Gareth,
for embedded components, in this case resistors, they are done during PCB manufacture. The resistors are printed during the manufacturing process then laser trimmed to get the final value. Whether they could trim them to the accuracy you'd require I'd have to check, as I've only gone to 5% for pull ups. If I was doing a commercial version it would be one of the options I would look at, as well as 0.1% SMD resistors.
This link may be of interest:
http://www.enme.umd.edu/ESCML/Papers/EmbResTrimming.pdf
for embedded components, in this case resistors, they are done during PCB manufacture. The resistors are printed during the manufacturing process then laser trimmed to get the final value. Whether they could trim them to the accuracy you'd require I'd have to check, as I've only gone to 5% for pull ups. If I was doing a commercial version it would be one of the options I would look at, as well as 0.1% SMD resistors.
This link may be of interest:
http://www.enme.umd.edu/ESCML/Papers/EmbResTrimming.pdf
I think conventional glassfiber PCBs are not suitable for high precision resistor printing. Ceramic substrate provides the low TC and mechanical stability.
I used the "measure and trim" approach; you can generate a suitable digital pattern, and the converter can be optimized bit-by-bit using an oscilloscope. Long term stability is another question.
I used the "measure and trim" approach; you can generate a suitable digital pattern, and the converter can be optimized bit-by-bit using an oscilloscope. Long term stability is another question.
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