Kai said

By the way, to fabricate a 16bit DAC with discretes like R2R ladder and such stuff will never work. All involved parts must not show any error bigger than 15ppm, including fabrication tolerance, temperature drift and long therm drift! (15ppm represents an error of less than 0.0015%.)

Actually, if I were to roll my own, Charles' method can be remarkably successful - these hybrid film devices track very very well and their temperature drifts are also stable to your required precision. How do you think "16 bit DACs" on monolithic silicon work ? Often not as well as specialist hand built ones !

Incidentally, you don't discuss the method I have used to give high resolution - namely running two multiplying DACs. That way we can get quite high bit resolution, certainly better than 12 bit (we use 2 x 12bit AD7537)

Steve