On Tue, Apr 04, 2006 at 07:09:39AM -0500, Timothy Miller wrote:
> I've been looking at DAC designs on Wikipedia. It seems that some
> high-precision designs use pulse-width or pulse-density modulation and
> a low-pass filter to remove the noise from the pulsing. For
> precisions higher than 16 bits, it becomes prohibitive to do anything
> else. The other major alternative is to use a decoder; you convert
> from N bits binary to 2**N bits one-hot and use a resistor array to
> analog. Imagine doing with 32 bits. I don't think we could fit the
> four billion resistors onto the card. :)
There are a zillion architectures for DACs. Analog Devices has a
couple of good books on the subject; audio designs usually use sigma-delta
schemes these days.
The last high-speed, high-resolution DAC I designed was a modified
version of one of ADI's, with a conventional R/2R ladder for the lower 9
bits, and a fully decoded 3-bit DAC for the upper 3 bits. It gave 12-bit
differential linearity with 10-bit trimming accuracy, and used an EPROM
linearization table to correct for static errors in the upper bits. It only
needed 29 resistors, all on a monolithic thin-film network for close
temperature coefficient match.
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