someone says we can use an offset-adjustable low-resolution dac, by adjusting the offset voltage by LSB/4, the resolution can increase by two bits, but why? how to understand the above words? who can help me?
Hello!
It seems tome that there is something wrong in your explanation.
As far as understand your problem, you are in need of DAC with at least two more Accurate bits than the bits in ADC, not with two more bits of Resolution.
There is a difference between "accuracy" and "resolution".
For example if you use two 8-bits DACs MC1408 you could produce a 16-bit DAC with approximately 16 bits of resolution but the accuracy will still approximately 8 bits.
Ref: http://www.515ic.com/View-55.html
Size: 117KB , MC1408-8.pdf (page 6)
The best solution is to use a single DAC with at least two more accurate bits.
I hope that is helpful, but you need still to reformulate your problem
BR
Petre Petrov