best structure for a 12-bit DAC?

I am surveying structures for a 12-bit ADC and for me the most concerned characteristic is monotonicity.
Resistor string can assure that but for a 12-bit design the cost(implemented in silicon) could be too high.
Can any one give me some suggestions?

By the way, TI's DAC7571 'seems' to be implemented by a simple resistor string.
Do you have any opinions about this?

Thanks!!

You can reduce the resistor string effort from

2^12-1=4095 resistors to

3*(2^4-1)=45 resistor by using

4 opamps

So the first string is taped on two positions in sequence and two opamps buffer the voltage difference on one segment to drive the second string. This second string also have taps which drive two buffer opamps. The third string is the final.

The offset of the first two opamps could disturb monotonic total behaviour. So for 2V you need

2V/4096~500uV offset voltage for monotonic behavior.

The other solution is to use an architecture w/o opamps. In this case the second string is exchanged by a second resistor. So in the position where the second string is inserted the first resistor is switched off. The mismatch define the INL but monotonic is easy.