for our application, so we gave up.

-Andy

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - Vista, California
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